Report only symlinks to regular files as extra files in check (closes #192)

gen never lists a symlink to a directory or a broken one, and lists a
symlink to a regular file only with --follow-symlinks. check's search for
extra files reported every symlink, so on a tree holding a directory
symlink no manifest gen writes could pass check --no-extra-files. The
search now resolves a symlink and reports an entry only if it is a
regular file, which also covers the pipes, sockets and devices it already
left out. The README's check entry says what is reported.

Judgement call: one regular-file check replaces the separate test for
pipes, sockets and devices, so a file of unknown type is not reported
either; gen does not list one.

Model: opus-5-5

README.md

@@ -289,9 +289,12 @@ are now tracked only in the [issues](https://git.eeqj.de/sneak/mfer/issues).
       else the directory holding the manifest, or the current directory for a
       manifest given by URL. So `mfer check /media/drive` checks a drive against
       the `index.mf` at its root, from any directory
-    - warns about each file under the base directory that the manifest does not
-      list, hidden files included; with `--no-extra-files` each one is a failure
-      instead
+    - warns about each regular file under the base directory that the manifest
+      does not list, hidden files included, and each symlink there to a regular
+      file, which gen lists only with `--follow-symlinks`; with
+      `--no-extra-files` each one is a failure instead. A named pipe, socket or
+      device, a symlink to a directory and a broken symlink are never reported,
+      since gen cannot list them
 - `mfer freshen` / `mfer freshen .`
     - rewrites `index.mf` to list the files now under the directory holding it,
       or under the one `--base` names, hashing only the files that are new or

internal/cli/entry_test.go

@@ -960,6 +960,53 @@ func TestCheckWarnsAboutUnlistedFiles(t *testing.T) {
 	}
 }
 
+// TestCheckReportsUnlistedSymlinkToFileOnly makes a tree holding a symlink
+// to a directory, one to a file and a broken one. gen lists the symlink to
+// the file only with --follow-symlinks, and never lists the other two, so
+// check --no-extra-files passes on the manifest gen --follow-symlinks writes
+// and fails only on the symlink to the file on the one plain gen writes.
+func TestCheckReportsUnlistedSymlinkToFileOnly(t *testing.T) {
+	t.Parallel()
+
+	for name, tc := range map[string]struct {
+		genFlags []string
+		exitCode int
+		extras   []string // what check reports as not in the manifest
+	}{
+		"gen --follow-symlinks": {[]string{"--follow-symlinks"}, 0, nil},
+		"plain gen":             {nil, 1, []string{"filelink"}},
+	} {
+		t.Run(name, func(t *testing.T) {
+			t.Parallel()
+
+			dir := t.TempDir()
+			fs := afero.NewOsFs()
+			writeTestTree(t, fs, dir)
+			require.NoError(t, os.Symlink(testSubdir, filepath.Join(dir, "dirlink")))
+			require.NoError(t, os.Symlink(testFileTxt, filepath.Join(dir, "filelink")))
+			require.NoError(t,
+				os.Symlink("nowhere", filepath.Join(dir, "brokenlink")))
+
+			opts := testOpts(slices.Concat(
+				[]string{testApp, cmdGenerate, "-q"}, tc.genFlags, []string{dir},
+			), fs)
+			require.Equal(t, 0, runCLI(opts), "stderr: %s", testStderr(t, opts))
+
+			opts = testOpts([]string{testApp, cmdCheck, testFlagNoExtra, dir}, fs)
+			exitCode := runCLI(opts)
+			stderr := testStderr(t, opts)
+
+			assert.Equal(t, tc.exitCode, exitCode, "stderr: %s", stderr)
+			assert.Equal(t, len(tc.extras),
+				strings.Count(stderr, "not in manifest"), stderr)
+
+			for _, extra := range tc.extras {
+				assert.Contains(t, stderr, "EXTRA: "+extra)
+			}
+		})
+	}
+}
+
 // TestCheckNeverReportsManifest keeps the manifest inside the checked tree,
 // under several names and path spellings, and names the tree both directly
 // and through a symlink: the manifest is never reported, even under

mfer/checker.go

@@ -264,11 +264,12 @@ func (c *Checker) Check(
 	return nil
 }
 
-// FindExtraFiles walks the filesystem and reports files not in the manifest,
-// hidden files and directories included. The manifest file itself is not
-// reported. Anything the search cannot read, such as a directory that cannot
-// be listed, is reported with StatusError and the search goes on. Results are
-// sent to the results channel. The channel is closed when done.
+// FindExtraFiles walks the filesystem and reports the regular files, and
+// symlinks to them, that are not in the manifest, hidden files and
+// directories included. The manifest file itself is not reported. Anything
+// the search cannot read, such as a directory that cannot be listed, is
+// reported with StatusError and the search goes on. Results are sent to the
+// results channel. The channel is closed when done.
 func (c *Checker) FindExtraFiles(ctx context.Context, results chan<- Result) error {
 	if results != nil {
 		defer close(results)
@@ -318,11 +319,6 @@ func (c *Checker) FindExtraFiles(ctx context.Context, results chan<- Result) err
 			return nil
 		}
 
-		// gen never lists a named pipe, a socket or a device.
-		if info.Mode()&(os.ModeNamedPipe|os.ModeSocket|os.ModeDevice) != 0 {
-			return nil
-		}
-
 		// A symlink is compared by what it points to, so a manifest reached
 		// through one is not reported either.
 		if info.Mode()&os.ModeSymlink != 0 {
@@ -332,6 +328,13 @@ func (c *Checker) FindExtraFiles(ctx context.Context, results chan<- Result) err
 			}
 		}
 
+		// gen lists regular files and symlinks to them only, so a named
+		// pipe, a socket, a device, a symlink to a directory and a broken
+		// symlink are never reported.
+		if !info.Mode().IsRegular() {
+			return nil
+		}
+
 		// Skip the manifest file itself, however its path is spelled
 		if os.SameFile(info, c.manifestInfo) {
 			return nil