Markdown syntax highlighting in IDE doesn't work for languages that don't have a parser, should fallback to TextMate grammars

[vsiva]

When you have a markdown fenced code block, with say Python code, and you try to render this inside IntelliJ IDEA, it won't show any syntax highlighting. This is because the LexerBasedCodeHighlighter has:

  override fun highlight(code: String, mimeType: MimeType): Flow<AnnotatedString> {
        val language = mimeType.toLanguageOrNull() ?: return flowOf(AnnotatedString(code))

Here, language is null if there's no plugin providing a valid Language.

IntelliJ packages TextMate grammars which are used by the editor in such a case. This code should probably look something like:

    val existingLanguage = mimeType.toLanguageOrNull()

    // Fall back on textmate if no language was found
    val language =
      existingLanguage
        ?: LanguageUtil.findRegisteredLanguage("textmate")
        ?: return flowOf(AnnotatedString(code))

    val fileExtension =
      if (existingLanguage == null) {
        // When using textmate, we have to determine the file extension ourselves from the MimeType
        mimeType.toFileExtension()
      } else {
        language.associatedFileType?.defaultExtension ?: return flowOf(AnnotatedString(code))
      }