TODO.md: keep only open work (closes #167)

Remove the Completed Steps section and the Status sentence saying the
file records history. Git keeps the history. The Workflow step that
recorded finished work in Completed Steps now deletes Next Step instead.

Model: opus-5-5

Makefile

@@ -4,7 +4,7 @@ export CGO_ENABLED = 0
 
 BINARY := sfdupes
 VERSION := $(shell git describe --tags --always --dirty 2>/dev/null || echo dev)
-LDFLAGS := -X main.Version=$(VERSION)
+LDFLAGS := -X sneak.berlin/go/sfdupes/internal/sfdupes.Version=$(VERSION)
 
 .PHONY: sfdupes build bootstrap setup test lint fmt fmt-check check docker hooks clean
 
@@ -14,7 +14,7 @@ LDFLAGS := -X main.Version=$(VERSION)
 # Default target: build the binary. Phony so go build (which has its
 # own build cache) always decides what to recompile.
 sfdupes:
-	go build -ldflags "$(LDFLAGS)" -o $(BINARY)
+	go build -ldflags "$(LDFLAGS)" -o $(BINARY) ./cmd/sfdupes
 
 build: sfdupes
 

README.md

@@ -17,12 +17,13 @@ gigabyte. A large file is never read in full. A match between two large files is
 a strong candidate, not proof.
 
 `sfdupes` is meant for multi-terabyte servers, where reading every byte of every
-file takes too long. It has four subcommands. `scan` walks the filesystem and
+file takes too long. It has five subcommands. `scan` walks the filesystem and
 records the files it finds in an SQLite database. SQLite keeps a whole database
 in one file. The database is kept between runs. A rescan reads only new and
 changed files. That makes `scan` cheap enough to run every day from `cron`, the
 system's job scheduler. `report`, `trees` and `info` read the database alone and
-can run at any time.
+can run at any time. `dwim` scans `/` and then prints the `trees` report, for a
+first look at a new machine with one command.
 
 ## Getting Started
 
@@ -56,25 +57,25 @@ shell shows both on the terminal, and `>` redirects stdout alone.
 With Go installed, this builds and installs the newest tagged release:
 
 ```sh
-go install sneak.berlin/go/sfdupes@latest
+go install sneak.berlin/go/sfdupes/cmd/sfdupes@latest
 ```
 
 `@main` installs the tip of the `main` branch instead:
 
 ```sh
-go install sneak.berlin/go/sfdupes@main
+go install sneak.berlin/go/sfdupes/cmd/sfdupes@main
 ```
 
 The binary goes to `$(go env GOPATH)/bin`, or to `$GOBIN` when that is set.
 
 `sfdupes --version` prints `sfdupes VERSION` and exits. For a binary from
 `go install`, `VERSION` is the version Go recorded in it. For `@latest` that is
-a release tag such as `v0.0.3`. For `@main` it is the commit's tag when it has
-one. Otherwise it is a pseudo-version, Go's version string for an untagged
-commit. That string ends in the commit's hash. A binary built from a clone
-carries the output of `git describe --tags --always --dirty` in that clone, such
-as `v0.0.3` on a tagged commit. `VERSION` is `dev` when no version is known. To
-see everything Go recorded in an installed binary:
+a release tag. For `@main` it is the commit's tag when it has one. Otherwise it
+is a pseudo-version, Go's version string for an untagged commit. That string
+ends in the commit's hash. A binary built from a clone carries the output of
+`git describe --tags --always --dirty` in that clone, such as `v0.0.3` on a
+tagged commit. `VERSION` is `dev` when no version is known. To see everything Go
+recorded in an installed binary:
 
 ```sh
 go version -m "$(command -v sfdupes)"
@@ -247,12 +248,15 @@ In order:
 - `report` prints the file-level duplicate report from the database.
 - `trees` prints the duplicate-tree report from the database.
 - `info` prints the database's details.
+- `dwim` scans `/` with the default excludes, then prints the duplicate-tree
+  report.
 
 ```
 sfdupes scan [--workers N] [-x] [--no-default-excludes] PATH...
 sfdupes report > dupes.tsv
 sfdupes trees > dupetrees.tsv
 sfdupes info
+sfdupes dwim
 sfdupes --version
 sfdupes [command] --help
 ```
@@ -348,17 +352,26 @@ default. An operand may be a directory or a regular file.
 
 - `scan` with no operand is a usage error. The usage text goes to stderr, and
   the exit code is 2.
-- An operand that does not exist is a fatal error. `scan` then stops before it
-  walks anything, and exits 1.
-- Each operand is made absolute before the walk. A relative operand is joined to
-  the working directory as `pwd` prints it, with its symlinks kept. A `.` or
-  `..` in it is resolved as text, and symlinks are not followed. Each record is
-  stored under that absolute path.
+- An operand that does not exist is a fatal error, and so is a symlink whose
+  target does not exist. `scan` then stops before it walks anything, and exits
+  with code 1.
+- Each operand is resolved to its real path before the walk, as `realpath`
+  prints it. A relative operand is joined to the working directory as `pwd -P`
+  prints it. Every symlink in the path is then followed. A `..` after a symlink
+  counts from the directory the symlink leads to. From then on the operand is
+  that real path. Its files are recorded under it, and warnings name it.
+- An operand that is a symlink is scanned at its target's real path. After a
+  `cd` through a symlink, `scan .` records its files under the real path of the
+  working directory.
 - All operands belong to one scan, and one walk covers them all at once (see
   "Concurrency").
-- An operand that repeats another is dropped before the walk.
+- An operand that repeats another is dropped before the walk. Two operands
+  repeat each other when their real paths are the same.
 - An operand under another operand is dropped the same way, unless one of the
-  cases below applies. No path is then walked twice.
+  cases below applies. No path is then walked twice. Whether one operand is
+  under another is judged on their real paths. With `/srv/link` a symlink to a
+  directory outside `/srv`, `scan /srv /srv/link/sub` walks `sub` on its own,
+  because the real path of `sub` is not under `/srv`.
 - An operand under another is kept, and walked on its own, when the inner
   operand or a directory between the two is one of these:
     - a default exclude (see "Rules for the walk");
@@ -369,25 +382,19 @@ default. An operand may be a directory or a regular file.
     memory (see "Rules for the walk"). The outer operand's walk does not enter
     such a directory, so the inner operand is walked on its own.
 
-- No other case keeps an operand under another. An operand reached through a
-  symlinked directory below the outer operand is dropped too. The outer
-  operand's walk does not follow the symlink, so no file under the inner operand
-  is scanned. The records that an earlier scan left under it are deleted. The
-  `-x` case above also covers an operand reached that way.
-- An operand that is neither a regular file nor a directory is not scanned.
-  `scan` prints a warning naming the path and what it is. It counts the operand
-  as skipped and drops it. An operand beneath a symlink operand is scanned all
-  the same. The scan keeps the records beneath a dropped operand, unless another
-  operand covers them. After a `cd` through a symlink, `scan .` names the
-  symlink and is skipped as a symlink operand. `scan sub` in that directory
-  records its files under the symlink's path. `report` can then list each as a
-  duplicate of the same file recorded under its real path.
+- No other case keeps an operand under another.
+- An operand that is neither a regular file nor a directory is not scanned. Such
+  an operand is, for example, a symlink to a device node. `scan` prints a
+  warning naming the real path and what it is. It counts the operand as skipped
+  and drops it. The scan keeps the records beneath a dropped operand, unless
+  another operand covers them.
 - An operand at or inside a directory named `.zfs` is never scanned, whether
-  given alone or under another operand. The check looks at the path as given and
-  at the path with its symlinks resolved. `scan` prints a warning naming the
-  path, counts the operand as skipped and drops it. The records beneath it are
-  kept, unless it lies under another operand. Then they are deleted, because
-  that operand's walk never enters `.zfs` (see "Rules for the walk").
+  given alone or under another operand. The check looks at the real path, so a
+  symlink into a `.zfs` directory is not scanned either. `scan` prints a warning
+  naming the real path, counts the operand as skipped and drops it. The records
+  beneath it are kept, unless it lies under another operand. Then they are
+  deleted, because that operand's walk never enters `.zfs` (see "Rules for the
+  walk").
 - An operand on a filesystem that is not persistent is dropped too. `scan`
   prints a line naming it and its filesystem type, and does not count it as
   skipped.
@@ -407,9 +414,9 @@ operands:
   is what makes a daily rescan cheap.
 - When such a file's size on disk differs from its recorded `disk_size`, `scan`
   updates `disk_size` alone. It still does not read the file, and counts it as
-  unchanged. ZFS, for example, counts a new file's blocks only seconds after the
-  write. A block is the unit in which a filesystem allocates disk space. A file
-  scanned within those seconds gets its real `disk_size` at the next scan.
+  unchanged. ZFS, for example, counts a new file's blocks up to seconds after
+  the write. A block is the unit in which a filesystem allocates disk space. A
+  file scanned within those seconds gets its real `disk_size` at the next scan.
 - `scan` hashes a file again when its size differs or its mtime is newer. The
   mtime is compared to the nanosecond, as finely as the filesystem records it. A
   same-size rewrite counts as a change whenever the filesystem gives it a later
@@ -484,12 +491,12 @@ walk practical on large or busy storage pools.
     The walk knows them by device ID and inode number. The device ID is the
     number by which the kernel tells filesystems apart. The inode number tells
     the files of one filesystem apart. So the walk passes over them whatever
-    path leads to them. The walk follows no symlink it finds. It does open each
-    operand at the path given, even when that path runs through a symlinked
-    directory. Such an operand can lead to the database files, and the walk
-    passes over them there as well. The walk prints no line for the database
-    files and does not count them as skipped. A record that an earlier scan left
-    for one of them is deleted.
+    path leads to them. The walk follows no symlink it finds. It opens each
+    operand at its real path, not the path given. An operand given through a
+    symlink can lead to the database files, and the walk passes over them there
+    as well. The walk prints no line for the database files and does not count
+    them as skipped. A record that an earlier scan left for one of them is
+    deleted.
 
 - By default the walk enters directories on other filesystems than its
   operand's. With `-x`, it never enters a directory on a different filesystem
@@ -658,6 +665,7 @@ Processing:
 - Records are grouped by signature, the four values
   `(size, head, tail, content)`.
 - Every group with two or more paths is a duplicate group.
+- Empty files form no group, because removing one frees nothing.
 - Within a group, paths are sorted in byte order. The first is `first`, and
   every other path is a `dupe`.
 - Groups are ordered by size, largest first, then by `first` path. The output is
@@ -706,7 +714,7 @@ The summary line on stderr gives:
 - the reclaimable bytes, the sum of `size` over all rows.
 
 ```
-report: 14 records read, 5 duplicate groups, 8 dupe files, 10.0 KiB reclaimable
+report: 14 records read, 4 duplicate groups, 7 dupe files, 10.0 KiB reclaimable
 ```
 
 ### `trees` mode
@@ -734,6 +742,9 @@ Processing:
 - `trees` builds the directory tree and computes every directory's digest. It
   then groups the directories by digest. Every group with two or more
   directories is a duplicate-tree group.
+- `trees` leaves out a group whose trees hold 0 bytes, because removing one
+  frees nothing. An empty file still counts toward the digest of a tree that
+  holds other files.
 - `trees` leaves out a group that a group of its members' parents already
   implies. A group is left out when its members' parents are distinct
   directories that all have the same digest. The parents' group, or an
@@ -797,6 +808,33 @@ The summary line on stderr gives:
 trees: 14 records read, 1 duplicate tree groups, 1 dupe trees, 3.0 KiB reclaimable
 ```
 
+### `dwim` mode
+
+`dwim`, short for "do what I mean", scans a new machine and reports its
+duplicate trees in one command. It takes no positional arguments and no flags of
+its own. Like `scan`, it should run as root, so that it can read every file.
+
+`dwim` runs what `sfdupes scan /` runs with no flags. The walk skips the default
+excludes and crosses into other filesystems. `--workers` keeps its default. The
+database, its creation and the scan lock are those of `scan`. Then `dwim` runs
+what `sfdupes trees` runs. The largest trees come first.
+
+The report goes to stdout, exactly as `trees` prints it. On stderr comes what
+`scan` prints, then what `trees` prints, then one last line:
+
+```
+dwim: run "sfdupes trees" to print this report again
+```
+
+The database keeps the scan, so `sfdupes trees` prints the same report later,
+even after the terminal is gone.
+
+`SIGINT` or `SIGTERM` stops the scan as it stops `scan` (see "Stopping a scan").
+`dwim` then prints no report and exits 1. A fatal scan error also ends it before
+the report, with the same message and exit code as `scan`. Warnings for skipped
+files do not stop it. `dwim` stops catching signals when the scan ends, so a
+signal during the report ends it at once, as it ends `trees`.
+
 ### `info` mode
 
 `info` takes no positional arguments and prints the database's details on
@@ -837,7 +875,7 @@ scan is writing. `info` writes its lines after the `count` display has ended.
 
 ### Database
 
-All four subcommands work on one SQLite database file.
+All five subcommands work on one SQLite database file.
 
