From 976c1562ddbc17e7bc185ca827aeffefced7a1b6 Mon Sep 17 00:00:00 2001
From: Jake Bailey <5341706+jakebailey@users.noreply.github.com>
Date: Fri, 30 May 2025 11:44:00 -0700
Subject: [PATCH 1/9] Cache FS in LS

---
 internal/project/project.go | 32 ++++++++++++++++++++++++++------
 1 file changed, 26 insertions(+), 6 deletions(-)

diff --git a/internal/project/project.go b/internal/project/project.go
index 75be8ee20f..3450ae5b13 100644
--- a/internal/project/project.go
+++ b/internal/project/project.go
@@ -17,6 +17,7 @@ import (
 	"github.com/microsoft/typescript-go/internal/tsoptions"
 	"github.com/microsoft/typescript-go/internal/tspath"
 	"github.com/microsoft/typescript-go/internal/vfs"
+	"github.com/microsoft/typescript-go/internal/vfs/cachedvfs"
 )
 
 //go:generate go tool golang.org/x/tools/cmd/stringer -type=Kind -output=project_stringer_generated.go
@@ -87,7 +88,7 @@ type ProjectHost interface {
 var _ compiler.CompilerHost = (*Project)(nil)
 
 type Project struct {
-	host ProjectHost
+	host *projectHostWithCachedFS
 
 	name string
 	kind Kind
@@ -141,9 +142,11 @@ func NewInferredProject(compilerOptions *core.CompilerOptions, currentDirectory
 }
 
 func NewProject(name string, kind Kind, currentDirectory string, host ProjectHost) *Project {
+	cachedHost := newProjectHostWithCachedFS(host)
+
 	host.Log(fmt.Sprintf("Creating %sProject: %s, currentDirectory: %s", kind.String(), name, currentDirectory))
 	project := &Project{
-		host:             host,
+		host:             cachedHost,
 		name:             name,
 		kind:             kind,
 		currentDirectory: currentDirectory,
@@ -151,11 +154,11 @@ func NewProject(name string, kind Kind, currentDirectory string, host ProjectHos
 	}
 	project.comparePathsOptions = tspath.ComparePathsOptions{
 		CurrentDirectory:          currentDirectory,
-		UseCaseSensitiveFileNames: host.FS().UseCaseSensitiveFileNames(),
+		UseCaseSensitiveFileNames: project.host.FS().UseCaseSensitiveFileNames(),
 	}
-	client := host.Client()
-	if host.IsWatchEnabled() && client != nil {
-		globMapper := createGlobMapper(host)
+	client := project.host.Client()
+	if project.host.IsWatchEnabled() && client != nil {
+		globMapper := createGlobMapper(project.host)
 		project.failedLookupsWatch = newWatchedFiles(client, lsproto.WatchKindCreate, globMapper)
 		project.affectingLocationsWatch = newWatchedFiles(client, lsproto.WatchKindChange|lsproto.WatchKindCreate|lsproto.WatchKindDelete, globMapper)
 	}
@@ -163,6 +166,22 @@ func NewProject(name string, kind Kind, currentDirectory string, host ProjectHos
 	return project
 }
 
+type projectHostWithCachedFS struct {
+	ProjectHost
+	fs *cachedvfs.FS
+}
+
+func newProjectHostWithCachedFS(host ProjectHost) *projectHostWithCachedFS {
+	return &projectHostWithCachedFS{
+		ProjectHost: host,
+		fs:          cachedvfs.From(host.FS()),
+	}
+}
+
+func (p *projectHostWithCachedFS) FS() vfs.FS {
+	return p.fs
+}
+
 // FS implements compiler.CompilerHost.
 func (p *Project) FS() vfs.FS {
 	return p.host.FS()
@@ -406,6 +425,7 @@ func (p *Project) updateGraph() bool {
 
 	start := time.Now()
 	p.log("Starting updateGraph: Project: " + p.name)
+	p.host.fs.ClearCache()
 	var writeFileNames bool
 	oldProgram := p.program
 	p.initialLoadPending = false

