Fail the clang-tidy Deps Wait When Listing Caches Keeps Failing

.github/workflows/clang_tidy.yml

@@ -16,6 +16,8 @@ on:
 
 permissions:
   contents: read
+  # Listing caches while waiting for this PR's deps cache.
+  actions: read
 
 concurrency:
   group: ${{ github.workflow }}-${{ github.event.pull_request.number }}
@@ -35,7 +37,7 @@ jobs:
           # The PR merge commit plus its first parent, the base it is diffed against.
           fetch-depth: 2
 
-      - name: Look for changed C++ files
+      - name: Look for changed files
         id: changes
         run: |
           if git -c core.quotePath=false diff --name-only HEAD^1 -- src tests | grep -qE '\.(cpp|cc|cxx|hpp|h|hxx)$'; then
@@ -43,18 +45,68 @@ jobs:
           else
             echo "No C++ changes under src/ or tests/."
           fi
+          if ! git diff --quiet HEAD^1 -- deps; then
+            echo "deps=true" >> "$GITHUB_OUTPUT"
+          fi
+          echo "deps-key=linux-clang-cache-orcaslicer_deps-build-${{ hashFiles('deps/**') }}" >> "$GITHUB_OUTPUT"
 
-      # Parsing needs the dependency headers, not a build of this PR's deps/, so
-      # a PR that changes deps/ falls back to the newest cache main has.
+      # Parsing needs the dependency headers, not a build of this PR's deps/.
+      # Without an exact match the job falls back to the newest cache main has,
+      # unless the PR changes deps/: its code may need the new headers, so the
+      # job waits for the cache this PR's Linux Build Deps job saves.
       - name: Restore cached deps
+        id: deps_cache
         if: steps.changes.outputs.cpp == 'true'
         uses: actions/cache/restore@v6
         with:
           path: ${{ github.workspace }}/deps/build/OrcaSlicer_dep
-          key: linux-clang-cache-orcaslicer_deps-build-${{ hashFiles('deps/**') }}
+          key: ${{ steps.changes.outputs.deps-key }}
+
+      - name: Restore the newest cached deps
+        if: steps.changes.outputs.cpp == 'true' && steps.deps_cache.outputs.cache-hit != 'true' && steps.changes.outputs.deps != 'true'
+        uses: actions/cache/restore@v6
+        with:
+          path: ${{ github.workspace }}/deps/build/OrcaSlicer_dep
+          key: ${{ steps.changes.outputs.deps-key }}
           restore-keys: linux-clang-cache-orcaslicer_deps-build-
           fail-on-cache-miss: true
 
+      # Linux Build Deps takes about 35 minutes on GitHub-hosted runners. A
+      # failing lookup is retried a few times, then fails the job instead of
+      # waiting out the deadline.
+      - name: Wait for this PR's deps cache
+        if: steps.changes.outputs.cpp == 'true' && steps.deps_cache.outputs.cache-hit != 'true' && steps.changes.outputs.deps == 'true'
+        timeout-minutes: 100
+        env:
+          GH_TOKEN: ${{ github.token }}
+          KEY: ${{ steps.changes.outputs.deps-key }}
+        run: |
+          deadline=$((SECONDS + 90 * 60))
+          failures=0
+          while true; do
+            if found=$(gh cache list --repo "$GITHUB_REPOSITORY" --ref "$GITHUB_REF" --key "$KEY" --json key --jq ".[] | select(.key == \"$KEY\") | .key"); then
+              [ -n "$found" ] && break
+              failures=0
+            elif [ $((++failures)) -ge 3 ]; then
+              echo "::error::Listing caches failed 3 times in a row."
+              exit 1
+            fi
+            if [ "$SECONDS" -ge "$deadline" ]; then
+              echo "::error::No deps cache $KEY after 90 minutes. Check the Linux Build Deps job, then rerun clang-tidy."
+              exit 1
+            fi
+            echo "Waiting for $KEY..."
+            sleep 60
+          done
+
+      - name: Restore this PR's deps cache
+        if: steps.changes.outputs.cpp == 'true' && steps.deps_cache.outputs.cache-hit != 'true' && steps.changes.outputs.deps == 'true'
+        uses: actions/cache/restore@v6
+        with:
+          path: ${{ github.workspace }}/deps/build/OrcaSlicer_dep
+          key: ${{ steps.changes.outputs.deps-key }}
+          fail-on-cache-miss: true
+
       - name: Apt-Install Dependencies
         if: steps.changes.outputs.cpp == 'true' && !vars.SELF_HOSTED
         uses: ./.github/actions/apt-install-deps