perf(ProjectManager): cache PathCollection per project in flushDocumentChanges (#1628)

Co-authored-by: Cursor <cursoragent@cursor.com>
Co-authored-by: Bronley Plumb <bronley@gmail.com>

Author: 3 people

src/lsp/ProjectManager.spec.ts

@@ -585,6 +585,41 @@ describe('ProjectManager', () => {
     });
 
     describe('flushDocumentChanges', () => {
+        it('reuses cached PathCollection across multiple flushes', async () => {
+            fsExtra.outputFileSync(`${rootDir}/source/main.brs`, ``);
+            fsExtra.outputJsonSync(`${rootDir}/bsconfig.json`, {});
+            await manager.syncProjects([workspaceSettings]);
+
+            //spy on PathCollection constructor to count how many are created
+            const project = manager.projects[0];
+            //first flush to warm the cache
+            await manager['flushDocumentChanges']({
+                actions: [{
+                    srcPath: s`${rootDir}/source/main.brs`,
+                    type: 'set',
+                    fileContents: 'sub main():end sub',
+                    allowStandaloneProject: true
+                }]
+            });
+
+            //grab the cached filterer
+            const cachedFilterer = manager['projectFiltererCache'].get(project);
+            expect(cachedFilterer).to.exist;
+
+            //second flush should reuse the same filterer instance
+            await manager['flushDocumentChanges']({
+                actions: [{
+                    srcPath: s`${rootDir}/source/main.brs`,
+                    type: 'set',
+                    fileContents: 'sub main2():end sub',
+                    allowStandaloneProject: true
+                }]
+            });
+
+            const cachedFilterer2 = manager['projectFiltererCache'].get(project);
+            expect(cachedFilterer2).to.equal(cachedFilterer);
+        });
+
         it('does not crash when getting undefined back from projects', async () => {
             fsExtra.outputFileSync(`${rootDir}/source/main.brs`, ``);
             fsExtra.outputJsonSync(`${rootDir}/project1/bsconfig.json`, {

src/lsp/ProjectManager.ts

@@ -72,6 +72,28 @@ export class ProjectManager {
 
     public busyStatusTracker = new BusyStatusTracker<LspProject>();
 
+    /**
+     * Cache for PathCollection instances per project. Avoids recreating PathCollection
+     * on every document flush, which is wasteful since file patterns only change when a project is reloaded.
+     */
+    private projectFiltererCache = new WeakMap<LspProject, PathCollection>();
+
+    /**
+     * Get or create a cached PathCollection for the given project.
+     * The filterer is invalidated when the project is removed and garbage collected.
+     */
+    private getProjectFilterer(project: LspProject): PathCollection {
+        let filterer = this.projectFiltererCache.get(project);
+        if (!filterer) {
+            filterer = new PathCollection({
+                rootDir: project.rootDir,
+                globs: project.filePatterns
+            });
+            this.projectFiltererCache.set(project, filterer);
+        }
+        return filterer;
+    }
+
     /**
      * Apply all of the queued document changes. This should only be called as a result of the documentManager flushing changes, and never called manually
      * @param event the document changes that have occurred since the last time we applied
@@ -101,10 +123,7 @@ export class ProjectManager {
             //wait for this project to finish activating
             await project.whenActivated();
 
-            const filterer = new PathCollection({
-                rootDir: project.rootDir,
-                globs: project.filePatterns
-            });
+            const filterer = this.getProjectFilterer(project);
             // only include files that are applicable to this specific project (still allow deletes to flow through since they're cheap)
             const projectActions = actions.filter(action => {
                 return (