sfdupes/scan_test.go

package main

import (
	"bytes"
	"context"
	"crypto/sha256"
	"database/sql"
	"encoding/hex"
	"errors"
	"fmt"
	"os"
	"path/filepath"
	"runtime"
	"slices"
	"strconv"
	"strings"
	"testing"
	"time"
)

// writeFile creates a file with the given content and returns its path.
func writeFile(t *testing.T, dir, name string, data []byte) string {
	t.Helper()

	p := filepath.Join(dir, name)

	err := os.MkdirAll(filepath.Dir(p), 0o750)
	if err != nil {
		t.Fatal(err)
	}

	err = os.WriteFile(p, data, 0o600)
	if err != nil {
		t.Fatal(err)
	}

	return p
}

// hexSum returns the lowercase-hex SHA-256 of data.
func hexSum(data []byte) string {
	s := sha256.Sum256(data)

	return hex.EncodeToString(s[:])
}

// pattern returns n bytes of deterministic content seeded by tag.
func pattern(tag byte, n int) []byte {
	data := make([]byte, n)
	for i := range data {
		data[i] = tag ^ byte(i)
	}

	return data
}

func TestHashHeadTail(t *testing.T) {
	t.Parallel()

	dir := t.TempDir()

	cases := []struct {
		name string
		data []byte
	}{
		{"empty", nil},
		{"one-byte", []byte("x")},
		{"under-one-chunk", pattern(1, chunk-1)},
		{"exactly-one-chunk", pattern(2, chunk)},
		{"overlapping-reads", pattern(3, chunk+chunk/2)},
		{"exactly-two-chunks", pattern(4, 2*chunk)},
		{"beyond-two-chunks", pattern(5, 3*chunk)},
	}
	for _, c := range cases {
		t.Run(c.name, func(t *testing.T) {
			t.Parallel()

			p := writeFile(t, dir, c.name, c.data)

			head, tail, err := hashHeadTail(p, int64(len(c.data)))
			if err != nil {
				t.Fatalf("hashHeadTail: %v", err)
			}

			n := min(chunk, len(c.data))
			if want := hexSum(c.data[:n]); head != want {
				t.Errorf("head = %s, want %s", head, want)
			}

			if want := hexSum(c.data[len(c.data)-n:]); tail != want {
				t.Errorf("tail = %s, want %s", tail, want)
			}
		})
	}
}

func TestHashHeadTailErrors(t *testing.T) {
	t.Parallel()

	dir := t.TempDir()

	_, _, err := hashHeadTail(filepath.Join(dir, "missing"), 1)
	if err == nil {
		t.Error("no error for a missing file")
	}

	// A zero-length file has constant hashes and is never opened: even
	// a missing path succeeds.
	head, tail, err := hashHeadTail(filepath.Join(dir, "missing"), 0)
	if err != nil || head != emptyHash || tail != emptyHash {
		t.Errorf("empty: head=%q tail=%q err=%v, want constant hashes",
			head, tail, err)
	}

	// A file that shrank between the stat and hash passes: reading at
	// the stat-reported size must fail rather than emit wrong hashes.
	p := writeFile(t, dir, "shrunk", []byte("tiny"))

	_, _, err = hashHeadTail(p, int64(2*chunk))
	if err == nil {
		t.Error("no error when the stat size exceeds the file size")
	}
}

// collectWalk runs a walk over roots and returns the emitted records
// and the number of warning events.
func collectWalk(t *testing.T, roots []string, oneFS bool,
	workers int,
) ([]fileRec, int) {
	t.Helper()

	var (
		recs []fileRec
		errs int
	)

	for ev := range startWalk(t.Context(), roots, oneFS, workers) {
		if ev.fail {
			errs++

			continue
		}

		recs = append(recs, ev.rec)
	}

	return recs, errs
}

// walkedPaths returns the sorted paths of the walked records.
func walkedPaths(recs []fileRec) []string {
	paths := make([]string, 0, len(recs))
	for _, r := range recs {
		paths = append(paths, r.path)
	}

	slices.Sort(paths)

	return paths
}

func TestWalk(t *testing.T) {
	t.Parallel()

	dir := t.TempDir()
	want := []string{
		writeFile(t, dir, "a.txt", []byte("a")),
		writeFile(t, dir, "sub/b.txt", []byte("bb")),
		writeFile(t, dir, "sub/deeper/c.txt", []byte("ccc")),
	}

	slices.Sort(want)

