srcmap-remapping

Source map concatenation and composition/remapping for Rust.

Merges or chains source maps from multiple build steps into a single map. Drop-in Rust equivalent of @ampproject/remapping.

Install

[dependencies]
srcmap-remapping = "0.2"

Usage

Concatenation

Merge source maps from multiple bundled files into one, adjusting line offsets. Used by bundlers (esbuild, Rollup, Webpack).

use srcmap_remapping::ConcatBuilder;
use srcmap_sourcemap::SourceMap;

let map_a = SourceMap::from_json(r#"{"version":3,"sources":["a.js"],"names":[],"mappings":"AAAA"}"#).unwrap();
let map_b = SourceMap::from_json(r#"{"version":3,"sources":["b.js"],"names":[],"mappings":"AAAA"}"#).unwrap();

let mut builder = ConcatBuilder::new(Some("bundle.js".to_string()));
builder.add_map(&map_a, 0);    // a.js starts at line 0
builder.add_map(&map_b, 100);  // b.js starts at line 100

let result = builder.build();

Composition / Remapping

Chain source maps through multiple transforms (e.g. TypeScript -> JavaScript -> minified) into a single map pointing to the original sources.

use srcmap_remapping::remap;
use srcmap_sourcemap::SourceMap;

let minified_map = SourceMap::from_json(outer_json).unwrap();

let result = remap(&minified_map, |source| {
    // Return the upstream source map for this source file, if any
    if source == "intermediate.js" {
        Some(SourceMap::from_json(ts_to_js_map_json).unwrap())
    } else {
        None // no upstream map — keep as-is
    }
});

// result now maps minified output directly to TypeScript sources

API

Concatenation

Composition

The loader function receives each source filename and returns Option<SourceMap>. Return Some to trace through an upstream map, or None to keep the source as-is.

remap_streaming accepts a MappingsIter (lazy VLQ iterator) and uses StreamingGenerator for on-the-fly encoding — 15-20% faster than remap for large maps.

Features

• Source and name deduplication across concatenated maps
• sourcesContent merging from all inputs
• ignoreList propagation through concatenation
• Name resolution prefers upstream names over outer names
• Lazy loading via the loader callback — only loads maps that are actually referenced
• Range mapping preservation through both concatenation and composition
• Streaming composition via remap_streaming for reduced-allocation pipelines

Part of srcmap

See also:

• srcmap-sourcemap - Parser and consumer
• srcmap-generator - Source map builder
• srcmap-codec - VLQ encode/decode

License

MIT