From e3b72e17ec206c960e81a1d376cd47e9c39cd42e Mon Sep 17 00:00:00 2001
From: Neil <4138956+nwparker@users.noreply.github.com>
Date: Sat, 12 Sep 2026 18:12:58 -0700
Subject: [PATCH] perf: skip nonmatching spans in quick open fuzzy scoring
 (#20349)

---
 src/shared/quick-open-fuzzy-scan.test.ts | 118 +++++++++++++++++++++++
 src/shared/quick-open-path-search.ts     |   9 +-
 2 files changed, 124 insertions(+), 3 deletions(-)
 create mode 100644 src/shared/quick-open-fuzzy-scan.test.ts

diff --git a/src/shared/quick-open-fuzzy-scan.test.ts b/src/shared/quick-open-fuzzy-scan.test.ts
new file mode 100644
index 00000000000..db209bfe471
--- /dev/null
+++ b/src/shared/quick-open-fuzzy-scan.test.ts
@@ -0,0 +1,118 @@
+import { expect, it } from 'vitest'
+import { compareFileNames } from './file-name-sort'
+import {
+  prepareQuickOpenFiles,
+  QuickOpenPathRanker,
+  rankQuickOpenFiles,
+  type QuickOpenIndexedFile
+} from './quick-open-path-search'
+
+function referenceScore(query: string, file: QuickOpenIndexedFile): number {
+  let qi = 0
+  let score = 0
+  let lastMatch = -1
+  for (let ti = 0; ti < file.lowerPath.length && qi < query.length; ti++) {
+    if (file.lowerPath[ti] !== query[qi]) {
+      continue
+    }
+    score += lastMatch === -1 ? 0 : ti - lastMatch - 1
+    if (ti > 0 && '/.-'.includes(file.lowerPath[ti - 1])) {
+      score -= 5
+    }
+    lastMatch = ti
+    qi++
+  }
+  if (qi < query.length) {
+    return -1
+  }
+  return score - (file.lowerFilename.includes(query) ? 100 : 0)
+}
+
+it.each(['az', 'aq'])('skips nonmatching path spans for %s', (query) => {
+  const [prepared] = prepareQuickOpenFiles([`a/${'x'.repeat(4000)}/z.ts`])
+  let pathReads = 0
+  const measured = {
+    ...prepared,
+    get lowerPath() {
+      pathReads++
+      return prepared.lowerPath
+    }
+  }
+  expect(rankQuickOpenFiles(query, [measured])).toEqual(rankQuickOpenFiles(query, [prepared]))
+  expect(pathReads).toBeLessThanOrEqual(20)
+})
+
+it('preserves code-unit scores and ordering for generated Unicode paths and queries', () => {
+  const alphabet = [
+    'a',
+    'b',
+    'c',
+    '/',
+    '\\',
+    '.',
+    '-',
+    '2',
+    '0',
+    'é',
+    'e\u0301',
+    'İ',
+    '😀',
+    '\ud800',
+    '\udc00'
+  ]
+  let seed = 43
+  const next = () => {
+    seed = (Math.imul(seed, 1664525) + 1013904223) >>> 0
+    return seed
+  }
+  const paths = ['a.../b', 'a/x/z', 'a/z', '😀.ts', 'a'.repeat(110), 'aa', 'same', 'same', '']
+  for (let index = 0; index < 1000; index++) {
+    const length = next() % 80
+    let path = ''
+    for (let offset = 0; offset < length; offset++) {
+      path += alphabet[next() % alphabet.length]
+    }
+    paths.push(path)
+  }
+  const files = prepareQuickOpenFiles(paths)
+  const queries = [
+    '',
+    ' ',
+    'az',
+    'ab',
+    'a',
+    'aa',
+    'q',
+    '😀',
+    '\ud800',
+    '\udc00',
+    'é',
+    'e\u0301',
+    'İ',
+    'a\\b',
+    '  A  '
+  ]
+  for (let index = 0; index < 100; index++) {
+    queries.push(`${alphabet[next() % alphabet.length]}${alphabet[next() % alphabet.length]}`)
+  }
+  for (const query of queries) {
+    const normalized = query.trim().replace(/\\/g, '/').toLowerCase()
+    const expected = files
+      .map((file) => ({ ...file, score: normalized ? referenceScore(normalized, file) : 0 }))
+      .filter((file) => file.score !== -1)
+      .sort(
+        (a, b) =>
+          a.score - b.score || compareFileNames(a.path, b.path) || a.inputIndex - b.inputIndex
+      )
+    for (const limit of [1, 16, 50]) {
+      const selected = expected.slice(0, limit).map(({ path, score }) => ({ path, score }))
+      expect(rankQuickOpenFiles(query, files, limit)).toEqual(selected)
+      const streamed = new QuickOpenPathRanker(query, limit)
+      paths.forEach((path) => streamed.consider(path))
+      expect(streamed.result()).toEqual({
+        paths: selected.map((entry) => entry.path),
+        totalCount: expected.length
+      })
+    }
+  }
+})
diff --git a/src/shared/quick-open-path-search.ts b/src/shared/quick-open-path-search.ts
index 5680abf8286..2e2dbff4d84 100644
--- a/src/shared/quick-open-path-search.ts
+++ b/src/shared/quick-open-path-search.ts
@@ -126,9 +126,12 @@ function fuzzyMatchIndexedFile(query: string, file: QuickOpenIndexedFile): numbe
   let score = 0
   let lastMatchIdx = -1
 
-  for (let ti = 0; ti < file.lowerPath.length && qi < query.length; ti++) {
-    if (file.lowerPath[ti] !== query[qi]) {
-      continue
+  while (qi < query.length) {
+    const next = lastMatchIdx + 1
+    const ti =
+      file.lowerPath[next] === query[qi] ? next : file.lowerPath.indexOf(query[qi], next + 1)
+    if (ti === -1) {
+      return -1
     }
     const gap = lastMatchIdx === -1 ? 0 : ti - lastMatchIdx - 1
     score += gap