wild (https://github.com/davidlattimore/wild) is a Rust-native linker,
typically 10-30% faster than mold on large release-LTO links. We have
~5 service binaries each doing release-LTO link, so the saving is
meaningful: ~30-90 sec wall-time on a fresh compile.
Approach (CI-only swap, zero local-dev impact):
1. Dockerfile.ci-builder-cpu installs wild 0.8.0 alongside mold (both
linkers present; revert path is trivial).
2. .cargo/config.toml keeps `-fuse-ld=mold` as the file default so
`cargo build` works locally without requiring wild on PATH.
3. compile-and-deploy-template.yaml's compile-services script does an
in-place sed substitution `mold -> wild` immediately before
`cargo build`, gated on `command -v wild` so a missing binary
silently falls back to mold instead of failing the build.
Why sed-in-script over RUSTFLAGS env var: RUSTFLAGS env var REPLACES
the entire target.<triple>.rustflags array (per cargo docs precedence:
env > target > build, mutually exclusive — they do NOT merge), which
would silently drop our existing -Wl,-z,relro/--as-needed/target-cpu
flags. Sed swap edits one token while preserving everything else.
Validation:
- python3 yaml.safe_load_all parses the template
- cargo check --workspace --release --locked succeeds locally (still
using mold per the unchanged config.toml default)
- Dockerfile syntax visually verified; wild tarball URL confirmed live
via curl https://api.github.com/repos/davidlattimore/wild/releases/latest
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
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