Extension API: Different Syntax Highlight Schemes for Output Window

[JustinGrote]

Currently the Output Pane syntax highlighting can be performed by having an extension register the text/x-code-output mime type ala https://marketplace.visualstudio.com/itemdetails?itemName=IBM.output-colorizer.

The problem is that there can be only one by one extension for all output windows and as soon as one extension does this it will conflict with others that try to do the same thing. There are multiple extensions (e.g. Azure Functions) that support streaming logs along with standard Git/Terraform/etc. output views, and being able to specify log highlighting on a per output window basis would go a long way to ensuring richer log views and more constant use of the Output Window.

Potential Implementations

1. Add a feature flag to add the window name to the output window mime type. For example if my Window is named Git then its mime type would be text/x-code-output-Git, if my window is named Terraform than mime type would be text/x-code-output-Terraform.

Now .tmlanguage highlighters can be registered on a per window name basis and different extensions can contribute different syntax highlighters for output windows rather than one "Global" one.

This would ensure broadest compatibility and probably least development effort, but more dynamic output window names may be tricky (perhaps allow wildcards in mime type definition for .tmlanguage)

2. Make this more explicit, such as registering an output window handler contribution and having vscode handle it natively, or have the extension specify the handler or mime type for the output window to ensure consistency.

Both 1 and 2 can be implemented together to cover both explicit and implicit specification types.

[sergei-dyshel]

For all interested, I've found a hacky workaround to change highlighting of output panel depending on its contents.

It seems that output channel is implemented as TextEditor which has document property on which you can use setTextDocumentLanguage. The problem is that setting language for this document changes language for all output channels (may be it's the same TextDocument reused or something). So the only way have separate highlighting for different channels is to exploit the fact that only one output can be visible at a time - subscribe to window.onDidChangeActiveTextEditor and apply different language, .e.g

  for (const editor of window.visibleTextEditors) {
    if (editor.document.fileName.startsWith('extension-output'))
      if (editor.document.lineAt(0).text.includes('this is my extension output'))
        vscode.languages.setTextDocumentLanguage(editor.document, 'myLogFormat');
      else
        vscode.languages.setTextDocumentLanguage(editor.document, 'Log');
  }

Also, there is no way to connect between this document/editor and OutputChannel name so one have to analyze text or cache document's name (i.e. extension-output-#7). But at least this workaround can be used to solve existing highlighting conflict between multiple extensions (such as #19561) until proper API is implemented.