Let documentSymbol return the correct results when mergeable elements are used

[keyboardDrummer]

Previously, the documentSymbol results would grow exponentially in size when using multiple elements with the same name such as in some of the examples for declaration merging.

Note that this implementation, although in line with the existing implementation, is different from what VSCode does. An example, given the code:

interface Box {
    height: number;
    width: number;
}

interface Box {
    scale: number;
}

VSCode will show:

Box
  height
  width
  scale

While this implementation shows:

Box
  height
  width
Box
  scale

[gitpod-io-legacy-app]

Open in Gitpod - starts a development workspace for this pull request in code review mode and opens it in a browser IDE.

[akosyakov]

Can you elaborate what was the issue? I cannot reproduce it.

I've tried the master state and latest VS Code and they both show:

Box
  height
  width
Box
  scale

[keyboardDrummer]

Hmm. Curious that both VSCode and.. Theia? still produce correct behavior. However, running the testcases added in the PR in the master code shows that this LSP server had incorrect behavior. You will see that:

interface Box {
    height: number;
    width: number;
}

interface Box {
    scale: number;
}

Returns something like

Box
  height
  width
  scale
Box
  height
  width
  scale

And

interface Box {
  width: number
}
interface Box {
  width: number
}

Returns

Box
  width
  width
Box
  width
  width

[akosyakov]

@keyboardDrummer thanks for taking time to check, indeed I was able to reproduce it by reverting changes to document-symbol and running new tests

[akosyakov]

We should probably do the same here for clients who cannot handle hierarchical symbols, can be a separate PR.