	// Files under a .zfs directory must never be walked.
	writeFile(t, dir, ".zfs/snapshot/hourly/a.txt", []byte("a"))

	// Symlinks are skipped, not followed.
	err := os.Symlink(want[0], filepath.Join(dir, "link"))
	if err != nil {
		t.Fatal(err)
	}

	recs, errs := collectWalk(t, []string{dir}, false, 4)
	if errs != 0 {
		t.Fatalf("errs = %d, want 0", errs)
	}

	if got := walkedPaths(recs); !slices.Equal(got, want) {
		t.Fatalf("paths = %q, want %q", got, want)
	}

	// The walk stats each file as it is discovered: every record must
	// carry the real size and a plausible mtime.
	for _, r := range recs {
		if r.size < 1 || r.size > 3 {
			t.Errorf("%s: size = %d, want 1..3", r.path, r.size)
		}

		if r.mtime <= 0 {
			t.Errorf("%s: mtime = %d, want positive", r.path, r.mtime)
		}
	}
}

func TestWalkDeepAndWide(t *testing.T) {
	t.Parallel()

	// Exercise the dispatcher with more directories than workers and
	// with nesting deeper than the worker count.
	dir := t.TempDir()
	deep := "deep" + strings.Repeat("/d", 30)

	want := make([]string, 0, 41)
	want = append(want, writeFile(t, dir, deep+"/f", []byte("x")))

	for i := range 40 {
		want = append(want, writeFile(t, dir,
			fmt.Sprintf("wide/%02d/f", i), []byte("y")))
	}

	slices.Sort(want)

	recs, errs := collectWalk(t, []string{dir}, false, 8)
	if errs != 0 {
		t.Fatalf("errs = %d, want 0", errs)
	}

	if got := walkedPaths(recs); !slices.Equal(got, want) {
		t.Fatalf("walked %d paths, want %d", len(got), len(want))
	}
}

func TestWalkMultipleRoots(t *testing.T) {
	t.Parallel()

	rootA := t.TempDir()
	rootB := t.TempDir()
	want := []string{
		writeFile(t, rootA, "a1", []byte("1")),
		writeFile(t, rootA, "sub/a2", []byte("2")),
		writeFile(t, rootB, "b1", []byte("3")),
	}

	slices.Sort(want)

	// Operands are enumerated concurrently by the shared pool; order
	// is unspecified.
	recs, errs := collectWalk(t, []string{rootA, rootB}, false, 4)
	if errs != 0 {
		t.Fatalf("errs = %d, want 0", errs)
	}

	if got := walkedPaths(recs); !slices.Equal(got, want) {
		t.Fatalf("paths = %q, want %q", got, want)
	}
}

func TestWalkFileAndSymlinkOperands(t *testing.T) {
	t.Parallel()

	dir := t.TempDir()
	f := writeFile(t, dir, "plain", []byte("data"))

	link := filepath.Join(dir, "link")

	err := os.Symlink(f, link)
	if err != nil {
		t.Fatal(err)
	}

	// A regular-file operand is emitted as itself, statted.
	recs, errs := collectWalk(t, []string{f}, false, 2)
	if errs != 0 || len(recs) != 1 || recs[0].path != f || recs[0].size != 4 {
		t.Fatalf("file operand: recs = %+v, errs = %d", recs, errs)
	}

	// A symlink operand is not followed and yields nothing.
	recs, errs = collectWalk(t, []string{link}, false, 2)
	if errs != 0 || len(recs) != 0 {
		t.Fatalf("symlink operand: recs = %+v, errs = %d", recs, errs)
	}
}

func TestWalkOneFilesystemSameFS(t *testing.T) {
	t.Parallel()

