ci: capture compiler warnings from all CI matrix builds

Author: sbryngelson

.github/workflows/test.yml

@@ -261,6 +261,33 @@ jobs:
           TEST_ALL: ${{ matrix.mpi == 'mpi' && '--test-all' || '' }}
           PRECISION: ${{ matrix.precision != '' && format('--{0}', matrix.precision) || '' }}
 
+      - name: Collect Compiler Warnings
+        if: always()
+        run: |
+          echo "::group::Compiler warnings"
+          for staging_dir in build/staging/*/; do
+            [ -f "$staging_dir/CMakeCache.txt" ] || continue
+            target=$(ls "$staging_dir/CMakeFiles/"*".dir" -d 2>/dev/null | head -1 | sed 's/.*CMakeFiles\///;s/\.dir//')
+            [ -z "$target" ] && continue
+            echo "=== Rebuilding $target for warnings ==="
+            cd "$staging_dir"
+            find fypp/ -name '*.f90' -exec touch {} + 2>/dev/null
+            make "$target" -j1 2>&1 | grep -E "Warning:|warning:" -B2 > /tmp/warnings_${target}.txt 2>&1 || true
+            count=$(grep -c "Warning:\|warning:" /tmp/warnings_${target}.txt 2>/dev/null || echo 0)
+            echo "--- $target: $count warnings ---"
+            cat /tmp/warnings_${target}.txt
+            cd - > /dev/null
+          done
+          echo "::endgroup::"
+
+      - name: Upload Warning Reports
+        if: always()
+        uses: actions/upload-artifact@v4
+        with:
+          name: warnings-${{ matrix.os }}-${{ matrix.mpi }}-${{ matrix.debug }}-intel-${{ matrix.intel }}
+          path: /tmp/warnings_*.txt
+          if-no-files-found: ignore
+
       - name: Test
         run:  |
           /bin/bash mfc.sh test -v --max-attempts 3 -j $(nproc) $ONLY_CHANGES $TEST_ALL $TEST_PCT