Preserve inferred project ATA state

tsc/internal/project/ata/ata_test.go

@@ -126,6 +126,41 @@ func TestATA(t *testing.T) {
 		assert.Assert(t, jqueryTypesFile != nil, "jquery types should be installed")
 	})
 
+	t.Run("inferred project retains typings after closing last file", func(t *testing.T) {
+		t.Parallel()
+
+		files := map[string]any{
+			"/user/username/projects/project/app.js": ``,
+			"/user/username/projects/project/package.json": `{
+				"name": "test",
+				"dependencies": {
+					"jquery": "^3.1.0"
+				}
+			}`,
+		}
+
+		session, _ := projecttestutil.SetupWithTypingsInstaller(files, &projecttestutil.TypingsInstallerOptions{
+			PackageToFile: map[string]string{
+				"jquery": `declare const $: { x: number }`,
+			},
+		})
+
+		uri := lsproto.DocumentUri("file:///user/username/projects/project/app.js")
+		session.DidOpenFile(context.Background(), uri, 1, files["/user/username/projects/project/app.js"].(string), lsproto.LanguageKindJavaScript)
+		session.WaitForBackgroundTasks()
+		_, err := session.GetLanguageService(context.Background(), uri)
+		assert.NilError(t, err)
+
+		session.DidCloseFile(context.Background(), uri)
+		session.WaitForBackgroundTasks()
+		session.DidOpenFile(context.Background(), uri, 1, files["/user/username/projects/project/app.js"].(string), lsproto.LanguageKindJavaScript)
+
+		ls, err := session.GetLanguageService(context.Background(), uri)
+		assert.NilError(t, err)
+		typingsFile := ls.GetProgram().GetSourceFile(projecttestutil.TestTypingsLocation + "/node_modules/@types/jquery/index.d.ts")
+		assert.Assert(t, typingsFile != nil, "jquery types should be available immediately after reopening")
+	})
+
 	t.Run("type acquisition with disableFilenameBasedTypeAcquisition:true", func(t *testing.T) {
 		t.Parallel()
 

tsc/internal/project/project.go

@@ -172,6 +172,32 @@ type Project struct {
 	typingsFiles []string
 }
 
+type inferredProjectATAState struct {
+	installedTypingsInfo *ata.TypingsInfo
+	typingsFiles         []string
+	typingsWatch         *WatchedFiles[PatternsAndIgnored]
+}
+
+func (p *Project) inferredProjectATAState() *inferredProjectATAState {
+	if p.installedTypingsInfo == nil {
+		return nil
+	}
+	return &inferredProjectATAState{
+		installedTypingsInfo: p.installedTypingsInfo,
+		typingsFiles:         slices.Clone(p.typingsFiles),
+		typingsWatch:         p.typingsWatch,
+	}
+}
+
+func (s *inferredProjectATAState) apply(project *Project) {
+	if s == nil {
+		return
+	}
+	project.installedTypingsInfo = s.installedTypingsInfo
+	project.typingsFiles = slices.Clone(s.typingsFiles)
+	project.typingsWatch = s.typingsWatch
+}
+
 var _ ls.Project = (*Project)(nil)
 