	// Everything in one filesystem: -x must not skip anything.
	dir := t.TempDir()
	want := []string{
		writeFile(t, dir, "a", []byte("a")),
		writeFile(t, dir, "sub/deep/b", []byte("b")),
	}

	recs, errs := collectWalk(t, []string{dir}, true, 4)
	if errs != 0 {
		t.Fatalf("errs = %d, want 0", errs)
	}

	if got := walkedPaths(recs); !slices.Equal(got, want) {
		t.Fatalf("paths = %q, want %q", got, want)
	}
}

func TestDeviceOfInfo(t *testing.T) {
	t.Parallel()

	dir := t.TempDir()

	fi1, err := os.Lstat(dir)
	if err != nil {
		t.Fatal(err)
	}

	fi2, err := os.Lstat(dir)
	if err != nil {
		t.Fatal(err)
	}

	dev1, ok1 := deviceOfInfo(fi1)

	dev2, ok2 := deviceOfInfo(fi2)
	if !ok1 || !ok2 || dev1 != dev2 {
		t.Fatalf("deviceOfInfo unstable: %d/%v vs %d/%v",
			dev1, ok1, dev2, ok2)
	}
}

// buildSmokeTree recreates the README smoke-test filesystem layout
// with deterministic content and returns the tree root.
func buildSmokeTree(t *testing.T) string {
	t.Helper()

	dir := t.TempDir()
	one := pattern(10, 2000)
	f1 := pattern(30, 3000)
	f2 := pattern(40, 100)

	writeFile(t, dir, "a/one.bin", one)
	writeFile(t, dir, "b/copy.bin", one)
	writeFile(t, dir, "b/copy2.bin", one)
	// Same size as one.bin, different content.
	writeFile(t, dir, "a/unique.bin", pattern(20, 2000))
	writeFile(t, dir, "tiny1", []byte("x"))
	writeFile(t, dir, "tiny2", []byte("x"))
	writeFile(t, dir, "tiny3", []byte("y"))
	writeFile(t, dir, "empty1", nil)
	writeFile(t, dir, "empty2", nil)
	writeFile(t, dir, "t1/f1", f1)
	writeFile(t, dir, "t1/sub/f2", f2)
	writeFile(t, dir, "t2/f1", f1)
	writeFile(t, dir, "t2/sub/f2", f2)
	writeFile(t, dir, "t3/f1", f1)
	writeFile(t, dir, "t3/sub/f2renamed", f2)

	return dir
}

// smokeTreeFiles is the number of regular files buildSmokeTree creates.
const smokeTreeFiles = 15

// syncTree synchronizes the database with the given roots and returns
// the scan stats.
func syncTree(t *testing.T, db *sql.DB, roots ...string) scanStats {
	t.Helper()

	st, err := syncScan(t.Context(), db, roots, 4, false)
	if err != nil {
		t.Fatalf("syncScan: %v", err)
	}

	return st
}

// dbRecords returns every record currently in the database.
func dbRecords(t *testing.T, db *sql.DB) []scanRec {
	t.Helper()

	recs, err := loadFileRows(t.Context(), db)
	if err != nil {
		t.Fatal(err)
	}

	return recs
}

// recordByPath finds the record with the given path.
func recordByPath(t *testing.T, recs []scanRec, path string) scanRec {
	t.Helper()

	for _, r := range recs {
		if r.path == path {
			return r
		}
	}

	t.Fatalf("no record for %q", path)

	return scanRec{}
}

// recordPaths returns the sorted paths of recs.
func recordPaths(recs []scanRec) []string {
	paths := make([]string, 0, len(recs))
	for _, r := range recs {
		paths = append(paths, r.path)
	}

	slices.Sort(paths)

	return paths
}

// assertSmokeDupeGroups checks the file-level duplicate groups for the
// smoke tree rooted at dir.
func assertSmokeDupeGroups(t *testing.T, dir string, parsed []scanRec) {
	t.Helper()

	groups := collectDupeGroups(parsed)
	if len(groups) != 5 {
		t.Fatalf("len(groups) = %d, want 5", len(groups))
	}

	wantSizes := []int64{3000, 2000, 100, 1, 0}
	for i, g := range groups {
		if g.size != wantSizes[i] {
			t.Errorf("groups[%d].size = %d, want %d",
				i, g.size, wantSizes[i])
		}
	}

	wantF1 := []string{
		filepath.Join(dir, "t1/f1"),
		filepath.Join(dir, "t2/f1"),
		filepath.Join(dir, "t3/f1"),
	}
	if !slices.Equal(groups[0].paths, wantF1) {
		t.Errorf("groups[0].paths = %q, want %q", groups[0].paths, wantF1)
	}
}

