Keep a non-root user's database in the XDG state directory (closes #171)

Without SFDUPES_DATABASE, a user other than root now uses
sfdupes/db.sqlite in the XDG state directory (~/.local/state by
default) instead of failing on /var/lib/sfdupes. scan creates the
missing directories there with mode 0700, as the XDG Base Directory
specification asks. An XDG_STATE_HOME that is not an absolute path is
a fatal error for every subcommand. Root keeps
/var/lib/sfdupes/db.sqlite. sfdupes --help and README say where the
database is. Adds github.com/adrg/xdg, the decided XDG library.

Model: opus-5-5

README.md

@@ -22,14 +22,14 @@ 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` work from the database and
-can run at any time. `dwim` scans `/` and then prints the `trees` report, for a
+can run at any time. `report` and `trees` leave out a copy that was deleted
-first look at a new machine with one command.
+after the scan. `dwim` scans `/` and then prints the `trees` report, for a first
+look at a new machine with one command.
 
 ## Getting Started
 
 ```sh
 make build
-export SFDUPES_DATABASE="$HOME/.local/share/sfdupes/db.sqlite"
 ./sfdupes scan /srv
 ./sfdupes report > dupes.tsv
 ./sfdupes trees > dupetrees.tsv
@@ -45,8 +45,10 @@ that stands for a piece of hardware, such as a disk or a terminal. `report`
 prints the file-level duplicates. `trees` prints the duplicate directory trees.
 `info` prints the database's path, size and record count.
 
-The database is `/var/lib/sfdupes/db.sqlite` unless `SFDUPES_DATABASE` names
+Root keeps the database in `/var/lib/sfdupes/db.sqlite`. Any other user keeps it
-another file. The first `scan` creates it.
+in `sfdupes/db.sqlite` in the XDG state directory, `~/.local/state` by default
+on Linux. `SFDUPES_DATABASE` names another file (see "Location"). The first
+`scan` creates the database.
 
 `report`, `trees` and `info` write their data to stdout. Progress, warnings and
 errors go to stderr. stdout and stderr are a program's two output streams. The
@@ -148,8 +150,9 @@ walk"). As the file `/etc/cron.d/sfdupes`:
 - `report`, `trees` and `info` need only read access to the database. The umask
   is the setting that removes permissions from the files a process creates.
   Under the usual umask of `022`, the first scan creates the database readable
-  by every user. An unprivileged user can then run those three commands against
+  by every user. Another user can then run those three commands against root's
-  root's database.
+  database, with `SFDUPES_DATABASE=/var/lib/sfdupes/db.sqlite` before the
+  command.
 
 ### Reading the reports
 
@@ -254,14 +257,15 @@ 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 `/`, then prints the duplicate-tree report.
+- `dwim` scans `/` with the default excludes, then prints the duplicate-tree
+  report.
 
 ```
 sfdupes scan [--workers N] [-x] [--no-default-excludes] [--exclude PATH]... PATH...
 sfdupes report > dupes.tsv
 sfdupes trees > dupetrees.tsv
 sfdupes info
-sfdupes dwim [--workers N] [-x] [--no-default-excludes] [--exclude PATH]...
+sfdupes dwim
 sfdupes --version
 sfdupes [command] --help
 ```
@@ -288,23 +292,23 @@ The reference below is also the program's specification.
 ### Settings
 
 - `SFDUPES_DATABASE` names the database file. When it is unset or empty, the
-  database is `/var/lib/sfdupes/db.sqlite`. There is no command-line flag for
+  database is at its default path (see "Location"). There is no command-line
-  it. The path names the file exactly, whatever characters it holds. A relative
+  flag for it. The path names the file exactly, whatever characters it holds. A
-  path is relative to the working directory.
+  relative path is relative to the working directory.
-- `--workers N` (`scan`, `dwim`) sets how many directories `scan` reads at once
+- `--workers N` (`scan`) sets how many directories `scan` reads at once while it
-  while it lists the trees. It also sets how many files `scan` reads at once
+  lists the trees. It also sets how many files `scan` reads at once while it
-  while it hashes them. The default is the number of CPUs. `N` must be at
+  hashes them. The default is the number of CPUs. `N` must be at least 1. A
-  least 1. A smaller value is a usage error, reported in one line on stderr with
+  smaller value is a usage error, reported in one line on stderr with exit 2
-  exit 2 before anything is scanned.
+  before anything is scanned.
-- `-x`, `--one-file-system` (`scan`, `dwim`) keeps the walk of each operand out
+- `-x`, `--one-file-system` (`scan`) keeps the walk of each operand out of
-  of directories on other filesystems, as the same flag does for `du` and
+  directories on other filesystems, as the same flag does for `du` and `rsync`.
-  `rsync`. By default the walk also enters directories on other filesystems.
+  By default the walk also enters directories on other filesystems.
-- `--no-default-excludes` (`scan`, `dwim`) lets the walk enter the default
+- `--no-default-excludes` (`scan`) lets the walk enter the default excludes.
-  excludes. Those are the system and temporary directories the walk otherwise
+  Those are the system and temporary directories the walk otherwise leaves out,
-  leaves out, such as `/var/tmp` on Linux (see "Rules for the walk").
+  such as `/var/tmp` on Linux (see "Rules for the walk").
-- `--exclude PATH` (`scan`, `dwim`) keeps the walk out of `PATH` and everything
+- `--exclude PATH` (`scan`) keeps the walk out of `PATH` and everything below
-  below it. `PATH` may be a directory or a file. The flag may be given more than
+  it. `PATH` may be a directory or a file. The flag may be given more than once.
-  once. The walk knows `PATH` by its device ID and inode number, as it knows the
+  The walk knows `PATH` by its device ID and inode number, as it knows the
   database files (see "Rules for the walk"). So the walk leaves `PATH` out
   whatever path leads to it. That includes a hard link to a file given as
   `PATH`. A symlink given as `PATH` excludes its target. An empty `PATH`, as in
@@ -315,10 +319,8 @@ The reference below is also the program's specification.
 - `--version`, `-v` prints `sfdupes VERSION` (see "Install") to stdout and
   exits 0. It writes nothing to stderr.
 - `--help`, `-h`, alone or after a subcommand, prints the help text to stderr
-  and exits 0. It writes nothing to stdout. The help of `sfdupes` and of `scan`
+  and exits 0. It writes nothing to stdout. `sfdupes scan --help` also lists the
-  names the database. The help of `report`, `trees`, `info` and `dwim` says what
+  default excludes of the system it runs on, and the filesystem types the walk
-  each prints. `sfdupes scan --help` and `sfdupes dwim --help` also list the
-  default excludes of the system they run on, and the filesystem types the walk
   never records anything on.
 
 ### Duplicate detection
@@ -848,8 +850,7 @@ The summary line on stderr gives:
 - the records read;
 - the duplicate-tree groups;
 - the dupe trees, which is the number of rows;
-- the reclaimable bytes, the sum of `size` over all rows, leaving out a row
+- the reclaimable bytes, the sum of `size` over all rows.
-  whose `dupe` lies inside another row's `dupe`.
 
 ```
 trees: 14 records read, 1 duplicate tree groups, 1 dupe trees, 3.0 KiB reclaimable
@@ -858,25 +859,14 @@ trees: 14 records read, 1 duplicate tree groups, 1 dupe trees, 3.0 KiB reclaimab
 ### `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. Like `scan`,
+duplicate trees in one command. It takes no positional arguments and no flags of
-it should run as root, so that it can read every file.
+its own. Like `scan`, it should run as root, so that it can read every file.
 
-`dwim` takes these flags of `scan`, with the same meaning (see "Settings"):
+`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
-- `--workers N`;
-- `-x`, `--one-file-system`;
-- `--no-default-excludes`;
-- `--exclude PATH`, which may be given more than once.
-
-`dwim` runs what `sfdupes scan /` runs with the same flags. With no flags, the
-walk skips the default excludes and crosses into other filesystems. The
 database, its creation and the scan lock are those of `scan`. Then `dwim` runs
 what `sfdupes trees` runs. The largest trees come first.
 
-```
-sfdupes dwim -x --exclude /srv/cache
-```
-
 The report goes to stdout, exactly as `trees` prints it. On stderr comes what
 `scan` prints, then what `trees` prints, then one last line:
 
@@ -938,7 +928,22 @@ All five subcommands work on one SQLite database file.
 #### Location
 
 The database is the file named by `SFDUPES_DATABASE`, when that is set and not
-empty, and otherwise `/var/lib/sfdupes/db.sqlite`.
+empty. Otherwise it is at its default path, which depends on the user:
+
+- For root, it is `/var/lib/sfdupes/db.sqlite`.
+- For any other user, it is `sfdupes/db.sqlite` in the XDG state directory. That
+  directory is `$XDG_STATE_HOME` when that is set and not empty. Otherwise it is
+  `~/.local/state` on Linux and `~/Library/Application Support` on macOS. An
+  `XDG_STATE_HOME` that is not an absolute path is a fatal error, exit 1, for
+  every subcommand. The error names `XDG_STATE_HOME`.
+
+`scan` creates each missing directory on the way to the database with mode 755.
+At the default path of a user other than root, it uses mode 700 instead, as the
+XDG Base Directory specification asks. Other users cannot enter a directory with
+mode 700, so they cannot read a database in it.
+
+All five subcommands use the same default, so a user's `report` reads the
+database that user's `scan` wrote.
 
 Each subcommand prints one line on stderr naming the database it uses, before
 anything else and whether or not stderr is a terminal. The line gives the path
@@ -978,9 +983,9 @@ Only one `scan` at a time can hold the lock.
 - For its whole run, `scan` holds a lock on a lock file beside the database. The
   lock is taken with the `flock(2)` system call, a request a program makes to
   the kernel, and only one process can hold it. The lock file's name is the
-  database's path, with symlinks resolved, plus `.lock`. By default that is
+  database's path, with symlinks resolved, plus `.lock`. For root, by default,
-  `/var/lib/sfdupes/db.sqlite.lock`. A path through a symlink names the same
+  that is `/var/lib/sfdupes/db.sqlite.lock`. A path through a symlink names the
-  lock file.
+  same lock file.
 - `scan` takes the lock before it walks the filesystem or opens the database.
   Just before that, it creates the database file, empty, if it is missing. So
   the lock file is named the same way before the first scan as after. A symlink

TODO.md

@@ -4,7 +4,7 @@
   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.
+- Record the step at the top of Completed Steps, 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
@@ -15,7 +15,8 @@
 
 - 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.
+  the `1.0.0` milestone are what remains before the tag. This file records
+  history and process, not the queue.
 
 # Next Step
 
@@ -23,6 +24,767 @@
   https://git.eeqj.de/sneak/sfdupes/milestone/17. The issues are not restated
   here, because a copy drifts as soon as the tracker moves.
 
