Stop the disk size tests failing at random on ZFS (closes #150)

One ZFS commit can take a file through several sizes, and unix.Sync can
return before the blocks are counted. A test that expected the size on
disk to be settled therefore failed at random. The test that needs the
size to change now calls unix.Sync in a loop until it does, for at most
30 seconds. It then rescans until the size reads the same before and
after a rescan, and compares disk_size exactly, within the same 30
seconds. The other two tests fail only on a disk_size outside their two
reads. They call unix.Sync once first, so a wrong 512 usually fails them.

Model: opus-5-5

Makefile

@@ -4,7 +4,7 @@ export CGO_ENABLED = 0
 
 BINARY := sfdupes
 VERSION := $(shell git describe --tags --always --dirty 2>/dev/null || echo dev)
-LDFLAGS := -X sneak.berlin/go/sfdupes/internal/sfdupes.Version=$(VERSION)
+LDFLAGS := -X main.Version=$(VERSION)
 
 .PHONY: sfdupes build bootstrap setup test lint fmt fmt-check check docker hooks clean
 
@@ -14,7 +14,7 @@ LDFLAGS := -X sneak.berlin/go/sfdupes/internal/sfdupes.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 $(BINARY) ./cmd/sfdupes
+	go build -ldflags "$(LDFLAGS)" -o $(BINARY)
 
 build: sfdupes
 

README.md

@@ -17,13 +17,12 @@ 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 five subcommands. `scan` walks the filesystem and
+file takes too long. It has four 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. `dwim` scans `/` and then prints the `trees` report, for a
+can run at any time.
-first look at a new machine with one command.
 
 ## Getting Started
 
@@ -57,25 +56,25 @@ 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/cmd/sfdupes@latest
+go install sneak.berlin/go/sfdupes@latest
 ```
 
 `@main` installs the tip of the `main` branch instead:
 
 ```sh
-go install sneak.berlin/go/sfdupes/cmd/sfdupes@main
+go install sneak.berlin/go/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. For `@main` it is the commit's tag when it has one. Otherwise it
+a release tag such as `v0.0.3`. For `@main` it is the commit's tag when it has
-is a pseudo-version, Go's version string for an untagged commit. That string
+one. Otherwise it is a pseudo-version, Go's version string for an untagged
-ends in the commit's hash. A binary built from a clone carries the output of
+commit. That string ends in the commit's hash. A binary built from a clone
-`git describe --tags --always --dirty` in that clone, such as `v0.0.3` on a
+carries the output of `git describe --tags --always --dirty` in that clone, such
-tagged commit. `VERSION` is `dev` when no version is known. To see everything Go
+as `v0.0.3` on a tagged commit. `VERSION` is `dev` when no version is known. To
-recorded in an installed binary:
+see everything Go recorded in an installed binary:
 
 ```sh
 go version -m "$(command -v sfdupes)"
@@ -248,15 +247,12 @@ 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
 ```
@@ -352,26 +348,17 @@ 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, and so is a symlink whose
+- An operand that does not exist is a fatal error. `scan` then stops before it
-  target does not exist. `scan` then stops before it walks anything, and exits
+  walks anything, and exits 1.
-  with code 1.
+- Each operand is made absolute before the walk. A relative operand is joined to
-- Each operand is resolved to its real path before the walk, as `realpath`
+  the working directory as `pwd` prints it, with its symlinks kept. A `.` or
-  prints it. A relative operand is joined to the working directory as `pwd -P`
+  `..` in it is resolved as text, and symlinks are not followed. Each record is
-  prints it. Every symlink in the path is then followed. A `..` after a symlink
+  stored under that absolute path.
-  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. Two operands
+- An operand that repeats another is dropped before the walk.
-  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. Whether one operand is
+  cases below applies. No path is then walked twice.
-  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");
@@ -382,19 +369,25 @@ 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.
+- No other case keeps an operand under another. An operand reached through a
-- An operand that is neither a regular file nor a directory is not scanned. Such
+  symlinked directory below the outer operand is dropped too. The outer
-  an operand is, for example, a symlink to a device node. `scan` prints a
+  operand's walk does not follow the symlink, so no file under the inner operand
-  warning naming the real path and what it is. It counts the operand as skipped
+  is scanned. The records that an earlier scan left under it are deleted. The
-  and drops it. The scan keeps the records beneath a dropped operand, unless
+  `-x` case above also covers an operand reached that way.
-  another operand covers them.
+- 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.
 - An operand at or inside a directory named `.zfs` is never scanned, whether
-  given alone or under another operand. The check looks at the real path, so a
+  given alone or under another operand. The check looks at the path as given and
-  symlink into a `.zfs` directory is not scanned either. `scan` prints a warning
+  at the path with its symlinks resolved. `scan` prints a warning naming the
-  naming the real path, counts the operand as skipped and drops it. The records
+  path, counts the operand as skipped and drops it. The records beneath it are
-  beneath it are kept, unless it lies under another operand. Then they are
+  kept, unless it lies under another operand. Then they are deleted, because
-  deleted, because that operand's walk never enters `.zfs` (see "Rules for the
+  that operand's walk never enters `.zfs` (see "Rules for the walk").
-  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.
@@ -414,9 +407,9 @@ 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 up to seconds after
+  unchanged. ZFS, for example, counts a new file's blocks only seconds after the
-  the write. A block is the unit in which a filesystem allocates disk space. A
+  write. A block is the unit in which a filesystem allocates disk space. A file
-  file scanned within those seconds gets its real `disk_size` at the next scan.
+  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
@@ -491,12 +484,12 @@ 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 opens each
+    path leads to them. The walk follows no symlink it finds. It does open each
-    operand at its real path, not the path given. An operand given through a
+    operand at the path given, even when that path runs through a symlinked
-    symlink can lead to the database files, and the walk passes over them there
+    directory. Such an operand can lead to the database files, and the walk
-    as well. The walk prints no line for the database files and does not count
+    passes over them there as well. The walk prints no line for the database
-    them as skipped. A record that an earlier scan left for one of them is
+    files and does not count them as skipped. A record that an earlier scan left
-    deleted.
+    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
@@ -665,7 +658,6 @@ 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
@@ -714,7 +706,7 @@ The summary line on stderr gives:
 - the reclaimable bytes, the sum of `size` over all rows.
 
 ```
-report: 14 records read, 4 duplicate groups, 7 dupe files, 10.0 KiB reclaimable
+report: 14 records read, 5 duplicate groups, 8 dupe files, 10.0 KiB reclaimable
 ```
 
