Add this.fromImport for JS importers

See sass/sass#3055
See webpack-contrib/sass-loader#905

CHANGELOG.md

@@ -1,3 +1,14 @@
+## 1.33.0
+
+### JS API
+
+* The `this` context for importers now has a `fromImport` field, which is `true`
+  if the importer is being invoked from an `@import` and `false` otherwise.
+  Importers should only use this to determine whether to load [import-only
+  files].
+
+[import-only files]: https://sass-lang.com/documentation/at-rules/import#import-only-files
+
 ## 1.32.13
 
 * **Potentially breaking bug fix:** Null values in `@use` and `@forward`

lib/src/importer/node/implementation.dart

@@ -13,6 +13,7 @@ import '../../node/function.dart';
 import '../../node/importer_result.dart';
 import '../../node/utils.dart';
 import '../../util/nullable.dart';
+import '../../node/render_context.dart';
 import '../utils.dart';
 
 /// An importer that encapsulates Node Sass's import logic.
@@ -40,8 +41,12 @@ import '../utils.dart';
 ///   4. Filesystem imports relative to an `includePaths` path.
 ///   5. Filesystem imports relative to a `SASS_PATH` path.
 class NodeImporter {
-  /// The `this` context in which importer functions are invoked.
-  final Object _context;
+  /// The options for the `this` context in which importer functions are
+  /// invoked.
+  ///
+  /// This is typed as [Object] because the public interface of [NodeImporter]
+  /// is shared with the VM, which can't handle JS interop types.
+  final Object _options;
 
   /// The include paths passed in by the user.
   final List<String> _includePaths;
@@ -50,7 +55,7 @@ class NodeImporter {
   final List<JSFunction> _importers;
 
   NodeImporter(
-      this._context, Iterable<String> includePaths, Iterable<Object> importers)
+      this._options, Iterable<String> includePaths, Iterable<Object> importers)
       : _includePaths = List.unmodifiable(_addSassPath(includePaths)),
         _importers = List.unmodifiable(importers.cast());
 
@@ -78,7 +83,8 @@ class NodeImporter {
     // The previous URL is always an absolute file path for filesystem imports.
     var previousString = _previousToString(previous);
     for (var importer in _importers) {
-      var value = call2(importer, _context, url, previousString);
+      var value =
+          call2(importer, _renderContext(forImport), url, previousString);
       if (value != null) {
         return _handleImportResult(url, previous, value, forImport);
       }
@@ -103,7 +109,8 @@ class NodeImporter {
     // The previous URL is always an absolute file path for filesystem imports.
     var previousString = _previousToString(previous);
     for (var importer in _importers) {
-      var value = await _callImporterAsync(importer, url, previousString);
+      var value =
+          await _callImporterAsync(importer, url, previousString, forImport);
       if (value != null) {
         return _handleImportResult(url, previous, value, forImport);
       }
@@ -193,13 +200,17 @@ class NodeImporter {
   }
 
   /// Calls an importer that may or may not be asynchronous.
-  Future<Object?> _callImporterAsync(
-      JSFunction importer, String url, String previousString) async {
+  Future<Object?> _callImporterAsync(JSFunction importer, String url,
+      String previousString, bool forImport) async {
     var completer = Completer<Object>();
 
-    var result = call3(importer, _context, url, previousString,
+    var result = call3(importer, _renderContext(forImport), url, previousString,
         allowInterop(completer.complete));
     if (isUndefined(result)) return await completer.future;
     return result;
   }
+
+  /// Returns the [RenderContext] in which to invoke importers.
+  RenderContext _renderContext(bool fromImport) => RenderContext(
+      options: _options as RenderContextOptions, fromImport: fromImport);
 }

lib/src/importer/node/interface.dart

@@ -5,7 +5,7 @@
 import 'package:tuple/tuple.dart';
 
 class NodeImporter {
-  NodeImporter(Object context, Iterable<String> includePaths,
+  NodeImporter(Object options, Iterable<String> includePaths,
       Iterable<Object> importers);
 
   Tuple2<String, String>? load(String url, Uri? previous, bool forImport) =>

lib/src/node.dart

@@ -204,7 +204,7 @@ List<AsyncCallable> _parseFunctions(RenderOptions options, DateTime start,
           'Invalid signature "$signature": ${error.message}', error.span);
     }
 
-    var context = _contextWithOptions(options, start);
+    var context = RenderContext(options: _contextOptions(options, start));
 
     var fiber = options.fiber;
     if (fiber != null) {
@@ -261,9 +261,8 @@ NodeImporter _parseImporter(RenderOptions options, DateTime start) {
     importers = [options.importer as JSFunction];
   }
 
