README.md

@@ -269,6 +269,15 @@ are now tracked only in the [issues](https://git.eeqj.de/sneak/mfer/issues).
     - recurses under current directory and writes out an `index.mf`
     - records every file's mode as `0000` unless given `--include-permissions`,
       which records each file's permission bits (`0777` at most)
+- `mfer gen /media/drive`
+    - writes `/media/drive/index.mf`, listing each file by its path under
+      `/media/drive`, so `mfer check /media/drive` verifies it. Given a file,
+      gen writes `index.mf` beside it and lists the file by its name; given
+      several paths, it writes `index.mf` in the current directory
+    - `--output` names another file to write instead. What gen lists depends
+      only on the paths it is given and the files under them, so with the same
+      `--seed` and an unchanged tree it writes the same bytes wherever the
+      manifest goes. The file it writes to is never listed
 - `mfer check` / `mfer check .`
     - verifies checksums of all files in manifest, displaying error and exiting
       nonzero if any files are missing or corrupted, or have permission bits

internal/cli/entry_test.go

@@ -1289,6 +1289,180 @@ func TestGenerateLeavesLeftoverTempFileOutOfListing(t *testing.T) {
 	assert.Equal(t, []string{testFileTxt}, manifestPaths(t, fs, output))
 }
 
+// writeTestTree writes file.txt and sub/nested.txt under dir.
+func writeTestTree(t *testing.T, fs afero.Fs, dir string) {
+	t.Helper()
+
+	require.NoError(t, fs.MkdirAll(filepath.Join(dir, testSubdir), 0o750))
+	writeTestFile(t, fs, filepath.Join(dir, testFileTxt), "hello")
+	writeTestFile(t, fs, filepath.Join(dir, testSubdir, "nested.txt"), "in sub")
+}
+
+// TestGenerateDefaultOutput runs gen without --output on one directory or
+// one file: it writes index.mf in that directory, or beside that file,
+// listing each file by its path under the directory index.mf is in, and
+// check given that directory passes.
+func TestGenerateDefaultOutput(t *testing.T) {
+	t.Parallel()
+
+	// Paths are relative to a temp dir holding file.txt and sub/nested.txt.
+	for name, tc := range map[string]struct {
+		input, output string
+		listed        []string
+	}{
+		"directory": {
+			".", defaultManifestName, []string{testFileTxt, "sub/nested.txt"},
+		},
+		"subdirectory": {testSubdir, testSubdirManifest, []string{"nested.txt"}},
+		"file":         {testFileTxt, defaultManifestName, []string{testFileTxt}},
+	} {
+		t.Run(name, func(t *testing.T) {
+			t.Parallel()
+
+			root := t.TempDir()
+			fs := afero.NewOsFs()
+			writeTestTree(t, fs, root)
+
+			opts := testOpts([]string{
+				testApp, cmdGenerate, "-q", filepath.Join(root, tc.input),
+			}, fs)
+			require.Equal(t, 0, runCLI(opts), "stderr: %s", testStderr(t, opts))
+
+			output := filepath.Join(root, tc.output)
+			assert.ElementsMatch(t, tc.listed, manifestPaths(t, fs, output))
+
+			opts = testOpts([]string{
+				testApp, cmdCheck, "-q", filepath.Dir(output),
+			}, fs)
+			assert.Equal(t, 0, runCLI(opts), "stderr: %s", testStderr(t, opts))
+		})
+	}
+}
+
+// TestGenerateSeveralPathsDefaultOutput runs gen without --output on two
+// directories: it writes index.mf in the current directory, listing both
+// directories' files, and writes no index.mf in either directory.
+//
+//nolint:paralleltest // changes the process-global working directory
+func TestGenerateSeveralPathsDefaultOutput(t *testing.T) {
+	root := t.TempDir()
+	fs := afero.NewOsFs()
+	dirs := []string{"first", "second"}
+
+	for _, dir := range dirs {
+		require.NoError(t, fs.MkdirAll(filepath.Join(root, dir), 0o750))
+		writeTestFile(t, fs, filepath.Join(root, dir, dir+".txt"), dir)
+	}
+
+	t.Chdir(root)
+
+	opts := testOpts(append([]string{testApp, cmdGenerate, "-q"}, dirs...), fs)
+	require.Equal(t, 0, runCLI(opts), "stderr: %s", testStderr(t, opts))
+
+	assert.ElementsMatch(t, []string{"first.txt", "second.txt"},