 ### `trees` mode
@@ -742,9 +734,6 @@ 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
@@ -808,33 +797,6 @@ 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
@@ -875,7 +837,7 @@ scan is writing. `info` writes its lines after the `count` display has ended.
 
 ### Database
 
-All five subcommands work on one SQLite database file.
+All four subcommands work on one SQLite database file.
 
 #### Location
 
@@ -891,8 +853,6 @@ 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
@@ -1176,9 +1136,9 @@ showing the count it stopped at.
 ### Error handling and exit codes
 
 - `0`: success, even when files were skipped with warnings.
-- `1`: a fatal error, a `scan` stopped by `SIGINT` or `SIGTERM`, or a `dwim`
+- `1`: a fatal error, or a `scan` stopped by `SIGINT` or `SIGTERM`. A fatal
-  stopped by either during its scan. A fatal error is one of these:
+  error is one of these:
-    - an operand that does not exist, or whose real path `scan` cannot find;
+    - an operand that does not exist, or whose details `scan` cannot read;
     - 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
@@ -1198,7 +1158,7 @@ showing the count it stopped at.
       `--workers abc`;
     - `scan` with no operand;
     - `--workers` below 1;
-    - `report`, `trees`, `info` or `dwim` with a positional argument.
+    - `report`, `trees` or `info` 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
@@ -1386,7 +1346,7 @@ 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 files
+    : > "$d/empty1"; : > "$d/empty2"                  # empty duplicates
     # 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"
@@ -1411,8 +1371,8 @@ 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.
+    - `tiny1` and `tiny2` form a pair, and so do `empty1` and `empty2`.
-    - `unique.bin`, `tiny3`, `empty1` and `empty2` appear nowhere.
+    - `unique.bin` and `tiny3` 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`.
@@ -1425,9 +1385,8 @@ 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
+    The test suite automates this scenario (see `scan_test.go`). It also checks
-    `internal/sfdupes/scan_test.go`). It also checks that `report` and `trees`
+    that `report` and `trees` never touch the scanned filesystem.
-    never touch the scanned filesystem.
 
 ## TODO
 

TODO.md

@@ -29,40 +29,13 @@
 Newest first. An entry ends with its date and its issue or branch, where those
 are known.
 
