Cinder

Cinder is an experimental Cargo-compatible development accelerator for Rust. It uses Cargo as the source of truth and takes a faster path only when it can prove that Cargo's result is still valid. Everything else runs through Cargo.

cinder run
cinder build -p my-app
cinder check -p my-library --lib
cinder test -p my-library --lib

Existing projects need no migration or Cinder-specific configuration. Cargo arguments, workspaces, manifests, lockfiles, features, build scripts, proc macros, native dependencies, configuration, wrappers, and toolchains remain authoritative.

Try it

Cinder currently requires Rust 1.85 or newer. Build it from source, put the release binary on PATH, and use cinder where you would use cargo:

cargo build --release
export PATH="/path/to/cinder/target/release:$PATH"

cd /path/to/an/existing/rust/project
cinder check

The accelerated artifact paths currently target macOS. Linux and Windows use the strict Cargo proxy, preserving command behavior without artifact acceleration.

What it accelerates

On a proven Cargo baseline, Cinder can:

• reuse an unchanged selected build, check, or test --no-run result;
• run the exact validated Cargo-built standard library test harness directly;
• restore one of the last eight validated source revisions for selected builds and runs;
• patch one unambiguous equal-length Rust string in a development executable on macOS, then sign and publish the result atomically.

Test bodies still execute on every test invocation. First-seen structural changes, unsupported command shapes, ambiguous artifacts, stale state, custom runners, nonstandard harnesses, release builds, and failed validation stay with Cargo.

Results

These are median end-to-end timings from real repositories on Apple Silicon. They include Cinder's validation and locking. Every fast sample required the expected path marker and a verified artifact or runtime result; the test row ran all seven tests in every sample.

Real workload	Trials	Cargo	Cinder	Result
Cap warm edit to stable visible desktop window	7 cycles	12.387s	5.088s	2.43x faster
Cap selected example build	15 + 15	237.942ms	16.238ms	14.65x faster
Cap selected example check	15 + 15	248.205ms	15.187ms	16.34x faster
Current Cap workspace, test -p cap-muxer-protocol --lib, 7 tests	21 + 21	134.066ms	13.876ms	9.66x faster
Handy selected binary check	15 + 15	278.439ms	24.392ms	11.42x faster
Zed selected binary check	10 + 10	587.644ms	33.711ms	17.43x faster
Bun real 489-line retained revision	7 + 7	12.06s	0.22s	54.82x faster

These results describe the named workloads, not universal Rust compilation speed. Full commands, revisions, sample arrays, negative controls, rejected experiments, and reproduction details are in the benchmark report and raw results.

Safety model

Cinder does not reimplement dependency resolution, feature selection, build scripts, proc macros, or toolchain selection. Before reuse it validates the Cargo invocation and environment, source and control inputs, project topology, artifact identity and digest, dep-info, fingerprints, build-script evidence, and relevant runtime contracts.

State is bounded, versioned, private to the user, and published through staged atomic promotion. Malformed, incomplete, changed, or ambiguous evidence is a normal cache miss. Cinder then delegates the original arguments, environment, output, and exit behavior to the real Cargo executable.

See the architecture notes for the complete boundary, including revision storage, compiler observation, code signing, concurrency, cleanup, and the opt-in first-seen check experiment.

Local evidence

Usage evidence is optional and privacy-safe:

CINDER_USAGE=1 cinder check -p my-package --lib
cinder stats
cinder stats --json

It records only command class, proven outcome, decision latency, and calendar day. It does not store repository identifiers, paths, arguments, source, commands, or environment values, and it never estimates time saved.

Development

The primary local gates are:

cargo fmt --all -- --check
cargo clippy --all-targets --all-features -- -D warnings
cargo test
cargo +1.85.0 test

Cinder is early-stage and is not yet distributed as a stable release.

License

Cinder is licensed under the MIT License.