Merge pull request #261 from minijackson/merge-github-caches

github/build-checks: merge caches

Author: minijackson

.github/workflows/build-checks.yml

@@ -51,9 +51,51 @@ jobs:
       - uses: nixbuild/nix-quick-install-action@2c9db80fb984ceb1bcaa77cdda3fdf8cfba92035 # v34
       - uses: nix-community/cache-nix-action@b426b118b6dc86d6952988d396aa7c6b09776d08 # v7.0.0
         with:
-          primary-key: build-${{ runner.os }}-${{ matrix.name }}-${{ hashFiles('.github/workflows/build-checks.yml', 'flake.lock') }}
+          # Store the result in its own cache,
+          # which will be merged below
+          primary-key: check-${{ runner.os }}-${{ matrix.name }}-${{ hashFiles('.github/workflows/build-checks.yml') }}
+          # Try and restore the main cache
+          restore-prefixes-first-match: |
+            all-checks-${{ runner.os }}-
+            check-${{ runner.os }}-${{ matrix.name }}-
+          # When saving the cache,
+          # try to keep it under 2GiB
+          gc-max-store-size: 2147483648
+          # Purge old versions of this check, if any
           purge: true
-          purge-last-accessed: 2629800 # 1 month
-          purge-prefixes: build-${{ runner.os }}-${{ matrix.name }}-
+          purge-created: 0
           purge-primary-key: never
+          purge-prefixes: check-${{ runner.os }}-${{ matrix.name }}-
+          # Only save if it's not a PR
+          save: ${{ github.event_name != 'pull_request' }}
       - run: nix build -L ".#${CHECK_ATTR}"
+
+  # TODO: this should be a matrix on the runners of the nix-build job.
+  # Currently works only because we only target x86_64-linux
+  merge-caches:
+    # Only save if it's not a PR
+    if: ${{ github.event_name != 'pull_request' }}
+    runs-on: ubuntu-latest
+    needs: nix-build
+    steps:
+      - uses: actions/checkout@11bd71901bbe5b1630ceea73d27597364c9af683 # v4.2.2
+        with:
+          persist-credentials: false
+      - uses: nixbuild/nix-quick-install-action@25aff27c252e0c8cdda3264805f7b6bcd92c8718 # v29
+      - uses: nix-community/cache-nix-action@8351fb9f51c580c96c509987ebb99e38aed956ce # v5.2.1
+        with:
+          primary-key: all-checks-${{ runner.os }}-${{ hashFiles('.github/workflows/build-checks.yml') }}
+          # Restore all caches of the nix-build job
+          # from the given runner OS
+          restore-prefixes-all-matches: check-${{ runner.os }}-
+          purge: true
+          # Purge every check,
+          # and old versions of the merged cache
+          purge-prefixes: |
+            check-${{ runner.os }}-
+            all-checks-${{ runner.os }}-
+          # Created more than 0 seconds ago relative to the start of the `Post Restore` phase
+          purge-created: 0
+          # Except the cache we just created,
+          # if we're on the main branch
+          purge-primary-key: ${{ github.ref == 'refs/heads/master' && 'never' || 'always' }}