scan: drop the stray [flags] from the usage line (closes #169)

The scan Use string already names every flag, so cobra no longer appends
its generic [flags]. A test checks the usage line in the help and in the
usage error against the one README.md shows.

Model: opus-5-5

README.md

@@ -802,8 +802,7 @@ 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, what removing every `dupe` path would free. A `dupe`
-  path inside another `dupe` path adds nothing, so each file is counted once.
+- the reclaimable bytes, the sum of `size` over all rows.
 
 ```
 trees: 14 records read, 1 duplicate tree groups, 1 dupe trees, 3.0 KiB reclaimable

TODO.md

@@ -29,9 +29,9 @@
 Newest first. An entry ends with its date and its issue or branch, where those
 are known.
 
-- The reclaimable total of `trees` counts each file once. A `dupe` tree inside
-  another `dupe` tree adds nothing, so the total is what removing every `dupe`
-  path frees (2026-11-11, https://git.eeqj.de/sneak/sfdupes/issues/168)
+- 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,

internal/sfdupes/cli.go

@@ -215,10 +215,13 @@ func newScanCommand() *cobra.Command {
 	short := "Walk trees and synchronize the scan database"
 
 	scanCmd := &cobra.Command{
-		Use:   cmdScan + " [--workers N] [-x] [--no-default-excludes] PATH...",
-		Short: short,
-		Long:  short + ".\n\n" + defaultExcludesHelp(runtime.GOOS),
-		Args:  cobra.MinimumNArgs(1),
+		Use: cmdScan + " [--workers N] [-x] [--no-default-excludes] 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" + defaultExcludesHelp(runtime.GOOS),
+		Args:                  cobra.MinimumNArgs(1),
 		PreRunE: func(cmd *cobra.Command, _ []string) error {
 			return checkScanWorkers(cmd, scanWorkers)
 		},

internal/sfdupes/cli_test.go

@@ -714,6 +714,34 @@ func TestRunHelp(t *testing.T) {
 	}
 }
 
+func TestRunScanUsageLine(t *testing.T) {
+	t.Parallel()
+
+	// README §Subcommands shows this usage line for scan, and the help
+	// and the usage error both print it.
+	const want = "\n  sfdupes scan [--workers N] [-x] [--no-default-excludes] PATH...\n"
+
+	cases := map[string][]string{
+		"help":          {cmdScan, "-h"},
+		"missing paths": {cmdScan},
+	}
+
+	for name, args := range cases {
+		t.Run(name, func(t *testing.T) {
+			t.Parallel()
+
+			var stdout, stderr bytes.Buffer
+
+			run(args, &stdout, &stderr)
+
+			if !strings.Contains(stderr.String(), want) {
+				t.Errorf("run(%v) stderr = %q, want the usage line %q",
+					args, stderr.String(), want)
+			}
+		})
+	}
+}
+
 func TestRunVersion(t *testing.T) {
 	t.Parallel()
 

internal/sfdupes/trees.go

@@ -100,7 +100,7 @@ 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()
 
@@ -111,7 +111,7 @@ 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
 }
@@ -145,19 +145,22 @@ 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:] {
@@ -165,10 +168,11 @@ 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()
@@ -176,44 +180,10 @@ 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
-}
-
-// reclaimableBytes returns the bytes that removing every dupe tree in
-// dupes would free. A dupe tree inside another dupe tree adds nothing,
-// since the outer one already counts its files.
-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
+	return dupeTrees, reclaimable, nil
 }
 
 // treeBuilder reconstructs the directory hierarchy from records added

internal/sfdupes/trees_test.go

@@ -303,7 +303,7 @@ 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()
 
@@ -487,33 +487,3 @@ func TestCollectTreeGroupsDifferingParents(t *testing.T) {
 		t.Fatalf("groups = %v, want %v", got, want)
 	}
 }
-
-// TestReclaimableBytesCountsNestedDupeOnce checks that a dupe tree
-// inside another dupe tree adds nothing to the reclaimable bytes:
-// removing /B and /C/x frees 1500 + 1000 bytes, and /B/x lies in /B.
-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, 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)
-	}
-}