-- `report` and `trees` leave out empty files. `report` writes no group of size
+- The three disk size tests in `scan_test.go` no longer fail at random on ZFS.
-  0, and `trees` writes no group whose trees hold 0 bytes. An empty file still
+  `unix.Sync` can return before ZFS has counted a file's blocks, and one ZFS
-  counts toward a tree's digest (2026-11-11,
+  commit can take a file through several sizes. The test that needs the size to
-  https://git.eeqj.de/sneak/sfdupes/issues/178)
+  change waits for it, for at most 30 seconds. Each test reads the size before
-- The Go code moved out of the repository root. `cmd/sfdupes/main.go` is the
+  and after its scan. The rewrite test rescans until the two reads match, then
-  command, and it calls `Main` in the package `internal/sfdupes`. `main.go`
+  compares exactly. The other two fail only on a `disk_size` outside the two
-  became `internal/sfdupes/cli.go`. Every other file kept its name. The install
+  reads (2026-11-02, https://git.eeqj.de/sneak/sfdupes/issues/150)
-  path is now `sneak.berlin/go/sfdupes/cmd/sfdupes` (2026-11-10,
-  https://git.eeqj.de/sneak/sfdupes/issues/157)
-
-- New subcommand `dwim`. It runs what `sfdupes scan /` runs with no flags, then
-  what `sfdupes trees` runs. Its last line on stderr says that `sfdupes trees`
-  prints the report again (2026-11-06,
-  https://git.eeqj.de/sneak/sfdupes/issues/154)
-
-- `scan` resolves each operand to its real path, symlinks followed, before the
-  walk. A symlink operand is scanned at its target instead of skipped. With
-  `/srv/link` a symlink to a directory outside `/srv`, `scan /srv /srv/link/sub`
-  walks `sub` on its own instead of dropping it and deleting its records
-  (2026-11-06, https://git.eeqj.de/sneak/sfdupes/issues/144)
-
-- `README.md` and a comment in `internal/sfdupes/scan.go` no longer say ZFS
-  counts a new file's blocks only seconds after the write. The count can land in
-  under a second. Both now say up to seconds after the write, as the comment on
-  `diskSizeOf` in `internal/sfdupes/scan_test.go` does (2026-11-03,
-  https://git.eeqj.de/sneak/sfdupes/issues/152)
-
-- The three disk size tests in `internal/sfdupes/scan_test.go` no longer fail at
-  random on ZFS. `unix.Sync` can return before ZFS has counted a file's blocks,
-  and one ZFS commit can take a file through several sizes. The test that needs
-  the size to change waits for it, for at most 30 seconds. Each test reads the
-  size before and after its scan. The rewrite test rescans until the two reads
-  match, then compares exactly. The other two fail only on a `disk_size` outside
-  the two reads (2026-11-02, https://git.eeqj.de/sneak/sfdupes/issues/150)
 
 - `TODO.md` rewritten from scratch by the same rules as `README.md`, sentence by
   sentence. Every completed step is kept, with its date and its issue or branch.
@@ -73,13 +46,9 @@ are known.
   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
-  `internal/sfdupes/cli_test.go` cite "Settings", where their rules now live.
+  `main_test.go` cite "Settings", where their rules now live. One comment each
-  One comment each in these files cites what the README now says:
+  in `scan_test.go`, `trees_test.go` and `exclude_test.go` cites what the README
-    - `internal/sfdupes/scan_test.go`;
+  now says (2026-11-02, https://git.eeqj.de/sneak/sfdupes/issues/135)
-    - `internal/sfdupes/trees_test.go`;
-    - `internal/sfdupes/exclude_test.go`.
-
-    (2026-11-02, https://git.eeqj.de/sneak/sfdupes/issues/135)
 
 - Each record holds `disk_size`, the bytes the file takes on disk. That is its
   allocated blocks, `st_blocks` × 512, from the `lstat` call the walk already
@@ -152,12 +121,12 @@ are known.
     https://git.eeqj.de/sneak/sfdupes/issues/109)
 