 #### Location
 
@@ -853,6 +891,8 @@ scan: new database /var/lib/sfdupes/db.sqlite (default)
 trees: database /srv/tmp/sfdupes/db.db (from SFDUPES_DATABASE)
 ```
 
+`dwim` prints the `scan` line first, and the `trees` line after the scan.
+
 A relative path is printed with the working directory in front of it. The
 working directory is printed as `pwd -P` prints it, with its symlinks resolved.
 The rest of the path is printed as set, so a `..` in it stays. The line names
@@ -1136,9 +1176,9 @@ showing the count it stopped at.
 ### Error handling and exit codes
 
 - `0`: success, even when files were skipped with warnings.
-- `1`: a fatal error, or a `scan` stopped by `SIGINT` or `SIGTERM`. A fatal
-  error is one of these:
-    - an operand that does not exist, or whose details `scan` cannot read;
+- `1`: a fatal error, a `scan` stopped by `SIGINT` or `SIGTERM`, or a `dwim`
+  stopped by either during its scan. A fatal error is one of these:
+    - an operand that does not exist, or whose real path `scan` cannot find;
     - a list of mounted filesystems that `scan` cannot read;
     - another `scan` holding the lock (see "The scan lock");
     - a database, its directory or its lock file that cannot be created or
@@ -1158,7 +1198,7 @@ showing the count it stopped at.
       `--workers abc`;
     - `scan` with no operand;
     - `--workers` below 1;
-    - `report`, `trees` or `info` with a positional argument.
+    - `report`, `trees`, `info` or `dwim` with a positional argument.
 
 A fatal error is reported on stderr, starting with `sfdupes:`. A failed write to
 stdout, such as a full disk, is reported the same way. Two cases never reach
@@ -1346,7 +1386,7 @@ All of the following, run in this directory, must pass:
     head -c 2000 /dev/urandom > "$d/a/unique.bin"     # same size, different content
     printf 'x' > "$d/tiny1"; printf 'x' > "$d/tiny2"  # 1-byte duplicates
     printf 'y' > "$d/tiny3"                           # 1-byte non-duplicate
-    : > "$d/empty1"; : > "$d/empty2"                  # empty duplicates
+    : > "$d/empty1"; : > "$d/empty2"                  # empty files
     # duplicate trees: t1 and t2 are identical; t3 differs by one filename
     mkdir -p "$d/t1/sub" "$d/t2/sub" "$d/t3/sub"
     head -c 3000 /dev/urandom > "$d/t1/f1"
@@ -1371,8 +1411,8 @@ All of the following, run in this directory, must pass:
       is the path that sorts first.
     - `t1/f1`, `t2/f1` and `t3/f1` form one group.
     - `t1/sub/f2`, `t2/sub/f2` and `t3/sub/f2renamed` form one group.
-    - `tiny1` and `tiny2` form a pair, and so do `empty1` and `empty2`.
-    - `unique.bin` and `tiny3` appear nowhere.
+    - `tiny1` and `tiny2` form a pair.
+    - `unique.bin`, `tiny3`, `empty1` and `empty2` appear nowhere.
     - The groups come in order of size, largest first.
 
     `trees` prints exactly one row, `$d/t1` as `first` and `$d/t2` as `dupe`.
@@ -1385,8 +1425,9 @@ All of the following, run in this directory, must pass:
     because its content changed. `copy.bin` and `copy2.bin` remain as one pair.
     `unique.bin` is gone from the database.
 
-    The test suite automates this scenario (see `scan_test.go`). It also checks
-    that `report` and `trees` never touch the scanned filesystem.
+    The test suite automates this scenario (see
+    `internal/sfdupes/scan_test.go`). It also checks that `report` and `trees`
+    never touch the scanned filesystem.
 
 ## TODO
 

TODO.md

@@ -1,581 +1,33 @@
 # Workflow
 
-- take an issue from the `1.0.0` milestone on the tracker; work not yet on the
-  tracker gets filed as an issue first
-- branch from `next`
-- do the work, with tests, in small focused commits
-- record it at the top of Completed Steps (`TODO.md` changes in the same commit
-  as the work)
-- push the branch and open a PR against `next` whose title ends with
-  ` (closes #N)`
-- an independent review gates each merge to `next`; every finding is addressed
-  or explicitly rebutted on the PR
-- only the owner merges `next` to `main`
+- Take an issue from the `1.0.0` milestone on the tracker. Work that is not on
+  the tracker yet is filed as an issue first.
+- Branch from `next`.
+- Do the work, with tests, in small focused commits.
+- Delete Next Step from `TODO.md`, in the same commit as the work.
+- Push the branch and open a PR against `next`. Its title ends with
+  ` (closes #N)`.
+- An independent review gates each merge to `next`. Every finding is addressed
+  or rebutted on the PR.
+- Only the owner merges `next` into `main`.
 
 # Status
 
-- pre-1.0
-- the Gitea tracker is authoritative for the pre-1.0 backlog: the open issues
-  under the `1.0.0` milestone are what remains before the tag, and this file
-  records history and process, not the queue
+- Pre-1.0.
+- The tracker is authoritative for the pre-1.0 backlog. The open issues under
+  the `1.0.0` milestone are what remains before the tag.
 
 # Next Step
 
-- take the next issue from the `1.0.0` milestone on the tracker:
-  https://git.eeqj.de/sneak/sfdupes/milestone/17 — the milestone is the source
-  of truth for what is left before 1.0.0. Individual issues are deliberately not
-  restated here; a copy in this file drifts out of date the moment the tracker
-  moves
-
-# Completed Steps
-
-- `README.md` rewritten from scratch, sentence by sentence, as a newcomer reads
-  it. It leads with what the program is and how to use it. A reference section
-  covers every setting and every subcommand. Development and testing come last.
-  Every statement was checked against the code on `next`. Five comments in
-  `main_test.go` cite "Settings", where their rules now live. One comment each
-  in `scan_test.go`, `trees_test.go` and `exclude_test.go` cites what the README
-  now says (2026-11-02, https://git.eeqj.de/sneak/sfdupes/issues/135)
-
-- each record holds `disk_size`, the bytes the file takes on disk: its allocated
-  blocks, `st_blocks` × 512, from the lstat the walk already does. `trees`
-  prints a `disk_size` column after `size`, the sum over the `dupe` copy's
-  files; on a compressed or sparse file it differs from `size`. A rescan updates
-  the `disk_size` of an unchanged file whose size on disk changed, without
-  reading the file (2026-10-27, https://git.eeqj.de/sneak/sfdupes/issues/147)
-
-- the database keeps the number of records and the sum of their sizes in the one
-  row of a `totals` table, which three triggers on `files` keep current. `info`
-  reads that row, and so do `scan`'s `load` phase and the `read` phases of
-  `report` and `trees` for their totals; no count reads every record any more.
-  The triggers make each write to `files` slower. `scan` keeps SQLite's
-  temporary data in memory, which wins back part of that time (2026-10-27,
-  https://git.eeqj.de/sneak/sfdupes/issues/146)
-
-- an operand at or inside a directory named `.zfs` is never scanned, whether
-  given alone or under another operand. `scan` warns about it, counts it as
-  skipped and does not walk it (2026-10-26,
-  https://git.eeqj.de/sneak/sfdupes/issues/142)
-
-- a file or directory removed while the scan runs is not an error, in the walk
-  or in the hash phase. The scan prints no line for it and does not count it as
-  skipped. When the first of several hard links to a file is gone, the hash
-  phase reads the next one instead. On a terminal every progress display starts
-  with the spinner, the hash phase's included. A phase with an exact total ends
-  its line with its percent and a 10-column bar at the terminal's right edge,
-  which no longer moves as the line's length changes. A line too wide for the
-  terminal now loses its rate before its bar. The time remaining is labelled
-  `remain`, not `eta` (2026-10-26, https://git.eeqj.de/sneak/sfdupes/issues/133)
-
-- the `head`, `tail` and `content` columns are BLOBs, each holding the raw 32
-  bytes of a SHA-256, half the size of the hex text they held. The hashes stay
-  raw from the hash phase through the database to `report` and `trees`. Reading
-  a record whose hash is not 32 bytes is an error (2026-10-26,
-  https://git.eeqj.de/sneak/sfdupes/issues/134)
-
-- the hash phase gives every file the walk records three hashes: `head` and
-  `tail`, the SHA-256 of its first and last 64 KiB, and `content`, the SHA-256
-  of the whole file under 100 MiB and of 1 MiB at each gigabyte from 100 MiB up.
-  The 10 MiB and 50 MiB thresholds, the size census, the records stored without
-  hashes and the content phase are gone, so a scan has four phases and a rescan
-  reads only new and changed files. `info` no longer counts the records with
-  hashes, since every record has them (2026-10-25,
-  https://git.eeqj.de/sneak/sfdupes/issues/132)
-
-- re-vendor `REPO_POLICIES.md` and the four scripts that pass `CACHEBUST` from
-  `sneak/prompts` `next` at `0653579`: in the `lint`, `test` and `builder`
-  stages of the `Dockerfile` the module download, and in `builder` the
-  system-package install, now come before `ARG CACHEBUST`, so Docker keeps them
-  until the base image, the install line, `go.mod` or `go.sum` changes, and
-  every step that lints, tests or compiles still comes after it;
-  `golangci-lint run` also keeps golangci-lint's cache. README says the same
-  (2026-10-18, https://git.eeqj.de/sneak/sfdupes/issues/109)
-
-- releases until 1.0 are `v0.0.N` tags on `main`'s tip, so
-  `go install sneak.berlin/go/sfdupes@latest` installs `main`'s tip once it has
-  passed the build; README "Install" says so, says what `@main` and `v0.0.1`
-  give, and how to check an installed binary. `go.mod` retracts `v0.0.1`, the
-  early build without a database. When the linker set no version,
-  `sfdupes --version` prints the main module's version that Go recorded in the
-  binary, the tag or the pseudo-version of a `go install` build, and `dev` only
-  when neither is known (2026-10-17,
-  https://git.eeqj.de/sneak/sfdupes/issues/116)
-
-- `scan` creates the database's directory where the database path leads: the
-  path with its last element cut off as text, never cleaned, so a `..` after a
-  symlinked directory is followed through the symlink, as when the file is
-  opened. With `SFDUPES_DATABASE=/srv/link/../new/db.sqlite` and `/srv/link` a
-  symlink to `/data/x`, it creates `/data/new` and the database in it, where it
-  used to create `/srv/new` and then fail (2026-10-17,
-  https://git.eeqj.de/sneak/sfdupes/issues/119)
-
-- `scan` never records its own database: once the database and its `.lock` file
-  are open, it notes the device and inode of the database file, its `-wal` and
-  `-shm` files and its `.lock` file, and the walk passes over a file with one of
-  them wherever the operands reach it, through a symlinked directory included,
-  printing no line and counting nothing. A record an earlier scan left for one
-  of them is deleted (2026-10-17, https://git.eeqj.de/sneak/sfdupes/issues/115)
-
-- `scan` never records or reads anything that is not on a persistent filesystem
-  (`tmpfs`, `proc`, `sysfs` and the other kernel or memory-backed types),
-  matched by the device ID of each such filesystem, listed as the scan starts
-  from `/proc/self/mountinfo` on Linux and the mounted-filesystem list on macOS,
-  however the walk or the content phase reaches it; no flag turns that off.
-  Below an operand, its walk does not enter the default excludes either, so
-  `sfdupes scan /` skips the kernel's view of the running system and the
-  temporary directories: on Linux `/proc`, `/sys`, `/dev`, `/run`, `/tmp` and
-  `/var/tmp`, on macOS `/dev`, `/private/tmp`, `/private/var/tmp`,
-  `/private/var/vm`, `/System/Volumes/VM` and `/System/Volumes/Data`, and a
-  Windows list, not used yet. An operand at or inside a default exclude is still
-  walked. The scan prints a line for each path it leaves out, without counting
-  it as skipped, and the records there count as outside the scanned operands, as
-  for `-x`. `--no-default-excludes` turns off the default excludes only, and
-  `scan --help` lists them (2026-10-17,
-  https://git.eeqj.de/sneak/sfdupes/issues/124)
-
-- the rate a progress display shows covers the items completed over the last 5
-  seconds, or since the line before when stderr is not a terminal, so it falls
