Expose inImportRule() as the test-only fakeFromImport() function (#1750)

Author: nex3

CHANGELOG.md

@@ -10,10 +10,16 @@
 
 * Deprecate passing non-`deg` units to `color.hwb()`'s `$hue` argument.
 
+### Dart API
+
+* Add a top-level `fakeFromImport()` function for testing custom importers
+  that use `AsyncImporter.fromImport`.
+
 ### JS API
 
 * Add a `charset` option that controls whether or not Sass emits a
   `@charset`/BOM for non-ASCII stylesheets.
+
 * Fix Sass npm package types for TS 4.7+ Node16 and NodeNext module resolution.
 
 ## 1.53.0

lib/sass.dart

@@ -5,6 +5,7 @@
 /// We strongly recommend importing this library with the prefix `sass`.
 library sass;
 
+import 'package:meta/meta.dart';
 import 'package:package_config/package_config_types.dart';
 import 'package:source_maps/source_maps.dart';
 
@@ -15,6 +16,7 @@ import 'src/compile_result.dart';
 import 'src/exception.dart';
 import 'src/import_cache.dart';
 import 'src/importer.dart';
+import 'src/importer/utils.dart';
 import 'src/logger.dart';
 import 'src/syntax.dart';
 import 'src/util/nullable.dart';
@@ -474,3 +476,10 @@ Future<String> compileStringAsync(
   result.sourceMap.andThen(sourceMap);
   return result.css;
 }
+
+/// Runs [callback] in a context where [AsyncImporter.fromImport] returns
+/// `true`.
+///
+/// This is only intended for use when testing custom importers.
+@visibleForTesting
+T fakeFromImport<T>(T callback()) => inImportRule(callback);

lib/src/importer/utils.dart

@@ -17,7 +17,7 @@ import '../io.dart';
 /// removed, at which point we can delete this and have one consistent behavior.
 bool get fromImport => Zone.current[#_inImportRule] as bool? ?? false;
 
-/// Runs [callback] in a context where [inImportRule] returns `true` and
+/// Runs [callback] in a context where [fromImport] returns `true` and
 /// [resolveImportPath] uses `@import` semantics rather than `@use` semantics.
 T inImportRule<T>(T callback()) =>
     runZoned(callback, zoneValues: {#_inImportRule: true});