Add REVERSE_RELATIVE_FILEPATH snippet variable and expand cross-platform/remote/out-of-workspace test coverage

[Copilot]

Description

Adds a reverse companion to RELATIVE_FILEPATH so snippets can compute a path from the current file back to the workspace folder.

• Snippet variable surface

  • Registered new built-in variable: REVERSE_RELATIVE_FILEPATH.

• Resolution behavior

  • Implemented in ModelBasedVariableResolver using existing label-service relative path behavior.
  • Returns:
    • undefined when the file is not in a workspace folder context.
    • . when the file is at workspace root.
    • .., ../.., etc. (platform separator aware) for nested paths.
  • Refactored resolver control flow to switch and extracted reverse-path computation into a dedicated helper for readability/maintainability.

• Docs and grammar parity

  • Updated snippet variable docs (snippet.md).
  • Updated snippet syntax grammar allowlist (snippets.tmLanguage.json) so the new variable is recognized in snippet JSON.

{
  "Print reverse path": {
    "prefix": "revpath",
    "body": "from ${REVERSE_RELATIVE_FILEPATH}"
  }
}

Testing

• Extended snippet variable tests to cover:
  • out-of-workspace case,
  • workspace-root case,
  • file-above-workspace-root case (relative path remains absolute and reverse resolves to undefined),
  • nested file case (.., ../..),
  • platform-specific separator behavior (including backslash cases),
  • Windows drive-letter path scenarios (C:\...),
  • remote URI scenarios (both in-workspace and out-of-workspace behavior).
• Ran:
  • npm run compile-check-ts-native
  • npm run test-node -- --grep "Snippet Variables Resolver"

[dmitrivMS]

see comments

[dmitrivMS]

@copilot that's it? one test?

[Copilot]

Added broader coverage for REVERSE_RELATIVE_FILEPATH in fc686605 (including deeply nested paths, workspace root, out-of-workspace, and backslash separator behavior).

[dmitrivMS]

@copilot I don't see any tests for Windows paths (C:...).
Also, what happens in remote scenarios?

[Copilot]

Added explicit coverage in 9483cf96/e1f10a2b for Windows drive paths (C:\workspace\dir\sub\text.txt -> ..\\..) and remote URIs: in-workspace remote paths resolve to parent traversal (..), while remote out-of-workspace paths resolve to undefined.

[dmitrivMS]

@copilot we should probably use a switch instead of else if tree here...

[Copilot]

Updated ModelBasedVariableResolver.resolve to use a switch and extracted reverse-path logic into a helper in 6292b69a (with follow-up polish in fc686605).

[dmitrivMS]

@copilot I don't see any tests for Windows paths (C:...).
Also, what happens in remote scenarios?

[dmitrivMS]

@copilot what will happen if file is not in workspace? if it's above workspace?

[Copilot]

For files outside the workspace (including above a workspace root), REVERSE_RELATIVE_FILEPATH resolves to undefined and RELATIVE_FILEPATH stays absolute. I added explicit coverage for the “above workspace” case in 78474ed5.