Inconsistency in workspace folder URIs

[kamrann]

This is my first experience trying to write an extension (LSP client) for VS Code. My Javascript experience is minimal.

Here's what I'm seeing (VS Code desktop on Windows):

• Add folder to workspace: C:/somewhere/x
  LSP Initialize sends workspaceFolders: [file:///workspace]
• Again, Add folder to workspace: C:/somewhere/y
  LSP workspaceFoldersChanged adds [file:///c%3A/somewhere/y]
  Why the different format?
• Again, Add folder to workspace: C:/somewhere/z
  LSP workspaceFoldersChanged adds [file:///c%3A/somewhere/z]
• Remove folder from workspace: C:/somewhere/x
  LSP server restarted
  Initialize sends workspaceFolders: [file:///workspace/y, file:///workspace/z]
  So now the exact same folders have suddenly become virtual?

From this point, further 'Add folder to workspace' invocations can yield either a file:///workspace/... or a file:///c%3A//..., which one I get is seemingly arbitrary.

On vscode.dev, the behaviour is different yet again. Opening a local folder yields URIs of the form file:///x. Unless I open a remote Github folder, in which case it's back to file:///workspace.

If these URIs were just opaque identifiers then it would merely be bizarre without being a major problem. But since an LSP server needs to be able to map between URIs and filepaths, this behaviour seems to make it impossible to create an extension that behaves reliably. Am I missing something?