No Diagnostics from CodeQL Language Server

[rjt-gupta]

Describe the bug
CodeQL Language Server suppresses diagnostics when a QL pack is loaded

Context:
We are building a headless Python LSP client for CodeQL to automate query synthesis. We are using the CodeQL CLI version 2.20.1 (via codeql execute language-server).

Current Implementation:

1. Server Start: codeql execute language-server --check-errors=ON_CHANGE -v
2. Initialization: Standard initialize request with rootUri pointing to a workspace.
3. Pack Setup: We create a valid codeql-pack.yml in the workspace with dependencies: { codeql/cpp-all: "^4.3.1" } and run codeql pack install.
4. Pack Loading: We send textDocument/didOpen for the codeql-pack.yml file to trigger pack resolution (this successfully fixes "unresolved module" errors).
5. Query Opening: We send textDocument/didOpen for a .ql query file inside the pack.

library: false
name: temp-workspace
version: 0.0.0
dependencies:
  codeql/cpp-all: ^4.3.1

The Issue:
When we do not open the codeql-pack.yml file (Pack Mode inactive), the server reports diagnostics correctly (e.g., "could not resolve module cpp" or syntax errors). However, we no other solution like qlpack.yml was working to correctly point the language server to standard library location, even with --search-path or putting the search path explicitly in initializationOptions

However, as soon as we do open the codeql-pack.yml file (Pack Mode active), the server stops reporting ALL diagnostics for subsequently opened query files.

• Semantic errors (e.g., import non_existent_module) -> 0 diagnostics
• Syntax errors (e.g., select 1 +) -> 0 diagnostics

Observations:

• The server does not send any workspace/configuration requests to the client.
• The server does not send any client/registerCapability requests.
• Providing a valid database path in initializationOptions does not resolve the issue.
• The didOpen for the pack file appears to successfully load the dependencies (because the "unresolved module" error disappears), but it seems to put the diagnostic engine into a silent state.

Question:
Is there a specific LSP notification, configuration option, or initialization parameter required to re-enable continuous diagnostic reporting (--check-errors=ON_CHANGE) after a QL pack has been loaded?

Technical Context:

CodeQL CLI Version: 2.20.1 (implied from dependencies)
Transport: Stdio with JSON-RPC 2.0
OS: Windows 11
Arguments: codeql execute language-server --check-errors=ON_CHANGE -v

Thanks for your time!
Rajat