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Problem
While using `mcpls` in a C++ project I noticed that it always return
the following error when calling get references from a '.h' header file:
Error: tool call error: tool call failed for `mcpls/get_references`
Caused by:
tools/call failed: Mcp error: -32603: no LSP server configured for language: c
After reviewing the documentation and creating an mcpls.toml with the
following, it continued to not work
[[lsp_servers]]
language_id = "cpp"
command = "clangd"
args = ["--background-index", "--clang-tidy"]
file_patterns = ["**/*.cpp", "**/*.cc", "**/*.cxx", "**/*.hpp", "**/*.c", "**/*.h"]
# and/or with
[[lsp_servers]]
language_id = "c"
command = "clangd"
args = ["--background-index", "--clang-tidy"]
file_patterns = ["**/*.c", "**/*.h"]
With the above changing resulting in the language detection for matching
file patterns to "plaintext"
Error: tool call error: tool call failed for `mcpls/get_references`
Caused by:
tools/call failed: Mcp error: -32603: no LSP server configured for language: plaintext
What changed
- serve() now initializes the translator with an effective extension map
built from both workspace mappings and LSP server file patterns:
- crates/mcpls-core/src/lib.rs:114:114
- Added ServerConfig::build_effective_extension_map() to overlay
extensions inferred from file_patterns:
- crates/mcpls-core/src/config/mod.rs:287:287
- Added a small parser for simple glob extensions (e.g. **/*.h, *.c):
- crates/mcpls-core/src/config/mod.rs:123:123
Tests added
- Pattern-derived mapping overrides default extension mapping (.c/.h -> cpp):
- crates/mcpls-core/src/config/mod.rs:700:700
- Complex non-simple patterns are ignored safely:
- crates/mcpls-core/src/config/mod.rs:721:721
Verification
- New tests passed.
- Full mcpls-core unit/integration tests passed.
- Existing unrelated doctest failure remains in lsp/types.rs (pre-existing visibility issue).
Fix was implemented by Codex
Add direct unit coverage for extract_extension_from_pattern edge cases, including empty input, no-dot patterns, dotfiles, and multi-dot filenames. Tighten the parser to reject dotfile basenames so hidden files like .gitignore do not get treated as language extensions. Update the translator initialization test to assert against build_effective_extension_map(), which matches the runtime code path introduced by the earlier file_patterns fix. Document the resulting C/C++ language detection behavior change in CHANGELOG.md.
Make get_diagnostics capability-aware so servers without pull diagnostics support fall back to cached published diagnostics instead of surfacing -32601. Wire LSP notification forwarding into normal server startup so publishDiagnostics, log messages, and showMessage notifications populate the translator cache during serve(). Add focused tests for notification ingestion and cached diagnostics fallback, and clarify the MCP tool description to reflect the new behavior.
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Codex called this a "fix" though i think it might be more of new functionality. The basic utility is that using Clangd, get_diagnostics calls an unsupported method; this change redirects it to the get_cached_diagnostics silently. In my workflow and perhaps a better solution is to direct codex/claude to only use the get_cached_diagnostics in the first place; at the moment I implement a Usage reference for your mcpls in my AGENTS.md files over multiple projects (Rust, C, C++ and Go) and the agents tend to encounter language specific failures from time to time. |
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Description
Fix get_diagnostics for language servers that do not support pull diagnostics, such
as clangd in this C++ setup.
The change makes diagnostics retrieval capability-aware: when a server supports
textDocument/diagnostic, mcpls uses it; otherwise it falls back to cached
textDocument/publishDiagnostics results instead of returning -32601 method not found.
It also wires LSP notification forwarding into normal server startup so published
diagnostics, logs, and messages are actually captured during serve().
Type of Change
change)
Related Issues
Fixes #(issue number)
Checklist
Additional Notes
unsupported
publishDiagnostics, window/logMessage, and window/showMessage are available during
a real session.