fix: allow passing an array as sass / scss importer

[j000]

Description

This change allows passing an array with multiple custom importers. Fixes #3526.

Additional context

JavaScript does not mind passing undefined to concat, so additional checks are not needed. In that case shallow copy is created, but it does not matter here.

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What is the purpose of this pull request?

• Bug fix
• New Feature
• Documentation update
• Other

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• Read the Contributing Guidelines.
• Read the Pull Request Guidelines and follow the Commit Convention.
• Check that there isn't already a PR that solves the problem the same way to avoid creating a duplicate.
• Provide a description in this PR that addresses what the PR is solving, or reference the issue that it solves (e.g. fixes #123).
• Ideally, include relevant tests that fail without this PR but pass with it.

[Shinigami92]

If options.importer would be undefined here, this would add an undefined value to the array 🤔
Do we really want this non-null assertion here?

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Beside that, does this really fix the issue? And if so: why?

[patak-dev]

I was thinking on something like this to fix the issue:

  const importer = [internalImporter]
  if (options.importer) {
    if( Array.isArray(options.importer) ) {
      importer.push(...options.importer)
    }
    else {
      importer.push(options.importer)
    }
  }

This could be written in a more compact form but I don't think we will gain in readability.

[Shinigami92]

@patak-js So your solution is exactly the same as before but using push instead of concat?

[patak-dev]

I was thinking on something like this to fix the issue:

  const importer = [internalImporter]
  if (options.importer) {
    if( Array.isArray(options.importer) ) {
      importer.push(...options.importer)
    }
    else {
      importer.push(options.importer)
    }
  }

This could be written in a more compact form but I don't think we will gain in readability.

[j000]

Well, you're right :) Anyway, here is another attempt.