 - The release rule was set. Until 1.0, each tip of `main` that passes the build
-  gets the next `v0.0.N` tag.
+  gets the next `v0.0.N` tag. `go install sneak.berlin/go/sfdupes@latest` then
-  `go install sneak.berlin/go/sfdupes/cmd/sfdupes@latest` then installs it.
+  installs it. `go.mod` retracts `v0.0.1`, the early build without a database.
-  `go.mod` retracts `v0.0.1`, the early build without a database. When the
+  When the linker set no version, `sfdupes --version` prints the version Go
-  linker set no version, `sfdupes --version` prints the version Go recorded in
+  recorded in the binary. That is the tag, or the pseudo-version of a
-  the binary. That is the tag, or the pseudo-version of a `go install` build. It
+  `go install` build. It prints `dev` only when neither is known. README
-  prints `dev` only when neither is known. README "Install" documented:
+  "Install" documented:
     - the rule;
     - what `@main` and `v0.0.1` give;
     - how to check an installed binary.
@@ -408,9 +377,8 @@ are known.
   `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
+- A test fails when either `hashWorker` cancellation check in `scan.go` is
-  `internal/sfdupes/scan.go` is removed (2026-10-04,
+  removed (2026-10-04, https://git.eeqj.de/sneak/sfdupes/issues/83)
-  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)
@@ -418,15 +386,15 @@ are known.
 - `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 `internal/sfdupes/scan.go`
+- A test fails when either walk cancellation check in `scan.go` is removed
-  is removed (2026-10-04, https://git.eeqj.de/sneak/sfdupes/issues/81)
+  (2026-10-04, https://git.eeqj.de/sneak/sfdupes/issues/81)
 
 - A test checks that `scan` refuses a database with another schema version
   (2026-10-04, https://git.eeqj.de/sneak/sfdupes/issues/64)
 
-- Four inaccurate comments in `internal/sfdupes/cancel_test.go` were corrected,
+- Four inaccurate comments in `cancel_test.go` were corrected, and
-  and `walkCancelInFlightDirs` was renamed to `walkCancelInFlightFiles`
+  `walkCancelInFlightDirs` was renamed to `walkCancelInFlightFiles` (2026-10-04,
-  (2026-10-04, https://git.eeqj.de/sneak/sfdupes/issues/33)
+  https://git.eeqj.de/sneak/sfdupes/issues/33)
 
 - The `-x` filesystem-boundary rules in `subdirJob` are tested (2026-10-04,
   https://git.eeqj.de/sneak/sfdupes/issues/17)
@@ -633,15 +601,15 @@ are known.
     - `loadRecords`;
     - `resolveRoots`.
 
-    The single exit point is `run` in `internal/sfdupes/cli.go`. It maps a
+    The single exit point is `run` in `main.go`. It maps a `fatalError`,
-    `fatalError`, anything a subcommand returned, to exit 1, and cobra's own
+    anything a subcommand returned, to exit 1, and cobra's own argument and flag
-    argument and flag errors to exit 2. So a runtime failure is never reported
+    errors to exit 2. So a runtime failure is never reported as a usage error,
-    as a usage error, nor printed with the usage text.
+    nor printed with the usage text. `main_test.go` drives the CLI in-process
-    `internal/sfdupes/cli_test.go` drives the CLI in-process and asserts the
+    and asserts the exit codes from README "Error handling" and the
-    exit codes from README "Error handling" and the stdout/stderr split. It also
+    stdout/stderr split. It also checks that a fatal error after the database is
-    checks that a fatal error after the database is open leaves no `-wal` or
+    open leaves no `-wal` or `-shm` file behind, for `scan`, `report` or `trees`
-    `-shm` file behind, for `scan`, `report` or `trees` (2026-08-09, branch
+    (2026-08-09, branch `db-close-on-fatal`,
-    `db-close-on-fatal`, https://git.eeqj.de/sneak/sfdupes/issues/4)
+    https://git.eeqj.de/sneak/sfdupes/issues/4)
 
 - `golangci-lint` was updated to v2.12.2 with the canonical config, merged as
   `38a01bd`. The pinned linter in the `Dockerfile` lint stage and
@@ -774,4 +742,6 @@ are known.
 
 # Accepted Divergences
 
-None.
+- Flat single-package layout, with the `.go` files in the repo root. That is
+  fine for a small single-binary tool per the Go styleguide, and the tracker
+  audit agrees.

cancel_test.go

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

cmd/sfdupes/main.go

@@ -1,29 +0,0 @@
-// 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()) }

db.go

@@ -1,4 +1,4 @@
-package sfdupes
+package main
 
 import (
 	"context"
@@ -146,44 +146,33 @@ 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, made absolute by absolutePath, and where the path came from,
+// path, with the working directory, its symlinks resolved, put in front
-// "default" or "from SFDUPES_DATABASE", for the line each subcommand
+// of it when it is relative, and where the path came from, "default" or
-// prints first on stderr.
+// "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
 	}
 
-	abs, err := absolutePath(path)
+	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()
 	if err != nil {
 		return "", "", fmt.Errorf("resolve database path %s: %w", path, err)
 	}
 
-	return abs, source, nil
+	// 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.
-// 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, nil
+	return strings.TrimSuffix(wd, "/") + "/" + path, source, nil
 }
 