From 163289ca5e1598f8c4b79c097b7310f1c7c92627 Mon Sep 17 00:00:00 2001
From: Jake Bailey <5341706+jakebailey@users.noreply.github.com>
Date: Fri, 30 May 2025 14:05:13 -0700
Subject: [PATCH 2/9] Don't replace FS out from under host

---
 internal/project/service_test.go              | 67 +++++++------------
 .../projecttestutil/projecttestutil.go        |  4 --
 2 files changed, 24 insertions(+), 47 deletions(-)

diff --git a/internal/project/service_test.go b/internal/project/service_test.go
index c4533383cc..1702fb7460 100644
--- a/internal/project/service_test.go
+++ b/internal/project/service_test.go
@@ -209,7 +209,7 @@ func TestService(t *testing.T) {
 				},
 				"include": ["src/index.ts"]
 			}`
-			service, host := projecttestutil.Setup(files)
+			service, _ := projecttestutil.Setup(files)
 			service.OpenFile("/home/projects/TS/p1/src/index.ts", files["/home/projects/TS/p1/src/index.ts"].(string), core.ScriptKindTS, "")
 			_, project := service.EnsureDefaultProjectForFile("/home/projects/TS/p1/src/index.ts")
 			programBefore := project.GetProgram()
@@ -250,7 +250,6 @@ func TestService(t *testing.T) {
 				},
 				"include": ["./**/*"]
 			}`
-			host.ReplaceFS(files)
 			err = service.OnWatchedFilesChanged(t.Context(), []*lsproto.FileEvent{
 				{
 					Type: lsproto.FileChangeTypeChanged,
@@ -270,14 +269,13 @@ func TestService(t *testing.T) {
 			t.Parallel()
 			t.Run("delete a file, close it, recreate it", func(t *testing.T) {
 				t.Parallel()
-				service, host := projecttestutil.Setup(defaultFiles)
-				service.OpenFile("/home/projects/TS/p1/src/x.ts", defaultFiles["/home/projects/TS/p1/src/x.ts"].(string), core.ScriptKindTS, "")
+				files := maps.Clone(defaultFiles)
+				service, _ := projecttestutil.Setup(files)
+				service.OpenFile("/home/projects/TS/p1/src/x.ts", files["/home/projects/TS/p1/src/x.ts"].(string), core.ScriptKindTS, "")
 				service.OpenFile("/home/projects/TS/p1/src/index.ts", defaultFiles["/home/projects/TS/p1/src/index.ts"].(string), core.ScriptKindTS, "")
 				assert.Equal(t, service.SourceFileCount(), 2)
 
-				files := maps.Clone(defaultFiles)
 				delete(files, "/home/projects/TS/p1/src/x.ts")
-				host.ReplaceFS(files)
 
 				service.CloseFile("/home/projects/TS/p1/src/x.ts")
 				assert.Check(t, service.GetScriptInfo("/home/projects/TS/p1/src/x.ts") == nil)
@@ -285,7 +283,6 @@ func TestService(t *testing.T) {
 				assert.Equal(t, service.SourceFileCount(), 1)
 