// assertSmokeTreeGroups checks the duplicate-tree groups for the smoke
// tree rooted at dir.
func assertSmokeTreeGroups(t *testing.T, dir string, parsed []scanRec) {
	t.Helper()

	super, dirs := buildHierarchy(parsed)
	super.compute()

	tg := collectTreeGroups(dirs, super)
	if len(tg) != 1 {
		t.Fatalf("len(tree groups) = %d, want 1", len(tg))
	}

	wantTrees := []string{filepath.Join(dir, "t1"), filepath.Join(dir, "t2")}
	if got := groupPaths(tg)[0]; !slices.Equal(got, wantTrees) {
		t.Fatalf("tree group = %q, want %q", got, wantTrees)
	}

	if tg[0][0].fileCount != 2 || tg[0][0].totalSize != 3100 {
		t.Fatalf("tree totals: %d files %d bytes, want 2 3100",
			tg[0][0].fileCount, tg[0][0].totalSize)
	}
}

func TestScanPipeline(t *testing.T) {
	t.Parallel()

	dir := buildSmokeTree(t)
	db := openTestDB(t)

	st := syncTree(t, db, dir)
	if st != (scanStats{added: smokeTreeFiles}) {
		t.Fatalf("stats = %+v, want %d added only", st, smokeTreeFiles)
	}

	parsed := dbRecords(t, db)
	if len(parsed) != smokeTreeFiles {
		t.Fatalf("len(records) = %d, want %d", len(parsed), smokeTreeFiles)
	}

	assertSmokeDupeGroups(t, dir, parsed)
	assertSmokeTreeGroups(t, dir, parsed)
}

func TestSyncScanUnchangedReuse(t *testing.T) {
	t.Parallel()

	dir := t.TempDir()
	db := openTestDB(t)
	a := writeFile(t, dir, "a.bin", pattern(1, 500))

	writeFile(t, dir, "b.bin", pattern(2, 600))

	st := syncTree(t, db, dir)
	if st != (scanStats{added: 2}) {
		t.Fatalf("first scan stats = %+v, want 2 added", st)
	}

	// An immediate rescan reuses every record without reading file
	// contents. Prove the files are not re-read by corrupting a stored
	// hash and observing that it survives the rescan.
	_, err := db.ExecContext(context.Background(),
		"UPDATE files SET head = 'sentinel' WHERE path = ?", []byte(a))
	if err != nil {
		t.Fatal(err)
	}

	st = syncTree(t, db, dir)
	if st != (scanStats{unchanged: 2}) {
		t.Fatalf("rescan stats = %+v, want 2 unchanged", st)
	}

	if r := recordByPath(t, dbRecords(t, db), a); r.head != "sentinel" {
		t.Fatalf("head = %q, want sentinel (file must not be re-read)",
			r.head)
	}
}

func TestSyncScanMtimeBump(t *testing.T) {
	t.Parallel()

	dir := t.TempDir()
	db := openTestDB(t)
	a := writeFile(t, dir, "a.bin", pattern(1, 500))

	syncTree(t, db, dir)

	// Bump the mtime forward: the file must be re-hashed even though
	// its size is unchanged.
	future := time.Now().Add(time.Hour)

	err := os.Chtimes(a, future, future)
	if err != nil {
		t.Fatal(err)
	}

	st := syncTree(t, db, dir)
	if st != (scanStats{updated: 1}) {
		t.Fatalf("mtime-bump stats = %+v, want 1 updated", st)
	}

	if r := recordByPath(t, dbRecords(t, db), a); r.mtime != future.Unix() {
		t.Fatalf("mtime = %d, want %d", r.mtime, future.Unix())
	}
}

func TestSyncScanAddRemove(t *testing.T) {
	t.Parallel()

	dir := t.TempDir()
	db := openTestDB(t)
	a := writeFile(t, dir, "a.bin", pattern(1, 500))

	writeFile(t, dir, "b.bin", pattern(2, 600))
	syncTree(t, db, dir)

