Say "skipped" in scan's warnings for skipped paths (closes #170)

A warning for a path the summary counts as skipped now reads
`scan: skipped PATH (REASON)`, naming the path once. This covers
unreadable directories, failed lstats, failed reads and dropped
operands. Each path of a hard-linked file that cannot be read gets its
own line, since each is counted. Lines for paths left out on purpose
(`--exclude`, default excludes, filesystems that are not persistent)
now read `scan: left out PATH (...)`, so a search for `scan: skipped`
finds only the counted paths.

Model: opus-5-5

README.md

@@ -255,7 +255,6 @@ In order:
    time, against what the database holds.
 4. **Keep the streams apart.** Everything on stdout is machine-readable data.
    Everything for a human reader, such as progress and warnings, goes to stderr.
-   The one exception is help that was asked for, which goes to stdout.
 
 ### Subcommands
 
@@ -325,13 +324,12 @@ The reference below is also the program's specification.
   "Operands").
 - `--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 stdout
-  and exits 0. It writes nothing to stderr. `sfdupes help` and
-  `sfdupes help COMMAND` do the same. The help of `sfdupes` and of `scan` names
-  the database. The help of `report`, `trees`, `info` and `dwim` says what 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.
+- `--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`
+  names the database. The help of `report`, `trees`, `info` and `dwim` says what
+  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
 

internal/sfdupes/cli.go

@@ -201,9 +201,8 @@ func run(args []string, stdout, stderr io.Writer) int {
 }
 
 // newRootCommand builds the command tree. Everything on stdout is
-// machine-readable data, the version line included, or help that was
-// asked for. The rest of the human-facing output (usage, errors) goes
-// to stderr.
+// machine-readable data, the version line included; all human-facing
+// output (help, usage, errors) goes to stderr.
 func newRootCommand(stdout, stderr io.Writer) *cobra.Command {
 	var showVersion bool
 
@@ -236,22 +235,11 @@ func newRootCommand(stdout, stderr io.Writer) *cobra.Command {
 			return errNoSubcommand
 		},
 	}
-	// Cobra prints the usage text of a usage error to the command's
-	// output writer, so that writer is stderr.
 	root.SetOut(stderr)
 	root.SetErr(stderr)
 	root.CompletionOptions.DisableDefaultCmd = true
 
-	// Cobra's default help also prints to the output writer. Help that
-	// was asked for, with --help, -h or the help subcommand, goes to
-	// stdout instead.
-	printHelp := root.HelpFunc()
-	root.SetHelpFunc(func(cmd *cobra.Command, args []string) {
-		cmd.SetOut(stdout)
-		printHelp(cmd, args)
-	})
-
-	// Cobra's built-in version flag prints to the output writer,
+	// Cobra's built-in version flag prints through the help writer,
 	// stderr; this one prints to stdout.
 	root.Flags().BoolVarP(&showVersion, "version", "v", false,
 		"print the version to stdout")

internal/sfdupes/cli_test.go

@@ -26,9 +26,6 @@ const usageMarker = "Usage:"
 // helpFlag asks for the help text.
 const helpFlag = "--help"
 
-// helpCommand is the subcommand that prints the help text.
-const helpCommand = "help"
-
 // workersFlag is the scan and dwim flag that sets the worker count.
 const workersFlag = "--workers"
 
@@ -703,12 +700,9 @@ func TestRunScanRejectsWorkersBelowOne(t *testing.T) {
 func TestRunHelp(t *testing.T) {
 	t.Parallel()
 
-	// README §Settings: help goes to stdout, exits 0, and leaves stderr
+	// README §Settings: help goes to stderr, exits 0, and leaves stdout
 	// empty.
-	cases := [][]string{
-		{helpFlag}, {"-h"}, {helpCommand},
-		{cmdScan, helpFlag}, {helpCommand, cmdScan},
-	}
+	cases := [][]string{{helpFlag}, {"-h"}, {cmdScan, helpFlag}}
 
 	for _, args := range cases {
 		var stdout, stderr bytes.Buffer
@@ -718,13 +712,14 @@ func TestRunHelp(t *testing.T) {
 			t.Errorf("run(%v) = %d, want %d", args, code, exitOK)
 		}
 
-		if !strings.Contains(stdout.String(), usageMarker) {
-			t.Errorf("run(%v) stdout = %q, want the help text",
-				args, stdout.String())
+		if !strings.Contains(stderr.String(), usageMarker) {
+			t.Errorf("run(%v) stderr = %q, want the help text",
+				args, stderr.String())
 		}
 
