configurationDefaults should overwrite values, not entire nested objects.

[vanowm]

Does this issue occur when all extensions are disabled?: No

When extension specifies configurationDefaults in package.json its content simply overrides existing data. This means if it contains nested objects, it takes the root of the object and copies it, instead overwriting values for each property of the object (aka merging)
This creates an issue when two extensions have the same root object, but different children. For example package.json of extension one

{
  "contributes": {
    "configurationDefaults": {
      "editor.tokenColorCustomizations": {
        "textMateRules": [
          {
            "scope": "my-extension-one",
            "settings": {
              "foreground": "green"
            }
          }
        ]
      }
    }
  }
}

and extension two:

{
  "contributes": {
    "configurationDefaults": {
      "editor.tokenColorCustomizations": {
        "[*Dark*]": {
          "textMateRules": [
            {
              "scope": "my-extension-two",
              "settings": {
                "foreground": "red"
              }
            }
          ]
        }
      }
    }
  }
}

VSCode will take the whole editor.tokenColorCustomizations object and overwrite it. Instead of merging them with another.
So in my tests one extension will override another and there is seems to be no telling which one will dominate when, sometimes it's one, another time is the other.

Also, if user config has the same multi-level-object setting, then it will override enterally the default config of the extension, instead of just the matching properties.

[RedCMD]

Can confirm
seems like an oversight

[vanowm]

All this time I was under impression config is a simple json structure where everything is essentially an object and can be accessed as such, like you could access children data by simply adding them as dot separated string: editor.tokenColorCustomizations.textMateRules.
It's incorrect, there is no such setting, there is only a editor.tokenColorCustomizations which might have a value as an object with a property textMateRules.
Therefore, you can't access children without getting whole setting value first.

This begs another question, what do we want it to merge, immediate children only or every nested child as well?

[vscodenpa]

We closed this issue because we don't plan to address it in the foreseeable future. If you disagree and feel that this issue is crucial: we are happy to listen and to reconsider.

If you wonder what we are up to, please see our roadmap and issue reporting guidelines.

Thanks for your understanding, and happy coding!

[sandy081]

This is now supported - #201603