+		manifestPaths(t, fs, filepath.Join(root, defaultManifestName)))
+
+	for _, dir := range dirs {
+		exists, err := afero.Exists(fs, filepath.Join(root, dir, defaultManifestName))
+		require.NoError(t, err)
+		assert.False(t, exists, "index.mf written in %s", dir)
+	}
+}
+
+// TestGenerateBytesDoNotDependOnOutput runs gen --seed on one tree, each
+// time writing to another file, over a file already there and beside an
+// earlier run's temp file: neither is listed, and what is listed depends
+// only on the tree, so every manifest has the same bytes.
+func TestGenerateBytesDoNotDependOnOutput(t *testing.T) {
+	t.Parallel()
+
+	root := t.TempDir()
+	tree := filepath.Join(root, "tree")
+	defaultOutput := filepath.Join(tree, defaultManifestName)
+
+	fs := afero.NewOsFs()
+	writeTestTree(t, fs, tree)
+
+	var first []byte
+
+	for _, output := range []string{
+		defaultOutput,
+		filepath.Join(tree, "listing.mf"),
+		filepath.Join(tree, testSubdir, "listing.mf"),
+		filepath.Join(root, "outside.mf"),
+	} {
+		writeTestFile(t, fs, output, "previous manifest")
+		writeTestFile(t, fs, manifestTempPath(output), "part of a manifest")
+
+		args := []string{testApp, cmdGenerate, "-q", "-f", "--seed", "mfer"}
+		if output != defaultOutput {
+			args = append(args, "-o", output)
+		}
+
+		args = append(args, tree)
+
+		opts := testOpts(args, fs)
+		require.Equal(t, 0, runCLI(opts),
+			"output %s, stderr: %s", output, testStderr(t, opts))
+
+		got, err := afero.ReadFile(fs, output)
+		require.NoError(t, err)
+		require.NoError(t, fs.Remove(output))
+
+		if first == nil {
+			first = got
+		}
+
+		assert.Equal(t, first, got, "output %s", output)
+	}
+}
+
+// TestGenerateRefusesExistingDefaultOutput runs gen without --output or
+// --force on a directory already holding index.mf: gen fails, naming that
+// file, and leaves it as it was.
+func TestGenerateRefusesExistingDefaultOutput(t *testing.T) {
+	t.Parallel()
+
+	output := filepath.Join(testDir, defaultManifestName)
+
+	fs := afero.NewMemMapFs()
+	require.NoError(t, fs.MkdirAll(testDir, 0o755))
+	writeTestFile(t, fs, testFile1, "hello")
+	writeTestFile(t, fs, output, "previous manifest")
+
+	opts := testOpts([]string{testApp, cmdGenerate, "-q", testDir}, fs)
+	assert.Equal(t, 1, runCLI(opts))
+	assert.Contains(t, testStderr(t, opts),
+		"output file "+output+" already exists (use --force to overwrite)")
+
+	content, err := afero.ReadFile(fs, output)
+	require.NoError(t, err)
+	assert.Equal(t, "previous manifest", string(content))
+}
+
+// TestGenerateRefusesEmptyOutput runs gen with --force and an --output
+// given an empty value, as an unset shell variable gives it, on a
+// directory already holding index.mf: gen fails and leaves that file as it
+// was.
+func TestGenerateRefusesEmptyOutput(t *testing.T) {
+	t.Parallel()
+
+	output := filepath.Join(testDir, defaultManifestName)
+
+	fs := afero.NewMemMapFs()
+	require.NoError(t, fs.MkdirAll(testDir, 0o755))
+	writeTestFile(t, fs, testFile1, "hello")
+	writeTestFile(t, fs, output, "previous manifest")
+
+	opts := testOpts([]string{testApp, cmdGenerate, "-q", "-f", "-o", "", testDir}, fs)
+	assert.Equal(t, 1, runCLI(opts))
+	assert.Contains(t, testStderr(t, opts), errEmptyOutput.Error())
+
+	content, err := afero.ReadFile(fs, output)
+	require.NoError(t, err)
+	assert.Equal(t, "previous manifest", string(content))
+}
+
 func TestGenerateAtomicWriteUsesTemp(t *testing.T) {
 	t.Parallel()
 

internal/cli/gen.go

@@ -4,6 +4,7 @@ import (
 	"context"
 	"errors"
 	"fmt"
+	"io"
 	"os"
 	"os/signal"
 	"path/filepath"
@@ -26,6 +27,8 @@ var (
 	// rendered message stays exactly as mfer has always printed it.
 	errOutputExists = errors.New(
 		"already exists (use --force to overwrite)")
+	// errEmptyOutput indicates --output given with an empty value.
+	errEmptyOutput = errors.New("--output must not be empty")
 )
 
