ci(codeql): force a clean recompile every run#41
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CodeQL was failing with "could not process any code written in Java/Kotlin" on PRs that touched no Java source — the README PR (#40) and the release-cut commit (#39, which only edits CHANGELOG.md). Diagnosis: gradle/actions/setup-gradle@v6 restores the build cache on every run. README- and CHANGELOG-only changes leave every input to the JavaCompile task identical, so Gradle reports the `classes` task as UP-TO-DATE and runs zero `javac` invocations. CodeQL's Java tracer wraps `javac`; no invocations means no extracted classes, which surfaces as the empty-database error at the analyze step. Confirmed by the run-duration pattern in `gh run list --workflow=codeql.yml`: - failing runs (#39 release-cut, #40 README) finished in ~1 min - successful runs (#35-#38 feature PRs that touched src/) took ~2 min The minute of "missing" wall-clock is exactly the javac step that didn't run. Fix: `--no-build-cache clean classes` forces a recompile every CodeQL invocation. Drops a `clean` task ahead of `classes` to guarantee no UP-TO-DATE skip, and `--no-build-cache` is belt-and-braces against the setup-gradle action's cache restore. Slightly slower CodeQL runs (~30s more on cold compile) but the analyze step gets real javac output to extract from.
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Summary
CodeQL was failing with "could not process any code written in Java/Kotlin" on PRs that touched no Java source — the README PR (#40) and the release-cut commit on `main` (#39, which only edits `CHANGELOG.md`).
Diagnosis
`gradle/actions/setup-gradle@v6` restores the build cache on every run. README- and CHANGELOG-only changes leave every input to the `JavaCompile` task identical, so Gradle reports the `classes` task as `UP-TO-DATE` and runs zero `javac` invocations. CodeQL's Java tracer wraps `javac`; no invocations means no extracted classes, which surfaces as the empty-database error at the analyze step.
Confirmed by the run-duration pattern in `gh run list --workflow=codeql.yml --limit=5`:
The minute of "missing" wall-clock on the failing runs is exactly the `javac` step that didn't execute. (The release-cut PR branch succeeded only because it was the first run after the previous javac compile shifted enough inputs.)
Fix
```yaml
name: Compile (drives CodeQL extraction)
run: ./gradlew --no-daemon --no-build-cache clean classes
```
`clean` forces a recompile every run.
`--no-build-cache` belt-and-braces against the setup-gradle action's cache restore.
Trade: ~30s slower CodeQL runs on cold compile. The analyze step gets real `javac` output to extract from, which is the actual job.
After merge
The README PR #40 will pass CodeQL on its next push (or after a no-op rebase). Same for any future README/CHANGELOG/workflow-only PRs.