CI: pass proper test configuration matching top-level make test

The test job was running the testsuite directly (cd testsuite && make)
without passing the configuration variables that the top-level 'make test'
target provides. This caused:

1. Performance tests running and timing out (SKIP_PERF_TESTS was not set)
2. Missing lint flags (-dcore-lint, -dstg-lint, -dcmm-lint, etc.)
3. Missing tool paths (TEST_HC, GHC_PKG, HP2PS, HPC, RUNGHC)

Fix by:
- Building the testsuite timeout tool before running tests
- Passing all the same variables as the Makefile's test target
- Running 'make -C testsuite/tests test' (the actual test runner)
- Splitting disk cleanup into its own step for clarity

Author: angerman

.github/workflows/nix-ci.yml

@@ -394,23 +394,41 @@ jobs:
       shell: bash
       run: ./mk/collect-metrics.sh start _build/metrics 0.5
 
+    - name: Free disk for tests
+      run: |
+        rm -rf .git
+        find . -name .git -type d -exec rm -rf {} + 2>/dev/null || true
+        rm -rf ~/.cabal-devx/packages/ 2>/dev/null || true
+        df -h .
+
+    - name: Build testsuite timeout tool
+      shell: devx {0}
+      run: |
+        set -eo pipefail
+        make -C testsuite/timeout
+
     - name: Run testsuite
       shell: devx {0}
       timeout-minutes: 120
       run: |
         set -eo pipefail
-        # Free disk: remove .git (not needed for tests) and cabal index
-        rm -rf .git
-        find . -name .git -type d -exec rm -rf {} + 2>/dev/null || true
-        rm -rf ~/.cabal-devx/packages/ 2>/dev/null || true
-        # Run testsuite from checkout's testsuite/ directory with dist GHC on PATH.
-        # Use THREADS=4 to match VM vCPU count (default is 1 = serial).
-        cd testsuite
-        PATH=$GITHUB_WORKSPACE/_build/dist/bin:$PATH \
-        METRICS_FILE=$GITHUB_WORKSPACE/_build/test-perf.csv \
-        SUMMARY_FILE=$GITHUB_WORKSPACE/_build/test-summary.txt \
-        JUNIT_FILE=$GITHUB_WORKSPACE/_build/test-junit.xml \
-        make THREADS=4
+        DIST_BIN="$GITHUB_WORKSPACE/_build/dist/bin"
+        # Pass the same variables the top-level 'make test' target uses.
+        # SKIP_PERF_TESTS=YES prevents performance tests from running
+        # (they timeout on CI). CANONICAL_TEST_HC_OPTS enables lint passes.
+        TEST_HC="$DIST_BIN/ghc" \
+        GHC_PKG="$DIST_BIN/ghc-pkg" \
+        HP2PS_ABS="$DIST_BIN/hp2ps" \
+        HPC="$DIST_BIN/hpc" \
+        RUNGHC="$DIST_BIN/runghc" \
+        TEST_CC="${CC:-cc}" \
+        TEST_HC_OPTS="-dcore-lint -dstg-lint -dcmm-lint -no-user-package-db -fno-dump-with-ways -fprint-error-index-links=never -rtsopts -fno-warn-missed-specialisations -fshow-warning-groups -fdiagnostics-color=never -fno-diagnostics-show-caret -Werror=compat -dno-debug-output" \
+        SKIP_PERF_TESTS=YES \
+        THREADS=4 \
+        METRICS_FILE="$GITHUB_WORKSPACE/_build/test-perf.csv" \
+        SUMMARY_FILE="$GITHUB_WORKSPACE/_build/test-summary.txt" \
+        JUNIT_FILE="$GITHUB_WORKSPACE/_build/test-junit.xml" \
+        make -C testsuite/tests test
 
     - name: Stop metrics collection
       if: ${{ !cancelled() }}