+# Completed Steps
+
+Newest first. An entry ends with its date and its issue or branch, where those
+are known.
+
+- Without `SFDUPES_DATABASE`, a user other than root keeps the database in
+  `sfdupes/db.sqlite` under the XDG state directory, `~/.local/state` by
+  default. Root keeps `/var/lib/sfdupes/db.sqlite`. `sfdupes --help` says where
+  the database is (2026-11-11, https://git.eeqj.de/sneak/sfdupes/issues/171)
+
+- New `scan` flag `--exclude PATH`, which may be repeated. The walk neither
+  enters nor records an excluded path, and keeps the records below it. An
+  operand at or below one is a fatal error (2026-11-11,
+  https://git.eeqj.de/sneak/sfdupes/issues/163)
+
+- `report` and `trees` leave out a copy that was deleted after the scan. Each
+  checks only the copy itself with `lstat`: the file, or the directory at the
+  top of a tree. A group left with one copy is not reported. A missing `scan`
+  operand is still a fatal error (2026-11-11,
+  https://git.eeqj.de/sneak/sfdupes/issues/173)
+- The usage line of `scan` no longer ends in `[flags]`. It is the line
+  `README.md` shows under "Subcommands" (2026-11-11,
+  https://git.eeqj.de/sneak/sfdupes/issues/169)
+- `report` and `trees` leave out empty files. `report` writes no group of size
+  0, and `trees` writes no group whose trees hold 0 bytes. An empty file still
+  counts toward a tree's digest (2026-11-11,
+  https://git.eeqj.de/sneak/sfdupes/issues/178)
+- The Go code moved out of the repository root. `cmd/sfdupes/main.go` is the
+  command, and it calls `Main` in the package `internal/sfdupes`. `main.go`
+  became `internal/sfdupes/cli.go`. Every other file kept its name. The install
+  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.
+  The policy-compliance checklist of 2026-07-22 is folded into its step
+  (2026-11-02, https://git.eeqj.de/sneak/sfdupes/issues/135)
+
+- `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
+  `internal/sfdupes/cli_test.go` cite "Settings", where their rules now live.
+  One comment each in these files cites what the README now says:
+    - `internal/sfdupes/scan_test.go`;
+    - `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
+  makes. `trees` prints a `disk_size` column after `size`. It is the sum over
+  the `dupe` copy's files. On a compressed or sparse file `disk_size` 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. Three triggers on `files` keep that row current.
+  `info` reads that row. 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. That 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.
+  The bar 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. That is 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 three hashes to every file that the walk records. `head`
+  and `tail` are the SHA-256 of its first and last 64 KiB. `content` is the
+  SHA-256 of the whole file under 100 MiB, and of 1 MiB at each gigabyte from
+  100 MiB up. Gone are:
+    - the 10 MiB and 50 MiB thresholds;
+    - the size census, which counted the sizes of every walked file and of every
+      record outside the operands. A file was hashed only when the census showed
+      another file of its size;
+    - the records without hashes;
+    - the content phase.
+
+    A scan has four phases, and a rescan reads only new and changed files.
+    `info` no longer counts the records with `head` and `tail` hashes, nor those
+    with a content hash, since every record has all three (2026-10-25,
+    https://git.eeqj.de/sneak/sfdupes/issues/132)
+
+- `REPO_POLICIES.md` and the four scripts that pass `CACHEBUST` were copied
+  again from `sneak/prompts` `next` at `0653579`. Two steps now come before
+  `ARG CACHEBUST`:
+    - the module download in the `lint`, `test` and `builder` stages of the
+      `Dockerfile`;
+    - the package install in `builder`.
+
+    Docker keeps them until one of these changes:
+    - the base image;
+    - the install line;
+    - `go.mod` or `go.sum`.
+
+    Every step that checks or compiles the code still comes after
+    `ARG CACHEBUST`. `golangci-lint run` also keeps the linter's own cache.
+    README says the same (2026-10-18,
+    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.
+  `go install sneak.berlin/go/sfdupes/cmd/sfdupes@latest` then installs it.
+  `go.mod` retracts `v0.0.1`, the early build without a database. When the
+  linker set no version, `sfdupes --version` prints the version Go recorded in
+  the binary. That is the tag, or the pseudo-version of a `go install` build. It
+  prints `dev` only when neither is known. README "Install" documented:
+    - the rule;
+    - what `@main` and `v0.0.1` give;
+    - how to check an installed binary.
+
+    (2026-10-17, https://git.eeqj.de/sneak/sfdupes/issues/116)
+
+- `scan` creates the database's directory where the database path leads. The
+  directory is the path with its last element cut off as text, so a `..` in it
+  stays. A `..` after a symlinked directory therefore goes through the symlink,
+  as it does when the file is opened. With
+  `SFDUPES_DATABASE=/srv/link/../new/db.sqlite` and `/srv/link` a symlink to
+  `/data/x`, it now creates `/data/new` and the database in it. 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 each of these:
+    - the database file;
+    - its `-wal` and `-shm` files;
+    - the `.lock` file.
+
+    The walk passes over any file with the device and inode of one of them,
+    however it reaches the file. It prints no line for such a file and counts
+    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 on a filesystem that is not persistent,
+  such as `tmpfs` or `proc`. Such a filesystem is one the kernel makes up or
+  keeps in memory. `scan` matches them by device ID, however the walk or the
+  content phase reaches a path. As the scan starts, it lists the mounted
+  filesystems of those types, from `/proc/self/mountinfo` on Linux and from the
+  mount list on macOS. No flag turns that off. Below an operand, the 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 those are:
+
+    ```
+    /proc, /sys, /dev, /run, /tmp, /var/tmp
+    ```
+
+    On macOS they are:
+
+    ```
+    /dev, /private/tmp, /private/var/tmp, /private/var/vm
+    /System/Volumes/VM, /System/Volumes/Data
+    ```
+
+    A Windows list exists in the code but is not used. 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. 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)
+
+- A progress display's rate covers the items completed over the last 5 seconds.
+  When stderr is not a terminal, it covers the items since the line before. It
+  falls to 0 while nothing completes. A burst after a wait no longer reads as a
+  steady rate of over 1,000 files a second. The time remaining still comes from
+  the phase's average. Once no item has completed for 10 seconds, the line shows
+  `stalled` and where the phase waits in place of the rate, as
+  `stalled disk/db`. The places are:
+    - `disk`;
+    - `db`;
+    - `out`, for stdout;
+    - `cpu`.
+
+    A phase that may wait in two places names both. Each phase's word is set in
+    the code that defines the phase. A line too wide for the terminal loses its
+    bar first, then its rate or those words. Four parts stay whole:
+    - the phase;
+    - the progress;
+    - the elapsed time;
+    - the ETA, the time remaining.
+
+    The content phase had one display for its checks and one for its reads. Both
+    lost those words on an 80-column terminal, at counts like those of README's
+    example. That happened for most elapsed times and ETAs in minutes. Every
+    other phase kept them whenever the elapsed time and the ETA were both in
+    minutes. The content phase writes its last partial batch, the records not
+    yet 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:
+    - the 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 records have `head` and `tail` hashes;
+    - how many records have a content hash;
+    - 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, a read of the database at one moment. The counts
+    come 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. The display
+  runs from the moment `report` 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. SQLite takes
+  that order from the `files_signature` index without sorting, so the first
+  record comes at once. `report` forms the duplicate groups itself and holds
+  only those of the size it is reading. It 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, from `[1/4] open` to
+  `[4/4] write`, each with the progress display `scan` uses. The display runs
+  from the moment `trees` 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;
+    - groups.
+
+    stdout and the summary line are unchanged. When stdout and stderr are the
+    same file, as one terminal is, no line of stdout 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`. It runs from the moment that the phase starts. It
+  shows:
+    - the progress;
+    - the elapsed time;
+    - the ETA, the time remaining.
+
+    `load` counts the records first. The walk's total is estimated from the
+    records under the operands. The content phase takes its total from SQLite's
+    grouping alone. Until the first record is returned, it says it is searching
+    the database. On a terminal a phase with an exact total draws its line
+    followed by the bar of the progress-bar library. Any other phase draws 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 the
+    terminal is, even after it is made narrower during a phase. A line too wide
+    leaves out its rate, then its bar. The rest stays whole. The line is cut
+    short only when the rest alone does not fit, as below about 70 columns late
+    in a large scan. When stderr is not a terminal, 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. The line says 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)
+
+- The canonical files and model scripts were copied again 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. Gone are
+      `Dockerfile.lint`, `script/verify-lint-image-pin` and `make test-race`;
+    - every `docker build` in `script/` passes a new `CACHEBUST` value. Every
+      stage of the `Dockerfile` declares it first, so every `RUN` step runs on
+      every build. 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` that
+      `script/bootstrap` installs. 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;
+    - a coding agent's settings file is deleted.
+
+    Since https://git.eeqj.de/sneak/sfdupes/issues/109 two steps come before
+    `ARG CACHEBUST`:
+    - the module download in `lint`, `test` and the build stage;
+    - the install of `git` and `make` in the build stage.
+
+    Docker keeps them between builds. Every step that checks or compiles the
+    code still runs on every build (2026-10-15,
+    https://git.eeqj.de/sneak/sfdupes/issues/95)
+
+- With `-x`, an operand under another operand is no longer dropped when a
+  directory between the two, the inner one included, is on a different
+  filesystem than the outer one. The inner operand is then walked on its own.
+  For a regular-file operand the check starts at its directory. 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, instead of deleting them. It counts their sizes in the size
+  census (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. A file that is now a FIFO or device node 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. A scan through a
+  symlink to the database therefore 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 the mtime to the nanosecond, as whole seconds in `mtime` plus
+  `mtime_nsec`, and compares it at that resolution. A same-size rewrite within
+  the same second is hashed again (2026-10-07,
+  https://git.eeqj.de/sneak/sfdupes/issues/12)
+
+- The narration was cut 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). The Workflow section 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`. 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.
+  `make test-race` is gone (2026-10-04,
+  https://git.eeqj.de/sneak/sfdupes/issues/18)
+
+- A bare `docker build .` failed, naming `script/cibuild` and `script/docker`,
+  rather than serve the gates, the lint and test steps, from cache. 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 (2026-10-04,
+  https://git.eeqj.de/sneak/sfdupes/issues/39)
+
+- `make fmt` and `make fmt-check` run `prettier` over all Markdown, and the
+  Gitea workflow checks it. All Markdown was 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;
+    - every subcommand going through `runE`.
+
+    (2026-10-04, https://git.eeqj.de/sneak/sfdupes/issues/16)
+
+- `.golangci.yml` was 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
+  `internal/sfdupes/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 `internal/sfdupes/scan.go`
+  is removed (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,
+  and `walkCancelInFlightDirs` was renamed to `walkCancelInFlightFiles`
+  (2026-10-04, 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)
+
+- `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. 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 (2026-10-04,
+  https://git.eeqj.de/sneak/sfdupes/issues/43)
+
+- `--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`: it commits what it has hashed,
+  deletes nothing more, and 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 and uses a real terminal test.
+  Warnings print through a spinner instead of racing its redraw (2026-10-03,
+  https://git.eeqj.de/sneak/sfdupes/issues/13)
+
+- These operands are warned about and skipped, and the records beneath them are
+  kept:
+    - symlinks;
+    - sockets;
+    - FIFOs;
+    - device nodes;
+    - `.zfs` directories.
+
+    (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)
+
+- Tests cover stdout write failures in `report` and `trees`. README states that
+  `| head` ends `sfdupes` by `SIGPIPE` and that `>&-` 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,
+  https://git.eeqj.de/sneak/sfdupes/issues/8)
+
+- Four characters are escaped in `report`, `trees` and warning paths:
+    - tab;
+    - newline;
+    - carriage return;
+    - backslash.
+
+    The root directory's path is `/` (2026-10-03,
+    https://git.eeqj.de/sneak/sfdupes/issues/7)
+
+- A plain `docker build .` stamps the `git` tag or short commit instead of
+  `dev`. `.dockerignore` sends `.git` without `.git/config`. The build stage
+  stamps the `VERSION` build argument, else `git describe --tags --always`. It
+  fails if the context carries `.git` and the version is still empty, `dev` or
+  `unknown`. The Gitea workflow checks out the full history (`fetch-depth: 0`),
+  so it stamps the same value as `make build` (2026-10-02, branch `next`,
+  https://git.eeqj.de/sneak/sfdupes/issues/67)
+
+- The 1 KiB end-window sampling was replaced with the hashes chosen by file
+  size, and README "Duplicate detection" documented every size threshold. A file
+  under 10 MiB was hashed in full, and its `head`, `tail` and `content` all held
+  that hash. A larger file got only its 64 KiB `head` and `tail` in the hash
+  phase. The content phase ran after the update phase. It read a file for
+  `content` only when its size, `head` and `tail` matched another record's, from
+  this scan or an earlier one. `content` was the whole file below 50 MiB, and
+  gigabyte-spaced 1 MiB samples at or above. It never read a file gone or
+  changed since its record was written. `report` and `trees` left out any record
+  without a `content` hash. The `content` column is part of the version 1
+  schema. Superseded by https://git.eeqj.de/sneak/sfdupes/issues/132
+  (2026-09-22, branch `next`, https://git.eeqj.de/sneak/sfdupes/issues/61)
+
+- The dead `files.dat` references were removed from `Makefile`, `.gitignore` and
+  `.dockerignore` (2026-09-21, branch `next`,
+  https://git.eeqj.de/sneak/sfdupes/issues/22)
+
+- The lint-image pin comments and `FROM` form in `Dockerfile` and
+  `Dockerfile.lint` were fixed. 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. `Dockerfile.lint` is gone,
+  and so is `script/verify-lint-image-pin`, which compared the two pins
+  (2026-08-10, branch `next`, https://git.eeqj.de/sneak/sfdupes/issues/25)
+
+- All linting ran in Docker, via `Dockerfile.lint` and `script/lint`. 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. `script/lint` builds that phase alone, and the
+  build stage depends on it 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
+  (2026-08-10, branch `next`, https://git.eeqj.de/sneak/sfdupes/issues/46)
+
+- The Docker build stage's prerequisites were installed by running
+  `script/bootstrap` instead of `apk add --no-cache make` inline.
+  `script/verify-linter-pin` failed the build unless the linter copied from the
+  lint stage was the version that `script/bootstrap` pinned. Builds then took up
+  to 5m14s from an empty cache, 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 (2026-08-09, branch `dockerfile-bootstrap`,
+  https://git.eeqj.de/sneak/sfdupes/issues/42)
+
+- The Docker layer cache is defeated for the gate steps, so `script/cibuild` and
+  `script/docker` cannot report a pass they did not earn. The `Dockerfile`
+  copies the tree before its gates. On an unchanged tree Docker served them from
+  cache, and the build exited 0 without running them. 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. Every stage of the `Dockerfile`
+  declares it before every step that checks or compiles the code. 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`
+  (2026-08-09, branch `cibuild-cache-bust`,
+  https://git.eeqj.de/sneak/sfdupes/issues/32)
+
+- `script/bootstrap` checked the installed `golangci-lint` version instead of
+  only its presence. The version lived only in `GOLANGCI_LINT_VERSION`, with the
+  `go install` module reference derived from it. Any installed version that was
+  not the pin was reinstalled, whether:
+    - older;
+    - newer;
+    - absent;
+    - unparseable.
+
+    `go install` writes into `GOBIN`, or `GOPATH/bin`, while `make lint` ran the
+    first `golangci-lint` on `PATH`. So bootstrap re-read the effective version
+    after installing. On a mismatch it printed both paths and both versions and
+    exited non-zero. It did not reorder `PATH` or delete anyone's binary. The
+    `--version` call kept its stderr and was bounded by `timeout(1)` where that
+    exists. `git`, `make` and `go` kept presence-only checks. The version check
+    was verified by bootstrapping this host from v2.10.1 to v2.12.2, and again
+    to a no-op. Stub runs of the script under `dash` covered:
+    - a thirteen-input version-parse matrix;
+    - a shadowed install, which must exit non-zero;
+    - an install destination not on `PATH`;
+    - `GOBIN` set;
+    - a wedged binary, which must hit the timeout.
+
+    `make check` and `make lint` were clean at v2.12.2, so v2.10.1 had not been
+    hiding findings on `main`. Superseded by
+    https://git.eeqj.de/sneak/sfdupes/issues/46, since the linter is no longer
+    installed on a host (2026-08-09, branch `bootstrap-version-check`,
+    https://git.eeqj.de/sneak/sfdupes/issues/24)
+
+- The hash worker pool unwinds on the error path. The pool is an owned,
+  context-aware `hashPool`. Every blocking send in the feeder and the workers
+  selects on `ctx.Done()`, and `jobs` is closed on every path out. `hashPhase`
+  defers `pool.stop()`, which cancels and then drains `results` until the last
+  goroutine has exited. Draining is what frees a worker parked on a send. `ctx`
+  is passed from `cmd.Context()` as the first parameter, through:
+    - `runScan`;
+    - `syncScan`;
+    - both worker pools;
+    - the whole database layer.
+
+    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 that it
+    never reached looks vanished to the update phase. That phase's own `BeginTx`
+    also fails on the cancelled context before deleting anything. The guard is
+    still the barrier once an interrupted scan may commit what it has. Tests
+    drive `run(scan)` against a database whose insert trigger aborts. They
+    assert that the scan fails instead of hanging, and that the goroutine count
+    returns to its pre-scan baseline. Other tests cancel a scan part-way through
+    the walk, deterministically, by counting the scan's own checks of
+    `ctx.Done()`. They assert that it stops at the guard with every record
+    intact. It then holds a partial size census and a still-populated record
+    index. Direct tests cover the remaining cancellation branches of both pools.
+    They test:
+    - `sendEvent`;
+    - the walk workers;
+    - `dispatchDirs`;
+    - `feedHashJobs`;
+    - `hashWorker`;
+    - `hashPhase`.
+
+    (2026-08-09, branch `hash-pool-cleanup`,
+    https://git.eeqj.de/sneak/sfdupes/issues/6)
+
+- The database is closed on every fatal exit path. `fatalf` and its `os.Exit(1)`
+  are gone. So the deferred `db.Close()` runs when a subcommand fails, and with
+  it the SQLite WAL checkpoint. These return errors instead:
+    - `runScan`;
+    - `runReport`;
+    - `runTrees`;
+    - `loadRecords`;
+    - `resolveRoots`.
+
+    The single exit point is `run` in `internal/sfdupes/cli.go`. It maps a
+    `fatalError`, anything a subcommand returned, to exit 1, and cobra's own
+    argument and flag errors to exit 2. So a runtime failure is never reported
+    as a usage error, nor printed with the usage text.
+    `internal/sfdupes/cli_test.go` drives the CLI in-process and asserts the
+    exit codes from README "Error handling" and the stdout/stderr split. It also
+    checks that a fatal error after the database is open leaves no `-wal` or
+    `-shm` file behind, for `scan`, `report` or `trees` (2026-08-09, branch
+    `db-close-on-fatal`, 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
+  `script/bootstrap` went from v2.12.1 to v2.12.2, and `.golangci.yml` was
+  replaced with the canonical file. Four thresholds now live under
+  `linters.settings`, as the v2 schema requires, so they are applied:
+    - `lll`;
+    - `funlen`;
+    - `cyclop`;
+    - `dupl`.
+
+    No new lint findings surfaced (2026-08-09, branch `golangci-v2.12.2`,
+    https://git.eeqj.de/sneak/sfdupes/issues/3)
+
+- `Makefile` targets were converted to scripts-to-rule-them-all `script/`
+  entrypoints, like the other managed repos. All 12 entrypoints exist:
+    - `bootstrap`, `setup` and `projectname`;
+    - `test`, `lint`, `fmt`, `fmt-check` and `check`;
+    - `docker`, `cibuild`, `precommit` and `install-precommit`.
+
+    Every `Makefile` target does nothing but call its script (2026-07-26, commit
+    `3abeacf`, https://git.eeqj.de/sneak/sfdupes/issues/1)
+
+- The binary is the default `make` target. Plain `make` builds `sfdupes`, where
+  it used to run `check` plus `build`. `make build` remains as an alias
+  (2026-07-24, branch `make-default-target`)
+
+- The phases became scan-wide, with concurrent operands and batched updates. All
+  operands seed the shared walk pool, and every pass runs once over the whole
+  scan. So the totals and ETAs cover the whole scan. The per-operand walk, hash
+  and update cycles and their stderr announcements are gone. The update pass
+  writes in batches, each in its own transaction. The filesystem is
+  authoritative and the database follows it, so one scan's changes need not land
+  all at once (2026-07-24, branch `scan-wide-phases`)
+
+- The stat pass was split back out of the walk. Phases are strictly sequential
+  again, per operand, with parallelism only inside each phase:
+    - walk;
+    - stat;
+    - hash;
+    - update.
+
+    The walk enumerates paths with per-directory workers, and the stat pass
+    lstats them with per-file workers. That restores the exact total and ETA of
+    the stat bar (2026-07-24, branch `parallel-phases`)
+
+- Each operand is announced on stderr before its passes. With per-operand walk,
+  hash and update cycles, a multi-operand run such as `scan /srv/*` showed pass
+  totals that looked like the whole run's (2026-07-24, branch
+  `scan-operand-progress`)
+
+- The walk became parallel. The walk pass was a single goroutine and took hours
+  at about 20 million files on a busy pool. One ZFS server took 4 hours for 22
+  million files. It is now a walk by a pool of per-directory workers that
+  records size and mtime as it goes. That folds away the separate stat pass and
+  halves the metadata reads. Each `PATH` operand commits in its own transaction,
+  so an interrupted scan keeps completed operands (2026-07-24, branch
+  `parallel-walk`)
+
+- `scan` gained a persistent database. It maintains an SQLite database that
+  survives between runs, with the absolute path as each record's key. The driver
+  is `modernc.org/sqlite`, pure Go, so cgo stays disabled. A rescan hashes only
+  new or changed files, by mtime and size. It deletes the records of files
+  vanished from under the scanned operands and leaves records outside them
+  untouched. So `scan` can run daily from `cron`. `report` and `trees` read the
+  database, with no positional arguments, instead of a scan stream. The database
+  is at `/var/lib/sfdupes/db.sqlite`, and `SFDUPES_DATABASE` overrides that. WAL
+  journaling plus a single-transaction update keep a report run during a scan
+  safe (2026-07-24, branch `persistent-database`)
+
+- The `origin` remote, `git@git.eeqj.de:sneak/sfdupes.git`, was added. `v0.0.1`
+  was tagged, and `main` and the tags were pushed (2026-07-23)
+
+- The `scan` command line was reworked. Required `PATH...` operands, parsed by
+  cobra, replace the `/srv` `-root` default. The new `-x`, `--one-file-system`
+  flag follows the GNU convention and stops at filesystem boundaries, which the
+  walk crosses by default (2026-07-23, branch `scan-required-paths`)
+
+- The repo was brought into compliance with `REPO_POLICIES.md` (the version of
+  2026-07-06), the existing repo checklist and the Go styleguide. The audit of
+  2026-07-22 found these gaps, and the branch closed them:
+    - `.gitignore`, with the standard patterns for secrets and for OS, editor
+      and Go files. The compiled `sfdupes` binary and `files.dat` had been
+      sitting untracked in the tree;
+    - `.editorconfig`;
+    - `LICENSE` and the README License section. MIT was assumed from house
+      convention, for the owner to confirm;
+    - `REPO_POLICIES.md` in the repo root;
+    - the canonical `.golangci.yml`, with its 150 findings fixed, so that
+      `make lint` is clean;
+    - the `Makefile` targets the policy requires:
+        - `test` and `lint`;
+        - `fmt` and `fmt-check`;
+        - `docker` and `hooks`.
+
+        `check` depended on `build`, which wrote the binary. `make check` must
+        not modify files, so `check` no longer depends on `build`;
+
+    - a test suite, which the policy required with a 30-second timeout and the
+      conditional `-v` rerun. At 64% coverage, it covers:
+        - parsing and grouping;
+        - digests and suppression;
+        - hashing and the scan pipeline;
+    - a multistage `Dockerfile` and `.dockerignore`. The `Dockerfile` had:
+        - hash-pinned images;
+        - a lint stage that failed fast;
+        - a build stage that ran `make check`;
+    - `.gitea/workflows/check.yml`, running `docker build .` on push with the
+      checkout action pinned by commit SHA;
+    - the README sections the policy requires. The first is a Description whose
+      first line names the project, its purpose and category, its license and
+      its author. Then come Getting Started and Rationale, and at the end TODO,
+      License and Author;
+    - the stale README non-goal "no git repository setup and no CI" removed;
+    - the pre-commit hook, installed with `make hooks` once that target existed.
+
+    The code was already `gofmt`-clean, so no standalone formatting commit was
+    needed (2026-07-23, branch `repo-policy-compliance`)
+
+- `git init` was run, with a README-only first commit. The code baseline was
+  committed on `main` (2026-07-22)
+
+- The `scan`, `report` and `trees` subcommands were implemented (pre-git
+  history)
+
 # Future Steps
 
