cargo-build-rx

Compile-time diagnostic and prescription tool for Rust projects.

Rust compile times are the #1 developer complaint. 42% of developers don't know the easy fixes. cargo-build-rx scans your project in under 2 seconds — no compilation required — and produces a ranked list of prescriptions to speed up your builds.

Installation

cargo install cargo-build-rx

Usage

# Run all checks
cargo build-rx

# JSON output (for CI or tooling)
cargo build-rx --format json

# Run only specific checks
cargo build-rx --only linker,profile

# Skip specific checks
cargo build-rx --skip dev-deps

# Only show fixes (hide warnings and info)
cargo build-rx --min-severity fix

Example output

cargo-build-rx — 5 prescriptions for my-web-app

   FIX [High] Default system linker detected
       mold is installed and would be 2-5x faster for linking.

       -> Add to .cargo/config.toml:
         [target.x86_64-unknown-linux-gnu]
         linker = "clang"
         rustflags = ["-C", "link-arg=-fuse-ld=mold"]

   FIX [Medium] Missing build-override opt-level for proc-macros
       Proc-macros and build scripts run at opt-level 0 by default.
       Compiling them with opt-level 3 makes them run faster during builds.

       -> In Cargo.toml [profile.dev.build-override]:
         opt-level = 3

  WARN [Medium] syn v1 and v2 both present
       Both syn 1.x and syn 2.x are compiled. syn is the most expensive
       proc-macro dependency. Updating all dependents to use syn 2.x can
       eliminate a full extra compilation of syn.

       -> Run: cargo update  # then check: cargo tree -d -p syn

  WARN [Medium] tokio uses "full" feature
       The "full" feature pulls in many sub-features, increasing compile time.
       Only enable the features you actually use (e.g., rt-multi-thread, macros, io-util).

  INFO [Low] 12 crates with build scripts
       12 crates have build.rs scripts.

Summary: 2 fixes, 2 warnings, 1 info

Exit code is 1 if any Fix-severity findings are present, 0 otherwise — useful for CI gates.

Checks

#	Check	What it detects
1	linker	Default ld on Linux (recommends mold/lld). macOS split-debuginfo.
2	profile	debuginfo=2, opt-level>0 in dev, missing build-override for proc-macros
3	duplicates	Multiple semver-incompatible versions (escalates for syn, serde, tokio)
4	proc-macros	syn v1+v2 split, total proc-macro count >15
5	build-scripts	Inventory of build.rs crates, flags those with native `links`
6	features	tokio/full, reqwest/default-tls, and other heavy default features
7	dev-deps	criterion, proptest, and other heavy dev-dependencies
8	toolchain	rustc >2 minor versions behind stable
9	workspace	Multi-crate workspace without workspace-hack crate
10	incremental	CARGO_INCREMENTAL=0 set in local dev environment

How it works

cargo-build-rx runs cargo metadata and reads your Cargo.toml, .cargo/config.toml, and environment. All checks are pure functions over this data — no compilation of your project is required. Typical runtime is under 2 seconds.

CI usage

# GitHub Actions example
- name: Check build hygiene
  run: |
    cargo install cargo-build-rx
    cargo build-rx --min-severity fix

The exit code is 1 when fixable issues are found, so it naturally fails the CI step.

JSON output

cargo build-rx --format json

Returns an array of findings, each with severity, category, impact, title, description, and optional fix with structured kind (CargoConfig, CargoToml, ShellCommand, or Manual).

License

Licensed under either of

Apache License, Version 2.0 (LICENSE-APACHE or http://www.apache.org/licenses/LICENSE-2.0)
MIT license (LICENSE-MIT or http://opensource.org/licenses/MIT)

at your option.

cargo-build-rx 0.1.0