-  to 0 while nothing completes, and a burst after a wait no longer reads as a
-  steady rate of over 1,000 files a second; the ETA still comes from the phase's
-  average. Once no item has completed for 10 seconds, the word `stalled` and
-  where the phase waits take the rate's place, as `stalled disk/db`: `disk`,
-  `db`, `out` for stdout or `cpu`, or two of them for a phase that may wait on
-  either, each phase giving its word where it is defined. A line too wide for
-  the terminal loses its bar first, then its rate or those words, so the phase,
-  progress, elapsed time and ETA stay whole. On an 80-column terminal, at counts
-  like those of README's example, the content phase's checks and reads lose
-  those words at most times in minutes, and every other phase keeps them
-  whenever the elapsed time and the ETA are both in minutes. The content phase's
-  last partial batch is now written under a display of its own (2026-10-16,
-  https://git.eeqj.de/sneak/sfdupes/issues/125)
-
-- new subcommand `info` prints the database's details on stdout, one per line as
-  a name, a tab and the value: its path and where it came from, the sizes of the
-  database file and of its `-wal` file when there is one, when the database file
-  was last changed, the schema version, the number of records, how many have
-  head and tail hashes and how many a content hash, and the sizes of all records
-  added up. It opens the database as `report` does, and shows two phases on
-  stderr, `[1/2] open` and `[2/2] count`; the schema version and the counts come
-  from one read-only transaction, the counts from one query (2026-10-16,
-  https://git.eeqj.de/sneak/sfdupes/issues/117)
-
-- `report` shows its work on stderr in two phases, `[1/2] open` and
-  `[2/2] read`, with the progress display `scan` and `trees` use, from the
-  moment it starts until the summary line: `open` says it is opening the
-  database, also while it waits on a busy one; `read` counts the records, then
-  reads them against that count in signature order, which SQLite takes from the
-  `files_signature` index without sorting, so the first record comes at once.
-  `report` forms the duplicate groups itself, holding only those of the size it
-  is reading, and writes them ordered by first path before it reads the next
-  size. stdout and the summary line are unchanged, and SQLite no longer needs a
-  temporary file to sort in (2026-10-16,
-  https://git.eeqj.de/sneak/sfdupes/issues/114)
-
-- `trees` shows its work on stderr in four phases, `[1/4] open`, `[2/4] read`,
-  `[3/4] group` and `[4/4] write`, each with the progress display `scan` uses,
-  from the moment it starts until the summary line: `open` says it is opening
-  the database, also while it waits on a busy one; `read` counts the records,
-  then reads them against that count; `group` counts the directories it groups,
-  and `write` the groups it writes. A display's rate names what its phase
-  counts: files, records, directories or groups. stdout and the summary line are
-  unchanged. When stdout and stderr are the same file, as one terminal is, none
-  of stdout's lines shares a line with the display; when they are not, the
-  display keeps being drawn while stdout waits on a slow reader (2026-10-16,
-  https://git.eeqj.de/sneak/sfdupes/issues/113)
-
-- each `scan` phase's progress display names the phase and its place among the
-  five, as `[2/5] walk`, from the moment it starts, with its progress, elapsed
-  time and ETA: `load` counts the records first, the walk's total is estimated
-  from the records under the operands, and the content phase counts the records
-  it checks from SQLite's grouping alone, then says it is searching the database
-  until the first one is returned. On a terminal a phase with an exact total
-  draws its line followed by the library's bar, and any other a spinner followed
-  by the line; every display is drawn again several times a second. No line
-  reaches the terminal's last column, however narrow, also after the terminal is
-  made narrower during a phase: a line too wide leaves out its rate, then its
-  bar, keeping the phase, progress, elapsed time and ETA whole, and is cut short
-  only when those alone do not fit, as below about 70 columns late in a large
-  scan. In plain mode the line is printed every 5 seconds whether or not an item
-  completed (2026-10-16, https://git.eeqj.de/sneak/sfdupes/issues/112)
-
-- `scan`, `report` and `trees` first print a line on stderr naming the database
-  they use, as an absolute path, and whether that path is the default or comes
-  from `SFDUPES_DATABASE`; `scan` says when the database is new. README
-  "Database" says when `scan` writes each file (2026-10-16,
-  https://git.eeqj.de/sneak/sfdupes/issues/111)
-
-- re-vendor the canonical files and model scripts from `sneak/prompts` `next` at
-  `e3f79c4`: golangci-lint v2.14.0; lint and test are phases of the `Dockerfile`
-  that write no image, and `make test` runs the suite under the race detector,
-  so `Dockerfile.lint`, `script/verify-lint-image-pin` and `make test-race` are
-  gone; every `docker build` in `script/` passes a new `CACHEBUST` value, which
-  every stage of the `Dockerfile` declares first, so every `RUN` step runs on
-  every build, while the steps that compile keep Go's build cache and the tests
-  run with `-count=1`; prettier runs on the host, from the node and yarn
-  `script/bootstrap` installs, so the `prettier` and `markdown` stages are gone
-  and the build stage installs `git` and `make` itself; a new push cancels the
-  workflow's older run on the same branch, and a run stops after 20 minutes;
-  `.claude/settings.json` is deleted (2026-10-15,
-  https://git.eeqj.de/sneak/sfdupes/issues/95). Since
-  https://git.eeqj.de/sneak/sfdupes/issues/109 the module download in `lint`,
-  `test` and the build stage, and the install of `git` and `make` in the build
-  stage, come before `ARG CACHEBUST`, and Docker keeps them between builds;
-  every step that lints, tests or compiles still runs on every build
-
-- with `-x`, an operand under another operand is walked on its own instead of
-  being dropped when a directory from it (from its directory, for a regular
-  file) up to but not including that operand is on a different filesystem than
-  that operand, whose walk then cannot reach it, and the records of files gone
-  from below it are deleted (2026-10-14,
-  https://git.eeqj.de/sneak/sfdupes/issues/106)
-
-- with `-x`, `scan` keeps the records below a directory on another filesystem
-  under its operand, and counts their sizes in the size census, instead of
-  deleting them (2026-10-14, https://git.eeqj.de/sneak/sfdupes/issues/99)
-
-- the hash and content phases open each file without blocking and check that it
-  is still a regular file, so one replaced by a FIFO or device node after it was
-  statted is warned about and skipped instead of hanging the scan (2026-10-14,
-  https://git.eeqj.de/sneak/sfdupes/issues/100)
-
-- the scan lock file is named from the database's path with symlinks resolved,
-  after `scan` creates the database file if it is missing, so a scan through a
-  symlink to the database fails while another scan holds the lock (2026-10-14,
-  https://git.eeqj.de/sneak/sfdupes/issues/101)
-
-- on a terminal, a warning for the last file of a phase no longer erases the
-  phase's finished bar: the bar is drawn again below the warning (2026-10-14,
-  https://git.eeqj.de/sneak/sfdupes/issues/102)
-
-- `scan` records mtime to the nanosecond, as whole seconds in `mtime` plus
-  `mtime_nsec`, and compares it at that resolution, so a same-size rewrite
-  within the same second is re-hashed (2026-10-07,
-  https://git.eeqj.de/sneak/sfdupes/issues/12)
-
-- cut the narration from `TODO.md` Completed Steps and from the comments in
-  `script/`, `Dockerfile` and `Dockerfile.lint` (gone since
-  https://git.eeqj.de/sneak/sfdupes/issues/95); §Workflow now branches from and
-  merges to `next` (2026-10-04, https://git.eeqj.de/sneak/sfdupes/issues/49)
-
-- `make test-race` ran the test suite under the race detector in a cgo-enabled
-  container, outside `make check` (2026-10-04,
-  https://git.eeqj.de/sneak/sfdupes/issues/18). Since
-  https://git.eeqj.de/sneak/sfdupes/issues/95 `make test` itself runs the suite
-  under the race detector, in the `Dockerfile`'s Debian-based `test` phase, and
-  `make test-race` is gone
-
-- a bare `docker build .` failed, naming `script/cibuild` and `script/docker`,
-  rather than serve the gates from cache (2026-10-04,
-  https://git.eeqj.de/sneak/sfdupes/issues/39). Since
-  https://git.eeqj.de/sneak/sfdupes/issues/95 a bare build succeeds, as
-  `REPO_POLICIES.md` requires, and may serve the gates from cache; the builds in
-  `script/` pass a new `CACHEBUST` value, so theirs always run
-
-- `make fmt` and `make fmt-check` run prettier over all Markdown, and CI checks
-  it; all Markdown reformatted (2026-10-04,
-  https://git.eeqj.de/sneak/sfdupes/issues/19)
-
-- `script/lint` writes no image, so a run no longer leaves an untagged one
-  behind (2026-10-04, https://git.eeqj.de/sneak/sfdupes/issues/48)
-
-- tests cover a missing database, `scan` keeping stdout empty, its skip warning,
-  the `report` and `trees` summary lines, and every subcommand going through
-  `runE` (2026-10-04, https://git.eeqj.de/sneak/sfdupes/issues/16)
-
-- `.golangci.yml` replaced with the current canonical copy, which uses
-  `gomodguard_v2`, so lint no longer prints a deprecation warning (2026-10-04,
-  https://git.eeqj.de/sneak/sfdupes/issues/26)
-
-- a test fails when either `hashWorker` cancellation check in `scan.go` is
-  removed (2026-10-04, https://git.eeqj.de/sneak/sfdupes/issues/83)
-
-- a database path holding `?`, `#` or `%` opens exactly the file it names
-  (2026-10-04, https://git.eeqj.de/sneak/sfdupes/issues/55)
-
-- `scan` rejects `--workers` below 1 as a usage error instead of running
-  single-threaded (2026-10-04, https://git.eeqj.de/sneak/sfdupes/issues/10)
-
-- a test fails when either walk cancellation check in `scan.go` is removed
-  (2026-10-04, https://git.eeqj.de/sneak/sfdupes/issues/81)
-
-- test that `scan` refuses a database with another schema version (2026-10-04,
-  https://git.eeqj.de/sneak/sfdupes/issues/64)
-
-- correct four inaccurate comments in `cancel_test.go` and rename
-  `walkCancelInFlightDirs` to `walkCancelInFlightFiles` (2026-10-04,
-  https://git.eeqj.de/sneak/sfdupes/issues/33)
-
-- test the `-x` filesystem-boundary rules in `subdirJob` (2026-10-04,
-  https://git.eeqj.de/sneak/sfdupes/issues/17)
-
-- `scan` creates the schema in one transaction; a version-0 database with a
-  `files` table is refused with a clear schema-version error (2026-10-04,
-  https://git.eeqj.de/sneak/sfdupes/issues/11)
-
-- README documents install, Docker, a daily cron scan and how to read and check
-  the reports (2026-10-04, https://git.eeqj.de/sneak/sfdupes/issues/54)
-
-- the `Dockerfile` build stage kept the Go module cache out of `builder`'s home
-  and copied the sources with `--chown`, so no `chown -R` walked them
-  (2026-10-04, https://git.eeqj.de/sneak/sfdupes/issues/43). Since
-  https://git.eeqj.de/sneak/sfdupes/issues/95 there is no `builder` user and
-  nothing changes owner: the build stage only compiles, as root, and the tests
-  run as `nobody` in the `test` phase
-
-- `--version` prints `sfdupes VERSION` to stdout; README documents it and
-  `--help` (2026-10-04, https://git.eeqj.de/sneak/sfdupes/issues/15)
-
-- `scan` stops cleanly on `SIGINT` or `SIGTERM`: commits what it has hashed,
-  deletes nothing more, exits 1 (2026-10-04,
-  https://git.eeqj.de/sneak/sfdupes/issues/5)
-
-- `report` and `trees` stream the records instead of holding them all in memory;
-  the schema gains the `files_signature` index (2026-10-04,
-  https://git.eeqj.de/sneak/sfdupes/issues/14)
-
-- progress prints at once on a non-terminal, uses a real terminal test, and
-  prints warnings through a spinner instead of racing its redraw (2026-10-03,
-  https://git.eeqj.de/sneak/sfdupes/issues/13)
-
-- warn about and skip symlink, socket, FIFO, device and `.zfs` operands, keeping
-  the records beneath them (2026-10-03,
-  https://git.eeqj.de/sneak/sfdupes/issues/9)