 				files["/home/projects/TS/p1/src/x.ts"] = ``
-				host.ReplaceFS(files)
 				service.OpenFile("/home/projects/TS/p1/src/x.ts", files["/home/projects/TS/p1/src/x.ts"].(string), core.ScriptKindTS, "")
 				assert.Equal(t, service.GetScriptInfo("/home/projects/TS/p1/src/x.ts").Text(), "")
 				assert.Check(t, service.Projects()[0].GetProgram().GetSourceFile("/home/projects/TS/p1/src/x.ts") != nil)
@@ -299,19 +296,17 @@ func TestService(t *testing.T) {
 				t.Parallel()
 				files := maps.Clone(defaultFiles)
 				delete(files, "/home/projects/TS/p1/tsconfig.json")
-				service, host := projecttestutil.Setup(files)
-				service.OpenFile("/home/projects/TS/p1/src/x.ts", defaultFiles["/home/projects/TS/p1/src/x.ts"].(string), core.ScriptKindTS, "")
-				service.OpenFile("/home/projects/TS/p1/src/index.ts", defaultFiles["/home/projects/TS/p1/src/index.ts"].(string), core.ScriptKindTS, "")
+				service, _ := projecttestutil.Setup(files)
+				service.OpenFile("/home/projects/TS/p1/src/x.ts", files["/home/projects/TS/p1/src/x.ts"].(string), core.ScriptKindTS, "")
+				service.OpenFile("/home/projects/TS/p1/src/index.ts", files["/home/projects/TS/p1/src/index.ts"].(string), core.ScriptKindTS, "")
 
 				delete(files, "/home/projects/TS/p1/src/x.ts")
-				host.ReplaceFS(files)
 
 				service.CloseFile("/home/projects/TS/p1/src/x.ts")
 				assert.Check(t, service.GetScriptInfo("/home/projects/TS/p1/src/x.ts") == nil)
 				assert.Check(t, service.Projects()[0].GetProgram().GetSourceFile("/home/projects/TS/p1/src/x.ts") == nil)
 
 				files["/home/projects/TS/p1/src/x.ts"] = ``
-				host.ReplaceFS(files)
 				service.OpenFile("/home/projects/TS/p1/src/x.ts", files["/home/projects/TS/p1/src/x.ts"].(string), core.ScriptKindTS, "")
 				assert.Equal(t, service.GetScriptInfo("/home/projects/TS/p1/src/x.ts").Text(), "")
 				assert.Check(t, service.Projects()[0].GetProgram().GetSourceFile("/home/projects/TS/p1/src/x.ts") != nil)
@@ -375,15 +370,14 @@ func TestService(t *testing.T) {
 
 		t.Run("change open file", func(t *testing.T) {
 			t.Parallel()
-			service, host := projecttestutil.Setup(defaultFiles)
-			service.OpenFile("/home/projects/TS/p1/src/x.ts", defaultFiles["/home/projects/TS/p1/src/x.ts"].(string), core.ScriptKindTS, "")
-			service.OpenFile("/home/projects/TS/p1/src/index.ts", defaultFiles["/home/projects/TS/p1/src/index.ts"].(string), core.ScriptKindTS, "")
+			files := maps.Clone(defaultFiles)
+			service, _ := projecttestutil.Setup(files)
+			service.OpenFile("/home/projects/TS/p1/src/x.ts", files["/home/projects/TS/p1/src/x.ts"].(string), core.ScriptKindTS, "")
+			service.OpenFile("/home/projects/TS/p1/src/index.ts", files["/home/projects/TS/p1/src/index.ts"].(string), core.ScriptKindTS, "")
 			_, project := service.EnsureDefaultProjectForFile("/home/projects/TS/p1/src/index.ts")
 			programBefore := project.GetProgram()
 
-			files := maps.Clone(defaultFiles)
 			files["/home/projects/TS/p1/src/x.ts"] = `export const x = 2;`
-			host.ReplaceFS(files)
 			assert.NilError(t, service.OnWatchedFilesChanged(t.Context(), []*lsproto.FileEvent{
 				{
 					Type: lsproto.FileChangeTypeChanged,
@@ -396,14 +390,13 @@ func TestService(t *testing.T) {
 
 		t.Run("change closed program file", func(t *testing.T) {
 			t.Parallel()
-			service, host := projecttestutil.Setup(defaultFiles)
-			service.OpenFile("/home/projects/TS/p1/src/index.ts", defaultFiles["/home/projects/TS/p1/src/index.ts"].(string), core.ScriptKindTS, "")
+			files := maps.Clone(defaultFiles)
+			service, _ := projecttestutil.Setup(files)
+			service.OpenFile("/home/projects/TS/p1/src/index.ts", files["/home/projects/TS/p1/src/index.ts"].(string), core.ScriptKindTS, "")
 			_, project := service.EnsureDefaultProjectForFile("/home/projects/TS/p1/src/index.ts")
 			programBefore := project.GetProgram()
 
