Ensure inferred project has up to date program when it might contain the requested file (microsoft#2608)

Author: andrewbranch

internal/project/projectcollectionbuilder.go

@@ -365,6 +365,9 @@ func (b *ProjectCollectionBuilder) DidRequestFile(uri lsproto.DocumentUri, logge
 			if result.Value() != nil {
 				if hasChanges {
 					b.cleanupInferredProject(logger)
+					if b.inferredProject.Value() != nil {
+						b.updateProgram(b.inferredProject, logger)
+					}
 				}
 				return
 			}

internal/project/projectcollectionbuilder_test.go

@@ -514,6 +514,52 @@ func TestProjectCollectionBuilder(t *testing.T) {
 		session.DidOpenFile(context.Background(), "file:///script.ts", 1, files["/script.ts"].(string), lsproto.LanguageKindTypeScript)
 		// Test should terminate
 	})
+
+	t.Run("file moves to inferred project after import is deleted", func(t *testing.T) {
+		t.Parallel()
+		// This test verifies that when a node_modules dependency file is open and its import
+		// is deleted from the project root, requesting language service for the dependency
+		// correctly moves it to an inferred project.
+		files := map[string]any{
+			"/project/tsconfig.json":               `{"compilerOptions": {"strict": true}}`,
+			"/project/index.ts":                    `import { helper } from "./node_modules/dep/index";`,
+			"/project/node_modules/dep/index.d.ts": `export declare function helper(): void;`,
+		}
+		session, _ := projecttestutil.Setup(files)
+
+		// Step 1: Open the project root file
+		rootUri := lsproto.DocumentUri("file:///project/index.ts")
+		session.DidOpenFile(context.Background(), rootUri, 1, files["/project/index.ts"].(string), lsproto.LanguageKindTypeScript)
+		_, err := session.GetLanguageService(context.Background(), rootUri)
+		assert.NilError(t, err)
+
+		// Step 2: Open the node_modules dependency file - should be in the configured project
+		depUri := lsproto.DocumentUri("file:///project/node_modules/dep/index.d.ts")
+		session.DidOpenFile(context.Background(), depUri, 1, files["/project/node_modules/dep/index.d.ts"].(string), lsproto.LanguageKindTypeScript)
+
+		snapshot, release := session.Snapshot()
+		configuredProject := snapshot.ProjectCollection.ConfiguredProject(tspath.Path("/project/tsconfig.json"))
+		assert.Assert(t, configuredProject != nil, "configured project should exist")
+		defaultProject := snapshot.GetDefaultProject(depUri)
+		assert.Equal(t, defaultProject, configuredProject, "dependency should be in the configured project initially")
+		release()
+
+		// Step 3: Delete the import from the root file
+		session.DidChangeFile(context.Background(), rootUri, 2, []lsproto.TextDocumentContentChangePartialOrWholeDocument{{
+			WholeDocument: &lsproto.TextDocumentContentChangeWholeDocument{Text: `// import removed`},
+		}})
+
+		// Step 4: Request language service for the dependency - it should now be in an inferred project
+		ls, err := session.GetLanguageService(context.Background(), depUri)
+		assert.NilError(t, err)
+		assert.Assert(t, ls != nil, "language service should be available for dependency")
+
+		snapshot, release = session.Snapshot()
+		defer release()
+		defaultProject = snapshot.GetDefaultProject(depUri)
+		assert.Assert(t, defaultProject != nil, "dependency should have a default project")
+		assert.Equal(t, defaultProject.Kind, project.KindInferred, "dependency should be in an inferred project after import is deleted")
+	})
 }
 
 func filesForSolutionConfigFile(solutionRefs []string, compilerOptions string, ownFiles []string) map[string]any {