-
-- `scan` holds a lock on a lock file beside the database for its whole run, so a
-  second `scan` fails at once with exit 1 (2026-10-03,
-  https://git.eeqj.de/sneak/sfdupes/issues/53)
-
-- test stdout write failures in `report` and `trees`; README states that
-  `| head` ends sfdupes by `SIGPIPE` and `>&-` writes to `/dev/null`
-  (2026-10-03, https://git.eeqj.de/sneak/sfdupes/issues/30)
-
-- `report` and `trees` open the database read-only, and `scan` leaves it out of
-  WAL mode, so reading needs only read access (2026-10-03, closes
-  https://git.eeqj.de/sneak/sfdupes/issues/8)
-
-- escape tabs, newlines, carriage returns and backslashes in report, trees and
-  warning paths; the root directory's path is `/` (2026-10-03,
-  https://git.eeqj.de/sneak/sfdupes/issues/7)
-
-- stamp the git tag or short commit in a plain `docker build .` instead of `dev`
-  (2026-10-02, branch `next`, closes
-  https://git.eeqj.de/sneak/sfdupes/issues/67): `.dockerignore` sends `.git`
-  without `.git/config`; the build stage stamps the `VERSION` build argument,
-  else `git describe --tags --always`, and fails if the context carries `.git`
-  and the version is still empty, `dev` or `unknown`. CI checks out the full
-  history (`fetch-depth: 0`) so it stamps the same value as `make build`.
-
-- replace the 1 KiB end-window sampling with the head/tail plus content-hash
-  ladder (2026-09-22, branch `next`, closes
-  https://git.eeqj.de/sneak/sfdupes/issues/61); README "Duplicate detection"
-  documents every rung. A file under 10 MiB is hashed in full, and its `head`,
-  `tail` and `content` all hold that hash. A larger file gets only its 64 KiB
-  `head` and `tail` in the hash phase; the content phase, after the update
-  phase, reads it for `content` (the whole file below 50 MiB, gigabyte-spaced 1
-  MiB samples at or above) only when its size, `head` and `tail` match another
-  record's from this scan or an earlier one, and never reads a file gone or
-  changed since its record was written. `report` and `trees` leave out any
-  record without a `content` hash. The `content` column is part of the version 1
-  schema.
-
-- remove the dead `files.dat` references from `Makefile`, `.gitignore` and
-  `.dockerignore` (2026-09-21, branch `next`, closes
-  https://git.eeqj.de/sneak/sfdupes/issues/22)
-
-- fix the lint-image pin comments and `FROM` form in `Dockerfile` and
-  `Dockerfile.lint` (2026-08-10, branch `next`, closes
-  https://git.eeqj.de/sneak/sfdupes/issues/25): both pins became the policy
-  `# image:vX.Y.Z, YYYY-MM-DD` comment over a bare `FROM image@sha256:...`,
-  without the false `(Debian-based)` note or the tag. Since
-  https://git.eeqj.de/sneak/sfdupes/issues/95 the `Dockerfile`'s `lint` phase
-  holds the only golangci-lint pin, in that form, so `Dockerfile.lint` and
-  `script/verify-lint-image-pin`, which compared the two pins, are gone.
-
-- run all linting in Docker via `Dockerfile.lint` and `script/lint` (2026-08-10,
-  branch `next`, closes https://git.eeqj.de/sneak/sfdupes/issues/46): per the
-  owner ruling the linter is never installed on a host, and
-  `golangci-lint config verify` runs before `golangci-lint run`.
-  `script/bootstrap` stopped installing or pinning the linter, and
-  `script/verify-linter-pin` was retired. Since
-  https://git.eeqj.de/sneak/sfdupes/issues/95 both commands run in the
-  `Dockerfile`'s `lint` phase, which `script/lint` builds alone and the build
-  stage depends on through `COPY --from=lint /src/go.sum /dev/null`;
-  `Dockerfile.lint` and `script/verify-lint-image-pin` are gone. Nothing inside
-  an image build may run docker, so the phase calls `golangci-lint` directly.
-
-- install the Docker build stage's prerequisites by running `script/bootstrap`
-  instead of `apk add --no-cache make` inline (2026-08-09, branch
-  `dockerfile-bootstrap`, closes https://git.eeqj.de/sneak/sfdupes/issues/42),
-  with `script/verify-linter-pin` failing the build unless the linter copied
-  from the lint stage was the version `script/bootstrap` pinned. Builds then
-  took up to 5m14s cold, mostly in a `chown -R` of the module cache, filed as
-  https://git.eeqj.de/sneak/sfdupes/issues/43. Since
-  https://git.eeqj.de/sneak/sfdupes/issues/95 the build stage installs `git` and
-  `make` with `apk add --no-cache` and only compiles; the `lint` and `test`
-  phases are the gates
-- bust the Docker layer cache for the gate steps, so `script/cibuild` and
-  `script/docker` cannot report a green they did not earn (2026-08-09, branch
-  `cibuild-cache-bust`, closes https://git.eeqj.de/sneak/sfdupes/issues/32): the
-  `Dockerfile` copies the tree before its gates, so on an unchanged tree Docker
-  served them from cache and the build exited 0 having run nothing. The fix was
-  a `CHECK_EPOCH` build argument; since
-  https://git.eeqj.de/sneak/sfdupes/issues/95 every `docker build` in `script/`
-  passes a new `CACHEBUST` value instead, which every stage of the `Dockerfile`
-  declares before every step that lints, tests or compiles. Run as root, the
-  tests fail `TestScanHardlinkRunFailsTogether`, because root reads through the
-  `chmod(0)` the test relies on, so the `test` phase runs them as `nobody`
-- check the installed golangci-lint version in `script/bootstrap` instead of
-  only its presence (2026-08-09, branch `bootstrap-version-check`, closes
-  https://git.eeqj.de/sneak/sfdupes/issues/24): the version lives only in
-  `GOLANGCI_LINT_VERSION`, with the `go install` module ref derived from it, and
-  any installed version that is not the pin — older, newer, absent or
-  unparseable — is reinstalled. `go install` writes into `GOBIN` (or
-  `GOPATH/bin`) while `make lint` runs the first `golangci-lint` on `PATH`, so
-  bootstrap re-reads the effective version after installing and, on a mismatch,
-  prints both paths and both versions and exits non-zero; it does not reorder
-  `PATH` or delete anyone's binary. The `--version` call keeps its stderr and is
-  bounded by `timeout(1)` where that exists. `git`, `make` and `go` keep
-  presence-only checks. Verified by bootstrapping this host from v2.10.1 to
-  v2.12.2 and again to a no-op, and by stub runs of the script under `dash`
-  covering a thirteen-input version-parse matrix, a shadowed install that must
-  exit non-zero, an install destination not on `PATH`, `GOBIN` set, and a wedged
-  binary that must hit the timeout; `make check` and `make lint` are clean at
-  v2.12.2, so v2.10.1 was not hiding any findings on `main`
-- unwind the hash worker pool on the error path (2026-08-09, branch
-  `hash-pool-cleanup`, closes https://git.eeqj.de/sneak/sfdupes/issues/6): the
-  pool is now an owned, context-aware `hashPool`: every blocking send in the
-  feeder and the workers selects on `ctx.Done()`, `jobs` is closed on every path
-  out, and `hashPhase` defers `pool.stop()`, which cancels and then drains
-  `results` until the last goroutine has exited — draining is what frees a
-  worker already parked on a send. `ctx` is threaded from `cmd.Context()`
-  through `runScan`, `syncScan`, both worker pools and the whole database layer,
-  as the first parameter everywhere. The walk pool gets the same treatment plus
-  a `ctx.Err()` guard after the walk: a cancelled walk yields a partial size
-  census, and every file it never reached looks vanished to the update phase.
-  That phase's own `BeginTx` also fails on the cancelled context before deleting
-  anything, but the guard is the barrier that still holds once an interrupted
-  scan may commit what it has. Tests drive `run(scan)` against a database whose
-  insert trigger aborts and assert that the scan fails instead of hanging and
-  that `runtime.NumGoroutine()` polls back to its pre-scan baseline; others
-  cancel a scan part-way through the walk, deterministically, by counting its
-  own consultations of `ctx.Done()`, and assert that it stops at the guard
-  holding a partial census and a still-populated record index, with every record
-  intact. Direct tests of `sendEvent`, the walk workers, `dispatchDirs`,
-  `feedHashJobs`, `hashWorker` and `hashPhase` cover the remaining cancellation
-  branches of both pools
-- guarantee the database is closed on every fatal exit path (2026-08-09, branch
-  `db-close-on-fatal`, closes https://git.eeqj.de/sneak/sfdupes/issues/4):
-  `fatalf` and its `os.Exit(1)` are gone, so the deferred `db.Close()` — and
-  with it the SQLite WAL checkpoint — now actually runs when a subcommand fails;
-  `runScan`, `runReport`, `runTrees`, `loadRecords` and `resolveRoots` return
-  errors instead. The single exit point is `run` in `main.go`: it maps a
-  `fatalError` (anything a subcommand returned) to exit 1 and cobra's own
-  argument and flag errors to exit 2, which keeps a runtime failure from being
-  reported as a usage error or printing the usage text. New `main_test.go`
-  drives the CLI in-process and asserts the exit codes from README §Error
-  handling plus the stdout/stderr split, including that a fatal error raised
-  after the database is open leaves no `-wal`/`-shm` sidecar behind for `scan`,
-  `report` or `trees`
-- update golangci-lint to v2.12.2 with the canonical config (2026-08-09, branch
-  `golangci-v2.12.2`, merged as `38a01bd`, closes
-  https://git.eeqj.de/sneak/sfdupes/issues/3): bumped the pinned linter in the
-  `Dockerfile` lint stage and `script/bootstrap` from v2.12.1 to v2.12.2, and
-  replaced `.golangci.yml` with the canonical file — the linter settings (`lll`,
-  `funlen`, `cyclop`, `dupl` thresholds) now live under `linters.settings` per
-  the v2 schema, so they are actually applied; no new lint findings surfaced
-- convert Makefile targets to scripts-to-rule-them-all `script/` entrypoints
-  like the other managed repos (2026-07-26, commit `3abeacf`, closes
-  https://git.eeqj.de/sneak/sfdupes/issues/1): all 12 `script/` entrypoints
-  exist (`bootstrap`, `setup`, `projectname`, `test`, `lint`, `fmt`,
-  `fmt-check`, `check`, `docker`, `cibuild`, `precommit`, `install-precommit`)
-  and every Makefile target is now a thin shim over them
-- make the binary the default Make target (2026-07-24, branch
-  `make-default-target`): plain `make` now builds `sfdupes` (previously it ran
-  `check` plus `build`); `make build` remains as an alias
-- scan-wide phases, concurrent operands, batched updates (2026-07-24, branch
-  `scan-wide-phases`): all operands seed the shared walk pool and every pass
-  runs once over the whole scan, so totals and ETAs are scan-global; the
-  per-operand walk/hash/update cycles and their stderr announcements are gone;
-  the update pass commits in batched transactions — the filesystem is
-  authoritative and the database an eventually-consistent reflection, so
-  scan-level atomicity is not required
-- split the stat pass back out of the walk (2026-07-24, branch
-  `parallel-phases`): phases are strictly sequential again — walk, stat, hash,
-  update per operand — with parallelism only inside each phase; the walk
-  enumerates paths with per-directory workers and the stat pass lstats them with
-  per-file workers, restoring the exact total/ETA stat bar
-- announce each operand on stderr before its passes (2026-07-24, branch
-  `scan-operand-progress`): with per-operand walk/hash/update cycles, a
-  multi-operand run (e.g. `scan /srv/*`) showed pass totals that looked like the
-  whole run's
-- parallel walk (2026-07-24, branch `parallel-walk`): the walk pass was a single
-  goroutine and took hours at ~20M files on a busy pool (observed: 22M files in
-  4h on a ZFS server); it is now a per-directory worker-pool traversal that
-  records size/mtime during the walk (folding away the separate stat pass,
-  halving metadata I/O), and each `PATH` operand commits in its own transaction
-  so an interrupted scan keeps completed operands
-
-- persistent scan database (2026-07-24, branch `persistent-database`): `scan`
-  now maintains a SQLite database (`modernc.org/sqlite`, pure Go, cgo stays
-  disabled) keyed by absolute path that survives between runs — a rescan hashes
-  only new or changed files (by mtime/size), deletes records for files vanished
-  from under the scanned operands, and leaves records outside them untouched, so
