Fix --watch not recompiling sources modified during a compilation (#2850)

Sources modified while a compilation is in progress are older than the output that compilation writes when it finishes, so --watch and --update wrongly consider them up to date and skip recompilation. Set the output's modification time to when compilation started so such sources compare as newer, including across restarts.

---------

Co-authored-by: Natalie Weizenbaum <nweiz@google.com>

Author: corebonts

CHANGELOG.md

@@ -1,4 +1,4 @@
-## 1.104.1-dev
+## 1.104.1
 
 * Fix a bug where loud comments before `@use` rules could be emitted multiple
   times under certain circumstances.
@@ -14,6 +14,11 @@
   This fixes a bug where `--watch` mode could enter an infinite loop recompiling
   the same CSS file over and over.
 
+* Sass now sets the modification time of output files to the time compilation
+  *started* rather than the time it *ended*. This ensures that, if a source file
+  is modified during compilation, `--watch` and `--update` mode will recompile
+  the outputs to include the new source file contents.
+
 ## 1.104.0
 
 * **Potentially breaking compatibility fix:** Colors now convert the special

lib/src/executable/compile_stylesheet.dart

@@ -85,6 +85,7 @@ Future<void> _compileStylesheetWithoutErrorHandling(
   String? destination, {
   bool ifModified = false,
 }) async {
+  var compilationStarted = DateTime.now();
   var importer = FilesystemImporter.cwd;
   if (ifModified) {
     try {
@@ -192,18 +193,25 @@ Future<void> _compileStylesheetWithoutErrorHandling(
       } else {
         ensureDir(p.dirname(destination));
         writeFile(destination, "${error.toCssString()}\n");
+        _trySetModificationTime(destination, compilationStarted);
       }
     }
     rethrow;
   }
 
   var css = result.css;
-  css += _writeSourceMap(options, result.sourceMap, destination);
+  css += _writeSourceMap(
+    options,
+    result.sourceMap,
+    destination,
+    compilationStarted,
+  );
   if (destination == null) {
     if (css.isNotEmpty) print(css);
   } else {
     ensureDir(p.dirname(destination));
     writeFile(destination, "$css\n");
+    _trySetModificationTime(destination, compilationStarted);
   }
 
   if (options.quiet || (!options.update && !options.watch)) return;
@@ -238,6 +246,7 @@ String _writeSourceMap(
   ExecutableOptions options,
   SingleMapping? sourceMap,
   String? destination,
+  DateTime compilationStarted,
 ) {
   if (sourceMap == null) return "";
 
@@ -268,6 +277,7 @@ String _writeSourceMap(
     var sourceMapPath = '${destination!}.map';
     ensureDir(p.dirname(sourceMapPath));
     writeFile(sourceMapPath, sourceMapText);
+    _trySetModificationTime(sourceMapPath, compilationStarted);
 
     url = p.toUri(p.relative(sourceMapPath, from: p.dirname(destination)));
   }
@@ -289,6 +299,20 @@ void _tryDelete(String path) {
   }
 }
 
+/// Backdate [path] to [time], ignoring failures.
+///
+/// We use the time that a compilation started as the modification time for
+/// output files so that if a source file is modified during compilation, it
+/// will be considered newer than the output and compilation will run again
+/// (immediately for `--watch` or on the next invocation for `--update`).
+void _trySetModificationTime(String path, DateTime time) {
+  try {
+    setModificationTime(path, time);
+  } on FileSystemException {
+    // The output is still usable with its actual modification time.
+  }
+}
+
 /// Return a Record of `(exitCode, error, stackTrace)` for the given error.
 (int, String, String?) _getErrorWithStackTrace(
   int exitCode,

lib/src/io/interface.dart

@@ -81,6 +81,9 @@ String realpath(String path) => throw '';
 /// Returns the modification time of the file at [path].
 DateTime modificationTime(String path) => throw '';
 
+/// Sets the modification time of the file at [path] to [time].
+void setModificationTime(String path, DateTime time) => throw '';
+
 /// Returns the value of the environment variable with the given [name], or
 /// `null` if it's not set.
 String? getEnvironmentVariable(String name) => throw '';

lib/src/io/js.dart

@@ -248,6 +248,18 @@ DateTime modificationTime(String path) {
   );
 }
 
+void setModificationTime(String path, DateTime time) {
+  if (!isNodeJs) {
+    throw UnsupportedError(
+      "setModificationTime() is only supported on Node.js",
+    );
+  }
+  return _systemErrorToFileSystemException(() {
+    var seconds = time.millisecondsSinceEpoch / 1000;
+    fs.utimesSync(path, seconds, seconds);
+  });
+}
+
 String? getEnvironmentVariable(String name) {
   var env = _process?.env;
   return env == null ? null : getProperty(env as Object, name) as String?;

lib/src/io/vm.dart

@@ -101,6 +101,9 @@ DateTime modificationTime(String path) {
   return stat.modified;
 }
 
+void setModificationTime(String path, DateTime time) =>
+    io.File(path).setLastModifiedSync(time);
+
 String? getEnvironmentVariable(String name) => io.Platform.environment[name];
 
 Future<Stream<WatchEvent>> watchDir(String path, {bool poll = false}) async {

pkg/sass-parser/CHANGELOG.md

@@ -1,4 +1,4 @@
-## 0.4.55-dev
+## 0.4.55
 
 * Omit an extra newline that was being added to the end of `Rule.selector` in
   the indented syntax.

pkg/sass-parser/package.json

@@ -1,6 +1,6 @@
 {
   "name": "sass-parser",
-  "version": "0.4.55-dev",
+  "version": "0.4.55",
   "description": "A PostCSS-compatible wrapper of the official Sass parser",
   "repository": "sass/dart-sass",
   "author": "Google Inc.",

pkg/sass_api/CHANGELOG.md

@@ -1,4 +1,4 @@
-## 17.10.1-dev
+## 17.10.1
 
 * Omit an extra newline that was being added to the end of `StyleRule.selector`
   in the indented syntax.

pkg/sass_api/pubspec.yaml

@@ -2,7 +2,7 @@ name: sass_api
 # Note: Every time we add a new Sass AST node, we need to bump the *major*
 # version because it's a breaking change for anyone who's implementing the
 # visitor interface(s).
-version: 17.10.1-dev
+version: 17.10.1
 description: Additional APIs for Dart Sass.
 homepage: https://github.com/sass/dart-sass
 

pubspec.yaml

@@ -1,5 +1,5 @@
 name: sass
-version: 1.104.1-dev
+version: 1.104.1
 description: A Sass implementation in Dart.
 homepage: https://github.com/sass/dart-sass