Codegen

Most of the API surface of s3s and s3s-aws is generated from the Smithy models in data/. A generated file is an output: the change belongs in the generator, and the output is committed together with it.

The loop

• just crawl refreshes the models and the error-code table under data/ (cargo run -p xtask -- crawl update).
• just codegen regenerates the workspace from that data, then runs cargo fmt --all and cargo check.
• just ci-rust ends with just assert_unchanged, which requires an empty git status, so a codegen run that leaves a diff fails CI. Run just codegen before pushing anything that touches the models, the data or an emitter.

The boundary

• Generated files carry a //! Auto generated by ... marker. They live under crates/s3s/src/{dto,xml,access,error,header}/generated.rs, crates/s3s/src/ops/generated/, crates/s3s-aws/src/{conv,proxy}/generated.rs and crates/s3s/tests/generated/.
• Hand-written code sits beside them (dto/mod.rs, xml/mod.rs, ops/mod.rs, ...). Edit that file, or the emitter, never the generated one.
• An emitter change and the output it produces belong to the same commit: every commit has to leave a consistent tree, and assert_unchanged enforces exactly that.

Where the generators live

codegen/src/v1/ holds one module per family (dto.rs, xml.rs, ops.rs, s3_trait.rs, access.rs, error.rs, headers.rs, aws_conv.rs, aws_proxy.rs, gen_tests/), driven from mod.rs: run() reads the model data and calls each module, write_file and write_dir_file write into the checkout, and postprocess() finishes the job. Output has to be deterministic and stable under cargo fmt, so iterate maps in a fixed order.

The MinIO variant

Every mergeable module is generated twice — into generated.rs and generated_minio.rs — and postprocess() merges the pair back into the first file: the differences become inline #[cfg(feature = "minio")] / #[cfg(not(feature = "minio"))] blocks, and the temporary *_minio.rs is deleted. Two consequences:

• Verify both builds. cargo test --all-features and a plain cargo test execute different halves of a merged file, and the same holds for cargo check with and without the feature.
• A type or a value subtree that differs between the two models is generated once per branch, so a test that covers it needs the same gates.

Generated tests

codegen/src/v1/gen_tests/ writes the coverage test suite into crates/s3s/tests/generated/. The same rule applies there: extend the emitter instead of editing the generated tests by hand.