-			files := maps.Clone(defaultFiles)
 			files["/home/projects/TS/p1/src/x.ts"] = `export const x = 2;`
-			host.ReplaceFS(files)
 			assert.NilError(t, service.OnWatchedFilesChanged(t.Context(), []*lsproto.FileEvent{
 				{
 					Type: lsproto.FileChangeTypeChanged,
@@ -429,20 +422,18 @@ func TestService(t *testing.T) {
 					let y: number = x;`,
 			}
 
-			service, host := projecttestutil.Setup(files)
+			service, _ := projecttestutil.Setup(files)
 			service.OpenFile("/home/projects/TS/p1/src/index.ts", files["/home/projects/TS/p1/src/index.ts"].(string), core.ScriptKindTS, "")
 			_, project := service.EnsureDefaultProjectForFile("/home/projects/TS/p1/src/index.ts")
 			program := project.GetProgram()
 			assert.Equal(t, len(program.GetSemanticDiagnostics(projecttestutil.WithRequestID(t.Context()), program.GetSourceFile("/home/projects/TS/p1/src/index.ts"))), 0)
 
-			filesCopy := maps.Clone(files)
-			filesCopy["/home/projects/TS/p1/tsconfig.json"] = `{
+			files["/home/projects/TS/p1/tsconfig.json"] = `{
 				"compilerOptions": {
 					"noLib": false,
 					"strict": true
 				}
 			}`
-			host.ReplaceFS(filesCopy)
 			assert.NilError(t, service.OnWatchedFilesChanged(t.Context(), []*lsproto.FileEvent{
 				{
 					Type: lsproto.FileChangeTypeChanged,
@@ -466,15 +457,13 @@ func TestService(t *testing.T) {
 				"/home/projects/TS/p1/src/x.ts":     `export declare const x: number | undefined;`,
 				"/home/projects/TS/p1/src/index.ts": `import { x } from "./x";`,
 			}
-			service, host := projecttestutil.Setup(files)
+			service, _ := projecttestutil.Setup(files)
 			service.OpenFile("/home/projects/TS/p1/src/index.ts", files["/home/projects/TS/p1/src/index.ts"].(string), core.ScriptKindTS, "")
 			_, project := service.EnsureDefaultProjectForFile("/home/projects/TS/p1/src/index.ts")
 			program := project.GetProgram()
 			assert.Equal(t, len(program.GetSemanticDiagnostics(projecttestutil.WithRequestID(t.Context()), program.GetSourceFile("/home/projects/TS/p1/src/index.ts"))), 0)
 
-			filesCopy := maps.Clone(files)
-			delete(filesCopy, "/home/projects/TS/p1/src/x.ts")
-			host.ReplaceFS(filesCopy)
+			delete(files, "/home/projects/TS/p1/src/x.ts")
 			assert.NilError(t, service.OnWatchedFilesChanged(t.Context(), []*lsproto.FileEvent{
 				{
 					Type: lsproto.FileChangeTypeDeleted,
@@ -499,15 +488,13 @@ func TestService(t *testing.T) {
 				"/home/projects/TS/p1/src/index.ts": `let x = 2;`,
 				"/home/projects/TS/p1/src/x.ts":     `let y = x;`,
 			}
-			service, host := projecttestutil.Setup(files)
+			service, _ := projecttestutil.Setup(files)
 			service.OpenFile("/home/projects/TS/p1/src/x.ts", files["/home/projects/TS/p1/src/x.ts"].(string), core.ScriptKindTS, "")
 			_, project := service.EnsureDefaultProjectForFile("/home/projects/TS/p1/src/x.ts")
 			program := project.GetProgram()
 			assert.Equal(t, len(program.GetSemanticDiagnostics(projecttestutil.WithRequestID(t.Context()), program.GetSourceFile("/home/projects/TS/p1/src/x.ts"))), 0)
 
