Contributing a language mapping causes VS Code to activate your extension on that language

[mjbvz]

Bug
The Python extension contributes the following language entry in its package.json:

     {
                "filenames": [
                    "Pipfile.lock"
                ],
                "id": "json"
            }

This seems to cause the python extension to be activated whenever a json file is opened, even though the extension does not provide any json language support

This was possibly caused by the move to automatic activation events

[joyceerhl]

@alexdima I think my initial implementation of onLanguage implicit activation was perhaps too naive. There seem to be a few issues:

• It's possible to have a language configuration extension that doesn't contribute any code, and we would now attempt to activate such an extension (this is a noop if there is no main/browser entrypoint in package.json, but results in unnecessary activation if all that's required is a language configuration)
• the bigger issue is that an extension which contributes extensions, filenames, filenamePatterns, firstLine, or mimeTypes for a language will now get activated anytime the language appears
  • I think it's maybe reasonable to preserve the existing implicit activation behavior if an alias is defined
  • for all of the others, we shouldn't infer onLanguage, or we should perhaps keep track of the filenames/filenamePatterns etc and activate the extension with the language contribution matching the specified pattern?

I know of at least two extensions which are impacted by the current behavior

• MakeCode
• Python

[alexdima]

I think it's maybe reasonable to preserve the existing implicit activation behavior if an alias is defined [...] for all of the others, we shouldn't infer onLanguage

👍 This makes good sense to me. We will infer onLanguage:X only for the one which is the "main" language definition, and the best evidence of that is the alias property. I wouldn't do anything beyond that (i.e. tracking filenames, patterns, etc.)

[joyceerhl]

infer onLanguage:X only for the one which is the "main" language definition

Would the presence of the configuration property be better evidence of a contribution being the main language definition?

[RedCMD]

injection based syntax highlighting can still have a configuration file