 - Possible later features, out of scope per README, are a byte-for-byte check of

cmd/sfdupes/main.go

@@ -5,8 +5,10 @@
 // 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
+// database of file signatures that the other subcommands read. The
-// /var/lib/sfdupes/db.sqlite) that the other subcommands read.
+// database is SFDUPES_DATABASE, or by default /var/lib/sfdupes/db.sqlite
+// for root and sfdupes/db.sqlite in the XDG state directory for any
+// other user.
 //
 // Usage:
 //

go.mod

@@ -3,6 +3,7 @@ module sneak.berlin/go/sfdupes
 go 1.25.7
 
 require (
+	github.com/adrg/xdg v0.5.3
 	github.com/schollz/progressbar/v3 v3.19.1
 	github.com/spf13/cobra v1.10.2
 	golang.org/x/sys v0.46.0

go.sum

@@ -1,3 +1,5 @@
+github.com/adrg/xdg v0.5.3 h1:xRnxJXne7+oWDatRhR1JLnvuccuIeCoBu2rtuLqQB78=
+github.com/adrg/xdg v0.5.3/go.mod h1:nlTsY+NNiCBGCK2tpm09vRqfVzrc2fLmXGpBLF0zlTQ=
 github.com/chengxilo/virtualterm v1.0.4 h1:Z6IpERbRVlfB8WkOmtbHiDbBANU7cimRIof7mk9/PwM=
 github.com/chengxilo/virtualterm v1.0.4/go.mod h1:DyxxBZz/x1iqJjFxTFcr6/x+jSpqN0iwWCOK1q10rlY=
 github.com/cpuguy83/go-md2man/v2 v2.0.6/go.mod h1:oOW0eioCTA6cOiMLiUPZOpcVxMig6NIQQ7OS05n1F4g=

internal/sfdupes/cancel_test.go

@@ -358,9 +358,8 @@ func TestRunScanInterrupted(t *testing.T) {
 	stderr := captureStderr(t)
 	dir := buildSmokeTree(t)
 
-	opts := scanOptions{workers: walkCancelWorkers}
+	err := runScan(t.Context(), []string{dir}, walkCancelWorkers, false,
-
+		false, nil)
-	err := runScan(t.Context(), []string{dir}, opts)
 	if err != nil {
 		t.Fatal(err)
 	}
@@ -383,7 +382,8 @@ func TestRunScanInterrupted(t *testing.T) {
 	go func() {
 		defer close(done)
 
-		err = runScan(cancelledContext(t), []string{dir}, opts)
+		err = runScan(cancelledContext(t), []string{dir}, walkCancelWorkers,
+			false, false, nil)
 	}()
 
 	awaitReturn(t, done, "runScan")
@@ -410,7 +410,8 @@ func TestRunScanInterrupted(t *testing.T) {
 			got, before)
 	}
 
-	err = runScan(t.Context(), []string{dir}, opts)
+	err = runScan(t.Context(), []string{dir}, walkCancelWorkers, false,
+		false, nil)
 	if err != nil {
 		t.Fatal(err)
 	}
@@ -436,7 +437,7 @@ func TestRunScanInterruptedMidHash(t *testing.T) {
 	dir := buildWalkCancelTree(t)
 
 	err := runScan(newWalkClock(hashCancelAtDone), []string{dir},
-		scanOptions{workers: walkCancelWorkers})
+		walkCancelWorkers, false, false, nil)
 	if !errors.Is(err, errInterrupted) {
 		t.Fatalf("runScan interrupted mid-hash = %v, want %v",
 			err, errInterrupted)

internal/sfdupes/cli.go

@@ -32,79 +32,17 @@ const (
 	cmdDwim   = "dwim"
 )
 
-// databaseHelp is the paragraph of the root and scan help that names
-// the database (README "Location").
-const databaseHelp = "scan and dwim store what they find in a database " +
-	"file. report, trees\nand info read it. The file is $" + databaseEnv +
-	" when that is set and\nnot empty, and otherwise " +
-	defaultDatabasePath + ", where creating it\nneeds root.\n"
-
-// escapesHelp is the paragraph of the report and trees help on how
-// paths are escaped (README "Report output format").
-const escapesHelp = `Four characters in a path are escaped, so each row stays one line:
-
-  \\  a backslash
-  \t  a tab
-  \n  a newline
-  \r  a carriage return
-`
-
-// reportHelp, treesHelp, infoHelp and dwimHelp follow the one-line
-// summary in the help of their subcommands.
-const (
-	reportHelp = `The report is tab-separated text on stdout: a header line, then one
-row per duplicate file. The columns are:
-
-  first   the path that sorts first, byte by byte, in its group of copies
-  dupe    another copy of that file
-  size    the file's size in bytes
-
-Rows are ordered by size, largest first, then by path.
-
-` + escapesHelp
-
-	treesHelp = `The report is tab-separated text on stdout: a header line, then one
-row per duplicate directory tree. The columns are:
-
-  first      the path that sorts first, byte by byte, in its group of copies
-  dupe       another copy of that tree
-  files      the number of regular files in one copy
-  size       their total size in bytes
-  disk_size  the bytes the dupe copy takes on disk
-
-Rows are ordered by size, largest first, then by path.
-
-` + escapesHelp
-
-	infoHelp = `The details go to stdout, one per line. Each line holds a name and its
-value, separated by a tab:
-
-  database                the path, and where it came from
-  database file size      in bytes, then rounded, as 2147483648 (2.0 GiB)
-  -wal file size          in bytes, then rounded; only if a -wal file exists
-  modified                when the database file last changed, in UTC
-  schema version          the version of the database's layout
-  records                 the number of records
-  size of recorded files  their total size, in bytes, then rounded
-`
-
-	dwimHelp = `dwim runs what "sfdupes scan /" runs with the same flags, then what
-"sfdupes trees" runs. Run it as root, so that the scan can read every
-file. The scan is stored in the database, as scan stores it, so
-"sfdupes trees" prints the report again later.
-`
-)
-
 // errNoSubcommand is returned by the root command when it is invoked
 // without a subcommand. That is a usage error, and the usage text
 // cobra prints for it is the whole message.
 var errNoSubcommand = errors.New("no subcommand")
 
-// errWorkersBelowOne is the usage error for a --workers value below 1.
+// errWorkersBelowOne is the usage error for a scan --workers value
+// below 1.
 var errWorkersBelowOne = errors.New("--workers must be at least 1")
 
-// errEmptyExcludeValue is the usage error for an empty --exclude value,
+// errEmptyExcludeValue is the usage error for an empty scan --exclude
-// as from --exclude "$DIR" with DIR unset. Taken as a path, it
+// value, as from --exclude "$DIR" with DIR unset. Taken as a path, it
 // would name the working directory.
 var errEmptyExcludeValue = errors.New("--exclude must not be empty")
 
@@ -184,6 +122,14 @@ func run(args []string, stdout, stderr io.Writer) int {
 	}
 }
 
+// databaseHelp says in sfdupes --help where the database is.
+const databaseHelp = `The database is the file SFDUPES_DATABASE names.
+When that is unset or empty, root uses /var/lib/sfdupes/db.sqlite. Any
+other user uses sfdupes/db.sqlite in the XDG state directory:
+$XDG_STATE_HOME, or ~/.local/state when that is unset or empty
+(~/Library/Application Support on macOS). An XDG_STATE_HOME that is
+not an absolute path is an error.`
+
 // newRootCommand builds the command tree. Everything on stdout is
 // machine-readable data, the version line included; all human-facing
 // output (help, usage, errors) goes to stderr.
@@ -202,9 +148,12 @@ func newRootCommand(stdout, stderr io.Writer) *cobra.Command {
 		return nil
 	})
 
+	short := "Find candidate duplicate files by size and head/tail/content SHA-256"
+
 	root := &cobra.Command{
 		Use:   "sfdupes",
-		Short: "Find candidate duplicate files by size and head/tail/content SHA-256",
+		Short: short,
+		Long:  short + ".\n\n" + databaseHelp,
 		Args:  cobra.NoArgs,
 		RunE: func(cmd *cobra.Command, args []string) error {
 			if showVersion {
@@ -255,116 +204,76 @@ func newRootCommand(stdout, stderr io.Writer) *cobra.Command {
 		}),
 	}
 
