Rust build insights

Build Insights helps you find what slows your Cargo builds down and catch regressions before they affect the whole team. You can compare local builds with CI, see how build times change, and inspect the crates compiled in each build.

Requirements

Follow the Rust project setup to connect your project and authenticate.

Report your builds#

Run your usual Cargo commands through Tuist:

bash

tuist cargo build --workspace
tuist cargo check --all-targets
tuist cargo +nightly build --features tracing

If you use mise, configure a Cargo wrapper to keep using ordinary cargo commands. Your arguments, toolchain selection, output, and exit code stay the same.

Find what slows a build down#

Open a build from Builds → Build Runs on the dashboard. Use the date, environment, and Rust-version filters to compare similar builds.

On Overview, use Compiler jobs to find slow crates. Sort by Duration or Started after (time since the Cargo command started), or search by crate name or root source file.

Each row is one rustc invocation for a crate, which can contain many source files. Crate root identifies its root source file; the duration is for the whole compiler job, not that file alone. A crate can appear more than once for different targets or configurations. Compiler messages are grouped in Warnings and Errors.

Read the timings#

The build duration is how long the whole Cargo command took. Compiler jobs can run in parallel, so their durations won't add up to the build duration.

Cargo only compiles crates that need rebuilding. Crates that are already up to date won't appear in the compiler list. With Tuist's compilation cache, restored jobs appear in the cache measurements, not as compiler executions.

Tuist doesn't measure build scripts separately or show a build Timeline. A large build shows the first 500 compiler jobs, with a notice if more were recorded.

Read cache measurements#

tuist cargo includes an experimental compilation cache implemented in the Tuist CLI. There is no separate tool to install; project and server settings come from tuist.toml. Unsupported compilations run normally.

Open a build's Cache tab to see task hits, task misses, hit rate, and downloaded and uploaded bytes. The tab appears when the build reports cache data.

Cacheable Tasks shows which compiler and build-script tasks reused cached outputs. Search or filter the tasks, inspect cache read/write latency, and expand a row to see its outputs.
CAS Outputs shows artifact downloads and uploads, with their sizes, durations, and throughput. The chart counts completed transfers; already-present artifacts and failed attempts remain in the table.

Hit means cached outputs were reused. Missed means the task compiled instead. Hits aren't split into local and remote; CAS Outputs shows the recorded artifact operations.

If detailed records are missing or incomplete, the page shows a notice. The summary still covers the whole build. Estimated compiler work avoided is not elapsed build time saved.

Experimental compilation cache

The first version caches only registry leaf libraries with verified inputs and outputs. Workspace crates, build scripts, procedural macros, dependencies on other crates, incremental compilation, native linking, and executables build normally. Cache keys retain absolute paths, so reuse across different checkout paths isn't supported yet.

Builds that run tests#

tuist cargo test reports the duration of the whole command, including its tests. Use nextest Test Insights to track individual test results. Nextest runs appear under Tests, not in build-duration charts.

For test sharding, tuist cargo test-build reports the time spent compiling and archiving the tests.

Other compiler tools#

Tuist preserves existing compiler wrappers configured through RUSTC_WRAPPER, CARGO_BUILD_RUSTC_WRAPPER, or Cargo configuration, and leaves RUSTC_WORKSPACE_WRAPPER intact. A pre-existing global wrapper disables Tuist's cache and compiler observer: Tuist cannot establish whether that wrapper actually ran rustc. Custom workspace wrappers can likewise leave fewer compiler jobs in the report.

Tuist finds Cargo through rustup. If you use a custom installation, set TUIST_CARGO_EXECUTABLE to its executable path. Calling Cargo by a direct toolchain path bypasses mise's wrapper. A Cargo alias can't replace a built-in command such as build.

If you use Cargo's nightly -C option, change into the workspace first instead: Tuist forwards -C commands but doesn't collect their build timings.

Troubleshooting#

If a build doesn't appear in the dashboard, enable debug output to see why its report wasn't sent:

bash

TUIST_DEBUG=1 tuist cargo build --workspace

Reporting doesn't change the result of your build.