azazel-parity-river

river's util module (the Wayland compositor's global allocator + monotonic clock helpers) built two ways, to prove azazel and zaza on a real systems project.

river's full build needs Wayland and pkg-config system libraries, which don't reproduce on every host — but this self-contained std-only utility builds anywhere. Both build a consumer that calls msecTimestamp, and link libc for river's c_allocator.

Pinned upstream

Repository	https://github.com/riverwm/river
Commit	f8f0e4ab88ad9671e9e164ef87cae3b839da33da
File	river/util.zig
Zig	0.16.0

Build it

cd azazel && ./fetch.sh && sh gen_build_spec.sh && zig build && ./zig-out/bin/consumer
cd zaza  && ./fetch.sh && zig build run

Both print river util: msecTimestamp = <n>.

Comparison

Build	What it does	Config
azazel	imports the util module + a consumer, links libc, as CUE data	project.cue, 15 lines
zaza	imports the util module + links libc via the Zig build graph	build.zig, 14 lines

Build process & what can be optimized

Both build roots stage the pinned upstream with fetch.sh into a git-ignored vendor/ (a curl for single-file slices, a shallow clone for source trees) — no upstream sources are committed. Then:

• azazel: sh gen_build_spec.sh runs CUE and emits build_spec.zig (the build declared as data), then zig build compiles it. The CUE step is memoized — it re-runs only when the model changes (~0.20s → ~0.01s otherwise).
• zaza: zig build drives the standard Zig build graph directly.

What actually makes it faster

Measured across the corpus (clean vs warm builds):

Lever	Speedup	Note
Content-addressed cache (rebuild)	89×	14.2s → 0.16s; Zig has it, both inherit it
Incremental (edit one file)	10.8×	14.2s → 1.32s; deps stay cached
CI dependency cache	2×	cold 13.3s → warm 6.6s; this repo's CI caches ~/.cache/zig
Memoized CUE codegen	20×	azazel's only overhead, gone
Parallelism (many cores)	1.1×	marginal — shared std + startup dominate
GPU	none	compilation is branchy, sequential, dependency-ordered

The instinct to parallelize like a C++ build doesn't transfer: Zig is one mostly-single-threaded compile per artifact with a fast self-hosted backend and a shared std that caches. For Zig, caching is the lever, not parallelism.

The real frontier is residency: a resident compile server that keeps the InternPool hot and recompiles only changed declarations, plus in-place binary patching (Zig's roadmap) and a shared content-addressed cache. azazel's build-as-data is positioned for it — the build is a query, and the cache key is computable from the pinned model without running the compiler. Full write-up and the cross-repo comparison: the corpus dashboard.