LSP diagnostics waits hardcoded at 5s/10s: slow servers return no diagnostics, indistinguishable from a clean file

Summary

The diagnostics wait timeouts in packages/opencode/src/lsp/client.ts are hardcoded at 5s (document) and 10s (full). For language servers that need longer to parse a translation unit, the client always gives up first and returns no diagnostics — which is indistinguishable from "the file is clean".

This is a correctness problem rather than a performance one: an agent consuming the LSP cannot tell "no problems found" from "we stopped waiting", so it reports false confidence or stops trusting the tool.

// packages/opencode/src/lsp/client.ts:14-15
const DIAGNOSTICS_DOCUMENT_WAIT_TIMEOUT_MS = 5_000
const DIAGNOSTICS_FULL_WAIT_TIMEOUT_MS = 10_000

Environment

• opencode 1.18.4 (also reproduced against dev @ 284214c)
• clangd 21.1.8, Linux x64
• Unreal Engine 5 game project, 23,382-entry compile_commands.json

Reproduction

Any C++ file in a large Unreal project. One translation unit pulls in ~3,764 transitive headers, and clangd needs roughly 20s to parse it — measured directly over stdio LSP, independent of opencode:

query	time
first open of a UE file (cold)	19–25s
same file again, still open	0.00s
a sibling file in the same module	19.03s

Against opencode:

$ opencode debug lsp diagnostics /path/to/HGGameUserSettings.cpp
{
  "/path/to/.clangd": []
}

The requested file is absent from the result entirely, after ~11s — consistent with 5s + 10s. The same file checked with the real compiler (clang++ -fsyntax-only, using the flags from compile_commands.json) compiles cleanly, and a deliberately broken variant reports its error correctly, so clangd and the configuration are both fine.

Not caused by configuration

Ruled out by measurement:

• Compile database staleness — 442 of 452 files present; clangd interpolates flags for the rest and returns correct symbols.
• Database size — scoping it 8.5× (23,382 → 2,741 entries) moved parse time only 27.1s → 24.5s.
• .clangd force-include — removing it gives 14.2s → 10.5s and reintroduces 82 false errors. Still at the threshold.
• --pch-storage=memory — no change (13.9s).

There is no configuration option to extend the wait.

Related

• #23982 — LSP initialize timeout too short for Java/Gradle (~15s vs ~114s needed). Same class of problem on a different constant, which suggests this isn't specific to C++ or to Unreal.

Suggested fix

Make the two waits configurable per LSP server, defaulting to the current constants so nothing changes for anyone who doesn't opt in:

"lsp": {
  "clangd": {
    "command": ["clangd", "--compile-commands-dir=..."],
    "timeout": { "document": 60000, "full": 120000 }
  }
}

With that applied locally, the same command returns the real diagnostic in 13s:

Error [3:13] Use of undeclared identifier 'this_symbol_does_not_exist'

I have a working patch (~35 lines across 5 files) and am happy to open a PR against this issue.