npm install
npm run build
When run above step we get following error:
thread '<unnamed>' panicked at <HOME_DIR>/.cargo/registry/src/index.crates.io-6f17d22bba15001f/swc_common-0.33.9/src/input.rs:31:9:
assertion failed: start <= end
note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace
This happens because end_pos gets overflowed here https://github.com/swc-project/swc/blob/eebf14fbef1be34c98db736ad549b1f11d5d8a98/common/src/syntax_pos/mod.rs#L688
This Happens because there is static instance of SWC Compiler which is cloned and used for transform and minify in next-swc: https://github.com/vercel/next.js/blob/canary/packages/next-swc/crates/napi/src/lib.rs#L85-L89.
The SWC Compiler has cm field which is Arc<SourceMap>, making the same sourcemap to be shared among every clone of compiler.
The SourceMap has start_pos field which calculates the start_pos of next SourceFile it needs to create. Which means this is effectively storing the count of every character present in sourcemap.
SourceMap.start_pos may be a AtomicUsize, but it's value gets stored in BytePos as a u32 via Pos trait implementation of it.
The end_pos calculated in SourceFile::new adds the file's length into the start_pos and stores it as a BytePos, i.e. a u32.
Because in Pos trait implementation of BytePos, we are using as u32 to directly convert type, this result in integer overflow to get un-noticed.
This gets detected later-on when in swc_common::StringInput we assert start and end positions: https://github.com/swc-project/swc/blob/main/crates/swc_common/src/input.rs#L31.
- Increase the size of BytePos to u64
- Not share SourceMap instance across both transform and minify routines