Istanbul-compatible JavaScript/TypeScript coverage instrumentation using the Oxc AST.

This crate parses JS/TS source with [oxc_parser], identifies statements, functions, and branches, injects coverage counter expressions, and emits instrumented code. The coverage map output is compatible with Istanbul's coverage-final.json format (consumed by Jest, Vitest, c8, nyc, Codecov).

Example

use oxc_coverage_instrument::{instrument, InstrumentOptions};

let source = "function add(a, b) { return a + b; }";
let result = instrument(source, "add.js", &InstrumentOptions::default()).unwrap();

println!("Instrumented code:\n{}", result.code);
println!("Functions found: {}", result.coverage_map.fn_map.len());

Coverage model

The coverage map tracks three dimensions:

• Statements: every executable statement gets a counter
• Functions: every function declaration, expression, arrow, and method
• Branches: if/else, ternary, switch cases, logical &&/||

Function names are derived from the same Oxc parser used by other Oxc-based tools, so they match consistently across the ecosystem.