	// Add one file, remove another.
	c := writeFile(t, dir, "c.bin", pattern(3, 700))

	err := os.Remove(a)
	if err != nil {
		t.Fatal(err)
	}

	st := syncTree(t, db, dir)
	if st != (scanStats{added: 1, removed: 1, unchanged: 1}) {
		t.Fatalf("add/remove stats = %+v, want 1 added 1 removed 1 unchanged",
			st)
	}

	want := []string{filepath.Join(dir, "b.bin"), c}
	if got := recordPaths(dbRecords(t, db)); !slices.Equal(got, want) {
		t.Fatalf("paths = %q, want %q", got, want)
	}
}

func TestSyncScanSizeChange(t *testing.T) {
	t.Parallel()

	dir := t.TempDir()
	db := openTestDB(t)
	p := writeFile(t, dir, "f", pattern(1, 100))

	syncTree(t, db, dir)

	// Rewrite with a different size but force the mtime back to the
	// recorded value: the size mismatch alone must trigger a re-hash.
	old := recordByPath(t, dbRecords(t, db), p)

	writeFile(t, dir, "f", pattern(1, 200))

	mt := time.Unix(old.mtime, 0)

	err := os.Chtimes(p, mt, mt)
	if err != nil {
		t.Fatal(err)
	}

	st := syncTree(t, db, dir)
	if st.updated != 1 {
		t.Fatalf("stats = %+v, want 1 updated", st)
	}

	if got := recordByPath(t, dbRecords(t, db), p); got.size != 200 {
		t.Fatalf("size = %d, want 200", got.size)
	}
}

func TestSyncScanScope(t *testing.T) {
	t.Parallel()

	dir := t.TempDir()
	db := openTestDB(t)

	writeFile(t, dir, "a/keep", pattern(1, 10))

	gone := writeFile(t, dir, "b/gone", pattern(2, 10))

	syncTree(t, db, dir)

	// Deleting a file outside the rescanned root must not remove its
	// record: records outside the scanned operands are untouched.
	err := os.Remove(gone)
	if err != nil {
		t.Fatal(err)
	}

	st := syncTree(t, db, filepath.Join(dir, "a"))
	if st.removed != 0 || st.unchanged != 1 {
		t.Fatalf("subtree stats = %+v, want 0 removed 1 unchanged", st)
	}

	if got := recordPaths(dbRecords(t, db)); len(got) != 2 {
		t.Fatalf("records = %q, want both retained", got)
	}

	// Rescanning the parent now removes the vanished file's record.
	st = syncTree(t, db, dir)
	if st.removed != 1 {
		t.Fatalf("parent stats = %+v, want 1 removed", st)
	}
}

func TestSyncScanRemovesNonRegular(t *testing.T) {
	t.Parallel()

	dir := t.TempDir()
	db := openTestDB(t)
	p := writeFile(t, dir, "f", pattern(1, 10))
	keep := writeFile(t, dir, "g", pattern(2, 10))

	syncTree(t, db, dir)

	// Replace the file with a symlink: it is no longer walked, so its
	// record must be deleted.
	err := os.Remove(p)
	if err != nil {
		t.Fatal(err)
	}

	err = os.Symlink(keep, p)
	if err != nil {
		t.Fatal(err)
	}

	st := syncTree(t, db, dir)
	if st.removed != 1 || st.unchanged != 1 {
		t.Fatalf("stats = %+v, want 1 removed 1 unchanged", st)
	}
}

func TestSyncScanOverlappingRoots(t *testing.T) {
	t.Parallel()

	dir := t.TempDir()
	db := openTestDB(t)

	writeFile(t, dir, "sub/f", pattern(1, 10))

	// A file reachable via two overlapping operands is deduplicated
	// by path in the shared walk and processed once.
	st := syncTree(t, db, dir, filepath.Join(dir, "sub"))
	if st != (scanStats{added: 1}) {
		t.Fatalf("stats = %+v, want 1 added", st)
	}

	if got := recordPaths(dbRecords(t, db)); len(got) != 1 {
		t.Fatalf("records = %q, want exactly one", got)
	}
}

func TestScanSkipsUniqueSizes(t *testing.T) {
	t.Parallel()

	dir := t.TempDir()
	db := openTestDB(t)
	a := writeFile(t, dir, "a.bin", pattern(1, 500))

	writeFile(t, dir, "b.bin", pattern(2, 600))

