Vendored patches

Hermes vendors code when a pinned Servo dependency needs a small, reviewable compatibility fix that cannot be expressed through the public API. Vendoring is a temporary maintenance cost, not a general fork strategy.

Patch inventory

Directory	Upstream version	Why Hermes carries it
third_party/gaol	0.2.1	Modern Linux syscall compatibility and a non-zero file-size limit for Servo shared-memory IPC
third_party/servo-media-gstreamer	0.4.0	Codec detection, Linux frame transfer, diagnostics, Web Audio, and media lifecycle fixes
third_party/surfman	0.13.0	Avoid process-global DRI_PRIME=1 selection and its race with media initialization

The root [patch.crates-io] section redirects Servo's dependency graph to these directories.

Rules for changing a patch

1. Reproduce the failure against the exact upstream version.
2. Keep the diff limited to the behavior Hermes needs.
3. Add a regression test when the behavior can be tested locally.
4. Update the directory's HERMES.md or README.md with the reason for the patch.
5. Preserve the upstream license files and attribution.
6. Prefer a fix that can be proposed upstream without Hermes-specific concepts.

Avoid opportunistic formatting, dependency upgrades, or unrelated cleanup inside a vendored tree. They make future comparison and removal needlessly difficult.

Validate the gaol patch

cargo test \
  --target-dir target \
  --manifest-path third_party/gaol/Cargo.toml \
  --test shared-memory

The separate target directory avoids leaving an untracked build tree inside the vendored crate.

Validate the media patch

cargo test --package servo-media-gstreamer --lib

Media also needs a manual playback check because successful unit tests cannot prove that the host's plugins, decoder selection, audio sink, and frame transfer work together.

Remove a patch

When an equivalent fix reaches the Servo dependency graph used by Hermes:

1. Update the pinned dependency version.
2. Remove the relevant [patch.crates-io] entry.
3. Regenerate Cargo.lock intentionally.
4. Run the original regression test and full QA.
5. Remove the vendored directory in the same commit.

The removal commit should explain which upstream release absorbed the patch.