-  var context = importers.isNotEmpty
-      ? _contextWithOptions(options, start)
-      : const Object();
+  var contextOptions =
+      importers.isNotEmpty ? _contextOptions(options, start) : Object();
 
   var fiber = options.fiber;
   if (fiber != null) {
@@ -288,29 +287,26 @@ NodeImporter _parseImporter(RenderOptions options, DateTime start) {
   }
 
   var includePaths = List<String>.from(options.includePaths ?? []);
-  return NodeImporter(context, includePaths, importers);
+  return NodeImporter(contextOptions, includePaths, importers);
 }
 
-/// Creates a `this` context that contains the render options.
-RenderContext _contextWithOptions(RenderOptions options, DateTime start) {
+/// Creates the [RenderContextOptions] for the `this` context in which custom
+/// functions and importers will be evaluated.
+RenderContextOptions _contextOptions(RenderOptions options, DateTime start) {
   var includePaths = List<String>.from(options.includePaths ?? []);
-  var context = RenderContext(
-      options: RenderContextOptions(
-          file: options.file,
-          data: options.data,
-          includePaths:
-              ([p.current, ...includePaths]).join(isWindows ? ';' : ':'),
-          precision: SassNumber.precision,
-          style: 1,
-          indentType: options.indentType == 'tab' ? 1 : 0,
-          indentWidth: _parseIndentWidth(options.indentWidth) ?? 2,
-          linefeed: _parseLineFeed(options.linefeed).text,
-          result: RenderContextResult(
-              stats: RenderContextResultStats(
-                  start: start.millisecondsSinceEpoch,
-                  entry: options.file ?? 'data'))));
-  context.options.context = context;
-  return context;
+  return RenderContextOptions(
+      file: options.file,
+      data: options.data,
+      includePaths: ([p.current, ...includePaths]).join(isWindows ? ';' : ':'),
+      precision: SassNumber.precision,
+      style: 1,
+      indentType: options.indentType == 'tab' ? 1 : 0,
+      indentWidth: _parseIndentWidth(options.indentWidth) ?? 2,
+      linefeed: _parseLineFeed(options.linefeed).text,
+      result: RenderContextResult(
+          stats: RenderContextResultStats(
+              start: start.millisecondsSinceEpoch,
+              entry: options.file ?? 'data')));
 }
 
 /// Parse [style] into an [OutputStyle].

lib/src/node/render_context.dart

@@ -8,8 +8,10 @@ import 'package:js/js.dart';
 @anonymous
 class RenderContext {
   external RenderContextOptions get options;
+  external bool? get fromImport;
 
-  external factory RenderContext({required RenderContextOptions options});
+  external factory RenderContext(
+      {required RenderContextOptions options, bool? fromImport});
 }
 
 @JS()

lib/src/parse/sass.dart

@@ -414,7 +414,7 @@ class SassParser extends StylesheetParser {
     do {
       containsTab = false;
       containsSpace = false;
-       nextIndentation = 0;
+      nextIndentation = 0;
 
       while (true) {
         var next = scanner.peekChar();

pubspec.yaml

@@ -1,5 +1,5 @@
 name: sass
-version: 1.32.13
+version: 1.33.0-dev
 description: A Sass implementation in Dart.
 author: Sass Team
 homepage: https://github.com/sass/dart-sass

test/node_api/importer_test.dart

@@ -556,6 +556,48 @@ void main() {
             }))));
       });
     });
+
+    group("includes a fromImport field that's", () {
+      test("true for an @import", () {
+        renderSync(RenderOptions(
+            data: '@import "foo"',
+            importer: allowInteropCaptureThis(
+                expectAsync3((RenderContext this_, _, __) {
+              expect(this_.fromImport, isTrue);
+              return NodeImporterResult(contents: '');
+            }))));
+      });
+
+      test("false for a @use", () {
+        renderSync(RenderOptions(
+            data: '@use "foo"',
+            importer: allowInteropCaptureThis(
+                expectAsync3((RenderContext this_, _, __) {
+              expect(this_.fromImport, isFalse);
+              return NodeImporterResult(contents: '');
+            }))));
+      });
+
+      test("false for a @forward", () {
+        renderSync(RenderOptions(
+            data: '@forward "foo"',
+            importer: allowInteropCaptureThis(
+                expectAsync3((RenderContext this_, _, __) {
+              expect(this_.fromImport, isFalse);
+              return NodeImporterResult(contents: '');
+            }))));
+      });
+
+      test("false for meta.load-css()", () {
+        renderSync(RenderOptions(
+            data: '@use "sass:meta"; @include meta.load-css("foo")',
+            importer: allowInteropCaptureThis(
+                expectAsync3((RenderContext this_, _, __) {
+              expect(this_.fromImport, isFalse);
+              return NodeImporterResult(contents: '');
+            }))));
+      });
+    });
   });
 
   group("gracefully handles an error when", () {