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

This instrumentation will generate a data struct mimics istanbuljs'sFileCoverageobject conforms fixture test suite from istanbuljs itself.

However, this doesn't mean instrumentation supports exact sameinterfaces 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 trybest attempt as possible.

NOTE: Package can have breaking changes without major semver bump

Given SWC's plugin interface itself is under experimental stage does not gaurantee semver-based major bump yet, this package also does not gaurantee semver compliant breaking changes yet. Please refer changelogs if you're encountering unexpected breaking behavior across versions.

First, install package via npm:

npm install --save-dev swc-plugin-coverage-instrument

Then add plugin into swc's configuration:

const pluginOptions: InstrumentationOptions = {...}jsc: {  ...  experimental: {    plugins: [      ["swc-plugin-coverage-instrument", pluginOptions]    ]  }}

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

interface InstrumentationOptions {  coverageVariable?: String,  compact?: bool,  reportLogic?: bool,  ignoreClassMethods?: Array<String>,  inputSourceMap?: object,  instrumentLog: {    // Currently there aren't logs other than spans.    // Enabling >= info can display span traces.    level: 'trace' | 'warn' | 'error' | 'info'    // Emits spans along with any logs    // Only effective if level sets higher than info.    enableTrace: bool  },  unstableExclude?: Array<String>}

There is a single interface exposed to create a visitor for the transform, which you can pass intobefore_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);

This package runs istanbuljs' fixture tests against SWC with its wasm plugin & custom transform both.spec contains set of the fixtures & unit test to run it, as well as supplimental packages to interop between instrumentation visitor to node.js runtime.swc-coverage-instrument-wasm exposesFileCoverageInterop allows to consumeFileCoverage struct inside of js, andswc-coverage-custom-transform is an example implementation to runbefore_custom_pass withswc-coverage-instrument visitor.

Few npm scripts are supported for wrapping those setups.

• build:all: Build all relative packages as debug build.
• test: Runs unit test for wasm plugin & custom transform.
• test:debug: Runs unit test, but only fordebug-test.yaml fixture. This is mainly for local dev debugging for individual test fixture behavior.