From a40693cf05647466422af308acfd1bf349337fa8 Mon Sep 17 00:00:00 2001
From: Joe Lencioni <joe.lencioni@airbnb.com>
Date: Fri, 5 Jun 2020 08:26:58 -0500
Subject: [PATCH] Cache micromatch in SearchSource globsToMatcher

I was profiling some Jest runs at Airbnb and noticed that on my
MacBook Pro, we can spend over 2 seconds at Jest startup time in
SearchSource getTestPaths. I believe that this will grow as the size
of the codebase increases.

Looking at the call stacks, it appears to be calling micromatch
repeatedly, which calls picomatch, which builds a regex out of the
globs. It seems that the parsing and regex building also triggers the
garbage collector frequently.

Upon testing, I noticed that the globs don't actually change between
these calls, so we can save a bunch of work by making a micromatch
matcher and reusing that function for all of the paths.

micromatch has some logic internally to handle lists of globs that
may include negated globs. A naive approach of just checking if it
matched any of the globs won't capture that, so I copied and
simplified the logic from within micromatch.

https://github.com/micromatch/micromatch/blob/fe4858b0/index.js#L27-L77

In my profiling of this change locally, this brings down the time of
startRun from about 2000ms to about 200ms.
---
 CHANGELOG.md                           |  2 ++
 packages/jest-core/src/SearchSource.ts | 50 ++++++++++++++++++++++++--
 2 files changed, 50 insertions(+), 2 deletions(-)

diff --git a/CHANGELOG.md b/CHANGELOG.md
index 85c66a5d976f..c87ad645b840 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -22,6 +22,8 @@
 
 ### Performance
 
+- `[jest-core]` Cache micromatch in SearchSource globsToMatcher ([#10131](https://github.com/facebook/jest/pull/10131))
+
 ## 26.0.1
 
 ### Fixes
diff --git a/packages/jest-core/src/SearchSource.ts b/packages/jest-core/src/SearchSource.ts
index 48c630f2adb4..586cd6ba7070 100644
--- a/packages/jest-core/src/SearchSource.ts
+++ b/packages/jest-core/src/SearchSource.ts
@@ -37,8 +37,54 @@ export type TestSelectionConfig = {
   watch?: boolean;
 };
 
-const globsToMatcher = (globs: Array<Config.Glob>) => (path: Config.Path) =>
-  micromatch([replacePathSepForGlob(path)], globs, {dot: true}).length > 0;
+const globsMatchers = new Map<
+  string,
+  {
+    isMatch: (str: string) => boolean;
+    negated: boolean;
+  }
+>();
+
+const globsToMatcher = (globs: Array<Config.Glob>) => {
+  const matchers = globs.map(glob => {
+    if (!globsMatchers.has(glob)) {
+      const state = micromatch.scan(glob, {dot: true});
+      const matcher = {
+        isMatch: micromatch.matcher(glob, {dot: true}),
+        negated: state.negated,
+      };
+      globsMatchers.set(glob, matcher);
+    }
+    return globsMatchers.get(glob)!;
+  });
+
+  return (path: Config.Path) => {
+    const replacedPath = replacePathSepForGlob(path);
+    let omit = false;
+    let keep = false;
+    let negatives = 0;
+
+    for (let i = 0; i < matchers.length; i++) {
+      const matcher = matchers[i];
+      const {isMatch, negated} = matcher;
+      if (negated) negatives++;
+
+      const matched = isMatch(replacedPath);
+
+      const match = negated ? !matched : matched;
+      if (!match) continue;
+
+      if (negated) {
+        omit = true;
+      } else {
+        omit = false;
+        keep = true;
+      }
+    }
+
+    return negatives === matchers.length ? !keep && !omit : keep && !omit;
+  };
+};
 
 const regexToMatcher = (testRegex: Config.ProjectConfig['testRegex']) => (
   path: Config.Path,