-	root.Long = root.Short + ".\n\n" + databaseHelp
+	dwimCmd := &cobra.Command{
-	reportCmd.Long = reportCmd.Short + ".\n\n" + reportHelp
+		Use:   cmdDwim,
-	treesCmd.Long = treesCmd.Short + ".\n\n" + treesHelp
+		Short: "Scan / with the default excludes, then print the duplicate-tree report",
-	infoCmd.Long = infoCmd.Short + ".\n\n" + infoHelp
+		Args:  cobra.NoArgs,
+		RunE: runE(func(ctx context.Context, _ []string) error {
+			return runDwim(ctx, "/", stdout)
+		}),
+	}
 
-	root.AddCommand(newScanCommand(), reportCmd, treesCmd, infoCmd,
+	root.AddCommand(newScanCommand(), reportCmd, treesCmd, infoCmd, dwimCmd)
-		newDwimCommand(stdout))
 
 	return root
 }
 
-// scanOptions holds the values of the flags that scan and dwim share:
+// newScanCommand builds the scan subcommand, with its --workers, -x,
-// --workers, -x, --no-default-excludes and --exclude.
+// --no-default-excludes and --exclude flags. Its help lists the default
-type scanOptions struct {
+// excludes of the system it runs on, and the filesystem types it never
-	workers           int
+// records anything on.
-	oneFS             bool
-	noDefaultExcludes bool
-	excludePaths      []string
-}
-
-// scanFlagsUsage names the flags that scan and dwim share, for their
-// usage lines.
-const scanFlagsUsage = "[--workers N] [-x] [--no-default-excludes] " +
-	"[--exclude PATH]..."
-
-// addScanFlags adds the flags that scan and dwim share to cmd, which
-// stores their values in opts.
-func addScanFlags(cmd *cobra.Command, opts *scanOptions) {
-	cmd.Flags().IntVar(&opts.workers, "workers", runtime.NumCPU(),
-		"concurrent workers for the walk and hash phases")
-	cmd.Flags().BoolVarP(&opts.oneFS, "one-file-system", "x", false,
-		"do not cross filesystem boundaries")
-	cmd.Flags().BoolVar(&opts.noDefaultExcludes, "no-default-excludes",
-		false, "enter the default excludes, the paths listed above")
-	// A string array, not a slice, so a comma in a path is not a
-	// separator.
-	cmd.Flags().StringArrayVar(&opts.excludePaths, "exclude", nil,
-		"never enter or record `PATH` or anything below it; repeatable")
-}
-
-// check rejects the flag values that are usage errors, before the
-// command runs. It is the PreRunE of scan and dwim.
-func (o *scanOptions) check(cmd *cobra.Command, _ []string) error {
-	err := checkScanWorkers(cmd, o.workers)
-	if err != nil {
-		return err
-	}
-
-	return rejectEmptyExcludeValue(cmd, o.excludePaths)
-}
-
-// newScanCommand builds the scan subcommand. Its help names the
-// database, and lists the default excludes of the system it runs on and
-// the filesystem types it never records anything on.
 func newScanCommand() *cobra.Command {
-	var opts scanOptions
+	var (
+		scanWorkers           int
+		scanOneFS             bool
+		scanNoDefaultExcludes bool
+		scanExclude           []string
+	)
 
 	short := "Walk trees and synchronize the scan database"
 
 	scanCmd := &cobra.Command{
-		Use: cmdScan + " " + scanFlagsUsage + " PATH...",
+		Use: cmdScan + " [--workers N] [-x] [--no-default-excludes] " +
+			"[--exclude PATH]... PATH...",
 		// The Use line already names every flag, so cobra must not
 		// append its generic "[flags]" to it.
 		DisableFlagsInUseLine: true,
 		Short:                 short,
-		Long: short + ".\n\n" + databaseHelp + "\n" +
+		Long:                  short + ".\n\n" + defaultExcludesHelp(runtime.GOOS),
-			defaultExcludesHelp(runtime.GOOS),
+		Args:                  cobra.MinimumNArgs(1),
-		Args:    cobra.MinimumNArgs(1),
+		PreRunE: func(cmd *cobra.Command, _ []string) error {
-		PreRunE: opts.check,
+			err := checkScanWorkers(cmd, scanWorkers)
+			if err != nil {
+				return err
+			}
+
+			return rejectEmptyExcludeValue(cmd, scanExclude)
+		},
 		RunE: runE(func(ctx context.Context, args []string) error {
 			ctx, stop := interruptContext(ctx)
 			defer stop()
 
-			return runScan(ctx, args, opts)
+			return runScan(ctx, args, scanWorkers, scanOneFS,
+				scanNoDefaultExcludes, scanExclude)
 		}),
 	}
-	addScanFlags(scanCmd, &opts)
+	scanCmd.Flags().IntVar(&scanWorkers, "workers", runtime.NumCPU(),
+		"concurrent workers for the walk and hash phases")
+	scanCmd.Flags().BoolVarP(&scanOneFS, "one-file-system", "x", false,
+		"do not cross filesystem boundaries")
+	scanCmd.Flags().BoolVar(&scanNoDefaultExcludes, "no-default-excludes",
+		false, "enter the default excludes, the paths listed above")
+	// A string array, not a slice, so a comma in a path is not a
+	// separator.
+	scanCmd.Flags().StringArrayVar(&scanExclude, "exclude", nil,
+		"never enter or record `PATH` or anything below it; repeatable")
 
 	return scanCmd
 }
 
-// newDwimCommand builds the dwim subcommand, which takes the scan flags
+// checkScanWorkers rejects a scan --workers value below 1. That is a
-// with the meaning they have for scan. Its help says what dwim runs,
+// usage error reported in one line: cobra prints the returned message
-// then lists the default excludes and the filesystem types the scan
+// without the usage text, and run exits 2.
-// never records anything on.
-func newDwimCommand(stdout io.Writer) *cobra.Command {
-	var opts scanOptions
-
-	short := "Scan /, then print the duplicate-tree report"
-
-	dwimCmd := &cobra.Command{
-		Use:                   cmdDwim + " " + scanFlagsUsage,
-		DisableFlagsInUseLine: true,
-		Short:                 short,
-		Long: short + ".\n\n" + dwimHelp + "\n" +
-			defaultExcludesHelp(runtime.GOOS),
-		Args:    cobra.NoArgs,
-		PreRunE: opts.check,
-		RunE: runE(func(ctx context.Context, _ []string) error {
-			return runDwim(ctx, "/", opts, stdout)
-		}),
-	}
-	addScanFlags(dwimCmd, &opts)
-
-	return dwimCmd
-}
-
-// checkScanWorkers rejects a --workers value below 1. That is a usage
-// error reported in one line: cobra prints the returned message without
-// the usage text, and run exits 2.
 func checkScanWorkers(cmd *cobra.Command, workers int) error {
 	if workers >= 1 {
 		return nil
@@ -375,7 +284,7 @@ func checkScanWorkers(cmd *cobra.Command, workers int) error {
 	return fmt.Errorf("%w, got %d", errWorkersBelowOne, workers)
 }
 
-// rejectEmptyExcludeValue rejects an empty --exclude value. That
+// rejectEmptyExcludeValue rejects an empty scan --exclude value. That
 // is a usage error reported in one line, as for --workers below 1.
 func rejectEmptyExcludeValue(cmd *cobra.Command, excludePaths []string) error {
 	if !slices.Contains(excludePaths, "") {

internal/sfdupes/cli_test.go

@@ -15,6 +15,7 @@ import (
 	"strings"
 	"testing"
 
+	"github.com/adrg/xdg"
 	"golang.org/x/sys/unix"
 )
 
@@ -22,12 +23,6 @@ import (
 // error prints and a runtime failure must not.
 const usageMarker = "Usage:"
 
-// helpFlag asks for the help text.
-const helpFlag = "--help"
-
-// workersFlag is the scan and dwim flag that sets the worker count.
-const workersFlag = "--workers"
-
 // TestMain stops the tests at once, saying why, when their temporary
 // directory is not on a persistent filesystem: scan records nothing
 // there (README "Rules for the walk"), so most scan tests would fail
@@ -559,13 +554,17 @@ func TestRunNamesDefaultDatabase(t *testing.T) {
 	// line.
 	t.Setenv(databaseEnv, "")
 
-	// Whether scan calls the database new depends on that machine too.
+	dbPath, err := defaultDatabasePath(os.Geteuid())
-	scanWant := "scan: database " + defaultDatabasePath + " (default)\n"
+	if err != nil {
+		t.Fatal(err)
+	}
 
-	_, err := os.Stat(defaultDatabasePath)
+	// Whether scan calls the database new depends on that machine too.
+	scanWant := "scan: database " + dbPath + " (default)\n"
+
+	_, err = os.Stat(dbPath)
 	if errors.Is(err, fs.ErrNotExist) {
-		scanWant = "scan: new database " + defaultDatabasePath +
+		scanWant = "scan: new database " + dbPath + " (default)\n"
-			" (default)\n"
 	}
 
 	missing := filepath.Join(t.TempDir(), "nope")
@@ -576,8 +575,8 @@ func TestRunNamesDefaultDatabase(t *testing.T) {
 	}{
 		cmdScan: {
 			run: func() error {
-				return runScan(t.Context(), []string{missing},
+				return runScan(t.Context(), []string{missing}, 1, false, false,
-					scanOptions{workers: 1})
+					nil)
 			},
 			want: scanWant,
 		},
@@ -585,21 +584,21 @@ func TestRunNamesDefaultDatabase(t *testing.T) {
 			run: func() error {
 				return runReport(cancelledContext(t), io.Discard)
 			},
-			want: "report: database " + defaultDatabasePath + " (default)\n" +
+			want: "report: database " + dbPath + " (default)\n" +
 				reportOpenLine + "\n" + reportOpenLine + "\n",
 		},
 		cmdTrees: {
 			run: func() error {
 				return runTrees(cancelledContext(t), io.Discard)
 			},
-			want: "trees: database " + defaultDatabasePath + " (default)\n" +
+			want: "trees: database " + dbPath + " (default)\n" +
 				treesOpenLine + "\n" + treesOpenLine + "\n",
 		},
 		cmdInfo: {
 			run: func() error {
 				return runInfo(cancelledContext(t), io.Discard)
 			},
-			want: "info: database " + defaultDatabasePath + " (default)\n" +
+			want: "info: database " + dbPath + " (default)\n" +
 				infoOpenLine + "\n" + infoOpenLine + "\n",
 		},
 	}
@@ -668,7 +667,7 @@ func TestRunScanRejectsWorkersBelowOne(t *testing.T) {
 
 			var stdout, stderr bytes.Buffer
 
-			args := []string{cmdScan, workersFlag, workers, t.TempDir()}
+			args := []string{cmdScan, "--workers", workers, t.TempDir()}
 
 			code := run(args, &stdout, &stderr)
 			if code != exitUsage {
@@ -699,7 +698,7 @@ func TestRunHelp(t *testing.T) {
 