 // reportEnumProgress renders enumeration progress until the channel
@@ -88,9 +91,40 @@ func (mfa *CLIApp) collectInputPaths(args cli.Args) ([]string, error) {
 	return paths, nil
 }
 
-// buildScannerOptions constructs scanner options from the CLI flags.
-func (mfa *CLIApp) buildScannerOptions(cmd *cli.Command) *mfer.ScannerOptions {
-	output := cmd.String("output")
+// outputPath returns the file gen writes the manifest to: the one --output
+// names, or else index.mf in the directory the only argument names, or
+// beside the file it names, or else in the current directory. An --output
+// given with an empty value is refused.
+func (mfa *CLIApp) outputPath(cmd *cli.Command) (string, error) {
+	if cmd.IsSet("output") {
+		output := cmd.String("output")
+		if output == "" {
+			return "", errEmptyOutput
+		}
+
+		return output, nil
+	}
+
+	if cmd.Args().Len() != 1 {
+		return defaultManifestName, nil
+	}
+
+	arg := cmd.Args().First()
+
+	// A path that does not exist is refused when it is enumerated.
+	info, err := mfa.Fs.Stat(arg)
+	if err == nil && !info.IsDir() {
+		return filepath.Join(filepath.Dir(arg), defaultManifestName), nil
+	}
+
+	return filepath.Join(arg, defaultManifestName), nil
+}
+
+// buildScannerOptions constructs scanner options from the CLI flags and
+// the path the manifest is written to.
+func (mfa *CLIApp) buildScannerOptions(
+	cmd *cli.Command, output string,
+) *mfer.ScannerOptions {
 	opts := &mfer.ScannerOptions{
 		IncludeDotfiles:    cmd.Bool("include-dotfiles"),
 		FollowSymLinks:     cmd.Bool("follow-symlinks"),
@@ -202,23 +236,54 @@ func (mfa *CLIApp) runEnumeratePhase(cmd *cli.Command, s *mfer.Scanner) error {
 	return nil
 }
 
+// runScanPhase reads the enumerated files and writes the manifest to out,
+// with optional progress reporting.
+func (mfa *CLIApp) runScanPhase(
+	ctx context.Context, cmd *cli.Command, s *mfer.Scanner, out io.Writer,
+) error {
+	var (
+		scanProgress chan mfer.ScanStatus
+		scanWg       sync.WaitGroup
+	)
+
+	if cmd.Bool("progress") {
+		scanProgress = make(chan mfer.ScanStatus, 1)
+
+		scanWg.Add(1)
+
+		go reportScanProgress(scanProgress, &scanWg)
+	}
+
+	err := s.ToManifest(ctx, out, scanProgress)
+
+	scanWg.Wait()
+
+	if err != nil {
+		return fmt.Errorf("generate manifest: %w", err)
+	}
+
+	return nil
+}
+
 func (mfa *CLIApp) generateManifestOperation(
 	ctx context.Context, cmd *cli.Command,
 ) error {
 	log.Debug("generateManifestOperation()")
 
-	s := mfer.NewScannerWithOptions(mfa.buildScannerOptions(cmd))
-
-	// Phase 1: Enumeration - collect paths and stat files
-	err := mfa.runEnumeratePhase(cmd, s)
+	outputPath, err := mfa.outputPath(cmd)
 	if err != nil {
 		return err
 	}
 
-	showProgress := cmd.Bool("progress")
+	s := mfer.NewScannerWithOptions(mfa.buildScannerOptions(cmd, outputPath))
+
+	// Phase 1: Enumeration - collect paths and stat files
+	err = mfa.runEnumeratePhase(cmd, s)
+	if err != nil {
+		return err
+	}
 