-		if got := stderr.String(); got != "" {
-			t.Errorf("run(%v) stderr = %q, want nothing", args, got)
+		if got := stdout.String(); got != "" {
+			t.Errorf("run(%v) stdout = %q, want nothing (data only)",
+				args, got)
 		}
 
 		// README §Location: the help of sfdupes and of scan says where
@@ -734,9 +729,9 @@ func TestRunHelp(t *testing.T) {
 			"scan and dwim store", databaseEnv, rootDatabasePath,
 			stateHomeEnv, "~/.local/state", "not an absolute path is an error",
 		} {
-			if !strings.Contains(stdout.String(), want) {
-				t.Errorf("run(%v) stdout = %q, want it to name %q",
-					args, stdout.String(), want)
+			if !strings.Contains(stderr.String(), want) {
+				t.Errorf("run(%v) stderr = %q, want it to name %q",
+					args, stderr.String(), want)
 			}
 		}
 	}
@@ -746,8 +741,8 @@ func TestRunHelp(t *testing.T) {
 
 	run([]string{cmdScan, "-h"}, &stdout, &stderr)
 
-	if !strings.Contains(stdout.String(), excludeFlag+" PATH") {
-		t.Errorf("scan -h stdout = %q, want %s PATH", stdout.String(),
+	if !strings.Contains(stderr.String(), excludeFlag+" PATH") {
+		t.Errorf("scan -h stderr = %q, want %s PATH", stderr.String(),
 			excludeFlag)
 	}
 }
@@ -756,8 +751,7 @@ 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. TestRunHelp and
-	// TestRunUsageErrors check which stream each goes to.
+	// and the usage error both print it.
 	const want = "\n  sfdupes scan [--workers N] [-x] [--no-default-excludes] " +
 		"[--exclude PATH]... PATH...\n"
 
@@ -770,13 +764,13 @@ func TestRunScanUsageLine(t *testing.T) {
 		t.Run(name, func(t *testing.T) {
 			t.Parallel()
 
-			var output bytes.Buffer
+			var stdout, stderr bytes.Buffer
 
-			run(args, &output, &output)
+			run(args, &stdout, &stderr)
 
-			if !strings.Contains(output.String(), want) {
-				t.Errorf("run(%v) output = %q, want the usage line %q",
-					args, output.String(), want)
+			if !strings.Contains(stderr.String(), want) {
+				t.Errorf("run(%v) stderr = %q, want the usage line %q",
+					args, stderr.String(), want)
 			}
 		})
 	}
@@ -842,9 +836,9 @@ func TestRunHelpDescribesOutput(t *testing.T) {
 		}
 
 		for _, want := range tc.want {
-			if !strings.Contains(stdout.String(), want) {
+			if !strings.Contains(stderr.String(), want) {
 				t.Errorf("run(%v) help lacks %q:\n%s",
-					args, want, stdout.String())
+					args, want, stderr.String())
 			}
 		}
 	}

internal/sfdupes/dwim_test.go

@@ -190,21 +190,21 @@ func TestRunDwimHelpListsScanFlags(t *testing.T) {
 
 	run([]string{cmdDwim, "-h"}, &stdout, &stderr)
 
-	if !strings.Contains(stdout.String(), want) {
-		t.Errorf("dwim -h stdout = %q, want the usage line %q",
-			stdout.String(), want)
+	if !strings.Contains(stderr.String(), want) {
+		t.Errorf("dwim -h stderr = %q, want the usage line %q",
+			stderr.String(), want)
 	}
 
-	if !strings.Contains(stdout.String(), excludeFlag+" PATH") {
-		t.Errorf("dwim -h stdout = %q, want %s PATH", stdout.String(),
+	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(stdout.String(), help) {
-		t.Errorf("dwim -h stdout = %q, want it to hold %q", stdout.String(),
+	if !strings.Contains(stderr.String(), help) {
+		t.Errorf("dwim -h stderr = %q, want it to hold %q", stderr.String(),
 			help)
 	}
 }

internal/sfdupes/exclude_test.go

@@ -196,8 +196,8 @@ func TestDefaultExcludesHelp(t *testing.T) {
 	run([]string{cmdScan, "-h"}, &stdout, &stderr)
 
 	help := strings.TrimSpace(defaultExcludesHelp(runtime.GOOS))
-	if !strings.Contains(stdout.String(), help) {
-		t.Errorf("scan --help = %q, want it to hold %q", stdout.String(), help)
+	if !strings.Contains(stderr.String(), help) {
+		t.Errorf("scan --help = %q, want it to hold %q", stderr.String(), help)
 	}
 }