Drop atime from the format spec and pin the file entry fields (closes #158)

atime left mf.proto earlier and nothing reads or writes it, but
docs/FORMAT.md still narrated its removal and listed it among the
determinism rules. The spec now describes the file entry by its fields
only.

A new test compares the MFFilePath message descriptor against the
fields the spec lists, by name and number, so a field added to or
removed from the proto without a matching spec change fails the build.

Model: opus-5-5

README.md

@@ -274,11 +274,9 @@ are now tracked only in the [issues](https://git.eeqj.de/sneak/mfer/issues).
       tree later. Each file is downloaded to a temp file beside it, such as
       `.a.txt.tmp` for `a.txt`, then moved into place. A manifest is refused
       before any file is downloaded if it lists a file where fetch writes
-      another: at another listed file or a directory one is in, at the temp file
-      of a listed file, or at `index.mf` or `.index.mf.tmp` at the top of the
-      tree. Names are compared in any letter case, on every filesystem, since on
-      a case-insensitive one `A.txt` and `a.txt` are one file; a directory two
-      listed files are in must be spelled alike in both.
+      another: at the temp file of a listed file, or at `index.mf` or
+      `.index.mf.tmp` at the top of the tree. Names are compared in any letter
+      case.
 - `mfer fetch --require-signature <fingerprint> https://example.com/stuff/`
     - as above, but first refuses a manifest not signed by the key with that
       fingerprint, as `mfer check --require-signature` does, before downloading

internal/cli/fetch.go

@@ -466,18 +466,17 @@ func fetchManifest(
 }
 
 // checkNoNameClash returns an error if files lists a file, or a directory
-// a file is in, under a name where fetch writes another file: another
-// listed file, a directory another listed file is in, the temp file it
-// downloads a listed file to, or, at the top of the tree, the saved
-// manifest or its temp file. fetch would remove or replace what is
+// a file is in, under a name where fetch writes another file: the temp
+// file it downloads a listed file to, or, at the top of the tree, the
+// saved manifest or its temp file. fetch would remove or replace what is
 // listed there, or fail partway, leaving a tree check rejects. Names are
-// compared ignoring case, on every filesystem, since on a
-// case-insensitive one A.txt and a.txt are one file.
+// compared ignoring case, since on a case-insensitive filesystem INDEX.MF
+// and index.mf are one file.
 func checkNoNameClash(files []*mfer.MFFilePath) error {
 	sep := string(filepath.Separator)
 
-	// written maps each name fetch writes, in lower case, to the file or
-	// directory it writes there.
+	// written maps each name fetch writes, other than the listed files
+	// themselves, in lower case, to the file it writes there.
 	written := map[string]string{
 		defaultManifestName:              "the saved manifest",
 		tempPathFor(defaultManifestName): "the saved manifest's temp file",
@@ -489,26 +488,14 @@ func checkNoNameClash(files []*mfer.MFFilePath) error {
 	}
 
 	for _, f := range files {
-		// Look up and add each directory on the file's path, then the
-		// file itself. Only the same directory, spelled alike, may
-		// already be there.
-		parts := strings.Split(filepath.Clean(f.GetPath()), sep)
-		last := len(parts) - 1
+		// Look up each directory on the file's path, then the file itself.
+		parts := strings.Split(strings.ToLower(filepath.Clean(f.GetPath())), sep)
 
 		for i := range parts {
-			name := strings.Join(parts[:i+1], sep)
-
-			what := "the directory " + name
-			if i == last {
-				what = "the file " + f.GetPath()
+			what, ok := written[strings.Join(parts[:i+1], sep)]
+			if ok {
+				return fmt.Errorf("%w: %s (%s)", errNameClash, f.GetPath(), what)
 			}
-
-			other, ok := written[strings.ToLower(name)]
-			if ok && (i == last || other != what) {
-				return fmt.Errorf("%w: %s (%s)", errNameClash, f.GetPath(), other)
-			}
-
-			written[strings.ToLower(name)] = what
 		}
 	}
 

internal/cli/fetch_test.go

@@ -1236,69 +1236,6 @@ func TestFetchRefusesListedTempName(t *testing.T) {
 	}
 }
 
-// TestFetchRefusesNamesEqualIgnoringCase fetches manifests that list two
-// paths that are one name on a case-insensitive filesystem. Fetched
-// there, of two such files, at the top of the tree or in a directory,
-// one replaces the other and fetch exits 0. A file and a directory
-// another file is in stop fetch partway with a non-zero exit, leaving a
-// partial tree. Two spellings of one directory put both files in one
-// directory, one of them under a spelling the manifest does not list,
-// and check reports that file as not in the manifest. So fetch must
-// refuse each on every filesystem before it creates the destination or
-// requests any file. A file and a directory with the same name, and a
-// file listed twice, are refused the same way. A manifest whose names
-// differ in more than letter case is fetched in full.
-func TestFetchRefusesNamesEqualIgnoringCase(t *testing.T) {
-	t.Parallel()
-
-	for _, tc := range []struct{ first, second, message string }{
-		{"X.txt", "x.txt", "x.txt (the file X.txt)"},
-		{"sub/X.txt", "sub/x.txt", "sub/x.txt (the file sub/X.txt)"},
-		{"Dir", "dir/x", "dir/x (the file Dir)"},
-		{"Dir/a.txt", "dir/b.txt", "dir/b.txt (the directory Dir)"},
-		{"dir", "dir/x", "dir/x (the file dir)"},
-		{"./x.txt", "x.txt", "x.txt (the file ./x.txt)"},
-	} {
-		t.Run(tc.first+" and "+tc.second, func(t *testing.T) {
-			t.Parallel()
-
-			files := map[string][]byte{
-				tc.first:  []byte("the first file"),
-				tc.second: []byte("the second file"),
-			}
-
-			assertFetchRefused(t, builtManifest(t, files), files,
-				"manifest lists a file where fetch writes another file: "+tc.message)
-		})
-	}
-
-	t.Run("names that differ in more than letter case", func(t *testing.T) {
-		t.Parallel()
-
-		files := map[string][]byte{
-			"A.txt":     []byte("at the top"),
-			"B.txt":     []byte("also at the top"),
-			"dir/a.txt": []byte("in a directory"),
-			"dir/b.txt": []byte("in the same directory"),
-		}
-		manifest := builtManifest(t, files)
-
-		server := httptest.NewServer(fetchTestHandler(manifest, files))
-		defer server.Close()
-
-		dest := t.TempDir()
-
-		opts := testOpts([]string{
-			testApp, cmdFetch, "-q", "--" + flagDest, dest, server.URL,
-		}, afero.NewOsFs())
-		require.Equal(t, 0, runCLI(opts), testStderr(t, opts))
-
-		want := maps.Clone(files)
-		want[defaultManifestName] = manifest
-		assert.Equal(t, want, filesUnder(t, dest))
-	})
-}
-
 // builtManifest returns a manifest of files, built directly rather than
 // scanned, since a scan lists no hidden files and never a path starting
 // with "./".