sccache (Vercel fork)

This is a Vercel-maintained fork of mozilla/sccache. It is maintained as a stack of patches managed with Graphite, each branch containing a single feature/fix on top of the upstream branch.

For full upstream documentation, see the upstream README or the upstream repository.

Branch structure

• upstream — Tracks mozilla/sccache main. This is the base of the stack.
• vercel/ci-fixes — Bottom of the stack (CI cleanup).
• vercel/multilevel-caching through vercel/fork-readme-ci — Stacked feature branches.
• main — Always points to the top of the stack (same commit as the topmost branch).

Patches

Each patch is a single Graphite branch with one commit. The stack order (bottom to top):

0. CI fixes (vercel/ci-fixes) — Removes coverage, benchmarks, snap, FreeBSD, and unsupported cross-compilation targets from upstream CI.

1. Multi-level caching (vercel/multilevel-caching) — Cherry-picked from upstream mozilla/sccache#2581. Adds hierarchical cache storage (e.g., disk -> redis -> s3). Drop once merged upstream.

2. Crate type allow hash (vercel/crate-type-allow-hash) — When SCCACHE_RUST_CRATE_TYPE_ALLOW_HASH is set, all crate types become cacheable. The env var value is hashed into the cache key only when unsupported crate types are present.

3. OpenDAL upgrade + Vercel Artifacts backend (vercel/opendal-upgrade-artifacts) — Upgrades opendal via [patch.crates-io] (apache/opendal#7334). Adds Vercel Artifacts cache backend with SCCACHE_VERCEL_ARTIFACTS_TOKEN, _ENDPOINT, _TEAM_ID, _TEAM_SLUG.

4. Reflink-based disk cache (vercel/file-clone-reflink) — Cherry-picked from upstream mozilla/sccache#2640. SCCACHE_FILE_CLONE=true stores entries uncompressed and restores via filesystem reflinks. Drop once merged upstream.

5. Directory dep-info hashing (vercel/fix-dir-dep-info) — Fixes mozilla/sccache#2653. Handles directories in rustc dep-info by recursively hashing contents.

6. This README + CI/release workflows + version suffix (vercel/fork-readme-ci) — Fork documentation, vercel-ci.yml, vercel-release.yml, and -vercel suffix on sccache --version.

Managing the stack

This fork uses Graphite to manage the patch stack. Install with npm i -g @withgraphite/graphite-cli.

Viewing the stack

gt log

Modifying a patch mid-stack

gt checkout vercel/<branch-to-edit>
# make changes
git add -A && git commit --amend --no-edit
gt restack                              # rebase all branches above
git checkout vercel/fork-readme-ci      # go to top
git branch -f main HEAD                 # point main at top of stack
git push --force-with-lease origin main vercel/<changed-branch> [other affected branches...]

Adding a new patch to the stack

gt checkout vercel/<branch-below>       # check out where to insert
gt create vercel/<new-branch> -m "commit message"
# make changes
git add -A && git commit -m "description"
gt restack                              # rebase everything above
git checkout vercel/fork-readme-ci
git branch -f main HEAD
git push --force-with-lease origin main vercel/<new-branch> [restacked branches...]

Then create a PR:

gh pr create --base vercel/<branch-below> --head vercel/<new-branch> --title "[N/M] description"

And update the base of the PR that was previously on top of <branch-below>:

gh pr edit <pr-number> --base vercel/<new-branch>

Dropping a merged upstream patch

If an upstream PR (e.g., #2581) gets merged:

gt checkout vercel/<branch-to-drop>
gt move --onto upstream                 # or onto the branch below it
# if the branch is now empty, delete it
gt restack
git checkout vercel/fork-readme-ci
git branch -f main HEAD

Rebasing on latest upstream

git fetch upstream
git checkout upstream
git reset --hard upstream/main          # update the upstream branch
git push --force-with-lease origin upstream
gt restack                              # rebase entire stack
git checkout vercel/fork-readme-ci
git branch -f main HEAD                 # point main at top
git push --force-with-lease origin --all

After any stack modification

Always finish with:

git checkout vercel/fork-readme-ci      # top of stack
git branch -f main HEAD                 # sync main
git push --force-with-lease origin main [affected branches...]

CI & Releases

• vercel-ci.yml — Runs cargo test on Ubuntu on every push/PR.
• vercel-release.yml — Manual trigger (workflow_dispatch). Builds static musl binaries for x86_64 and aarch64 Linux, then creates a GitHub release tagged vercel-YYYYMMDD with the patch stack in the release description.

Verification

After modifying the stack, verify with:

cargo fmt --all
cargo clippy --locked --all-targets -- -D warnings -A unknown-lints -A clippy::type_complexity -A clippy::new-without-default
cargo build
cargo test

Generate a per-file diff manifest:

for commit in $(git log --reverse --format="%H" upstream..HEAD); do
  echo "### $(git log --oneline -1 $commit)"
  git diff-tree --no-commit-id --name-status -r $commit
  echo
done