-			filesCopy := maps.Clone(files)
-			delete(filesCopy, "/home/projects/TS/p1/src/index.ts")
-			host.ReplaceFS(filesCopy)
+			delete(files, "/home/projects/TS/p1/src/index.ts")
 			assert.NilError(t, service.OnWatchedFilesChanged(t.Context(), []*lsproto.FileEvent{
 				{
 					Type: lsproto.FileChangeTypeDeleted,
@@ -561,9 +548,7 @@ func TestService(t *testing.T) {
 			})
 
 			// Add the missing file
-			filesCopy := maps.Clone(files)
-			filesCopy["/home/projects/TS/p1/src/y.ts"] = `export const y = 1;`
-			host.ReplaceFS(filesCopy)
+			files["/home/projects/TS/p1/src/y.ts"] = `export const y = 1;`
 			assert.NilError(t, service.OnWatchedFilesChanged(t.Context(), []*lsproto.FileEvent{
 				{
 					Type: lsproto.FileChangeTypeCreated,
@@ -602,9 +587,7 @@ func TestService(t *testing.T) {
 			}))
 
 			// Add a new file through failed lookup watch
-			filesCopy := maps.Clone(files)
-			filesCopy["/home/projects/TS/p1/src/z.ts"] = `export const z = 1;`
-			host.ReplaceFS(filesCopy)
+			files["/home/projects/TS/p1/src/z.ts"] = `export const z = 1;`
 			assert.NilError(t, service.OnWatchedFilesChanged(t.Context(), []*lsproto.FileEvent{
 				{
 					Type: lsproto.FileChangeTypeCreated,
@@ -629,7 +612,7 @@ func TestService(t *testing.T) {
 				}`,
 				"/home/projects/TS/p1/src/index.ts": `a;`,
 			}
-			service, host := projecttestutil.Setup(files)
+			service, _ := projecttestutil.Setup(files)
 			service.OpenFile("/home/projects/TS/p1/src/index.ts", files["/home/projects/TS/p1/src/index.ts"].(string), core.ScriptKindTS, "")
 			_, project := service.EnsureDefaultProjectForFile("/home/projects/TS/p1/src/index.ts")
 			program := project.GetProgram()
@@ -638,9 +621,7 @@ func TestService(t *testing.T) {
 			assert.Equal(t, len(program.GetSemanticDiagnostics(projecttestutil.WithRequestID(t.Context()), program.GetSourceFile("/home/projects/TS/p1/src/index.ts"))), 1)
 
 			// Add a new file through wildcard watch
-			filesCopy := maps.Clone(files)
-			filesCopy["/home/projects/TS/p1/src/a.ts"] = `const a = 1;`
-			host.ReplaceFS(filesCopy)
+			files["/home/projects/TS/p1/src/a.ts"] = `const a = 1;`
 			assert.NilError(t, service.OnWatchedFilesChanged(t.Context(), []*lsproto.FileEvent{
 				{
 					Type: lsproto.FileChangeTypeCreated,
diff --git a/internal/testutil/projecttestutil/projecttestutil.go b/internal/testutil/projecttestutil/projecttestutil.go
index fc6f9f9cb0..bbbea7b534 100644
--- a/internal/testutil/projecttestutil/projecttestutil.go
+++ b/internal/testutil/projecttestutil/projecttestutil.go
@@ -57,10 +57,6 @@ func (p *ProjectServiceHost) Client() project.Client {
 	return p.ClientMock
 }
 
