feat: support index source map

[SyMind]

No description provided.

[gemini-code-assist]

Summary of Changes

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This pull request introduces support for IndexSourceMap, a more efficient representation for source maps, particularly beneficial when dealing with concatenated sources. By allowing source maps to be composed of multiple sections with offsets, it avoids the costly process of merging individual mappings, leading to improved performance and reduced memory usage for complex bundles. The changes include new data structures, a new trait method, and optimized implementations for ConcatSource and CachedSource.

Highlights

• New IndexSourceMap Structure: Introduced IndexSourceMap to represent source maps as a collection of sections, improving performance for concatenated sources by avoiding expensive mapping merges.
• Enhanced Source Trait: Added an index_map method to the Source trait, providing a more efficient way to generate source maps for complex source structures, with a default implementation that wraps a regular SourceMap.
• Optimized ConcatSource: Implemented index_map for ConcatSource to intelligently combine source map sections from its children, correctly handling line and column offsets, including UTF-16 code unit counting.
• Cached IndexSourceMap Results: Enhanced CachedSource to cache IndexSourceMap results, preventing redundant computations and improving performance for cached sources.
• Comprehensive Testing and Benchmarking: Included a new benchmark to measure the performance of index_map and added extensive unit tests for IndexSourceMap serialization, flattening, and various concatenation scenarios.

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Changelog

• benches/benchmark_repetitive_react_components.rs
  • Added benchmark_repetitive_react_components_index_map to benchmark the new index_map functionality.
• src/cached_source.rs
  • Imported IndexSourceMap.
  • Added columns_index_map and line_only_index_map fields to CachedData for caching IndexSourceMap results.
  • Implemented the index_map method for CachedSource to utilize the new caching mechanism.
  • Added new tests to verify index_map caching behavior and correctness.
• src/concat_source.rs
  • Imported IndexSourceMap, Section, and SectionOffset.
  • Implemented the index_map method for ConcatSource, which iterates through child sources, offsets their index maps, and combines them into a single IndexSourceMap.
  • Added logic to correctly calculate line and column offsets, including handling UTF-16 code units for column counting.
  • Added numerous unit tests to cover various ConcatSource scenarios with IndexSourceMap, including raw sources, single/multiple original sources, raw prefixes/suffixes, same-line concatenation, mixed sources, nested sources, and empty children.
• src/lib.rs
  • Exported IndexSourceMap, Section, and SectionOffset from the source module.
• src/source.rs
  • Imported encode_mappings helper.
  • Added index_map method to the Source trait with a default implementation that converts a regular SourceMap into a single-section IndexSourceMap.
  • Implemented index_map for BoxSource to delegate to the inner source.
  • Defined new structs: SectionOffset, Section, and IndexSourceMap.
  • Implemented IndexSourceMap with methods for creation, file management, accessing sections, and to_source_map for flattening into a regular SourceMap.
  • Added to_json and to_writer methods for IndexSourceMap serialization.
  • Added unit tests for IndexSourceMap serialization, flattening with various offsets, and the default index_map implementation.

Activity

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[codspeed-hq]

Merging this PR will not alter performance

✅ 11 untouched benchmarks
🆕 1 new benchmark
⏩ 6 skipped benchmarks¹

Performance Changes

	Benchmark	BASE	HEAD	Efficiency
🆕	repetitive_react_components_index_map	N/A	2.1 ms	N/A

---

_{Comparing support-index-source-map (ba214a1) with main (74beb79)}

Footnotes

1. 6 benchmarks were skipped, so the baseline results were used instead. If they were deleted from the codebase, click here and archive them to remove them from the performance reports. ↩

[gemini-code-assist]

Code Review

This pull request introduces support for Index Source Maps, which is a great feature for improving performance with concatenated sources. The implementation is thorough, covering Source, ConcatSource, and CachedSource, and includes a comprehensive set of tests that cover many edge cases. The logic for generating index maps in ConcatSource and flattening them back into regular source maps in IndexSourceMap seems solid. I've found a couple of minor areas for improvement in src/source.rs for idiomatic code and robustness, but overall this is an excellent contribution.

[gemini-code-assist]

This while loop can be simplified to a single call to resize_with, which is more idiomatic and potentially more efficient for growing the vector.

            global_sources_content.resize_with(global_sources.len(), || "".into());