dart-sass problem with imports within absolute path imports

[Moritz Kobel]

We use frontend dependencies as webjars.

There we import resources:

@import "/webjars/bootstrap/4.6.0-1/scss/mixins";

The referenced file contains relative imports (e.g. @import "vendor/rfs";).

This works fine with sass-asset-pipeline, but not with sass-dart-asset-pipeline #287.

The problem can be reproduced even without webjars:

create sass-dart-asset-pipeline/assets/stylesheets/absolute-import/main.scss:

@import "/bootstrap/bootstrap";

create test in sass-dart-asset-pipeline/src/test/groovy/asset/pipeline/dart/SassProcessorSpec.groovy

void "should compile absolute imports"() {
		given:
		AssetPipelineConfigHolder.resolvers = []
		AssetPipelineConfigHolder.registerResolver(new FileSystemAssetResolver('test','assets'))
		def assetFile = AssetHelper.fileForFullName('absolute-import/main.scss')
		def processor = new SassProcessor()
		when:
		def output = processor.process(assetFile.inputStream.text,assetFile)
		then:
		output.contains('Twitter')
}

Then the test fails (the absolute bootstrap.scss is found, but inside the import cannot be resolved):

$ ./gradlew :sass-dart-asset-pipeline:test
[...]

> Task :sass-dart-asset-pipeline:test

asset.pipeline.dart.SassProcessorSpec > should compile absolute imports STANDARD_ERROR
    [Test worker] ERROR asset.pipeline.dart.SassAssetFileLoader - Unable to find the asset for variables imported by absolute-import//bootstrap/bootstrap

asset.pipeline.dart.SassProcessorSpec > should compile absolute imports FAILED
    com.caoccao.javet.exceptions.JavetExecutionException: Error: Cannot invoke method getByteDigest() on null object
      ╷
    8 │ @import "variables";
      │         ^^^^^^^^^^^
      ╵
      /bootstrap/bootstrap 8:9  @import
      stdin 1:9                 root stylesheet
        at com.caoccao.javet.interop.V8Runtime.execute(V8Runtime.java:828)
        at com.caoccao.javet.interop.executors.V8StringExecutor.execute(V8StringExecutor.java:77)
        at com.caoccao.javet.interop.IV8Executable.executeVoid(IV8Executable.java:159)
        at asset.pipeline.dart.SassProcessor.process(SassProcessor.groovy:104)
        at asset.pipeline.dart.SassProcessorSpec.should compile absolute imports(SassProcessorSpec.groovy:115)

7 tests completed, 1 failed

> Task :sass-dart-asset-pipeline:test FAILED

Is this an sass-dart-asset-pipeline implementation issue or can I fix the behaviour within the project configuration?