perf: ImportDelcaration Dirname#1891
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Two targeted improvements to cut per-file cost in the TaggedTemplateExpression|CallExpression visitor and the module resolution path: 1. babel-plugin.ts — hoist isRelative and fileDir out of the importSources.some() callback in ImportDeclaration. dirname() parses the full absolute file path on every iteration; computing it once per ImportDeclaration call removes O(importSources) redundant string allocations per import. 2. resolve-binding.ts — wrap resolveRequest() in cache.load() so that module resolution results are cached for the lifetime of a build (when cache: true). resolve.sync and custom resolvers both walk node_modules and read package.json files synchronously; caching the result eliminates repeated I/O for the same (filename, request) pair. Benchmark (module-traversal-cache, 75 samples): initial run: 137 -> 151 ops/sec (+10%) cache: 181 -> 201 ops/sec (+11%) no-cache: 156 -> 167 ops/sec (+7%)
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added 3 commits
May 8, 2026 18:17
…tion fileDir is now null when state.filename is absent, and isRelative encodes the null check, eliminating the redundant state.filename guard inside the .some() callback.
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Summary
One targeted improvement to cut per-file cost in the
ImportDeclarationvisitor.babel-plugin.ts— computerelativeFileDironce upfront instead of inside.some()In the
ImportDeclarationvisitor,dirname(state.filename)and theuserLandModule[0] === '.'check were both computed inside the.some()callback — once per entry inimportSourcesper import declaration.dirname()parses the full absolute file path and allocates a new string on every call. These are now combined into a singlerelativeFileDirvariable computed once before the loop:nullif the import is not relative or there is no filename (skipping resolution entirely), or the resolved directory otherwise.Benchmark
Using the existing
module-traversal-cacheperf test (75 samples each):initial runcacheno-cacheTesting
module-traversal.test.ts(49 tests) pass with no changes.yarn benchmark packages/babel-plugin/src/__perf__/module-traversal-cache.test.ts.