	// Neither size is shared, so neither file is read: both records
	// are written without hashes and no duplicates are reported.
	st := syncTree(t, db, dir)
	if st != (scanStats{added: 2}) {
		t.Fatalf("stats = %+v, want 2 added", st)
	}

	recs := dbRecords(t, db)
	for _, r := range recs {
		if r.head != "" || r.tail != "" {
			t.Errorf("%s: head = %q tail = %q, want unhashed",
				r.path, r.head, r.tail)
		}
	}

	if groups := collectDupeGroups(recs); len(groups) != 0 {
		t.Fatalf("groups = %+v, want none from unhashed records", groups)
	}

	// A new same-size file makes 500 a shared size: the next scan
	// hashes both the new file and the previously unhashed unchanged
	// one, and they group as duplicates.
	c := writeFile(t, dir, "c.bin", pattern(1, 500))

	st = syncTree(t, db, dir)
	if st != (scanStats{added: 1, updated: 1, unchanged: 1}) {
		t.Fatalf("rescan stats = %+v, want 1 added 1 updated 1 unchanged",
			st)
	}

	groups := collectDupeGroups(dbRecords(t, db))
	if len(groups) != 1 {
		t.Fatalf("groups = %+v, want the a/c pair", groups)
	}

	if want := []string{a, c}; !slices.Equal(groups[0].paths, want) {
		t.Fatalf("group paths = %q, want %q", groups[0].paths, want)
	}
}

func TestTreesUnhashedNeverEqual(t *testing.T) {
	t.Parallel()

	// Two trees identical except for unhashed same-name, same-size
	// files (possible when the trees were scanned separately) must not
	// compare equal: unhashed content is unknown.
	shared := pattern(1, 100)
	recs := []scanRec{
		{path: "/x/t1/f1", size: 100, head: hexSum(shared), tail: hexSum(shared)},
		{path: "/x/t2/f1", size: 100, head: hexSum(shared), tail: hexSum(shared)},
		{path: "/x/t1/u", size: 50},
		{path: "/x/t2/u", size: 50},
	}

	super, dirs := buildHierarchy(recs)
	super.compute()

	if tg := collectTreeGroups(dirs, super); len(tg) != 0 {
		t.Fatalf("tree groups = %d, want 0 (unhashed files differ)",
			len(tg))
	}
}

func TestScanHardlinksReadOnce(t *testing.T) {
	t.Parallel()

	dir := t.TempDir()
	db := openTestDB(t)
	a := writeFile(t, dir, "a.bin", pattern(1, 300))
	b := filepath.Join(dir, "b.bin")

	err := os.Link(a, b)
	if err != nil {
		t.Fatal(err)
	}

	st := syncTree(t, db, dir)
	if st != (scanStats{added: 2}) {
		t.Fatalf("stats = %+v, want 2 added", st)
	}

	// Both paths share the single read's hashes and group together.
	recs := dbRecords(t, db)

	ra := recordByPath(t, recs, a)
	rb := recordByPath(t, recs, b)

	if ra.head == "" || ra.head != rb.head || ra.tail != rb.tail {
		t.Fatalf("hardlink hashes differ: %+v vs %+v", ra, rb)
	}

	if groups := collectDupeGroups(recs); len(groups) != 1 {
		t.Fatalf("groups = %+v, want the hardlink pair", groups)
	}
}

func TestScanHardlinkRunFailsTogether(t *testing.T) {
	t.Parallel()

	dir := t.TempDir()
	db := openTestDB(t)
	a := writeFile(t, dir, "a.bin", pattern(1, 300))

	err := os.Link(a, filepath.Join(dir, "b.bin"))
	if err != nil {
		t.Fatal(err)
	}

	// Unreadable inode: the run's single read fails, so both paths are
	// skipped — proof that hard links are read once, not per path.
	err = os.Chmod(a, 0)
	if err != nil {
		t.Fatal(err)
	}

	st := syncTree(t, db, dir)
	if st.skipped != 2 || st.added != 0 {
		t.Fatalf("stats = %+v, want both hardlink paths skipped", st)
	}
}