 // createDatabaseDirectory creates the directory the database at path

db_test.go

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

exclude.go

@@ -1,4 +1,4 @@
-package sfdupes
+package main
 
 // 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

exclude_darwin.go

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

exclude_other.go

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

exclude_test.go

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

info.go

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

info_test.go

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

internal/sfdupes/dwim.go

@@ -1,37 +0,0 @@
-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

@@ -1,83 +0,0 @@
-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)
-	}
-}

main.go

@@ -1,6 +1,23 @@
-// Package sfdupes implements the sfdupes command and the database its
+// Command sfdupes quickly identifies candidate duplicate files across
-// subcommands share.
+// very large filesystems without reading every byte of every file.
-package sfdupes
+// 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
 
 import (
 	"context"
@@ -28,7 +45,6 @@ const (
 	cmdReport = "report"
 	cmdTrees  = "trees"
 	cmdInfo   = "info"
-	cmdDwim   = "dwim"
 )
 
 // errNoSubcommand is returned by the root command when it is invoked
@@ -68,22 +84,20 @@ func buildVersion(linkerVersion string, info *debug.BuildInfo) string {
 	return info.Main.Version
 }
 
-// Main runs the command line in os.Args and returns the process exit
+func main() {
-// 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.
-	return run(os.Args[1:], os.Stdout, os.Stderr)
+	os.Exit(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, info and dwim
+// runs before the process ends. The report, trees and info subcommands
-// subcommands write their data to stdout.
+// 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.
@@ -187,16 +201,7 @@ func newRootCommand(stdout, stderr io.Writer) *cobra.Command {
 		}),
 	}
 
-	dwimCmd := &cobra.Command{
+	root.AddCommand(newScanCommand(), reportCmd, treesCmd, infoCmd)
-		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
 }

main_test.go

@@ -1,4 +1,4 @@
-package sfdupes //nolint:testpackage // drives the unexported run
+package main
 
 import (
 	"bytes"
@@ -14,8 +14,6 @@ import (
 	"strconv"
 	"strings"
 	"testing"
-
-	"golang.org/x/sys/unix"
 )
 
 // usageMarker is the first line of cobra's usage text, which a usage
@@ -622,7 +620,6 @@ 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"},
 	}
@@ -800,7 +797,7 @@ func TestRunVersionWriteFailureIsFatal(t *testing.T) {
 func scanFixture(t *testing.T) []string {
 	t.Helper()
 
-	dir := realTempDir(t)
+	dir := t.TempDir()
 
 	dupes := []string{
 		writeFile(t, dir, "one/a.bin", pattern(1, 300)),
@@ -870,7 +867,7 @@ func TestRunScanSucceedsDespiteWarnings(t *testing.T) {
 	path := testDBPath(t)
 	t.Setenv(databaseEnv, path)
 
-	dir := realTempDir(t)
+	dir := t.TempDir()
 	writeFile(t, dir, "a.bin", pattern(1, 300))
 
 	// Same size as a.bin, so the scan reads it, and the read fails.
@@ -898,278 +895,58 @@ func TestRunScanSucceedsDespiteWarnings(t *testing.T) {
 	assertNoSidecars(t, path)
 }
 
-// realTempDir returns a new temporary directory by its real path, so
+func TestRunScanSkipsSymlinkOperand(t *testing.T) {
-// tests hold where the temporary directory is reached through a
-// symlink.
-func realTempDir(t *testing.T) string {
-	t.Helper()
-
-	dir, err := filepath.EvalSymlinks(t.TempDir())
-	if err != nil {
-		t.Fatal(err)
-	}
-
-	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)
+	dir := t.TempDir()
-	f := writeFile(t, dir, "target/sub/f", pattern(1, 10))
+	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)
+	err := os.Symlink(filepath.Join(dir, "target"), link)
-
+	if err != nil {
-	summary := "scan: 1 files seen (1 added, 0 updated, 0 removed, " +
+		t.Fatal(err)
-		"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}) {
+	// Scanning a directory through the symlink stores a record beneath
-		t.Errorf("records = %q, want %q", got, []string{f})
+	// 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"))
 }
 
-// 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 := realTempDir(t)
+	dir := t.TempDir()
-	f := writeFile(t, dir, "target/sub/f", pattern(1, 10))
+	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, filepath.Join(link, "sub"))
+	err := os.Symlink(filepath.Join(dir, "target"), 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})
-	}
-}
-
-// 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)
 	}
 
