Incremental builds

Configured crates discover locale assets and validate derived messages against the fallback locale at compile time. Cargo also needs explicit asset tracking so locale changes, additions, renames, and deletions trigger that work again.

The es-fluent-build helper emits the rebuild directives and writes a catalog of resolvable fallback messages. Derive output uses that catalog to make a missing fallback message value a compile-time error.

Setup

Add es-fluent-build to your build dependencies:

[build-dependencies]
es-fluent-build = "0.18"

Call the tracking helper from Cargo’s selected custom-build target. The default path is build.rs:

// build.rs
fn main() {
    es_fluent_build::track_i18n_assets();
}

A custom [package] build = "support/i18n.rs" path uses the same helper call. This guarantees your project recompiles whenever locale files or folders are added, removed, or renamed. Run cargo es-fluent doctor to verify the helper through Cargo’s selected target and its local module graph. A warning means static inspection could not prove the integration and requires manual verification.