-  `scan` can be cronned daily; `report` and `trees` read the database (no
-  positional arguments) instead of a scan stream. Database at
-  `/var/lib/sfdupes/db.sqlite`, overridable via `SFDUPES_DATABASE`; WAL
-  journaling plus a single-transaction update keep a report run during a scan
-  safe
-- add the `origin` remote (`git@git.eeqj.de:sneak/sfdupes.git`), tag `v0.0.1`,
-  and push `main` plus tags (2026-07-23)
-- `scan` CLI rework (2026-07-23, branch `scan-required-paths`): required
-  `PATH...` operands via cobra flags replacing the `/srv` `-root` default; new
-  `-x`/`--one-file-system` flag (GNU convention) to stop at filesystem
-  boundaries, which are crossed by default
-- bring the repo into full policy compliance (2026-07-23, branch
-  `repo-policy-compliance`; checklist below)
-- `git init` with README-only first commit; code baseline committed on `main`
-  (2026-07-22)
-- implement `scan`, `report`, and `trees` subcommands (pre-git history)
+- Take the next issue from the `1.0.0` milestone,
+  https://git.eeqj.de/sneak/sfdupes/milestone/17. The issues are not restated
+  here, because a copy drifts as soon as the tracker moves.
 
 # Future Steps
 
-- possible later features (explicitly out of scope per README): full-content
-  verification of candidates, removal-script helpers
+- Possible later features, out of scope per README, are a byte-for-byte check of
+  candidates and helper scripts for removal.
 
-# Repo Policy Compliance
+# Accepted Divergences
 
-Audited 2026-07-22 against `REPO_POLICIES.md` (2026-07-06), the existing repo
-checklist, and the Go styleguide. Code is already gofmt-clean, so no standalone
-formatting commit is needed.
-
-- [x] `.gitignore` missing — the compiled `sfdupes` binary and `files.dat` sit
-      untracked in the tree; needs OS/editor/Go artifacts plus secrets patterns
-- [x] `.editorconfig` missing
-- [x] `LICENSE` missing and README has no License section (MIT assumed from
-      house convention — user to confirm)
-- [x] `REPO_POLICIES.md` missing from repo root
-- [x] `.golangci.yml` missing (install canonical copy); code must then pass
-      `make lint` (150 findings fixed; `make lint` is clean)
-- [x] `Makefile` lacks required targets `test`, `lint`, `fmt`, `fmt-check`,
-      `docker`, `hooks`; `check` currently depends on `build`, which writes the
-      binary (`make check` must not modify files)
-- [x] no tests — `go test ./...` has nothing to run; policy requires real tests
-      with a 30-second timeout and the conditional `-v` rerun pattern (suite
-      covers parsing, grouping, digests, suppression, hashing, and the scan
-      pipeline; 64% coverage)
-- [x] `Dockerfile` missing — Go multistage with hash-pinned images: fail-fast
-      lint stage, build stage running `make check`
-- [x] `.dockerignore` missing
-- [x] `.gitea/workflows/check.yml` missing (`docker build .` on push, checkout
-      action pinned by commit SHA)
-- [x] README lacks required sections: Description first line
-      (name/purpose/category/license/author), Getting Started, Rationale, TODO,
-      License, Author
-- [x] README non-goal "no git repository setup and no CI" is stale now that the
-      repo is under git with CI
-- [x] pre-commit hook not installed (`make hooks` once the target exists)
-
-Accepted divergences (no action):
-
-- flat single-package layout with `.go` files in the repo root — fine for a
-  small single-binary tool per the Go styleguide; the tracker audit agrees
+None.

cmd/sfdupes/main.go

@@ -0,0 +1,29 @@
+// Command sfdupes quickly identifies candidate duplicate files across
+// very large filesystems without reading every byte of every file.
+// Files are considered duplicates when their sizes are equal and they
+// agree on three SHA-256 hashes: of the first 64 KiB, of the last 64
+// KiB, and of the content. The content hash covers the whole file under
+// 100 MiB, and 1 MiB at each gigabyte at 100 MiB or more, so a large
+// file is never read in full. scan maintains a persistent SQLite
+// database of file signatures (SFDUPES_DATABASE, default
+// /var/lib/sfdupes/db.sqlite) that the other subcommands read.
+//
+// Usage:
+//
+//	sfdupes scan [--workers N] [-x] [--no-default-excludes] PATH...
+//	sfdupes report > dupes.tsv
+//	sfdupes trees > dupetrees.tsv
+//	sfdupes info
+//	sfdupes dwim
+//	sfdupes --version
+//
+// See README.md for the complete specification.
+package main
+
+import (
+	"os"
+
+	"sneak.berlin/go/sfdupes/internal/sfdupes"
+)
+
+func main() { os.Exit(sfdupes.Main()) }

internal/sfdupes/cancel_test.go

@@ -1,4 +1,4 @@
-package main
+package sfdupes //nolint:testpackage // cancels the unexported runScan and hashWorker
 
 import (
 	"context"

internal/sfdupes/cli.go

@@ -1,23 +1,6 @@
-// Command sfdupes quickly identifies candidate duplicate files across
-// very large filesystems without reading every byte of every file.
-// Files are considered duplicates when their sizes are equal and they
-// agree on three SHA-256 hashes: of the first 64 KiB, of the last 64
-// KiB, and of the content. The content hash covers the whole file under
-// 100 MiB, and 1 MiB at each gigabyte at 100 MiB or more, so a large
-// file is never read in full. scan maintains a persistent SQLite
-// database of file signatures (SFDUPES_DATABASE, default
-// /var/lib/sfdupes/db.sqlite) that the other subcommands read.
-//
-// Usage:
-//
-//	sfdupes scan [--workers N] [-x] [--no-default-excludes] PATH...
-//	sfdupes report > dupes.tsv
-//	sfdupes trees > dupetrees.tsv
-//	sfdupes info
-//	sfdupes --version
-//
-// See README.md for the complete specification.
-package main
+// Package sfdupes implements the sfdupes command and the database its
+// subcommands share.
+package sfdupes
 
 import (
 	"context"
@@ -45,6 +28,7 @@ const (
 	cmdReport = "report"
 	cmdTrees  = "trees"
 	cmdInfo   = "info"
+	cmdDwim   = "dwim"
 )
 
 // errNoSubcommand is returned by the root command when it is invoked
@@ -84,20 +68,22 @@ func buildVersion(linkerVersion string, info *debug.BuildInfo) string {
 	return info.Main.Version
 }
 
-func main() {
+// Main runs the command line in os.Args and returns the process exit
+// code.
+func Main() int {
 	// Once the reader of a stdout pipe has gone, as in "sfdupes report |
 	// head", the Go runtime ends the process with SIGPIPE on the next
 	// write instead of returning an error (README "Error handling").
 	// Registering for SIGPIPE with os/signal would change that.
-	os.Exit(run(os.Args[1:], os.Stdout, os.Stderr))
+	return run(os.Args[1:], os.Stdout, os.Stderr)
 }
 
 // run executes args against the command tree and returns the process
 // exit code. It is the program's single exit point: the subcommands
 // return their errors instead of exiting, so every deferred cleanup —
 // above all closing the database, which checkpoints the SQLite WAL —
-// runs before the process ends. The report, trees and info subcommands
-// write their data to stdout.
+// runs before the process ends. The report, trees, info and dwim
+// subcommands write their data to stdout.
 func run(args []string, stdout, stderr io.Writer) int {
 	// A nil slice makes cobra fall back to os.Args, which would let a
 	// test binary's own flags reach the command tree.
@@ -201,7 +187,16 @@ func newRootCommand(stdout, stderr io.Writer) *cobra.Command {
 		}),
 	}
 
-	root.AddCommand(newScanCommand(), reportCmd, treesCmd, infoCmd)
+	dwimCmd := &cobra.Command{
+		Use:   cmdDwim,
+		Short: "Scan / with the default excludes, then print the duplicate-tree report",
+		Args:  cobra.NoArgs,
+		RunE: runE(func(ctx context.Context, _ []string) error {
+			return runDwim(ctx, "/", stdout)
+		}),
+	}
+
+	root.AddCommand(newScanCommand(), reportCmd, treesCmd, infoCmd, dwimCmd)
 
 	return root
 }

internal/sfdupes/cli_test.go

@@ -1,4 +1,4 @@
-package main
+package sfdupes //nolint:testpackage // drives the unexported run
 
 import (
 	"bytes"
@@ -14,6 +14,8 @@ import (
 	"strconv"
 	"strings"
 	"testing"
+
+	"golang.org/x/sys/unix"
 )
 
 // usageMarker is the first line of cobra's usage text, which a usage
@@ -620,6 +622,7 @@ func TestRunUsageErrors(t *testing.T) {
 		"report with args":   {[]string{cmdReport, "x"}, usageMarker},
 		"trees with args":    {[]string{cmdTrees, "x"}, usageMarker},
 		"info with args":     {[]string{cmdInfo, "x"}, usageMarker},
+		"dwim with args":     {[]string{cmdDwim, "x"}, usageMarker},
 		"unknown flag":       {[]string{cmdScan, "--nope", "/"}, usageMarker},
 		"unknown subcommand": {[]string{"nope"}, "unknown command"},
 	}
@@ -797,7 +800,7 @@ func TestRunVersionWriteFailureIsFatal(t *testing.T) {
 func scanFixture(t *testing.T) []string {
 	t.Helper()
 
-	dir := t.TempDir()
+	dir := realTempDir(t)
 
 	dupes := []string{
 		writeFile(t, dir, "one/a.bin", pattern(1, 300)),
@@ -867,7 +870,7 @@ func TestRunScanSucceedsDespiteWarnings(t *testing.T) {
 	path := testDBPath(t)
 	t.Setenv(databaseEnv, path)
 
-	dir := t.TempDir()
+	dir := realTempDir(t)
 	writeFile(t, dir, "a.bin", pattern(1, 300))
 
 	// Same size as a.bin, so the scan reads it, and the read fails.
@@ -895,58 +898,278 @@ func TestRunScanSucceedsDespiteWarnings(t *testing.T) {
 	assertNoSidecars(t, path)
 }
 
-func TestRunScanSkipsSymlinkOperand(t *testing.T) {
-	path := testDBPath(t)
-	t.Setenv(databaseEnv, path)
+// realTempDir returns a new temporary directory by its real path, so
+// tests hold where the temporary directory is reached through a
+// symlink.
+func realTempDir(t *testing.T) string {
+	t.Helper()
 
-	dir := t.TempDir()
-	writeFile(t, dir, "target/sub/f", pattern(1, 10))
-
-	link := filepath.Join(dir, "link")
-
-	err := os.Symlink(filepath.Join(dir, "target"), link)
+	dir, err := filepath.EvalSymlinks(t.TempDir())
 	if err != nil {
 		t.Fatal(err)
 	}
 
-	// Scanning a directory through the symlink stores a record beneath
-	// the symlink's own path for a file beneath its target.
-	scanOK(t, filepath.Join(link, "sub"))
-
-	assertOperandSkipped(t, path, link, "symlink",
-		filepath.Join(link, "sub", "f"))
+	return dir
 }
 
+// symlink creates link pointing at target.
+func symlink(t *testing.T, target, link string) {
+	t.Helper()
+
+	err := os.Symlink(target, link)
+	if err != nil {
+		t.Fatal(err)
+	}
+}
+
+// TestRunScanFollowsSymlinkOperand scans link, a symlink to target.
+// The operand is scanned at its real path, and its file is recorded
+// there.
+func TestRunScanFollowsSymlinkOperand(t *testing.T) {
+	path := testDBPath(t)
+	t.Setenv(databaseEnv, path)
+
+	dir := realTempDir(t)
+	f := writeFile(t, dir, "target/sub/f", pattern(1, 10))
+
+	link := filepath.Join(dir, "link")
+	symlink(t, filepath.Join(dir, "target"), link)
+
+	stderr := scanOK(t, link)
+
+	summary := "scan: 1 files seen (1 added, 0 updated, 0 removed, " +
+		"0 unchanged), 0 skipped\n"
+	if !strings.Contains(stderr, summary) {
+		t.Errorf("stderr = %q, want %q", stderr, summary)
+	}
+
+	if got := storedPaths(t, path); !slices.Equal(got, []string{f}) {
+		t.Errorf("records = %q, want %q", got, []string{f})
+	}
+}
+
+// TestRunScanWalksOperandUnderSymlinkOperand scans link and link/sub,
+// with link a symlink to target. Both resolve under target, so
+// target/sub is walked once, as part of target.
 func TestRunScanWalksOperandUnderSymlinkOperand(t *testing.T) {
 	path := testDBPath(t)
 	t.Setenv(databaseEnv, path)
 
-	dir := t.TempDir()
-	writeFile(t, dir, "target/sub/f", pattern(1, 10))
+	dir := realTempDir(t)
+	f := writeFile(t, dir, "target/sub/f", pattern(1, 10))
 
 	link := filepath.Join(dir, "link")
+	symlink(t, filepath.Join(dir, "target"), link)
 
-	err := os.Symlink(filepath.Join(dir, "target"), link)
+	stderr := scanOK(t, link, filepath.Join(link, "sub"))
+
+	summary := "scan: 1 files seen (1 added, 0 updated, 0 removed, " +
+		"0 unchanged), 0 skipped\n"
+	if !strings.Contains(stderr, summary) {
+		t.Errorf("stderr = %q, want %q", stderr, summary)
+	}
+
+	if got := storedPaths(t, path); !slices.Equal(got, []string{f}) {
+		t.Errorf("records = %q, want %q", got, []string{f})
+	}
+}
+
+// TestRunScanWalksSymlinkedOperandBelowOperand is the case of
+// https://git.eeqj.de/sneak/sfdupes/issues/144: scan dir dir/link/sub,
+// with dir/link a symlink to a directory outside dir. The walk of dir