-	symlink(t, filepath.Join(dir, "data", "proj"),
+	// link is dropped as a symlink, but link/sub must still be scanned,
-		filepath.Join(dir, "home", "proj"))
+	// not dropped as lying under link.
+	scanOK(t, link, filepath.Join(link, "sub"))
 
-	// t.Chdir also sets PWD to the path through the symlink, as a
+	db, err := openDB(path, reportParams)
-	// 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)
 	}
 
-	link := filepath.Join(dir, "link")
+	t.Cleanup(func() { _ = db.Close() })
-	symlink(t, fifo, link)
 
-	stderr := scanOK(t, link)
+	recordByPath(t, dbRecords(t, db), filepath.Join(link, "sub", "f"))
-
-	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(realTempDir(t), ".zfs")
+	zfs := filepath.Join(t.TempDir(), ".zfs")
 	f := writeFile(t, zfs, "snapshot/hourly/f", pattern(1, 10))
 
 	// No scan records a file inside a .zfs directory, so the record
@@ -1220,7 +997,7 @@ func TestRunScanSkipsOperandInsideZFS(t *testing.T) {
 	path := testDBPath(t)
 	t.Setenv(databaseEnv, path)
 
-	dir := realTempDir(t)
+	dir := t.TempDir()
 	hourly := filepath.Join(dir, ".zfs", "snapshot", "hourly")
 	writeFile(t, hourly, "f", pattern(1, 10))
 	f := writeFile(t, dir, "f", pattern(2, 10))
@@ -1264,19 +1041,23 @@ func TestRunScanSkipsOperandInsideZFS(t *testing.T) {
 
 // TestRunScanSkipsOperandThroughSymlinkIntoZFS scans snaps/daily, where
 // snaps is a symlink to pool/.zfs/snapshot. The operand is warned about
-// by its real path, counted as skipped, and not walked.
+// by the path given, counted as skipped, and not walked.
 func TestRunScanSkipsOperandThroughSymlinkIntoZFS(t *testing.T) {
 	t.Setenv(databaseEnv, testDBPath(t))
 
-	dir := realTempDir(t)
+	dir := t.TempDir()
 	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)
 
-	stderr := scanOK(t, filepath.Join(snaps, "daily"))
+	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)
 
-	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"
@@ -1288,19 +1069,24 @@ func TestRunScanSkipsOperandThroughSymlinkIntoZFS(t *testing.T) {
 }
 
 // TestRunScanWalksOperandThroughSymlink scans data/daily, where data is
-// a symlink to pool/data. The operand is scanned as usual, and its file
+// a symlink to a directory outside any .zfs directory. The operand is
-// is recorded by its real path.
+// scanned as usual, and its file is recorded by the path given.
 func TestRunScanWalksOperandThroughSymlink(t *testing.T) {
 	path := testDBPath(t)
 	t.Setenv(databaseEnv, path)
 
-	dir := realTempDir(t)
+	dir := t.TempDir()
-	f := writeFile(t, dir, "pool/data/daily/f", pattern(1, 10))
+	writeFile(t, dir, "pool/data/daily/f", pattern(1, 10))
 
 	data := filepath.Join(dir, "data")
-	symlink(t, filepath.Join(dir, "pool", "data"), data)
 
-	stderr := scanOK(t, filepath.Join(data, "daily"))
+	err := os.Symlink(filepath.Join(dir, "pool", "data"), data)
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	daily := filepath.Join(data, "daily")
+	stderr := scanOK(t, daily)
 
 	summary := "scan: 1 files seen (1 added, 0 updated, 0 removed, " +
 		"0 unchanged), 0 skipped\n"
@@ -1308,9 +1094,14 @@ func TestRunScanWalksOperandThroughSymlink(t *testing.T) {
 		t.Errorf("stderr = %q, want %q", stderr, summary)
 	}
 
-	if got := storedPaths(t, path); !slices.Equal(got, []string{f}) {
+	db, err := openDB(path, reportParams)
-		t.Errorf("records = %q, want %q", got, []string{f})
+	if err != nil {
+		t.Fatal(err)
 	}
+
+	t.Cleanup(func() { _ = db.Close() })
+
+	recordByPath(t, dbRecords(t, db), filepath.Join(daily, "f"))
 }
 
 func TestRunReportSucceeds(t *testing.T) {

progress.go

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

progress_test.go

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

report.go

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

report_test.go

@@ -1,4 +1,4 @@
-package sfdupes //nolint:testpackage // checks the unexported dupeGroup results
+package main
 
 import (
 	"bytes"
@@ -434,27 +434,6 @@ 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()
 

scan.go

@@ -1,4 +1,4 @@
-package sfdupes
+package main
 
 import (
 	"cmp"
@@ -209,30 +209,29 @@ func interrupted(walked int) error {
 	return errInterrupted
 }
 
