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perf: skip unnecessary import detection work#546

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perf/optimize-import-detection
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perf: skip unnecessary import detection work#546
TheAlexLichter wants to merge 1 commit into
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perf/optimize-import-detection

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@TheAlexLichter TheAlexLichter commented Jun 21, 2026 •
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This PR improves unimport performance:

  • It skips expensive import detection when code contains no registered auto-import candidates.
  • It also defers static-import parsing until needed while preserving addons, virtual imports, custom parsers, and debug logging.

Benchmark

According to my local benchmarks via Nuxt, I saw a 48% reduction for the "transform-heavy workload". As comparison: Just the old "fail-fast precheck" took 929.1ms.

Median
origin/main 1,162.4 ms
This branch 603.4 ms

A manually constructed "worst case" scenario got roughly 6% worse (late hits using injectAtEnd).

Summary by CodeRabbit

  • New Features

    • Import detection can now skip processing when unnecessary, improving performance.

  • Tests

    • Added test coverage for addon transformations and injections in edge cases.

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coderabbitai Bot commented Jun 21, 2026 •
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Review Change Stack

📝 Walkthrough

Walkthrough

src/context.ts gains a canSkipImportDetection helper and a RE_IDENTIFIER regex. Inside injectImports, an early-return branch calls this helper to bypass detectImports/resolveImports when no relevant identifiers are found. src/utils.ts moves strippedCode inside its lazy-init block. Tests cover the new skip and addon-hook paths.

Changes

Import Detection Skip Optimization

Layer / File(s) Summary
canSkipImportDetection logic and early-return in injectImports
src/context.ts		 Adds RE_IDENTIFIER regex and canSkipImportDetection async function. Checks parser mode, addon hook presence, virtual-import handling, autoImport === false, and identifier matches against ctx.getImportMap(). Inserts early-return branch in injectImports that calls this helper, emitting an optional debug log and returning an empty imports list when skipping is safe.
Lazy strippedCode computation fix
src/utils.ts		 Moves strippedCode = stripCommentsAndStrings(s.original) inside the if (!_staticImports) guard in findStaticImportsLazy, so it is computed only on first access.
Tests for skip paths and addon hooks with no candidates
test/addon-match-imports.test.ts, test/inject.test.ts		 Adds a test asserting addon match imports resolve ElInput even without registered candidates. Adds three tests confirming that with zero auto-detectable candidates, addon transform and injectImportsStringified hooks still run, and debugLog emits the expected "0 imports detected" message.

Estimated code review effort

🎯 3 (Moderate) | ⏱️ ~20 minutes

Poem

🐇 When no imports are found in the code so bare,
I skip all the scanning with thoughtful flair!
A regex, a flag, and a hook-check or two —
The bunny leaps fast when there's nothing to do.
Addon hooks still fire, and the debug log sings,
"Zero imports detected!" — efficiency rings! 🎉

🚥 Pre-merge checks | ✅ 4 | ❌ 1

❌ Failed checks (1 warning)

Check name Status Explanation Resolution
Docstring Coverage ⚠️ Warning Docstring coverage is 0.00% which is insufficient. The required threshold is 80.00%. Write docstrings for the functions missing them to satisfy the coverage threshold.
✅ Passed checks (4 passed)
Check name Status Explanation
Title check ✅ Passed The title 'perf: skip unnecessary import detection work' directly and clearly describes the main change: a performance optimization that skips import detection when it's not needed.
Linked Issues check ✅ Passed Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check ✅ Passed Check skipped because no linked issues were found for this pull request.
Description Check ✅ Passed Check skipped - CodeRabbit’s high-level summary is enabled.

✏️ Tip: You can configure your own custom pre-merge checks in the settings.

✨ Finishing Touches
📝 Generate docstrings
  • Create stacked PR
  • Commit on current branch
🧪 Generate unit tests (beta)
  • Create PR with unit tests
  • Commit unit tests in branch perf/optimize-import-detection

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@TheAlexLichter TheAlexLichter marked this pull request as draft June 21, 2026 12:14
@TheAlexLichter TheAlexLichter marked this pull request as ready for review June 21, 2026 12:22
@TheAlexLichter TheAlexLichter requested a review from antfu June 21, 2026 12:23
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