feat(core): Cache ignore instances for performance (#16185)

packages/core/src/utils/gitIgnoreParser.ts

@@ -6,7 +6,7 @@
 
 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;
@@ -14,30 +14,30 @@ export interface GitIgnoreFilter {
 
 export class GitIgnoreParser implements GitIgnoreFilter {
   private projectRoot: string;
-  private cache: Map<string, string[]> = new Map();
-  private globalPatterns: string[] | undefined;
-  private processedExtraPatterns: string[] = [];
+  private cache: Map<string, Ignore> = new Map();
+  private globalPatterns: Ignore | undefined;
+  private processedExtraPatterns: Ignore;
 
   constructor(
     projectRoot: string,
     private readonly extraPatterns?: string[],
   ) {
     this.projectRoot = path.resolve(projectRoot);
+    this.processedExtraPatterns = ignore();
     if (this.extraPatterns) {
       // extraPatterns are assumed to be from project root (like .geminiignore)
-      this.processedExtraPatterns = this.processPatterns(
-        this.extraPatterns,
-        '.',
+      this.processedExtraPatterns.add(
+        this.processPatterns(this.extraPatterns, '.'),
       );
     }
   }
 
-  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);
 
@@ -198,15 +198,13 @@ 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());
           }
         }
       }
 
       // Apply extra patterns (e.g. from .geminiignore) last for precedence
-      if (this.processedExtraPatterns.length > 0) {
-        ig.add(this.processedExtraPatterns);
-      }
+      ig.add(this.processedExtraPatterns);
 
       return ig.ignores(normalizedPath);
     } catch (_error) {