+// does not follow link, so dir/link/sub is walked on its own at its
+// real path, and the record an earlier scan stored there survives.
+func TestRunScanWalksSymlinkedOperandBelowOperand(t *testing.T) {
+	path := testDBPath(t)
+	t.Setenv(databaseEnv, path)
+
+	dir := realTempDir(t)
+	a := writeFile(t, dir, "a", pattern(1, 10))
+
+	outside := realTempDir(t)
+	f := writeFile(t, outside, "sub/f", pattern(2, 10))
+
+	symlink(t, outside, filepath.Join(dir, "link"))
+
+	scanOK(t, filepath.Join(outside, "sub"))
+
+	stderr := scanOK(t, dir, filepath.Join(dir, "link", "sub"))
+
+	summary := "scan: 2 files seen (1 added, 0 updated, 0 removed, " +
+		"1 unchanged), 0 skipped\n"
+	if !strings.Contains(stderr, summary) {
+		t.Errorf("stderr = %q, want %q", stderr, summary)
+	}
+
+	want := []string{a, f}
+	slices.Sort(want)
+
+	if got := storedPaths(t, path); !slices.Equal(got, want) {
+		t.Errorf("records = %q, want %q", got, want)
+	}
+}
+
+// TestRunScanDropsSymlinkOperandInsideOperand scans dir and link, with
+// link, outside dir, a symlink to dir/real. link resolves inside dir,
+// so it is dropped as covered by dir, and its file is recorded once.
+func TestRunScanDropsSymlinkOperandInsideOperand(t *testing.T) {
+	path := testDBPath(t)
+	t.Setenv(databaseEnv, path)
+
+	dir := realTempDir(t)
+	f := writeFile(t, dir, "real/f", pattern(1, 10))
+
+	link := filepath.Join(realTempDir(t), "link")
+	symlink(t, filepath.Join(dir, "real"), link)
+
+	stderr := scanOK(t, dir, link)
+
+	summary := "scan: 1 files seen (1 added, 0 updated, 0 removed, " +
+		"0 unchanged), 0 skipped\n"
+	if !strings.Contains(stderr, summary) {
+		t.Errorf("stderr = %q, want %q", stderr, summary)
+	}
+
+	if got := storedPaths(t, path); !slices.Equal(got, []string{f}) {
+		t.Errorf("records = %q, want %q", got, []string{f})
+	}
+}
+
+// TestRunScanDanglingSymlinkOperandIsFatal scans a valid directory and
+// a symlink whose target does not exist. The scan fails with exit 1 and
+// an error naming the symlink as given, before it walks anything, so no
+// database is created.
+func TestRunScanDanglingSymlinkOperandIsFatal(t *testing.T) {
+	path := testDBPath(t)
+	t.Setenv(databaseEnv, path)
+
+	dir := realTempDir(t)
+	writeFile(t, dir, "f", pattern(1, 10))
+
+	dangling := filepath.Join(realTempDir(t), "dangling")
+	symlink(t, filepath.Join(dir, "missing"), dangling)
+
+	stdout := captureStdout(t)
+
+	var stderr bytes.Buffer
+
+	code := run([]string{cmdScan, dir, dangling}, os.Stdout, &stderr)
+	if code != exitFatal {
+		t.Errorf("run(scan %s %s) = %d, want %d", dir, dangling, code,
+			exitFatal)
+	}
+
+	assertFatalOutput(t, stderr.String(), stdout())
+
+	want := "sfdupes: resolve " + dangling + ": "
+	if !strings.Contains(stderr.String(), want) {
+		t.Errorf("stderr = %q, want %q", stderr.String(), want)
+	}
+
+	_, err := os.Stat(path)
+	if !errors.Is(err, fs.ErrNotExist) {
+		t.Errorf("database: stat error %v, want it missing", err)
+	}
+}
+
+// TestRunScanFromSymlinkedWorkingDirectoryRecordsRealPath runs scan .
+// after a cd through home/proj, a symlink to data/proj. The file is
+// recorded under data/proj, its real path.
+func TestRunScanFromSymlinkedWorkingDirectoryRecordsRealPath(t *testing.T) {
+	path := testDBPath(t)
+	t.Setenv(databaseEnv, path)
+
+	dir := realTempDir(t)
+	f := writeFile(t, dir, "data/proj/f", pattern(1, 10))
+
+	err := os.Mkdir(filepath.Join(dir, "home"), 0o750)
 	if err != nil {
 		t.Fatal(err)
 	}
 
-	// link is dropped as a symlink, but link/sub must still be scanned,
-	// not dropped as lying under link.
-	scanOK(t, link, filepath.Join(link, "sub"))
+	symlink(t, filepath.Join(dir, "data", "proj"),
+		filepath.Join(dir, "home", "proj"))
 
-	db, err := openDB(path, reportParams)
+	// t.Chdir also sets PWD to the path through the symlink, as a
+	// shell does after cd.
+	t.Chdir(filepath.Join(dir, "home", "proj"))
+
+	scanOK(t, ".")
+
+	if got := storedPaths(t, path); !slices.Equal(got, []string{f}) {
+		t.Errorf("records = %q, want %q", got, []string{f})
+	}
+}
+
+// TestRunScanFollowsSymlinkBeforeDotDot scans a path with a ".." after
+// home/proj, a symlink to data/proj: home/proj/.. from dir, and .. after
+// a cd through home/proj. As with realpath, the ".." counts from
+// data/proj, so data is scanned and home is not.
+func TestRunScanFollowsSymlinkBeforeDotDot(t *testing.T) {
+	for _, tc := range []struct{ wd, operand string }{
+		{"", "home/proj/.."},
+		{"home/proj", ".."},
+	} {
+		t.Run(tc.operand, func(t *testing.T) {
+			path := testDBPath(t)
+			t.Setenv(databaseEnv, path)
+
+			dir := realTempDir(t)
+			f := writeFile(t, dir, "data/proj/f", pattern(1, 10))
+			g := writeFile(t, dir, "data/g", pattern(2, 10))
+			writeFile(t, dir, "home/h", pattern(3, 10))
+			symlink(t, filepath.Join(dir, "data", "proj"),
+				filepath.Join(dir, "home", "proj"))
+
+			// t.Chdir also sets PWD to the path given, as a shell does
+			// after cd.
+			t.Chdir(filepath.Join(dir, tc.wd))
+
+			scanOK(t, tc.operand)
+
+			want := []string{f, g}
+			slices.Sort(want)
+
+			if got := storedPaths(t, path); !slices.Equal(got, want) {
+				t.Errorf("records = %q, want %q", got, want)
+			}
+		})
+	}
+}
+
+// TestRunScanSkipsSymlinkToFIFOOperand scans link, a symlink to a FIFO.
+// The scan warns about the FIFO by its real path, counts it as skipped,
+// and exits 0.
+func TestRunScanSkipsSymlinkToFIFOOperand(t *testing.T) {
+	t.Setenv(databaseEnv, testDBPath(t))
+
+	dir := realTempDir(t)
+	fifo := filepath.Join(dir, "fifo")
+
+	err := unix.Mkfifo(fifo, 0o600)
 	if err != nil {
 		t.Fatal(err)
 	}
 
-	t.Cleanup(func() { _ = db.Close() })
+	link := filepath.Join(dir, "link")
+	symlink(t, fifo, link)
 
-	recordByPath(t, dbRecords(t, db), filepath.Join(link, "sub", "f"))
+	stderr := scanOK(t, link)
+
+	warning := "walk " + fifo + ": skipping FIFO operand\n"
+	if !strings.Contains(stderr, warning) {
+		t.Errorf("stderr = %q, want %q", stderr, warning)
+	}
+
+	summary := "scan: 0 files seen (0 added, 0 updated, 0 removed, " +
+		"0 unchanged), 1 skipped\n"
+	if !strings.Contains(stderr, summary) {
+		t.Errorf("stderr = %q, want %q", stderr, summary)
+	}
 }
 
 func TestRunScanSkipsZFSOperand(t *testing.T) {
-	zfs := filepath.Join(t.TempDir(), ".zfs")
+	zfs := filepath.Join(realTempDir(t), ".zfs")
 	f := writeFile(t, zfs, "snapshot/hourly/f", pattern(1, 10))
 
 	// No scan records a file inside a .zfs directory, so the record
@@ -997,7 +1220,7 @@ func TestRunScanSkipsOperandInsideZFS(t *testing.T) {
 	path := testDBPath(t)
 	t.Setenv(databaseEnv, path)
 
-	dir := t.TempDir()
+	dir := realTempDir(t)
 	hourly := filepath.Join(dir, ".zfs", "snapshot", "hourly")
 	writeFile(t, hourly, "f", pattern(1, 10))
 	f := writeFile(t, dir, "f", pattern(2, 10))
@@ -1041,23 +1264,19 @@ func TestRunScanSkipsOperandInsideZFS(t *testing.T) {
 
 // TestRunScanSkipsOperandThroughSymlinkIntoZFS scans snaps/daily, where
 // snaps is a symlink to pool/.zfs/snapshot. The operand is warned about
-// by the path given, counted as skipped, and not walked.
+// by its real path, counted as skipped, and not walked.
 func TestRunScanSkipsOperandThroughSymlinkIntoZFS(t *testing.T) {
 	t.Setenv(databaseEnv, testDBPath(t))
 
-	dir := t.TempDir()
+	dir := realTempDir(t)
 	writeFile(t, dir, "pool/.zfs/snapshot/daily/f", pattern(1, 10))
 
 	snaps := filepath.Join(dir, "snaps")
+	symlink(t, filepath.Join(dir, "pool", ".zfs", "snapshot"), snaps)
 
-	err := os.Symlink(filepath.Join(dir, "pool", ".zfs", "snapshot"), snaps)
-	if err != nil {
-		t.Fatal(err)
-	}
-
-	daily := filepath.Join(snaps, "daily")
-	stderr := scanOK(t, daily)
+	stderr := scanOK(t, filepath.Join(snaps, "daily"))
 
+	daily := filepath.Join(dir, "pool", ".zfs", "snapshot", "daily")
 	warning := "walk " + daily + ": skipping operand inside a .zfs directory\n"
 	summary := "scan: 0 files seen (0 added, 0 updated, 0 removed, " +
 		"0 unchanged), 1 skipped\n"
@@ -1069,24 +1288,19 @@ func TestRunScanSkipsOperandThroughSymlinkIntoZFS(t *testing.T) {
 }
 
 // TestRunScanWalksOperandThroughSymlink scans data/daily, where data is
-// a symlink to a directory outside any .zfs directory. The operand is
-// scanned as usual, and its file is recorded by the path given.
+// a symlink to pool/data. The operand is scanned as usual, and its file
+// is recorded by its real path.
 func TestRunScanWalksOperandThroughSymlink(t *testing.T) {
 	path := testDBPath(t)
 	t.Setenv(databaseEnv, path)
 
-	dir := t.TempDir()
-	writeFile(t, dir, "pool/data/daily/f", pattern(1, 10))
+	dir := realTempDir(t)
+	f := writeFile(t, dir, "pool/data/daily/f", pattern(1, 10))
 
 	data := filepath.Join(dir, "data")
+	symlink(t, filepath.Join(dir, "pool", "data"), data)
 
-	err := os.Symlink(filepath.Join(dir, "pool", "data"), data)
-	if err != nil {
-		t.Fatal(err)
-	}
-
-	daily := filepath.Join(data, "daily")
-	stderr := scanOK(t, daily)
+	stderr := scanOK(t, filepath.Join(data, "daily"))
 
 	summary := "scan: 1 files seen (1 added, 0 updated, 0 removed, " +
 		"0 unchanged), 0 skipped\n"
@@ -1094,14 +1308,9 @@ func TestRunScanWalksOperandThroughSymlink(t *testing.T) {
 		t.Errorf("stderr = %q, want %q", stderr, summary)
 	}
 
-	db, err := openDB(path, reportParams)
-	if err != nil {
-		t.Fatal(err)
+	if got := storedPaths(t, path); !slices.Equal(got, []string{f}) {
+		t.Errorf("records = %q, want %q", got, []string{f})
 	}
-
-	t.Cleanup(func() { _ = db.Close() })
-
-	recordByPath(t, dbRecords(t, db), filepath.Join(daily, "f"))
 }
 
 func TestRunReportSucceeds(t *testing.T) {

internal/sfdupes/db.go

@@ -1,4 +1,4 @@
-package main
+package sfdupes
 
 import (
 	"context"
@@ -146,33 +146,44 @@ var errHashSize = errors.New("hash is not 32 bytes")
 
 // databasePath resolves the database location: SFDUPES_DATABASE when
 // set and non-empty, the compiled-in default otherwise. It returns the
-// path, with the working directory, its symlinks resolved, put in front
-// of it when it is relative, and where the path came from, "default" or
-// "from SFDUPES_DATABASE", for the line each subcommand prints first on
-// stderr.
+// path, made absolute by absolutePath, and where the path came from,
+// "default" or "from SFDUPES_DATABASE", for the line each subcommand
+// prints first on stderr.
 func databasePath() (string, string, error) {
 	path, source := defaultDatabasePath, "default"
 	if p := os.Getenv(databaseEnv); p != "" {
 		path, source = p, "from "+databaseEnv
 	}
 
-	if filepath.IsAbs(path) {
-		return path, source, nil
-	}
-
-	// The working directory as the kernel reports it, with no symlink
-	// in it, as README "Database" says. os.Getwd may return PWD
-	// instead, which can name it through a symlink.
-	wd, err := unix.Getwd()
+	abs, err := absolutePath(path)
 	if err != nil {
 		return "", "", fmt.Errorf("resolve database path %s: %w", path, err)
 	}
 
-	// Not filepath.Abs or filepath.Join: they clean the path, which
-	// drops each ".." together with the directory name before it. When
-	// that directory is a symlink, the cleaned path names another file.
+	return abs, source, nil
+}
+
+// absolutePath returns path unchanged when it is absolute, and
+// otherwise the working directory, a "/" and path. The working
+// directory is the one the kernel reports, with no symlink in it;
+// os.Getwd may return PWD instead, which can name it through a symlink.
+// The result is not cleaned, as filepath.Abs and filepath.Join would
+// clean it. Cleaning drops each ".." together with the directory name
+// before it. When that name is a symlink, the cleaned path names
+// another file than the one the system reaches by following the symlink
+// first.
+func absolutePath(path string) (string, error) {
+	if filepath.IsAbs(path) {
+		return path, nil
+	}
+
+	wd, err := unix.Getwd()
+	if err != nil {
+		return "", err
+	}
+
 	// The working directory ends in "/" only when it is the root.
-	return strings.TrimSuffix(wd, "/") + "/" + path, source, nil
+	return strings.TrimSuffix(wd, "/") + "/" + path, nil
 }
 
 // createDatabaseDirectory creates the directory the database at path

internal/sfdupes/db_test.go

@@ -1,4 +1,4 @@
-package main
+package sfdupes //nolint:testpackage // calls the unexported database openers
 
 import (
 	"context"

internal/sfdupes/dwim.go

@@ -0,0 +1,37 @@