 	// README §Settings: help goes to stderr, exits 0, and leaves stdout
 	// empty.
-	cases := [][]string{{helpFlag}, {"-h"}, {cmdScan, helpFlag}}
+	cases := [][]string{{"--help"}, {"-h"}, {cmdScan, "--help"}}
 
 	for _, args := range cases {
 		var stdout, stderr bytes.Buffer
@@ -718,6 +717,22 @@ func TestRunHelp(t *testing.T) {
 			t.Errorf("run(%v) stdout = %q, want nothing (data only)",
 				args, got)
 		}
+
+		if args[0] == cmdScan {
+			continue
+		}
+
+		// README §Location: sfdupes --help says where the database is,
+		// and that XDG_STATE_HOME must be an absolute path.
+		for _, want := range []string{
+			databaseEnv, rootDatabasePath, stateHomeEnv, "~/.local/state",
+			"not an absolute path is an error",
+		} {
+			if !strings.Contains(stderr.String(), want) {
+				t.Errorf("run(%v) stderr = %q, want it to name %q",
+					args, stderr.String(), want)
+			}
+		}
 	}
 
 	// The scan help lists --exclude with its argument.
@@ -760,73 +775,6 @@ func TestRunScanUsageLine(t *testing.T) {
 	}
 }
 
-func TestRunHelpDescribesDatabaseAndOutput(t *testing.T) {
-	t.Parallel()
-
-	// README §Settings: the help names the database, and says what
-	// report, trees, info and dwim print.
-	database := []string{
-		"scan and dwim store", databaseEnv, defaultDatabasePath, "needs root",
-	}
-	escapes := []string{`\\`, `\t`, `\n`, `\r`}
-
-	// The subcommand whose help is printed; none for the root.
-	cases := []struct {
-		subcommand []string
-		want       []string
-	}{
-		{nil, database},
-		{[]string{cmdScan}, database},
-		{
-			[]string{cmdReport},
-			append([]string{
-				"tab-separated", "\n  first ", "\n  dupe ", "\n  size ",
-				"largest first",
-			}, escapes...),
-		},
-		{
-			[]string{cmdTrees},
-			append([]string{
-				"tab-separated", "\n  first ", "\n  dupe ", "\n  files ",
-				"\n  size ", "\n  disk_size ", "largest first",
-			}, escapes...),
-		},
-		{
-			[]string{cmdInfo},
-			[]string{
-				"\n  database ", "\n  database file size ",
-				"\n  -wal file size ", "\n  modified ",
-				"\n  schema version ", "\n  records ",
-				"\n  size of recorded files ",
-			},
-		},
-		{
-			[]string{cmdDwim},
-			[]string{
-				"sfdupes scan /", "as root", "sfdupes trees", "database",
-			},
-		},
-	}
-
-	for _, tc := range cases {
-		var stdout, stderr bytes.Buffer
-
-		args := slices.Concat(tc.subcommand, []string{helpFlag})
-
-		code := run(args, &stdout, &stderr)
-		if code != exitOK {
-			t.Fatalf("run(%v) = %d, want %d", args, code, exitOK)
-		}
-
-		for _, want := range tc.want {
-			if !strings.Contains(stderr.String(), want) {
-				t.Errorf("run(%v) help lacks %q:\n%s",
-					args, want, stderr.String())
-			}
-		}
-	}
-}
-
 func TestRunVersion(t *testing.T) {
 	t.Parallel()
 
@@ -1609,6 +1557,75 @@ func TestRunDatabasePathUsedAsGiven(t *testing.T) {
 	})
 }
 
+func TestRunNonRootUsesStateDirectory(t *testing.T) {
+	// README §Location: without SFDUPES_DATABASE, a user other than
+	// root keeps the database in the XDG state directory. scan creates
+	// the missing directories with mode 0700, and report and trees read
+	// the same file.
+	if os.Geteuid() == 0 {
+		t.Skip("root uses " + rootDatabasePath)
+	}
+
+	t.Cleanup(xdg.Reload)
+
+	state := filepath.Join(t.TempDir(), "state")
+	t.Setenv(stateHomeEnv, state)
+	t.Setenv(databaseEnv, "")
+	xdg.Reload()
+
+	assertRunsUseDatabase(t, filepath.Join(state, "sfdupes"), "db.sqlite")
+
+	for _, dir := range []string{state, filepath.Join(state, "sfdupes")} {
+		fi, err := os.Stat(dir)
+		if err != nil {
+			t.Fatal(err)
+		}
+
+		if got := fi.Mode().Perm(); got != stateDirPerm {
+			t.Errorf("%s mode = %#o, want %#o", dir, got, stateDirPerm)
+		}
+	}
+}
+
+func TestRunRelativeStateHomeFails(t *testing.T) {
+	// README §Location: without SFDUPES_DATABASE, a user other than
+	// root whose XDG_STATE_HOME is not an absolute path gets an error
+	// naming it from every subcommand, which exits 1 before it does
+	// anything else.
+	if os.Geteuid() == 0 {
+		t.Skip("root does not use " + stateHomeEnv)
+	}
+
+	t.Setenv(stateHomeEnv, "relative/state")
+	t.Setenv(databaseEnv, "")
+
+	want := "sfdupes: " + stateHomeEnv +
+		" must be an absolute path, got \"relative/state\"\n"
+
+	// A scan that got past the check would stop at this missing
+	// operand, before it creates anything.
+	missing := filepath.Join(t.TempDir(), "missing")
+
+	for _, args := range [][]string{
+		{cmdScan, missing}, {cmdReport}, {cmdTrees}, {cmdInfo},
+	} {
+		var stdout, stderr bytes.Buffer
+
+		code := run(args, &stdout, &stderr)
+		if code != exitFatal || stderr.String() != want {
+			t.Errorf("run(%v) = %d with stderr %q, want %d and %q",
+				args, code, stderr.String(), exitFatal, want)
+		}
+	}
+
+	// dwim scans /, so runDwim gets the missing operand instead.
+	err := runDwim(t.Context(), missing, io.Discard)
+	if !errors.Is(err, errStateHomeNotAbsolute) {
+		t.Errorf("runDwim: error = %v, want %v", err,
+			errStateHomeNotAbsolute)
+	}
+}
+
 // holdScanLock takes the lock on the database at path, as a running
 // scan does, and holds it until the test ends. It fails the test when
 // the lock is already held.

internal/sfdupes/db.go

@@ -15,28 +15,40 @@ import (
 	"strings"
 	"time"
 
+	"github.com/adrg/xdg"
 	"golang.org/x/sys/unix"
 	// The pure-Go SQLite driver, registered as "sqlite"; keeps cgo
 	// disabled.
 	_ "modernc.org/sqlite"
 )
 
-// defaultDatabasePath is where the persistent scan database lives when
+// rootDatabasePath is the database root uses when SFDUPES_DATABASE is
-// SFDUPES_DATABASE is not set.
+// not set.
-const defaultDatabasePath = "/var/lib/sfdupes/db.sqlite"
+const rootDatabasePath = "/var/lib/sfdupes/db.sqlite"
 
 // databaseEnv is the environment variable that overrides the database
 // path.
 const databaseEnv = "SFDUPES_DATABASE"
 
+// stateHomeEnv is the environment variable that names the XDG state
+// directory.
+const stateHomeEnv = "XDG_STATE_HOME"
+
 // schemaVersion is the database schema version this build reads and
 // writes, stored in PRAGMA user_version.
 const schemaVersion = 1
 
-// dbDirPerm is the mode for a database parent directory created by
+// dbDirPerm is the mode for a directory scan creates for root's
-// scan.
+// default database or for SFDUPES_DATABASE.
 const dbDirPerm = 0o755
 
+// stateDirPerm is the mode for a directory scan creates for the
+// database at a user's default path in the XDG state directory. It is
+// the mode the XDG Base Directory specification asks for, and it keeps
+// other users from reading the database, which lists every scanned
+// path.
+const stateDirPerm = 0o700
+
 // dbFilePerm is the mode for a database file created by scan, the mode
 // SQLite gives a database file it creates.
 const dbFilePerm = 0o644
@@ -144,15 +156,48 @@ var errScanRunning = errors.New("another scan is running")
 // 32 bytes of a SHA-256.
 var errHashSize = errors.New("hash is not 32 bytes")
 
+// errStateHomeNotAbsolute reports an XDG_STATE_HOME that is set to a
+// path that is not absolute.
+var errStateHomeNotAbsolute = errors.New(
+	stateHomeEnv + " must be an absolute path")
+
+// defaultDatabasePath is the database used when SFDUPES_DATABASE is not
+// set: rootDatabasePath for root (euid 0), and db.sqlite in the
+// directory sfdupes under the XDG state directory for any other user.
+// xdg reads XDG_STATE_HOME and HOME once, when the program starts. For
+// any other user, an XDG_STATE_HOME that is set and not an absolute
+// path is an error, where xdg would use its default instead. The path
+// is joined as text, not cleaned, for the reason absolutePath gives.
+func defaultDatabasePath(euid int) (string, error) {
+	if euid == 0 {
+		return rootDatabasePath, nil
+	}
+
+	stateHome := os.Getenv(stateHomeEnv)
+	if stateHome != "" && !filepath.IsAbs(stateHome) {
+		return "", fmt.Errorf("%w, got %q", errStateHomeNotAbsolute,
+			stateHome)
+	}
+
+	stateDir := strings.TrimSuffix(xdg.StateHome, "/")
+
+	return stateDir + "/sfdupes/db.sqlite", nil
+}
+
 // databasePath resolves the database location: SFDUPES_DATABASE when
-// set and non-empty, the compiled-in default otherwise. It returns the
+// set and non-empty, defaultDatabasePath otherwise. It returns the
 // 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"
+	path, source := os.Getenv(databaseEnv), "from "+databaseEnv
-	if p := os.Getenv(databaseEnv); p != "" {
+	if path == "" {
-		path, source = p, "from "+databaseEnv
+		def, err := defaultDatabasePath(os.Geteuid())
+		if err != nil {
+			return "", "", err
+		}
+
+		path, source = def, "default"
 	}
 
 	abs, err := absolutePath(path)
@@ -188,15 +233,23 @@ func absolutePath(path string) (string, error) {
 
 // createDatabaseDirectory creates the directory the database at path
 // goes in, and any directory above it, if missing. path is absolute, as
-// databasePath returns it. The directory is path with its last element
+// databasePath returns it. Each directory gets mode dbDirPerm, or
-// cut off as text, by filepath.Split. filepath.Dir would clean it,
+// stateDirPerm when databasePath uses a user's default path in the XDG
-// dropping each ".." together with the directory name before it; when
+// state directory: the user is not root and SFDUPES_DATABASE is unset
-// that name is a symlink, the cleaned path names another directory than
+// or empty. The directory is path with its last element cut off as
-// the one the system reaches when it opens path.
+// text, by filepath.Split. filepath.Dir would clean it, dropping each
+// ".." together with the directory name before it; when that name is a
+// symlink, the cleaned path names another directory than the one the
+// system reaches when it opens path.
 func createDatabaseDirectory(path string) error {
 	dir, _ := filepath.Split(path)
 
