SWC-coverage-instrument

swc-coverage-instrument is a set of packages to support istanbuljs compatible coverage instrumentation in SWC's transform passes. Instrumentation transform can be performed either via SWC's wasm-based plugin, or using custom passes in rust side transform chains.

What does compatible exactly means?

This instrumentation will generate a data struct mimics istanbuljs's FileCoverage [object] (https://github.com/istanbuljs/istanbuljs/blob/c7693d4608979ab73ebb310e0a1647e2c51f31b6/packages/istanbul-lib-coverage/lib/file-coverage.js#L97=) conforms fixture test suite from istanbuljs itself.

However, this doesn't mean instrumentation supports exact same interfaces surrounding coverage object as well as supporting exact same options. There are some fundamental differences between runtime, and ast visitor architecture between different compilers does not allow identical behavior. This package will try best attempt as possible.

NOTE: Package can have breaking changes without major semver bump

While stablzing its interfaces, this package does not gaurantee semver compliant breaking changes yet. Please refer changelogs if you're encountering unexpected breaking behavior across versions.

Usage

Using custom transform pass in rust

There is a single interface exposed to create a visitor for the transform, which you can pass into before_custom_pass.

let visitor = swc_coverage_instrument::create_coverage_instrumentation_visitor(
    source_map: std::sync::Arc<SourceMapper>,
    comments: C,
    instrument_options: InstrumentOptions,
    filename: String,
);

let fold = as_folder(visitor);

InstrumentationOptions is a subset of istanbul's instrumentation options. Refer istanbul's option for the same configuration flags. However there are few exceptions or differences, referencing InstrumentOptions will list all possible options.

For the logging, this package does not init any subscriber by itself. Caller should setup proper tracing-subscriber as needed.