srcmap-generator

High-performance source map generator for Rust.

Builds source maps incrementally by adding mappings one at a time. Outputs standard ECMA-426 source map v3 JSON. Drop-in Rust equivalent of @jridgewell/gen-mapping.

Install

[dependencies]
srcmap-generator = "0.1"

Usage

use srcmap_generator::SourceMapGenerator;

let mut gen = SourceMapGenerator::new(Some("bundle.js".to_string()));

// Register sources and names
let src = gen.add_source("src/app.ts");
gen.set_source_content(src, "const x = 1;".to_string());
let name = gen.add_name("x");

// Add mappings (generated_line, generated_col, source, original_line, original_col)
gen.add_mapping(0, 0, src, 0, 6);
gen.add_named_mapping(1, 0, src, 1, 0, name);

// Skip redundant mappings automatically
gen.maybe_add_mapping(1, 5, src, 1, 0); // skipped — same source position

let json = gen.to_json();
// {"version":3,"file":"bundle.js","sources":["src/app.ts"],...}

API

`SourceMapGenerator`

Method	Description
`new(file) -> Self`	Create a new generator with optional output filename
`add_source(path) -> u32`	Register a source file, returns its index (deduped)
`set_source_content(idx, content)`	Set inline source content
`add_name(name) -> u32`	Register a name, returns its index (deduped)
`set_source_root(root)`	Set the `sourceRoot` prefix
`add_mapping(gen_line, gen_col, src, orig_line, orig_col)`	Add a mapping
`add_named_mapping(gen_line, gen_col, src, orig_line, orig_col, name)`	Add a mapping with a name
`add_generated_mapping(gen_line, gen_col)`	Add a generated-only mapping (no source)
`maybe_add_mapping(gen_line, gen_col, src, orig_line, orig_col) -> bool`	Add only if different from previous
`add_range_mapping(gen_line, gen_col, src, orig_line, orig_col)`	Add a range mapping (ECMA-426)
`add_named_range_mapping(gen_line, gen_col, src, orig_line, orig_col, name)`	Add a named range mapping
`add_to_ignore_list(source_idx)`	Mark a source as ignored (third-party)
`to_json() -> String`	Serialize to source map v3 JSON
`to_decoded_map() -> SourceMap`	Build a `SourceMap` directly (no JSON roundtrip)
`mapping_count() -> usize`	Number of mappings added

Parallel encoding

Enable the parallel feature for multi-threaded VLQ encoding via rayon. Automatically used for maps with 4K+ mappings.

[dependencies]
srcmap-generator = { version = "0.1", features = ["parallel"] }

`StreamingGenerator`

On-the-fly VLQ encoder that emits mappings as they are added, without collecting into a Vec. Ideal for composition pipelines where mappings arrive in sorted order.

Method	Description
`new(file) -> Self`	Create a new streaming generator
`add_source(path) -> u32`	Register a source file (deduped)
`add_name(name) -> u32`	Register a name (deduped)
`set_source_root(root)`	Set the `sourceRoot` prefix
`set_debug_id(id)`	Set the `debugId` field
`add_to_ignore_list(source_idx)`	Mark a source as ignored (third-party)
`add_mapping(...)`	Add a mapping (encoded immediately)
`add_named_mapping(...)`	Add a mapping with a name
`add_range_mapping(...)`	Add a range mapping (ECMA-426)
`add_named_range_mapping(...)`	Add a named range mapping
`to_json() -> String`	Serialize to source map v3 JSON
`to_decoded_map() -> SourceMap`	Build a `SourceMap` directly

Features

Automatic deduplication of sources and names
maybe_add_mapping skips redundant mappings to reduce output size
Range mappings (rangeMappings field, ECMA-426 Stage 2)
Streaming generation via StreamingGenerator — zero-allocation VLQ encoding
ignoreList support for filtering third-party sources in DevTools
Parallel VLQ encoding for large maps (opt-in via parallel feature)
Hand-rolled JSON serialization — no serde overhead in output path

Part of srcmap

License

MIT

srcmap-generator 0.2.0