-	err := os.MkdirAll(dir, dbDirPerm)
+	perm := os.FileMode(dbDirPerm)
+	if os.Geteuid() != 0 && os.Getenv(databaseEnv) == "" {
+		perm = stateDirPerm
+	}
+
+	err := os.MkdirAll(dir, perm)
 	if err != nil {
 		return fmt.Errorf("create database directory: %w", err)
 	}

internal/sfdupes/db_test.go

@@ -9,10 +9,13 @@ import (
 	"io/fs"
 	"os"
 	"path/filepath"
+	"runtime"
 	"slices"
 	"strings"
 	"testing"
 	"time"
+
+	"github.com/adrg/xdg"
 )
 
 // testDBPath returns a database path inside a fresh temp dir, with
@@ -56,11 +59,16 @@ func TestDatabasePath(t *testing.T) {
 
 	t.Chdir(dir)
 
+	defaultPath, err := defaultDatabasePath(os.Geteuid())
+	if err != nil {
+		t.Fatal(err)
+	}
+
 	fromEnv := "from " + databaseEnv
 	cases := []struct {
 		env, path, source string
 	}{
-		{"", defaultDatabasePath, "default"},
+		{"", defaultPath, "default"},
 		{"/custom/place.sqlite", "/custom/place.sqlite", fromEnv},
 		{"/custom/link/../place.sqlite", "/custom/link/../place.sqlite",
 			fromEnv},
@@ -89,6 +97,48 @@ func TestDatabasePath(t *testing.T) {
 	}
 }
 
+func TestDefaultDatabasePath(t *testing.T) {
+	// README §Location: root's database is /var/lib/sfdupes/db.sqlite.
+	// Any other user's is db.sqlite in sfdupes under XDG_STATE_HOME, or
+	// under ~/.local/state when XDG_STATE_HOME is unset or empty. For
+	// that user, an XDG_STATE_HOME that is not an absolute path is an
+	// error.
+	if runtime.GOOS != goosLinux {
+		t.Skip("macOS has another default state directory")
+	}
+
+	t.Cleanup(xdg.Reload)
+	t.Setenv("HOME", "/home/someone")
+
+	cases := []struct {
+		euid      int
+		stateHome string
+		want      string
+		wantErr   error
+	}{
+		{0, "", rootDatabasePath, nil},
+		{0, "/elsewhere/state", rootDatabasePath, nil},
+		{0, "relative/state", rootDatabasePath, nil},
+		{1000, "", "/home/someone/.local/state/sfdupes/db.sqlite", nil},
+		{1000, "relative/state", "", errStateHomeNotAbsolute},
+		{1000, "~/state", "", errStateHomeNotAbsolute},
+		{1000, "/elsewhere/state", "/elsewhere/state/sfdupes/db.sqlite", nil},
+		{1000, "/elsewhere/state/", "/elsewhere/state/sfdupes/db.sqlite", nil},
+	}
+
+	for _, tc := range cases {
+		t.Setenv(stateHomeEnv, tc.stateHome)
+		xdg.Reload()
+
+		got, err := defaultDatabasePath(tc.euid)
+		if got != tc.want || !errors.Is(err, tc.wantErr) {
+			t.Errorf("defaultDatabasePath(%d) with %s=%q = %q, %v; want %q, %v",
+				tc.euid, stateHomeEnv, tc.stateHome, got, err, tc.want,
+				tc.wantErr)
+		}
+	}
+}
+
 func TestOpenScanDatabaseCreates(t *testing.T) {
 	t.Parallel()
 

internal/sfdupes/dwim.go

@@ -5,20 +5,20 @@ import (
 	"fmt"
 	"io"
 	"os"
+	"runtime"
 )
 
 // runDwim implements the dwim subcommand: it runs what "sfdupes scan
-// root" runs with the scan flags in opts, then what "sfdupes trees"
+// root" runs with no flags, then what "sfdupes trees" runs, and ends
-// runs, and ends with a line on stderr saying how to print the report
+// with a line on stderr saying how to print the report again. The dwim
-// again. The dwim command passes "/" as root. It catches SIGINT and
+// command passes "/" as root. It catches SIGINT and SIGTERM as scan
-// SIGTERM as scan does, but only during the scan. An error from the
+// does, but only during the scan. An error from the scan, an interrupt
-// scan, an interrupt included, ends it before the report. During the
+// included, ends it before the report. During the report, a signal
-// report, a signal ends it at once, as it ends trees.
+// ends it at once, as it ends trees.
-func runDwim(
+func runDwim(ctx context.Context, root string, stdout io.Writer) error {
-	ctx context.Context, root string, opts scanOptions, stdout io.Writer,
-) error {
 	scanCtx, stop := interruptContext(ctx)
-	err := runScan(scanCtx, []string{root}, opts)
+	err := runScan(scanCtx, []string{root}, runtime.NumCPU(), false, false,
+		nil)
 
 	stop()
 

internal/sfdupes/dwim_test.go

@@ -2,10 +2,7 @@ package sfdupes //nolint:testpackage // calls the unexported runDwim
 
 import (
 	"bytes"
-	"errors"
-	"os"
 	"path/filepath"
-	"runtime"
 	"strings"
 	"testing"
 )
@@ -31,7 +28,7 @@ func TestRunDwimPrintsLargestTreesFirst(t *testing.T) {
 
 	stderr := captureStderr(t)
 
-	err := runDwim(t.Context(), root, scanOptions{workers: 1}, &stdout)
+	err := runDwim(t.Context(), root, &stdout)
 	if err != nil {
 		t.Fatalf("runDwim: %v; stderr: %s", err, stderr())
 	}
@@ -70,7 +67,7 @@ func TestRunDwimScanErrorPrintsNoReport(t *testing.T) {
 
 	stderr := captureStderr(t)
 
-	err := runDwim(t.Context(), missing, scanOptions{workers: 1}, &stdout)
+	err := runDwim(t.Context(), missing, &stdout)
 	if err == nil {
 		t.Fatal("runDwim on a missing root: error = nil, want it fatal")
 	}
@@ -84,127 +81,3 @@ func TestRunDwimScanErrorPrintsNoReport(t *testing.T) {
 		t.Errorf("stderr = %q, want nothing from trees or dwim", got)
 	}
 }
-
-func TestRunDwimExcludeLeavesTreeOut(t *testing.T) {
-	// dwim passes its --exclude paths to the scan: an excluded copy is
-	// not recorded, so its pair is not reported.
-	t.Setenv(databaseEnv, testDBPath(t))
-
-	root := realTempDir(t)
-
-	kept := []string{
-		filepath.Dir(writeFile(t, root, "a1/f.bin", pattern(1, 300))),
-		filepath.Dir(writeFile(t, root, "a2/f.bin", pattern(1, 300))),
-	}
-	writeFile(t, root, "b1/f.bin", pattern(2, 5000))
-	excluded := filepath.Dir(writeFile(t, root, "b2/f.bin", pattern(2, 5000)))
-
-	var stdout bytes.Buffer
-
-	stderr := captureStderr(t)
-
-	opts := scanOptions{workers: 1, excludePaths: []string{excluded}}
-
-	err := runDwim(t.Context(), root, opts, &stdout)
-	if err != nil {
-		t.Fatalf("runDwim: %v; stderr: %s", err, stderr())
-	}
-
-	lines := strings.Split(strings.TrimSuffix(stdout.String(), "\n"), "\n")
-	if len(lines) != 2 {
-		t.Fatalf("stdout = %q, want a header and one group",
-			stdout.String())
-	}
-
-	want := kept[0] + "\t" + kept[1] + "\t1\t300\t"
-	if !strings.HasPrefix(lines[1], want) {
-		t.Errorf("group = %q, want it to start %q", lines[1], want)
-	}
-
-	skipped := "scan: skipped " + excluded + " (--exclude)\n"
-	if got := stderr(); !strings.Contains(got, skipped) {
-		t.Errorf("stderr = %q, want it to contain %q", got, skipped)
-	}
-}
-
-func TestRunDwimTakesScanFlags(t *testing.T) {
-	// The dwim command parses and checks the scan flags as scan does.
-	// Each case stops before the walk of / begins, and before the
-	// database is created. "dwim --exclude /" excludes its own operand.
-	cases := map[string]struct {
-		args []string
-		code int
-		want string
-	}{
-		"--exclude /": {
-			[]string{cmdDwim, excludeFlag, "/"},
-			exitFatal,
-			"sfdupes: scan /: operand excluded by --exclude /\n",
-		},
-		"--exclude empty": {
-			[]string{cmdDwim, excludeFlag, ""},
-			exitUsage,
-			"Error: --exclude must not be empty\n",
-		},
-		"--workers 0": {
-			[]string{cmdDwim, workersFlag, "0", "-x", "--no-default-excludes"},
-			exitUsage,
-			"Error: --workers must be at least 1, got 0\n",
-		},
-	}
-
-	for name, tc := range cases {
-		t.Run(name, func(t *testing.T) {
-			path := testDBPath(t)
-			t.Setenv(databaseEnv, path)
-
-			stdout := captureStdout(t)
-			stderr := captureStderr(t)
-
-			code := run(tc.args, os.Stdout, os.Stderr)
-			if code != tc.code {
-				t.Errorf("run(%q) = %d, want %d", tc.args, code, tc.code)
-			}
-
-			if !strings.HasSuffix(stderr(), tc.want) || stdout() != "" {
-				t.Errorf("stdout, stderr = %q, %q, want \"\" and stderr "+
-					"ending %q", stdout(), stderr(), tc.want)
-			}
-
-			_, err := os.Lstat(path)
-			if !errors.Is(err, os.ErrNotExist) {
-				t.Errorf("lstat %s: %v, want no database", path, err)
-			}
-		})
-	}
-}
-
-func TestRunDwimHelpListsScanFlags(t *testing.T) {
-	t.Parallel()
-
-	// README "Subcommands" shows this usage line for dwim.
-	const want = "\n  sfdupes dwim [--workers N] [-x] [--no-default-excludes] " +
-		"[--exclude PATH]...\n"
-
-	var stdout, stderr bytes.Buffer
-
-	run([]string{cmdDwim, "-h"}, &stdout, &stderr)
-
-	if !strings.Contains(stderr.String(), want) {
-		t.Errorf("dwim -h stderr = %q, want the usage line %q",
-			stderr.String(), want)
-	}
-
-	if !strings.Contains(stderr.String(), excludeFlag+" PATH") {
-		t.Errorf("dwim -h stderr = %q, want %s PATH", stderr.String(),
-			excludeFlag)
-	}
-
-	// README "Settings": the help lists the default excludes and the
-	// filesystem types the walk never records anything on.
-	help := strings.TrimSpace(defaultExcludesHelp(runtime.GOOS))
-	if !strings.Contains(stderr.String(), help) {
-		t.Errorf("dwim -h stderr = %q, want it to hold %q", stderr.String(),
-			help)
-	}
-}

internal/sfdupes/exclude.go

@@ -254,7 +254,7 @@ func readMountInfo(mountinfo io.Reader) (map[uint64]string, error) {
 	return devices, lines.Err()
 }
 