 func NewConfiguredProject(

tsc/internal/project/projectcollection.go

@@ -31,6 +31,9 @@ type ProjectCollection struct {
 	// inferredProject is a fallback project that is used when no configured
 	// project can be found for an open file.
 	inferredProject *Project
+	// inferredProjectATAState preserves acquired typings while there is no active
+	// inferred project, so reopening a loose file does not wait for ATA again.
+	inferredProjectATAState *inferredProjectATAState
 	// apiState tracks the projects and files that API clients have explicitly
 	// opened so they are kept loaded across snapshots.
 	apiState APIState
@@ -328,14 +331,15 @@ func (c *ProjectCollection) findDefaultConfiguredProjectWorker(path tspath.Path,
 // clone creates a shallow copy of the project collection.
 func (c *ProjectCollection) clone() *ProjectCollection {
 	return &ProjectCollection{
-		toPath:              c.toPath,
-		configFileRegistry:  c.configFileRegistry,
-		configuredProjects:  c.configuredProjects,
-		syntheticProjects:   c.syntheticProjects,
-		openFiles:           c.openFiles,
-		inferredProject:     c.inferredProject,
-		fileDefaultProjects: c.fileDefaultProjects,
-		apiState:            c.apiState,
+		toPath:                  c.toPath,
+		configFileRegistry:      c.configFileRegistry,
+		configuredProjects:      c.configuredProjects,
+		syntheticProjects:       c.syntheticProjects,
+		openFiles:               c.openFiles,
+		inferredProject:         c.inferredProject,
+		inferredProjectATAState: c.inferredProjectATAState,
+		fileDefaultProjects:     c.fileDefaultProjects,
+		apiState:                c.apiState,
 	}
 }
 

tsc/internal/project/projectcollectionbuilder.go

@@ -56,11 +56,12 @@ type ProjectCollectionBuilder struct {
 	defaultProjectsInvalidated bool
 	openFilesChanged           bool
 
-	fileDefaultProjects map[tspath.Path]ID
-	configuredProjects  *dirty.SyncMap[ConfiguredProjectID, *Project]
-	syntheticProjects   *dirty.SyncMap[SyntheticProjectID, *Project]
-	inferredProject     *dirty.Box[*Project]
-	createdPrograms     []*Project
+	fileDefaultProjects     map[tspath.Path]ID
+	configuredProjects      *dirty.SyncMap[ConfiguredProjectID, *Project]
+	syntheticProjects       *dirty.SyncMap[SyntheticProjectID, *Project]
+	inferredProject         *dirty.Box[*Project]
+	inferredProjectATAState *inferredProjectATAState
+	createdPrograms         []*Project
 
 	apiState APIState
 }
@@ -105,6 +106,7 @@ func newProjectCollectionBuilder(
 		configuredProjects:                 dirty.NewSyncMap(oldProjectCollection.configuredProjects),
 		syntheticProjects:                  dirty.NewSyncMap(oldProjectCollection.syntheticProjects),
 		inferredProject:                    dirty.NewBox(oldProjectCollection.inferredProject),
+		inferredProjectATAState:            oldProjectCollection.inferredProjectATAState,
 		apiState:                           oldAPIState.clone(),
 		client:                             client,
 	}
@@ -148,6 +150,10 @@ func (b *ProjectCollectionBuilder) Finalize(logger *logging.LogTree) (*ProjectCo
 		ensureCloned()
 		newProjectCollection.inferredProject = newInferredProject
 	}
+	if b.inferredProjectATAState != b.base.inferredProjectATAState {
+		ensureCloned()
+		newProjectCollection.inferredProjectATAState = b.inferredProjectATAState
+	}
 
 	configFileRegistry := b.configFileRegistryBuilder.Finalize()
 	if configFileRegistry != b.base.configFileRegistry {
@@ -1343,6 +1349,7 @@ func (b *ProjectCollectionBuilder) deleteInferredProject(logger *logging.LogTree
 			return true
 		})
 	}
+	b.inferredProjectATAState = project.inferredProjectATAState()
 	b.inferredProject.Delete()
 	return true
 }
@@ -1360,6 +1367,7 @@ func (b *ProjectCollectionBuilder) updateOrCreateInferredProject(
 	project := b.inferredProject.Value()
 	if project == nil {
 		project = NewInferredProject(b.sessionOptions.CurrentDirectory, compilerOptions, rootFileNames, projectReferences, contentMappers, b, logger)
+		b.inferredProjectATAState.apply(project)
 		project.CommandLine.Errors = configFileParsingDiagnostics
 		b.inferredProject.Set(project)
 		return true