// injectedWriteFailure is the message the injected database trigger
// aborts with, so the test can recognize its own failure in the error
// the scan reports.
const injectedWriteFailure = "injected write failure"

// hashLeakFiles is the size of the fixture for the hash-phase failure
// test. The batch commit inside the hash phase is what fails, so the
// tree must hold more than updateBatchSize files for the failure to
// happen at all; the surplus over that is what is still queued when it
// does, and it exceeds the depth of both pool channels so that the
// workers have nowhere left to put their results. An abandoned pool
// therefore parks forever, which is exactly what this test detects.
const hashLeakFiles = updateBatchSize + 2*workQueueDepth

// hashLeakWorkers is the worker count for that scan: a fixed, modest
// number keeps the leak deterministic on any machine.
const hashLeakWorkers = 4

// goroutineSettle bounds how long a goroutine count is given to come
// back down to its target. Only a failing run ever waits this long.
const goroutineSettle = 5 * time.Second

// goroutinePoll is the interval between goroutine-count samples.
const goroutinePoll = 10 * time.Millisecond

// writeEmptyFiles creates n empty files directly in dir. Zero-length
// files are never opened by the hasher — their hashes are constant —
// so a fixture this size costs directory entries and no read I/O,
// while still queueing n runs through the hash pool.
func writeEmptyFiles(t *testing.T, dir string, n int) {
	t.Helper()

	for i := range n {
		err := os.WriteFile(
			filepath.Join(dir, strconv.Itoa(i)), nil, 0o600)
		if err != nil {
			t.Fatal(err)
		}
	}
}

// injectWriteFailure creates a scan database at path carrying the real
// schema plus a trigger that aborts every insert. Reads are untouched,
// so a scan loads its index and walks normally and then fails on the
// first record it tries to commit — a genuine database write failure
// partway through the hash phase.
func injectWriteFailure(t *testing.T, path string) {
	t.Helper()

	db, err := openScanDatabase(t.Context(), path)
	if err != nil {
		t.Fatal(err)
	}

	_, err = db.ExecContext(t.Context(),
		"CREATE TRIGGER refuse_insert BEFORE INSERT ON files "+
			"BEGIN SELECT RAISE(ABORT, '"+injectedWriteFailure+"'); END")
	if err != nil {
		t.Fatal(err)
	}

	err = db.Close()
	if err != nil {
		t.Fatal(err)
	}
}

// baselineGoroutines waits for the goroutine count to stop moving and
// returns it. Handles closed by earlier tests take a moment to reap
// their driver goroutines, so a single sample would make the baseline
// itself flaky.
func baselineGoroutines(t *testing.T) int {
	t.Helper()

	deadline := time.Now().Add(goroutineSettle)
	last := runtime.NumGoroutine()

	for time.Now().Before(deadline) {
		time.Sleep(goroutinePoll)

		n := runtime.NumGoroutine()
		if n == last {
			return n
		}

		last = n
	}

	return last
}

// settledGoroutines polls runtime.NumGoroutine until it is back at or
// below want and returns the last count seen. Polling, rather than one
// sample after a fixed sleep, is what keeps this from being a race
// between the assertion and goroutines that are already exiting.
func settledGoroutines(t *testing.T, want int) int {
	t.Helper()

	deadline := time.Now().Add(goroutineSettle)

	for {
		n := runtime.NumGoroutine()
		if n <= want || time.Now().After(deadline) {
			return n
		}

		time.Sleep(goroutinePoll)
	}
}

// TestScanHashWriteFailureUnwindsPool drives the scan entry point
// against a database that refuses every write. The hash phase gives up
// partway through with thousands of runs still queued, which used to
// leave the feeder parked on a full job channel and every worker parked
// on a full result channel for the life of the process.
func TestScanHashWriteFailureUnwindsPool(t *testing.T) {
	path := testDBPath(t)
	t.Setenv(databaseEnv, path)

	dir := t.TempDir()

	writeEmptyFiles(t, dir, hashLeakFiles)
	injectWriteFailure(t, path)

	base := baselineGoroutines(t)

	var stderr bytes.Buffer

	code := run([]string{
		cmdScan, "--workers", strconv.Itoa(hashLeakWorkers), dir,
	}, &stderr)
	if code != exitFatal {
		t.Fatalf("run(scan) = %d, want %d; stderr: %s",
			code, exitFatal, stderr.String())
	}

	if !strings.Contains(stderr.String(), injectedWriteFailure) {
		t.Errorf("stderr = %q, want the injected write failure",
			stderr.String())
	}

	if got := settledGoroutines(t, base); got > base {
		t.Errorf("goroutines = %d after the failed scan, want %d back",
			got, base)
	}
}