-// resolveRoots converts each PATH operand to its real path: absolute,
+// resolveRoots converts each PATH operand to an absolute, lexically
-// with every symlink in it followed. Database records are keyed by
+// cleaned path (symlinks are not resolved) and verifies that it
-// that path, so scan results depend neither on the working directory
+// exists. Database records are keyed by absolute path, so scan results
-// nor on the symlinks an operand was given through. An operand that
+// must not depend on the working directory.
-// 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) {
-	resolved := make([]string, 0, len(roots))
+	abs := make([]string, 0, len(roots))
 
 	for _, root := range roots {
-		a, err := absolutePath(root)
+		a, err := filepath.Abs(root)
 		if err != nil {
 			return nil, fmt.Errorf("resolve %s: %w", root, err)
 		}
 
-		r, err := filepath.EvalSymlinks(a)
+		// A nonexistent operand is a fatal error before any scanning.
+		_, err = os.Lstat(a)
 		if err != nil {
-			return nil, fmt.Errorf("resolve %s: %w", root, err)
+			return nil, err
 		}
 
-		resolved = append(resolved, r)
+		abs = append(abs, a)
 	}
 
-	return resolved, nil
+	return abs, nil
 }
 
 // pruneRoots drops operands already covered by another operand:
@@ -418,16 +417,14 @@ 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. The operands are real paths from resolveRoots,
+// directory named .zfs. Every other operand is warned about, counted as
-// so these checks apply to what a symlink operand points at. Every
+// skipped, and dropped. A dropped operand is no longer a root, so the
-// other operand is warned about, counted as skipped, and dropped. A
+// records stored beneath it are treated as if it had not been given:
-// dropped operand is no longer a root, so the records stored beneath it
+// those under no other root count as outside the roots and are not
-// are treated as if it had not been given: those under no other root
+// deleted as unverified. An operand on a filesystem in rules that is not
-// count as outside the roots and are not deleted as unverified. An
+// persistent is dropped the same way, with a line saying so that is not
-// operand on a filesystem in rules that is not persistent is dropped
+// a warning, and is not counted as skipped. An operand that fails lstat
-// the same way, with a line saying so that is not a warning, and is not
+// here is kept, and the walk warns about it unless it no longer exists.
-// 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))
 
@@ -557,7 +554,7 @@ 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
-		// up to seconds after the write.
+		// only seconds after the write.
 		if old.diskSize != ev.rec.diskSize {
 			s.diskSizes = append(s.diskSizes, ev.rec)
 		}
@@ -897,13 +894,19 @@ 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. resolveRoots has already followed the
+// inside a directory named .zfs, neither as given nor with its symlinks
-// operand's symlinks, so a symlink here is an operand replaced by one
+// resolved. Symlinks are never followed, including as operands.
-// 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.
+	// inside one either, not even through a symlink. An operand whose
-	if slices.Contains(strings.Split(filepath.Dir(root), "/"), ".zfs") {
+	// 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") {
 		return fmt.Sprintf("walk %s: skipping operand inside a .zfs directory",
 			root)
 	}

scan_dev_darwin.go

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

scan_dev_other.go

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

scan_test.go

@@ -1,4 +1,4 @@
-package sfdupes //nolint:testpackage // drives the unexported syncTree
+package main
 
 import (
 	"bytes"
@@ -1094,7 +1094,7 @@ func TestScanOneFilesystemWalksNestedFileOperand(t *testing.T) {
 func buildSmokeTree(t *testing.T) string {
 	t.Helper()
 
-	dir := realTempDir(t)
+	dir := t.TempDir()
 	one := pattern(10, 2000)
 	f1 := pattern(30, 3000)
 	f2 := pattern(40, 100)
@@ -1185,12 +1185,11 @@ func assertSmokeDupeGroups(t *testing.T, dir string, db *sql.DB) {
 	t.Helper()
 
 	groups := dupeGroups(t, db)
-	if len(groups) != 4 {
+	if len(groups) != 5 {
-		t.Fatalf("len(groups) = %d, want 4", len(groups))
+		t.Fatalf("len(groups) = %d, want 5", len(groups))
 	}
 
