Go extractor does not support build-mode: none, preventing overlay/incremental analysis on PRs

Go extractor の build-mode の処理と、issue で参照されている buildless オプションから始めます。宣言されているオプション（trap.cache.* を含む）について codeql-extractor.yml を確認します。build-mode: none で再現し、既存の workaround と抽出動作を比較します。Go がそのモードを受け入れ、これらの環境変数なしで overlay またはインクリメンタル抽出が機能すれば完了です。

Problem

The Go extractor (CodeQL CLI 2.25.1) does not support build-mode: none:

A fatal error occurred: Go does not support the none build mode.
Please try using one of the following build modes instead: autobuild, manual.

This means Go cannot benefit from overlay/incremental analysis on pull requests. JavaScript gets this automatically — in our monorepo we see Overlay filter removed 4311 out of 4312 files from extraction on JS PRs, reducing a full extraction to just the changed files. Go still does a full extraction of every package on every PR (~2.5 min for autobuild + ~1.5 min for analysis in a large monorepo).

Current workaround

We use legacy env var hacks to skip the actual go build:

env:
  CODEQL_EXTRACTOR_GO_FAST_PACKAGE_INFO: y
  CODEQL_EXTRACTOR_GO_BUILD_COMMAND: false

This avoids compilation but still runs full type extraction for every Go package on every PR.

Expected behavior

Setting build-mode: none should work for Go, enabling overlay/incremental analysis on PRs (as it already does for JavaScript/TypeScript). The Go extractor already has a buildless/standalone extraction path (DEPRECATED: Use --build-mode none instead appears in the extractor options for the buildless flag), so the extraction capability exists — it just isn't wired up to accept build-mode: none.

Additional context

• We also noticed that Go's extractor does not declare trap.cache.* options in codeql-extractor.yml, so TRAP caching is also unavailable for Go.
• The v3→v4 action upgrade enabled overlay for JS automatically, but there's no path to get the same benefit for Go.
• codeql-action v4.35.1, CodeQL CLI 2.25.1