lib/ignore: Add central check for internal files, used in scanning, pulling and requests

GitHub-Pull-Request: https://github.com/syncthing/syncthing/pull/3779

lib/ignore/ignore.go

@@ -401,3 +401,20 @@ func parseIgnoreFile(fd io.Reader, currentFile string, modtimes map[string]time.
 
 	return patterns, nil
 }
+
+// IsInternal returns true if the file, as a path relative to the folder
+// root, represents an internal file that should always be ignored. The file
+// path must be clean (i.e., in canonical shortest form).
+func IsInternal(file string) bool {
+	internals := []string{".stfolder", ".stignore", ".stversions"}
+	pathSep := string(os.PathSeparator)
+	for _, internal := range internals {
+		if file == internal {
+			return true
+		}
+		if strings.HasPrefix(file, internal+pathSep) {
+			return true
+		}
+	}
+	return false
+}

lib/ignore/ignore_test.go

@@ -812,3 +812,34 @@ func TestGobwasGlobIssue18(t *testing.T) {
 		}
 	}
 }
+
+func TestIsInternal(t *testing.T) {
+	cases := []struct {
+		file     string
+		internal bool
+	}{
+		{".stfolder", true},
+		{".stignore", true},
+		{".stversions", true},
+		{".stfolder/foo", true},
+		{".stignore/foo", true},
+		{".stversions/foo", true},
+
+		{".stfolderfoo", false},
+		{".stignorefoo", false},
+		{".stversionsfoo", false},
+		{"foo.stfolder", false},
+		{"foo.stignore", false},
+		{"foo.stversions", false},
+		{"foo/.stfolder", false},
+		{"foo/.stignore", false},
+		{"foo/.stversions", false},
+	}
+
+	for _, tc := range cases {
+		res := IsInternal(filepath.FromSlash(tc.file))
+		if res != tc.internal {
+			t.Errorf("Unexpected result: IsInteral(%q): %v should be %v", tc.file, res, tc.internal)
+		}
+	}
+}