 	// Check if output file exists
-	outputPath := cmd.String("output")
 	if exists, _ := afero.Exists(mfa.Fs, outputPath); exists && !cmd.Bool("force") {
 		return fmt.Errorf("output file %s %w", outputPath, errOutputExists)
 	}
@@ -249,25 +314,9 @@ func (mfa *CLIApp) generateManifestOperation(
 	}()
 
 	// Phase 2: Scan - read file contents and generate manifest
-	var (
-		scanProgress chan mfer.ScanStatus
-		scanWg       sync.WaitGroup
-	)
-
-	if showProgress {
-		scanProgress = make(chan mfer.ScanStatus, 1)
-
-		scanWg.Add(1)
-
-		go reportScanProgress(scanProgress, &scanWg)
-	}
-
-	err = s.ToManifest(ctx, outFile, scanProgress)
-
-	scanWg.Wait()
-
+	err = mfa.runScanPhase(ctx, cmd, s, outFile)
 	if err != nil {
-		return fmt.Errorf("generate manifest: %w", err)
+		return err
 	}
 
 	// Close file before rename to ensure all data is flushed

internal/cli/mfer.go

@@ -211,9 +211,10 @@ func (mfa *CLIApp) generateCommand() *cli.Command {
 			},
 			&cli.StringFlag{
 				Name:    "output",
-				Value:   defaultManifestName,
 				Aliases: []string{"o"},
-				Usage:   "Specify output filename",
+				Usage: "File to write the manifest to (default: index.mf in " +
+					"the directory given, or beside the file given; with no " +
+					"path or several, index.mf in the current directory)",
 			},
 			&cli.BoolFlag{
 				Name:    "force",

mfer/scanner.go

@@ -160,7 +160,9 @@ func (s *Scanner) EnumeratePath(
 	return s.enumerateFS(afs, abs, progress)
 }
 
-// EnumeratePaths walks multiple directory paths and adds all files to the scanner.
+// EnumeratePaths adds to the scanner the files under each directory path,
+// listed by their paths under it, and each file path, listed by its name
+// as EnumerateFile lists it.
 // If progress is non-nil, status updates are sent as files are discovered.
 // The progress channel is closed when the method returns.
 func (s *Scanner) EnumeratePaths(
@@ -177,9 +179,19 @@ func (s *Scanner) EnumeratePaths(
 			return err
 		}
 
-		afs := afero.NewReadOnlyFs(afero.NewBasePathFs(s.fs, abs))
+		info, err := s.fs.Stat(abs)
+		if err != nil {
+			return err
+		}
+
+		if info.IsDir() {
+			afs := afero.NewReadOnlyFs(afero.NewBasePathFs(s.fs, abs))
+			err = s.enumerateFS(afs, abs, progress)
+		} else {
+			err = s.enumerateFileWithInfo(
+				filepath.Base(abs), filepath.Dir(abs), info, progress)
+		}
 
-		err = s.enumerateFS(afs, abs, progress)
 		if err != nil {
 			return err
 		}

mfer/scanner_test.go

@@ -134,6 +134,28 @@ func TestScannerEnumeratePaths(t *testing.T) {
 	assert.Equal(t, FileCount(2), s.FileCount())
 }
 
+// TestScannerEnumeratePathsFile gives EnumeratePaths a directory and a
+// file: the file is listed by its name, as EnumerateFile lists it.
+func TestScannerEnumeratePathsFile(t *testing.T) {
+	t.Parallel()
+
+	fs := afero.NewMemMapFs()
+	require.NoError(t, fs.MkdirAll("/dir/sub", 0o755))
+	require.NoError(t, fs.MkdirAll("/other", 0o755))
+	require.NoError(t, afero.WriteFile(fs, "/dir/sub/one.txt", []byte("1"), 0o644))
+	require.NoError(t, afero.WriteFile(fs, "/other/two.txt", []byte("2"), 0o644))
+
+	s := NewScannerWithOptions(&ScannerOptions{Fs: fs})
+	require.NoError(t, s.EnumeratePaths(nil, "/dir", "/other/two.txt"))
+
+	paths := make([]RelFilePath, 0, s.FileCount())
+	for _, f := range s.Files() {
+		paths = append(paths, f.Path)
+	}
+
+	assert.Equal(t, []RelFilePath{"sub/one.txt", "two.txt"}, paths)
+}
+
 func TestScannerExcludeDotfiles(t *testing.T) {
 	t.Parallel()