+package sfdupes
+
+import (
+	"context"
+	"fmt"
+	"io"
+	"os"
+	"runtime"
+)
+
+// runDwim implements the dwim subcommand: it runs what "sfdupes scan
+// root" runs with no flags, then what "sfdupes trees" runs, and ends
+// with a line on stderr saying how to print the report again. The dwim
+// command passes "/" as root. It catches SIGINT and SIGTERM as scan
+// does, but only during the scan. An error from the scan, an interrupt
+// included, ends it before the report. During the report, a signal
+// ends it at once, as it ends trees.
+func runDwim(ctx context.Context, root string, stdout io.Writer) error {
+	scanCtx, stop := interruptContext(ctx)
+	err := runScan(scanCtx, []string{root}, runtime.NumCPU(), false, false)
+
+	stop()
+
+	if err != nil {
+		return err
+	}
+
+	err = runTrees(ctx, stdout)
+	if err != nil {
+		return err
+	}
+
+	fmt.Fprintln(os.Stderr,
+		`dwim: run "sfdupes trees" to print this report again`)
+
+	return nil
+}

internal/sfdupes/dwim_test.go

@@ -0,0 +1,83 @@
+package sfdupes //nolint:testpackage // calls the unexported runDwim
+
+import (
+	"bytes"
+	"path/filepath"
+	"strings"
+	"testing"
+)
+
+func TestRunDwimPrintsLargestTreesFirst(t *testing.T) {
+	// dwim scans its root, then prints the trees report, the larger of
+	// two duplicate-tree pairs first, and ends by saying how to print
+	// the report again.
+	t.Setenv(databaseEnv, testDBPath(t))
+
+	root := realTempDir(t)
+
+	small := []string{
+		filepath.Dir(writeFile(t, root, "a1/f.bin", pattern(1, 300))),
+		filepath.Dir(writeFile(t, root, "a2/f.bin", pattern(1, 300))),
+	}
+	large := []string{
+		filepath.Dir(writeFile(t, root, "b1/f.bin", pattern(2, 5000))),
+		filepath.Dir(writeFile(t, root, "b2/f.bin", pattern(2, 5000))),
+	}
+
+	var stdout bytes.Buffer
+
+	stderr := captureStderr(t)
+
+	err := runDwim(t.Context(), root, &stdout)
+	if err != nil {
+		t.Fatalf("runDwim: %v; stderr: %s", err, stderr())
+	}
+
+	lines := strings.Split(strings.TrimSuffix(stdout.String(), "\n"), "\n")
+	if len(lines) != 3 {
+		t.Fatalf("stdout = %q, want a header and two groups",
+			stdout.String())
+	}
+
+	wantFirst := large[0] + "\t" + large[1] + "\t1\t5000\t"
+	if !strings.HasPrefix(lines[1], wantFirst) {
+		t.Errorf("first group = %q, want it to start %q", lines[1], wantFirst)
+	}
+
+	wantSecond := small[0] + "\t" + small[1] + "\t1\t300\t"
+	if !strings.HasPrefix(lines[2], wantSecond) {
+		t.Errorf("second group = %q, want it to start %q",
+			lines[2], wantSecond)
+	}
+
+	last := "\ndwim: run \"sfdupes trees\" to print this report again\n"
+	if got := stderr(); !strings.HasSuffix(got, last) {
+		t.Errorf("stderr = %q, want it to end %q", got, last)
+	}
+}
+
+func TestRunDwimScanErrorPrintsNoReport(t *testing.T) {
+	// A fatal scan error ends dwim before the report: a root that does
+	// not exist fails the scan as it fails scan itself.
+	t.Setenv(databaseEnv, testDBPath(t))
+
+	missing := filepath.Join(realTempDir(t), "missing")
+
+	var stdout bytes.Buffer
+
+	stderr := captureStderr(t)
+
+	err := runDwim(t.Context(), missing, &stdout)
+	if err == nil {
+		t.Fatal("runDwim on a missing root: error = nil, want it fatal")
+	}
+
+	if got := stdout.String(); got != "" {
+		t.Errorf("stdout = %q, want no report", got)
+	}
+
+	if got := stderr(); strings.Contains(got, "trees:") ||
+		strings.Contains(got, "dwim:") {
+		t.Errorf("stderr = %q, want nothing from trees or dwim", got)
+	}
+}

internal/sfdupes/exclude.go

@@ -1,4 +1,4 @@
-package main
+package sfdupes
 
 // This file holds two rules for the walk (README "Rules for the walk"):
 // the default excludes, the paths a scan's walk does not enter below an

internal/sfdupes/exclude_darwin.go

@@ -1,6 +1,6 @@
 //go:build darwin
 
-package main
+package sfdupes
 
 import (
 	"slices"

internal/sfdupes/exclude_other.go

@@ -1,6 +1,6 @@
 //go:build !darwin
 
-package main
+package sfdupes
 
 import (
 	"fmt"

internal/sfdupes/exclude_test.go

@@ -1,4 +1,4 @@
-package main
+package sfdupes //nolint:testpackage // checks the unexported defaultExcludes
 
 import (
 	"bytes"
@@ -286,7 +286,7 @@ func TestRunScanTempDirOperand(t *testing.T) {
 	path := testDBPath(t)
 	t.Setenv(databaseEnv, path)
 
-	dir := t.TempDir()
+	dir := realTempDir(t)
 	if !underAnyRoot(dir, defaultExcludes(runtime.GOOS)) {
 		t.Skip(dir + " is not inside a default exclude")
 	}

internal/sfdupes/info.go

@@ -1,4 +1,4 @@
-package main
+package sfdupes
 
 import (
 	"context"

internal/sfdupes/info_test.go

@@ -1,4 +1,4 @@
-package main
+package sfdupes //nolint:testpackage // seeds the database with unexported scanRec
 
 import (
 	"fmt"

internal/sfdupes/progress.go

@@ -1,4 +1,4 @@
-package main
+package sfdupes
 
 import (
 	"fmt"

internal/sfdupes/progress_test.go

@@ -1,4 +1,4 @@
-package main
+package sfdupes //nolint:testpackage // drives the unexported startProgress
 
 import (
 	"fmt"

internal/sfdupes/report.go

@@ -1,4 +1,4 @@
-package main
+package sfdupes
 
 import (
 	"context"
@@ -195,10 +195,11 @@ func (w *reportWriter) add(r scanRec) error {
 }
 
 // endGroup ends the paths read with w.sig: two or more are a duplicate
-// group, held with its paths sorted until writeGroups writes it.
+// group, held with its paths sorted until writeGroups writes it. Empty
+// files form no group, since removing one frees nothing.
 func (w *reportWriter) endGroup() {
-	if len(w.paths) < minGroupSize {
-		// A path with no duplicate is dropped, and its slice reused.
+	if len(w.paths) < minGroupSize || w.sig.size == 0 {
+		// The paths are dropped, and their slice reused.
 		w.paths = w.paths[:0]
 
 		return

internal/sfdupes/report_test.go

@@ -1,4 +1,4 @@
-package main
+package sfdupes //nolint:testpackage // checks the unexported dupeGroup results
 
 import (
 	"bytes"
@@ -434,6 +434,27 @@ func TestDupeGroups(t *testing.T) {
 	}
 }
 
+// TestDupeGroupsLeavesOutEmptyFiles checks that empty files form no
+// duplicate group, while 1-byte files still do.
+func TestDupeGroupsLeavesOutEmptyFiles(t *testing.T) {
+	t.Parallel()
+
+	e, x := sha256.Sum256(nil), testHash("x")
+	recs := []scanRec{
+		{size: 0, head: e, tail: e, content: e, path: "/a/.gitkeep"},
+		{size: 0, head: e, tail: e, content: e, path: "/b/.gitkeep"},
+		{size: 0, head: e, tail: e, content: e, path: "/c/__init__.py"},
+		{size: 1, head: x, tail: x, content: x, path: "/tiny1"},
+		{size: 1, head: x, tail: x, content: x, path: "/tiny2"},
+	}
+
+	groups := dupeGroupsOf(t, recs)
+	if len(groups) != 1 || groups[0].size != 1 ||
+		!slices.Equal(groups[0].paths, []string{"/tiny1", "/tiny2"}) {
+		t.Fatalf("groups = %+v, want only /tiny1 /tiny2 of size 1", groups)
+	}
+}
+
 func TestDupeGroupsContentSeparates(t *testing.T) {
 	t.Parallel()
 

internal/sfdupes/scan.go

@@ -1,4 +1,4 @@
-package main
+package sfdupes
 
 import (
 	"cmp"
@@ -209,29 +209,30 @@ func interrupted(walked int) error {
 	return errInterrupted
 }
 
-// resolveRoots converts each PATH operand to an absolute, lexically
-// cleaned path (symlinks are not resolved) and verifies that it
-// exists. Database records are keyed by absolute path, so scan results
-// must not depend on the working directory.
+// resolveRoots converts each PATH operand to its real path: absolute,
+// with every symlink in it followed. Database records are keyed by
+// that path, so scan results depend neither on the working directory
+// nor on the symlinks an operand was given through. An operand that
+// cannot be resolved, because it or a symlink's target does not exist
+// or cannot be read, is a fatal error before any scanning.
 func resolveRoots(roots []string) ([]string, error) {
-	abs := make([]string, 0, len(roots))
+	resolved := make([]string, 0, len(roots))
 
 	for _, root := range roots {
-		a, err := filepath.Abs(root)
+		a, err := absolutePath(root)
 		if err != nil {
 			return nil, fmt.Errorf("resolve %s: %w", root, err)
 		}
 
-		// A nonexistent operand is a fatal error before any scanning.
-		_, err = os.Lstat(a)
+		r, err := filepath.EvalSymlinks(a)
 		if err != nil {
-			return nil, err
+			return nil, fmt.Errorf("resolve %s: %w", root, err)
 		}
 
-		abs = append(abs, a)
+		resolved = append(resolved, r)
 	}
 
-	return abs, nil
+	return resolved, nil
 }
 
 // pruneRoots drops operands already covered by another operand:
@@ -417,14 +418,16 @@ func (s *scanState) runPhases(ctx context.Context, roots []string,
 
 // walkableRoots returns the operands the walk can start from: regular
 // files, and directories not named .zfs, none of them inside a
-// directory named .zfs. Every other operand is warned about, counted as
-// skipped, and dropped. A dropped operand is no longer a root, so the
-// records stored beneath it are treated as if it had not been given:
-// those under no other root count as outside the roots and are not
-// deleted as unverified. An operand on a filesystem in rules that is not
-// persistent is dropped the same way, with a line saying so that is not
-// a warning, and is not counted as skipped. An operand that fails lstat
-// here is kept, and the walk warns about it unless it no longer exists.
+// directory named .zfs. The operands are real paths from resolveRoots,
+// so these checks apply to what a symlink operand points at. Every
+// other operand is warned about, counted as skipped, and dropped. A
+// dropped operand is no longer a root, so the records stored beneath it
+// are treated as if it had not been given: those under no other root
+// count as outside the roots and are not deleted as unverified. An
+// operand on a filesystem in rules that is not persistent is dropped
+// the same way, with a line saying so that is not a warning, and is not
+// counted as skipped. An operand that fails lstat here is kept, and the
+// walk warns about it unless it no longer exists.
 func (s *scanState) walkableRoots(roots []string, rules walkRules) []string {
 	kept := make([]string, 0, len(roots))
 
@@ -554,7 +557,7 @@ func (s *scanState) walkPhase(events <-chan walkEvent, roots []string) {
 
 		// The space a file takes on disk can change while its size and
 		// mtime stay the same. ZFS, for one, counts a new file's blocks
-		// only seconds after the write.
+		// up to seconds after the write.
 		if old.diskSize != ev.rec.diskSize {
 			s.diskSizes = append(s.diskSizes, ev.rec)
 		}
@@ -894,19 +897,13 @@ func sendEvent(ctx context.Context, events chan<- walkEvent,
 // operandWarning returns the one-line warning for an operand the walk
 // does not start from, naming the path and what it is, or "" for one it
 // does: a regular file, or a directory not named .zfs, that is not
-// inside a directory named .zfs, neither as given nor with its symlinks
-// resolved. Symlinks are never followed, including as operands.
+// inside a directory named .zfs. resolveRoots has already followed the
+// operand's symlinks, so a symlink here is an operand replaced by one
+// after it was resolved, and is not followed.
 func operandWarning(root string, fi fs.FileInfo) string {
 	// The walk never enters a .zfs directory, so it starts from nothing
-	// inside one either, not even through a symlink. An operand whose
-	// symlinks cannot be resolved is checked as given.
-	resolved, err := filepath.EvalSymlinks(root)
-	if err != nil {
-		resolved = root
-	}
-
-	if slices.Contains(strings.Split(filepath.Dir(root), "/"), ".zfs") ||
-		slices.Contains(strings.Split(filepath.Dir(resolved), "/"), ".zfs") {
+	// inside one either.
+	if slices.Contains(strings.Split(filepath.Dir(root), "/"), ".zfs") {
 		return fmt.Sprintf("walk %s: skipping operand inside a .zfs directory",
 			root)
 	}

internal/sfdupes/scan_dev_darwin.go

@@ -1,6 +1,6 @@
 //go:build darwin
 
-package main
+package sfdupes
 
 import "syscall"
 

internal/sfdupes/scan_dev_other.go

@@ -1,6 +1,6 @@
 //go:build !darwin
 
-package main
+package sfdupes
 
 import "syscall"
 

internal/sfdupes/scan_test.go

@@ -1,4 +1,4 @@
-package main
+package sfdupes //nolint:testpackage // drives the unexported syncTree
 
 import (
 	"bytes"
@@ -43,10 +43,16 @@ func writeFile(t *testing.T, dir, name string, data []byte) string {
 }
 
 // diskSizeOf returns the bytes the file at path takes on disk, from its
-// own lstat: st_blocks counts 512-byte units. ZFS counts a new file's