-	// The empty files empty1 and empty2 form no group.
+	wantSizes := []int64{3000, 2000, 100, 1, 0}
-	wantSizes := []int64{3000, 2000, 100, 1}
 	for i, g := range groups {
 		if g.size != wantSizes[i] {
 			t.Errorf("groups[%d].size = %d, want %d",
@@ -2311,24 +2310,33 @@ func TestUnderRoot(t *testing.T) {
 }
 
 // TestRunScanPassesOverDatabase scans a tree that holds the scan's own
-// database, and in one case also a hard link to the database file. The
+// database, reached directly and through a symlinked directory. The
-// walk knows the database's files by device ID and inode number, so it
+// walk passes over the database file, its -wal and -shm files and its
-// passes over the database file, its -wal and -shm files, its .lock
+// .lock file with no line and no count, and the record an earlier scan
-// file and the hard link with no line and no count. The record an
+// left for the .lock file is deleted. A rescan of the unchanged tree
-// earlier scan left for the .lock file is deleted. A rescan of the
+// updates nothing, and report lists none of the database's files.
-// unchanged tree updates nothing, and report lists none of the
-// database's files.
 func TestRunScanPassesOverDatabase(t *testing.T) {
-	for _, viaHardLink := range []bool{false, true} {
+	for _, viaSymlink := range []bool{false, true} {
-		t.Run(fmt.Sprintf("via hard link %v", viaHardLink), func(t *testing.T) {
+		t.Run(fmt.Sprintf("via symlink %v", viaSymlink), func(t *testing.T) {
-			tree := realTempDir(t)
+			base := t.TempDir()
-			hardLink := filepath.Join(tree, "hardlink")
+			tree := filepath.Join(base, "real", "tree")
+			operand := tree
 
 			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)
 
@@ -2338,7 +2346,7 @@ func TestRunScanPassesOverDatabase(t *testing.T) {
 			}
 
 			err = applyChanges(t.Context(), db, []scanRec{
-				{path: filepath.Join(tree, "db.sqlite.lock")},
+				{path: filepath.Join(operand, "db.sqlite.lock")},
 			}, nil, nil)
 			if err != nil {
 				t.Fatal(err)
@@ -2346,30 +2354,17 @@ func TestRunScanPassesOverDatabase(t *testing.T) {
 
 			closeScanDatabase(t.Context(), db, dbPath)
 
-			if viaHardLink {
+			assertScanSummary(t,
-				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)",
-				tree)
+				operand)
-			stderr += assertScanSummary(t,
+			assertScanSummary(t,
 				"4 files seen (0 added, 0 updated, 0 removed, 4 unchanged)",
-				tree)
+				operand)
-
-			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, hardLink) ||
+				!strings.Contains(report, filepath.Join(operand, "empty2")) {
-				!strings.Contains(report, filepath.Join(tree, "b")) {
+				t.Errorf("report = %q, want the empty files and none of "+
-				t.Errorf("report = %q, want a and b and none of "+
 					"the database's files", report)
 			}
 		})
@@ -2393,9 +2388,8 @@ 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. It returns
+// the database is the only one that names one of its files.
-// everything the scan printed to stderr.
+func assertScanSummary(t *testing.T, counts string, operands ...string) {
-func assertScanSummary(t *testing.T, counts string, operands ...string) string {
 	t.Helper()
 
 	stderr := scanOK(t, operands...)
@@ -2409,6 +2403,4 @@ func assertScanSummary(t *testing.T, counts string, operands ...string) string {
 		t.Errorf("scan %q: stderr = %q, want only the line naming the "+
 			"database to name one of its files", operands, stderr)
 	}
-
-	return stderr
 }

trees.go

@@ -1,4 +1,4 @@
-package sfdupes
+package main
 
 import (
 	"context"
@@ -301,9 +301,7 @@ 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. A group whose
+// tree size descending then by first path ascending.
-// 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 {
@@ -317,9 +315,7 @@ func collectTreeGroups(allDirs []*treeNode, super *treeNode,
 	var dupes [][]*treeNode
 
 	for _, g := range groups {
-		// The members share a digest, so they share a total size.
+		if len(g) < minGroupSize || suppressed(g, super) {
-		if len(g) < minGroupSize || g[0].totalSize == 0 ||
-			suppressed(g, super) {
 			continue
 		}
 

trees_test.go

@@ -1,8 +1,7 @@
-package sfdupes //nolint:testpackage // checks the unexported treeNode results
+package main
 
 import (
 	"bytes"
-	"crypto/sha256"
 	"database/sql"
 	"os"
 	"slices"
@@ -436,35 +435,6 @@ 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()