[vscode] onEnterRules in languages.configuration are ignored

[planger]

Bug Description:

It looks like onEnterRules in language configurations of VS Code extensions are ignored in Theia.

As the Theia examples include the vscode.python extension, we can use it for testing.

vscode.python defines that hitting enter after e.g. if TRUE: the next line should indent once:

  "onEnterRules": [
    {
      "beforeText": "^\\s*(?:def|class|for|if|elif|else|while|try|with|finally|except|async).*?:\\s*$",
      "action": {
        "indent": "indent"
      }
    }
  ]

Steps to Reproduce:

1. Start for instance the browser-app by running yarn browser start
2. Create a file that ends with .py, such as test.py
3. Type if TRUE: and then hit enter.

In VS Code this is handled correctly:

In Theia, however, this is ignored:

Additional Information

• Operating System: Ubuntu Linux
• Theia Version: Reproduced with master and Theia 1.19

[planger]

On a first glance, it seems to work if (but only if) the language configuration is set programmatically by the extension. That works fine, e.g., for built-in javascript, html, etc.

But it doesn't work if it is set declaratively, e.g. for vscode.python or another extension where I manually added a rule to onEnterRules in order to test previousLineText declaratively via the package.json. For those, the languages.configuration object that comes in at PluginContributionHandler#handleContributions does not contain the onEnterRules.

[planger]

Just to avoid duplicate work: I'll look into this issue in more detail in the next days.