-// blocks only seconds after the write, and fsync does not hasten that.
-// A test therefore calls unix.Sync, which waits for it, before the scan
-// whose disk_size it compares with this.
+// own lstat: st_blocks counts 512-byte units. ZFS counts a write's
+// blocks only when it commits the write, up to seconds later, and one
+// commit can take the file through several growing sizes. So this value
+// can change at any moment. Neither fsync nor unix.Sync hastens that,
+// but a unix.Sync call often takes long enough that the blocks are
+// counted when it returns. A test that needs the value to change waits
+// for the change. A test that compares it with a scan's disk_size reads
+// it before and after the scan. The rewrite test rescans until the two
+// reads match, then compares exactly. The other two tests fail only on
+// a disk_size outside the two reads.
 func diskSizeOf(t *testing.T, path string) int64 {
 	t.Helper()
 
@@ -1088,7 +1094,7 @@ func TestScanOneFilesystemWalksNestedFileOperand(t *testing.T) {
 func buildSmokeTree(t *testing.T) string {
 	t.Helper()
 
-	dir := t.TempDir()
+	dir := realTempDir(t)
 	one := pattern(10, 2000)
 	f1 := pattern(30, 3000)
 	f2 := pattern(40, 100)
@@ -1179,11 +1185,12 @@ func assertSmokeDupeGroups(t *testing.T, dir string, db *sql.DB) {
 	t.Helper()
 
 	groups := dupeGroups(t, db)
-	if len(groups) != 5 {
-		t.Fatalf("len(groups) = %d, want 5", len(groups))
+	if len(groups) != 4 {
+		t.Fatalf("len(groups) = %d, want 4", len(groups))
 	}
 
-	wantSizes := []int64{3000, 2000, 100, 1, 0}
+	// The empty files empty1 and empty2 form no group.
+	wantSizes := []int64{3000, 2000, 100, 1}
 	for i, g := range groups {
 		if g.size != wantSizes[i] {
 			t.Errorf("groups[%d].size = %d, want %d",
@@ -1448,20 +1455,26 @@ func TestScanStoresDiskSize(t *testing.T) {
 
 	unix.Sync() // see diskSizeOf
 
-	want := diskSizeOf(t, p)
-	if want == 0 || want >= length {
+	size := diskSizeOf(t, p)
+	if size == 0 || size >= length {
 		t.Fatalf("the file takes %d bytes on disk, want more than none "+
-			"and fewer than its length %d", want, length)
+			"and fewer than its length %d", size, length)
 	}
 
 	for _, operand := range []string{filepath.Dir(p), p} {
 		db := openTestDB(t)
+
+		// ZFS may count the blocks during the scan; see diskSizeOf.
+		before := diskSizeOf(t, p)
+
 		syncTree(t, db, operand)
 
+		after := diskSizeOf(t, p)
+
 		got := recordByPath(t, dbRecords(t, db), p).diskSize
-		if got != want {
-			t.Errorf("scan of %s: disk_size = %d, want %d",
-				operand, got, want)
+		if got < before || got > after {
+			t.Errorf("scan of %s: disk_size = %d, want %d to %d",
+				operand, got, before, after)
 		}
 	}
 }
@@ -1479,7 +1492,7 @@ func TestSyncScanRewriteUpdatesDiskSize(t *testing.T) {
 
 	syncTree(t, db, dir)
 
-	before := recordByPath(t, dbRecords(t, db), p).diskSize
+	recorded := recordByPath(t, dbRecords(t, db), p).diskSize
 
 	pokeAt(t, p, 512*1024, pattern(7, 64*1024))
 
@@ -1492,22 +1505,53 @@ func TestSyncScanRewriteUpdatesDiskSize(t *testing.T) {
 		t.Fatal(err)
 	}
 
-	unix.Sync() // see diskSizeOf
+	// Wait for ZFS to count the write; see diskSizeOf.
+	deadline := time.Now().Add(30 * time.Second)
+	for diskSizeOf(t, p) == recorded {
+		if time.Now().After(deadline) {
+			t.Fatalf("the file still takes %d bytes on disk 30 seconds "+
+				"after the write into its hole", recorded)
+		}
 
-	want := diskSizeOf(t, p)
-	if want == before {
-		t.Fatalf("the file still takes %d bytes on disk after the write "+
-			"into its hole", want)
+		unix.Sync()
 	}
 
-	st := syncTree(t, db, dir)
-	if st != (scanStats{walked: 1, updated: 1}) {
-		t.Fatalf("rescan stats = %+v, want 1 updated", st)
-	}
+	// ZFS may still be counting, so the size may change during a rescan.
+	// Only a rescan with the same size on both sides of it can be compared
+	// exactly. A rescan that keeps the old size still fails, because the
+	// wait made before differ from it.
+	for {
+		before := diskSizeOf(t, p)
 
-	got := recordByPath(t, dbRecords(t, db), p).diskSize
-	if got != want {
-		t.Errorf("disk_size = %d, want %d", got, want)
+		st := syncTree(t, db, dir)
+
+		after := diskSizeOf(t, p)
+
+		if st != (scanStats{walked: 1, updated: 1}) {
+			t.Fatalf("rescan stats = %+v, want 1 updated", st)
+		}
+
+		if before == after {
+			got := recordByPath(t, dbRecords(t, db), p).diskSize
+			if got != after {
+				t.Errorf("disk_size = %d, want %d", got, after)
+			}
+
+			return
+		}
+
+		if time.Now().After(deadline) {
+			t.Fatalf("the size on disk was still changing 30 seconds after "+
+				"the write into its hole: %d, then %d", before, after)
+		}
+
+		// A later mtime makes the next rescan read the file again.
+		later = later.Add(time.Second)
+
+		err = os.Chtimes(p, later, later)
+		if err != nil {
+			t.Fatal(err)
+		}
 	}
 }
 
@@ -1533,15 +1577,21 @@ func TestSyncScanUnchangedUpdatesDiskSize(t *testing.T) {
 
 	unix.Sync() // see diskSizeOf
 
+	// ZFS may count the blocks during the rescan; see diskSizeOf.
+	before := diskSizeOf(t, p)
+
 	// A file read again would count as updated.
 	st := syncTree(t, db, dir)
+
+	after := diskSizeOf(t, p)
+
 	if st != (scanStats{walked: 1, unchanged: 1}) {
 		t.Fatalf("rescan stats = %+v, want 1 unchanged", st)
 	}
 
 	got := recordByPath(t, dbRecords(t, db), p).diskSize
-	if want := diskSizeOf(t, p); got != want {
-		t.Errorf("disk_size = %d, want %d", got, want)
+	if got < before || got > after {
+		t.Errorf("disk_size = %d, want %d to %d", got, before, after)
 	}
 }
 
@@ -2261,33 +2311,24 @@ func TestUnderRoot(t *testing.T) {
 }
 
 // TestRunScanPassesOverDatabase scans a tree that holds the scan's own
-// database, reached directly and through a symlinked directory. The
-// walk passes over the database file, its -wal and -shm files and its
-// .lock file with no line and no count, and the record an earlier scan
-// left for the .lock file is deleted. A rescan of the unchanged tree
-// updates nothing, and report lists none of the database's files.
+// database, and in one case also a hard link to the database file. The
+// walk knows the database's files by device ID and inode number, so it
+// passes over the database file, its -wal and -shm files, its .lock
+// file and the hard link with no line and no count. The record an
+// earlier scan left for the .lock file is deleted. A rescan of the
+// unchanged tree updates nothing, and report lists none of the
+// database's files.
 func TestRunScanPassesOverDatabase(t *testing.T) {
-	for _, viaSymlink := range []bool{false, true} {
-		t.Run(fmt.Sprintf("via symlink %v", viaSymlink), func(t *testing.T) {
-			base := t.TempDir()
-			tree := filepath.Join(base, "real", "tree")
-			operand := tree
+	for _, viaHardLink := range []bool{false, true} {
+		t.Run(fmt.Sprintf("via hard link %v", viaHardLink), func(t *testing.T) {
+			tree := realTempDir(t)
+			hardLink := filepath.Join(tree, "hardlink")
 
 			writeFile(t, tree, "a", pattern(1, 100))
 			writeFile(t, tree, "b", pattern(1, 100))
 			writeFile(t, tree, "empty1", nil)
 			writeFile(t, tree, "empty2", nil)
 
-			if viaSymlink {
-				err := os.Symlink(filepath.Join(base, "real"),
-					filepath.Join(base, "link"))
-				if err != nil {
-					t.Fatal(err)
-				}
-
-				operand = filepath.Join(base, "link", "tree")
-			}
-
 			dbPath := filepath.Join(tree, "db.sqlite")
 			t.Setenv(databaseEnv, dbPath)
 
@@ -2297,7 +2338,7 @@ func TestRunScanPassesOverDatabase(t *testing.T) {
 			}
 
 			err = applyChanges(t.Context(), db, []scanRec{
-				{path: filepath.Join(operand, "db.sqlite.lock")},
+				{path: filepath.Join(tree, "db.sqlite.lock")},
 			}, nil, nil)
 			if err != nil {
 				t.Fatal(err)
@@ -2305,17 +2346,30 @@ func TestRunScanPassesOverDatabase(t *testing.T) {
 
 			closeScanDatabase(t.Context(), db, dbPath)
 
-			assertScanSummary(t,
+			if viaHardLink {
+				err = os.Link(dbPath, hardLink)
+				if err != nil {
+					t.Fatal(err)
+				}
+			}
+
+			stderr := assertScanSummary(t,
 				"4 files seen (4 added, 0 updated, 1 removed, 0 unchanged)",
-				operand)
-			assertScanSummary(t,
+				tree)
+			stderr += assertScanSummary(t,
 				"4 files seen (0 added, 0 updated, 0 removed, 4 unchanged)",
-				operand)
+				tree)
+
+			if strings.Contains(stderr, hardLink) {
+				t.Errorf("scan stderr = %q, want no line naming %s",
+					stderr, hardLink)
+			}
 
 			report := runStdout(t, cmdReport)
 			if strings.Contains(report, "db.sqlite") ||
-				!strings.Contains(report, filepath.Join(operand, "empty2")) {
-				t.Errorf("report = %q, want the empty files and none of "+
+				strings.Contains(report, hardLink) ||
+				!strings.Contains(report, filepath.Join(tree, "b")) {
+				t.Errorf("report = %q, want a and b and none of "+
 					"the database's files", report)
 			}
 		})
@@ -2339,8 +2393,9 @@ func TestRunScanPassesOverDatabaseOperands(t *testing.T) {
 
 // assertScanSummary scans operands and fails the test unless the
 // summary line gives counts with nothing skipped, and the line naming
-// the database is the only one that names one of its files.
-func assertScanSummary(t *testing.T, counts string, operands ...string) {
+// the database is the only one that names one of its files. It returns
+// everything the scan printed to stderr.
+func assertScanSummary(t *testing.T, counts string, operands ...string) string {
 	t.Helper()
 
 	stderr := scanOK(t, operands...)
@@ -2354,4 +2409,6 @@ func assertScanSummary(t *testing.T, counts string, operands ...string) {
 		t.Errorf("scan %q: stderr = %q, want only the line naming the "+
 			"database to name one of its files", operands, stderr)
 	}
+
+	return stderr
 }

internal/sfdupes/trees.go

@@ -1,4 +1,4 @@
-package main
+package sfdupes
 
 import (
 	"context"
@@ -301,7 +301,9 @@ func fileEntry(name string, r scanRec) string {
 // collectTreeGroups groups directories by digest, counting each one on
 // prog as it is grouped, and returns every maximal group with two or
 // more members, each group's members sorted by path, groups ordered by
-// tree size descending then by first path ascending.
+// tree size descending then by first path ascending. A group whose
+// trees hold 0 bytes is left out, since removing one frees nothing. The
+// groups it implies hold 0 bytes too, so leaving it out hides nothing.
 func collectTreeGroups(allDirs []*treeNode, super *treeNode,
 	prog *progress,
 ) [][]*treeNode {
@@ -315,7 +317,9 @@ func collectTreeGroups(allDirs []*treeNode, super *treeNode,
 	var dupes [][]*treeNode
 
 	for _, g := range groups {
-		if len(g) < minGroupSize || suppressed(g, super) {
+		// The members share a digest, so they share a total size.
+		if len(g) < minGroupSize || g[0].totalSize == 0 ||
+			suppressed(g, super) {
 			continue
 		}
 

internal/sfdupes/trees_test.go

@@ -1,7 +1,8 @@
-package main
+package sfdupes //nolint:testpackage // checks the unexported treeNode results
 
 import (
 	"bytes"
+	"crypto/sha256"
 	"database/sql"
 	"os"
 	"slices"
@@ -435,6 +436,35 @@ func TestCollectTreeGroupsSiblings(t *testing.T) {
 	}
 }
 
+// TestCollectTreeGroupsLeavesOutEmptyTrees checks that directories
+// holding only empty files form no group, and that an empty file still
+// counts toward the digest of a tree that holds other files.
+func TestCollectTreeGroupsLeavesOutEmptyTrees(t *testing.T) {
+	t.Parallel()
+
+	h, tl, c, e := testHash("h"), testHash("t"), testHash("c"),
+		sha256.Sum256(nil)
+	recs := []scanRec{
+		{size: 0, head: e, tail: e, content: e, path: "/e/a/.gitkeep"},
+		{size: 0, head: e, tail: e, content: e, path: "/e/b/.gitkeep"},
+		{size: 10, head: h, tail: tl, content: c, path: "/p/x1/f"},
+		{size: 0, head: e, tail: e, content: e, path: "/p/x1/.gitkeep"},
+		{size: 10, head: h, tail: tl, content: c, path: "/p/x2/f"},
+		{size: 0, head: e, tail: e, content: e, path: "/p/x2/.gitkeep"},
+		// Without the empty file, /p/x3 is no copy of /p/x1.
+		{size: 10, head: h, tail: tl, content: c, path: "/p/x3/f"},
+	}
+
+	super, dirs := treeOf(t, recs)
+
+	got := groupPaths(collectTreeGroups(dirs, super, nil))
+
+	want := [][]string{{"/p/x1", "/p/x2"}}
+	if !slices.EqualFunc(got, want, slices.Equal) {
+		t.Fatalf("groups = %v, want %v", got, want)
+	}
+}
+
 func TestCollectTreeGroupsDifferingParents(t *testing.T) {
 	t.Parallel()