feat(core): Cache ignore instances for performance

This commit optimizes file filtering by caching compiled `ignore`
instances within the `GitIgnoreParser` instead of raw string arrays.

Previously, `.gitignore` files were parsed into an array of rule
strings on every check, leading to redundant processing. The `node-ignore`
library supports adding pre-compiled `ignore` instances, which is
more efficient.

This change modifies the internal cache from `Map<string, string[]>` to
`Map<string, Ignore>` and updates the logic in `isIgnored` to create,
cache, and reuse these compiled instances. This reduces the overhead
associated with parsing ignore files, especially in large projects with
many nested `.gitignore` files.

Fixes #11610

Author: EricRahm

packages/core/src/utils/gitIgnoreParser.ts

@@ -6,16 +6,16 @@
 
 import * as fs from 'node:fs';
 import * as path from 'node:path';
-import ignore from 'ignore';
+import ignore, { type Ignore } from 'ignore';
 
 export interface GitIgnoreFilter {
   isIgnored(filePath: string): boolean;
 }
 
 export class GitIgnoreParser implements GitIgnoreFilter {
   private projectRoot: string;
-  private cache: Map<string, string[]> = new Map();
-  private globalPatterns: string[] | undefined;
+  private cache: Map<string, Ignore> = new Map();
+  private globalPatterns: Ignore | undefined;
   private processedExtraPatterns: string[] = [];
 
   constructor(
@@ -32,12 +32,12 @@ export class GitIgnoreParser implements GitIgnoreFilter {
     }
   }
 
-  private loadPatternsForFile(patternsFilePath: string): string[] {
+  private loadPatternsForFile(patternsFilePath: string): Ignore {
     let content: string;
     try {
       content = fs.readFileSync(patternsFilePath, 'utf-8');
     } catch (_error) {
-      return [];
+      return ignore();
     }
 
     const isExcludeFile = patternsFilePath.endsWith(
@@ -52,7 +52,7 @@ export class GitIgnoreParser implements GitIgnoreFilter {
           .join(path.posix.sep);
 
     const rawPatterns = content.split('\n');
-    return this.processPatterns(rawPatterns, relativeBaseDir);
+    return ignore().add(this.processPatterns(rawPatterns, relativeBaseDir));
   }
 
   private processPatterns(
@@ -155,7 +155,7 @@ export class GitIgnoreParser implements GitIgnoreFilter {
         );
         this.globalPatterns = fs.existsSync(excludeFile)
           ? this.loadPatternsForFile(excludeFile)
-          : [];
+          : ignore();
       }
       ig.add(this.globalPatterns);
 
@@ -198,7 +198,7 @@ export class GitIgnoreParser implements GitIgnoreFilter {
             this.cache.set(dir, patterns);
             ig.add(patterns);
           } else {
-            this.cache.set(dir, []); // Cache miss
+            this.cache.set(dir, ignore());
           }
         }
       }