-// defaultExcludesHelp describes, for the scan and dwim help, the
+// defaultExcludesHelp describes, for the scan command's help, the
 // default excludes of the system goos names and, where the scan lists
 // the mounted filesystems, the types it never records anything on.
 func defaultExcludesHelp(goos string) string {

internal/sfdupes/scan.go

@@ -98,16 +98,17 @@ func scanPhase(name string) string {
 // runs, and the lock is released after it. When ctx is cancelled, as by
 // the SIGINT or SIGTERM that interruptContext catches, the scan keeps
 // what it has hashed (see syncScan), prints how many files its walk
-// reached, and returns errInterrupted. opts.workers must be at least 1;
+// reached, and returns errInterrupted. workers must be at least 1; the
-// the scan and dwim commands reject anything less. Before the lock is
+// scan command rejects anything less. Before the lock is taken, the
-// taken, the scan lists the filesystems that are not persistent, on
+// scan lists the filesystems that are not persistent, on which the walk
-// which the walk records nothing; unless opts.noDefaultExcludes is set,
+// records nothing; unless noDefaultExcludes is set, the walk does not
-// the walk does not enter the default excludes either. The walk neither
+// enter the default excludes either. The walk neither enters nor
-// enters nor records the paths in opts.excludePaths, the --exclude
+// records the paths in excludePaths, the --exclude values; an operand
-// values; an operand at or below one is a fatal error. Once the
+// at or below one is a fatal error. Once the database is open, the scan
-// database is open, the scan notes its files, which the walk passes
+// notes its files, which the walk passes over.
-// over.
+func runScan(ctx context.Context, roots []string, workers int,
-func runScan(ctx context.Context, roots []string, opts scanOptions) error {
+	oneFS, noDefaultExcludes bool, excludePaths []string,
+) error {
 	dbPath, source, err := databasePath()
 	if err != nil {
 		return err
@@ -122,7 +123,7 @@ func runScan(ctx context.Context, roots []string, opts scanOptions) error {
 
 	var rules walkRules
 
-	rules.excludePaths, err = excludePathInodes(opts.excludePaths)
+	rules.excludePaths, err = excludePathInodes(excludePaths)
 	if err != nil {
 		return fmt.Errorf("--exclude: %w", err)
 	}
@@ -137,7 +138,7 @@ func runScan(ctx context.Context, roots []string, opts scanOptions) error {
 		return fmt.Errorf("list the mounted filesystems: %w", err)
 	}
 
-	if !opts.noDefaultExcludes {
+	if !noDefaultExcludes {
 		rules.defaultExcludes = defaultExcludes(runtime.GOOS)
 	}
 
@@ -166,7 +167,7 @@ func runScan(ctx context.Context, roots []string, opts scanOptions) error {
 		return err
 	}
 
-	st, err := syncScan(ctx, db, roots, opts.workers, opts.oneFS, rules)
+	st, err := syncScan(ctx, db, roots, workers, oneFS, rules)
 	if errors.Is(err, context.Canceled) {
 		return interrupted(st.walked)
 	}

internal/sfdupes/scan_test.go

@@ -2196,7 +2196,7 @@ func TestScanHashWriteFailureUnwindsPool(t *testing.T) {
 	var stderr bytes.Buffer
 
 	code := run([]string{
-		cmdScan, workersFlag, strconv.Itoa(hashLeakWorkers), dir,
+		cmdScan, "--workers", strconv.Itoa(hashLeakWorkers), dir,
 	}, io.Discard, &stderr)
 	if code != exitFatal {
 		t.Fatalf("run(scan) = %d, want %d; stderr: %s",

internal/sfdupes/trees.go

@@ -101,7 +101,7 @@ func runTrees(ctx context.Context, stdout io.Writer) error {
 		label: treesPhase("write"), unit: "groups", total: int64(len(dupes)),
 		stalledOn: "out",
 	})
-	dupeTrees, err := writeTreeGroups(stdout, dupes, prog)
+	dupeTrees, reclaimable, err := writeTreeGroups(stdout, dupes, prog)
 
 	prog.finish()
 
@@ -112,7 +112,7 @@ func runTrees(ctx context.Context, stdout io.Writer) error {
 	fmt.Fprintf(os.Stderr,
 		"trees: %d records read, %d duplicate tree groups, %d dupe trees, "+
 			"%s reclaimable\n",
-		records, len(dupes), dupeTrees, humanBytes(reclaimableBytes(dupes)))
+		records, len(dupes), dupeTrees, humanBytes(reclaimable))
 
 	return nil
 }
@@ -146,19 +146,22 @@ func readTree(ctx context.Context, db *sql.DB,
 // a row for every member of each group but its first, counting each
 // group on prog once its rows are written. The disk_size column is the
 // dupe's own. stdout may be the terminal prog is drawn on, so the lines
-// go through prog's writer. It returns the number of rows (dupe trees).
+// go through prog's writer. It returns the number of rows (dupe trees)
+// and the bytes they could reclaim.
 func writeTreeGroups(stdout io.Writer, dupes [][]*treeNode,
 	prog *progress,
-) (int, error) {
+) (int, int64, error) {
 	out := prog.writer(stdout)
 
 	_, err := fmt.Fprintln(out, "first\tdupe\tfiles\tsize\tdisk_size")
 	if err != nil {
-		return 0, fmt.Errorf("write stdout: %w", err)
+		return 0, 0, fmt.Errorf("write stdout: %w", err)
 	}
 
 	dupeTrees := 0
 
+	var reclaimable int64
+
 	for _, g := range dupes {
 		first := g[0]
 		for _, n := range g[1:] {
@@ -166,10 +169,11 @@ func writeTreeGroups(stdout io.Writer, dupes [][]*treeNode,
 				escapePath(first.path), escapePath(n.path),
 				first.fileCount, first.totalSize, n.diskSize)
 			if err != nil {
-				return 0, fmt.Errorf("write stdout: %w", err)
+				return 0, 0, fmt.Errorf("write stdout: %w", err)
 			}
 
 			dupeTrees++
+			reclaimable += first.totalSize
 		}
 
 		prog.increment()
@@ -177,44 +181,10 @@ func writeTreeGroups(stdout io.Writer, dupes [][]*treeNode,
 
 	err = out.Flush()
 	if err != nil {
-		return 0, fmt.Errorf("write stdout: %w", err)
+		return 0, 0, fmt.Errorf("write stdout: %w", err)
 	}
 
-	return dupeTrees, nil
+	return dupeTrees, reclaimable, nil
-}
-
-// reclaimableBytes returns the sum of the size column over the rows
-// that writeTreeGroups writes for dupes, leaving out a row whose dupe
-// lies inside another row's dupe.
-func reclaimableBytes(dupes [][]*treeNode) int64 {
-	isDupe := make(map[*treeNode]bool)
-
-	for _, g := range dupes {
-		for _, n := range g[1:] {
-			isDupe[n] = true
-		}
-	}
-
-	var total int64
-
-	for n := range isDupe {
-		if !insideDupe(n, isDupe) {
-			total += n.totalSize
-		}
-	}
-
-	return total
-}
-
-// insideDupe reports whether a directory above n is in isDupe.
-func insideDupe(n *treeNode, isDupe map[*treeNode]bool) bool {
-	for p := n.parent; p != nil; p = p.parent {
-		if isDupe[p] {
-			return true
-		}
-	}
-
-	return false
 }
 
 // treeBuilder reconstructs the directory hierarchy from records added

internal/sfdupes/trees_test.go

@@ -313,7 +313,7 @@ func TestWriteTreeGroupsOnTerminal(t *testing.T) {
 		label: treesPhase("write"), unit: "groups", total: int64(len(dupes)),
 	}, terminalWidth, time.Hour, time.Now)
 
-	_, err := writeTreeGroups(os.Stderr, dupes, p)
+	_, _, err := writeTreeGroups(os.Stderr, dupes, p)
 
 	p.finish()
 
@@ -587,64 +587,3 @@ func TestCollectTreeGroupsKeepsGroupLeftWithTwoCopies(t *testing.T) {
 		t.Errorf("groups = %v, want %v", got, want)
 	}
 }
-
-// TestReclaimableBytesCountsNestedDupeOnce checks that a dupe tree
-// inside another dupe tree adds nothing to the reclaimable bytes. /B/x
-// lies in /B, so the total adds the sizes of /B and /C/x, 1500 + 1000.
-func TestReclaimableBytesCountsNestedDupeOnce(t *testing.T) {
-	t.Parallel()
-
-	fh, ft, fc := testHash("fh"), testHash("ft"), testHash("fc")
-	gh, gt, gc := testHash("gh"), testHash("gt"), testHash("gc")
-	recs := []scanRec{
-		{size: 1000, head: fh, tail: ft, content: fc, path: "/A/x/f"},
-		{size: 500, head: gh, tail: gt, content: gc, path: "/A/y/g"},
-		{size: 1000, head: fh, tail: ft, content: fc, path: "/B/x/f"},
-		{size: 500, head: gh, tail: gt, content: gc, path: "/B/y/g"},
-		{size: 1000, head: fh, tail: ft, content: fc, path: "/C/x/f"},
-	}
-
-	super, dirs := treeOf(t, recs)
-	dupes := collectTreeGroups(dirs, super, everyPathExists, nil)
-
-	wantGroups := [][]string{{"/A", "/B"}, {"/A/x", "/B/x", "/C/x"}}
-	if got := groupPaths(dupes); !slices.EqualFunc(got, wantGroups,
-		slices.Equal) {
-		t.Fatalf("groups = %v, want %v", got, wantGroups)
-	}
-
-	if got := reclaimableBytes(dupes); got != 2500 {
-		t.Errorf("reclaimableBytes = %d, want 2500", got)
-	}
-}
-
-// TestReclaimableBytesCountsDupeInsideGrandparentDupeOnce checks that a
-// dupe tree adds nothing when a dupe tree above its parent holds it.
-// /B/m/x lies in /B, and /B/m is no dupe, since the group of /A and /B
-// implies that of /A/m and /B/m. The total adds the sizes of /B and
-// /C/x, 1300 + 1000.
-func TestReclaimableBytesCountsDupeInsideGrandparentDupeOnce(t *testing.T) {
-	t.Parallel()
-
-	f, w := testHash("f"), testHash("w")
-	recs := []scanRec{
-		{size: 1000, head: f, tail: f, content: f, path: "/A/m/x/f"},
-		{size: 300, head: w, tail: w, content: w, path: "/A/m/w"},
-		{size: 1000, head: f, tail: f, content: f, path: "/B/m/x/f"},
-		{size: 300, head: w, tail: w, content: w, path: "/B/m/w"},
-		{size: 1000, head: f, tail: f, content: f, path: "/C/x/f"},
-	}
-
-	super, dirs := treeOf(t, recs)
-	dupes := collectTreeGroups(dirs, super, everyPathExists, nil)
-
-	wantGroups := [][]string{{"/A", "/B"}, {"/A/m/x", "/B/m/x", "/C/x"}}
-	if got := groupPaths(dupes); !slices.EqualFunc(got, wantGroups,
-		slices.Equal) {
-		t.Fatalf("groups = %v, want %v", got, wantGroups)
-	}
-
-	if got := reclaimableBytes(dupes); got != 2300 {
-		t.Errorf("reclaimableBytes = %d, want 2300", got)
-	}
-}