// TestSyncScanCancelledWalkKeepsRecords checks the other half of the
// cancellation path: a scan whose context is already cancelled stops
// with that error instead of treating its truncated walk as the truth
// and deleting the record of every file it never reached.
//
//nolint:paralleltest // counts goroutines: must not run beside others
func TestSyncScanCancelledWalkKeepsRecords(t *testing.T) {
	dir := buildSmokeTree(t)
	db := openTestDB(t)

	syncTree(t, db, dir)

	before := recordPaths(dbRecords(t, db))

	ctx, cancel := context.WithCancel(t.Context())
	cancel()

	base := baselineGoroutines(t)

	_, err := syncScan(ctx, db, []string{dir}, 4, false)
	if !errors.Is(err, context.Canceled) {
		t.Fatalf("syncScan on a cancelled context = %v, want %v",
			err, context.Canceled)
	}

	if got := recordPaths(dbRecords(t, db)); !slices.Equal(got, before) {
		t.Errorf("records = %q after a cancelled scan, want %q",
			got, before)
	}

	if got := settledGoroutines(t, base); got > base {
		t.Errorf("goroutines = %d after the cancelled scan, want %d back",
			got, base)
	}
}

func TestHashRuns(t *testing.T) {
	t.Parallel()

	rec := func(path string, dev, ino uint64) fileRec {
		return fileRec{path: path, dev: dev, ino: ino}
	}

	runs := hashRuns([]fileRec{
		rec("/c", 1, 7),
		rec("/a", 1, 7),
		rec("/b", 1, 9),
		// No inode identity: never merged, even with matching zeros.
		rec("/z1", 0, 0),
		rec("/z2", 0, 0),
	})

	got := make([][]string, 0, len(runs))
	for _, run := range runs {
		paths := make([]string, 0, len(run))
		for _, r := range run {
			paths = append(paths, r.path)
		}

		got = append(got, paths)
	}

	want := [][]string{{"/z1"}, {"/z2"}, {"/a", "/c"}, {"/b"}}
	if !slices.EqualFunc(got, want, slices.Equal) {
		t.Fatalf("runs = %v, want %v", got, want)
	}
}

func TestPruneRoots(t *testing.T) {
	t.Parallel()

	// Duplicates and operands under other operands are dropped; /cc is
	// not under /c (sibling with a shared prefix).
	got := pruneRoots([]string{"/a/b", "/a", "/c", "/a", "/a/b/c", "/cc"})

	want := []string{"/a", "/c", "/cc"}
	if !slices.Equal(got, want) {
		t.Fatalf("pruneRoots = %q, want %q", got, want)
	}
}

func TestReportsNeverTouchFilesystem(t *testing.T) {
	t.Parallel()

	dir := buildSmokeTree(t)
	db := openTestDB(t)

	syncTree(t, db, dir)

	// Remove the scanned tree entirely; the analysis must be
	// unaffected because it reads the database alone.
	err := os.RemoveAll(dir)
	if err != nil {
		t.Fatal(err)
	}

	recs := dbRecords(t, db)

	assertSmokeDupeGroups(t, dir, recs)
	assertSmokeTreeGroups(t, dir, recs)
}

func TestUnderRoot(t *testing.T) {
	t.Parallel()

	const abRoot = "/a/b"

	cases := []struct {
		path string
		root string
		want bool
	}{
		{"/a/b/c", abRoot, true},
		{abRoot, abRoot, true},
		{"/a/bc", abRoot, false},
		{"/a", abRoot, false},
		{"/x/y", "/", true},
		{"/", "/", true},
	}
	for _, c := range cases {
		if got := underRoot(c.path, c.root); got != c.want {
			t.Errorf("underRoot(%q, %q) = %v, want %v",
				c.path, c.root, got, c.want)
		}
	}
}