-func (p *ProjectServiceHost) ReplaceFS(files map[string]any) {
-	p.fs = bundled.WrapFS(vfstest.FromMap(files, false /*useCaseSensitiveFileNames*/))
-}
-
 var _ project.ServiceHost = (*ProjectServiceHost)(nil)
 
 func Setup(files map[string]any) (*project.Service, *ProjectServiceHost) {

From a68ac7447b46300a37454c6e66d0900960233f5a Mon Sep 17 00:00:00 2001
From: Jake Bailey <5341706+jakebailey@users.noreply.github.com>
Date: Fri, 30 May 2025 16:38:04 -0700
Subject: [PATCH 3/9] Fix files map use

---
 internal/project/service_test.go | 86 ++++++++++++++++++++++----------
 1 file changed, 59 insertions(+), 27 deletions(-)

diff --git a/internal/project/service_test.go b/internal/project/service_test.go
index 1702fb7460..cfd358a015 100644
--- a/internal/project/service_test.go
+++ b/internal/project/service_test.go
@@ -168,6 +168,7 @@ func TestService(t *testing.T) {
 			service, _ := projecttestutil.Setup(files)
 			service.OpenFile("/home/projects/TS/p1/src/index.ts", files["/home/projects/TS/p1/src/index.ts"].(string), core.ScriptKindTS, "")
 			assert.Check(t, service.GetScriptInfo("/home/projects/TS/p1/y.ts") == nil)
+			files = nil // Avoid using initial file set after this point
 
 			err := service.ChangeFile(
 				lsproto.VersionedTextDocumentIdentifier{
@@ -209,11 +210,12 @@ func TestService(t *testing.T) {
 				},
 				"include": ["src/index.ts"]
 			}`
-			service, _ := projecttestutil.Setup(files)
+			service, host := projecttestutil.Setup(files)
 			service.OpenFile("/home/projects/TS/p1/src/index.ts", files["/home/projects/TS/p1/src/index.ts"].(string), core.ScriptKindTS, "")
 			_, project := service.EnsureDefaultProjectForFile("/home/projects/TS/p1/src/index.ts")
 			programBefore := project.GetProgram()
 			assert.Equal(t, len(programBefore.GetSourceFiles()), 2)
+			files = nil // Avoid using initial file set after this point
 
 			err := service.ChangeFile(
 				lsproto.VersionedTextDocumentIdentifier{
@@ -242,14 +244,16 @@ func TestService(t *testing.T) {
 			)
 			assert.NilError(t, err)
 
-			files["/home/projects/TS/p1/tsconfig.json"] = `{
+			err = host.FS().WriteFile("/home/projects/TS/p1/tsconfig.json", `{
 				"compilerOptions": {
 					"noLib": true,
 					"module": "nodenext",
 					"strict": true,
 				},
 				"include": ["./**/*"]
-			}`
+			}`, false)
+			assert.NilError(t, err)
+
 			err = service.OnWatchedFilesChanged(t.Context(), []*lsproto.FileEvent{
 				{
 					Type: lsproto.FileChangeTypeChanged,
@@ -270,20 +274,23 @@ func TestService(t *testing.T) {
 			t.Run("delete a file, close it, recreate it", func(t *testing.T) {
 				t.Parallel()
 				files := maps.Clone(defaultFiles)
-				service, _ := projecttestutil.Setup(files)
+				service, host := projecttestutil.Setup(files)
 				service.OpenFile("/home/projects/TS/p1/src/x.ts", files["/home/projects/TS/p1/src/x.ts"].(string), core.ScriptKindTS, "")
-				service.OpenFile("/home/projects/TS/p1/src/index.ts", defaultFiles["/home/projects/TS/p1/src/index.ts"].(string), core.ScriptKindTS, "")
+				service.OpenFile("/home/projects/TS/p1/src/index.ts", files["/home/projects/TS/p1/src/index.ts"].(string), core.ScriptKindTS, "")
 				assert.Equal(t, service.SourceFileCount(), 2)
+				files = nil // Avoid using initial file set after this point
 
-				delete(files, "/home/projects/TS/p1/src/x.ts")
+				assert.NilError(t, host.FS().Remove("/home/projects/TS/p1/src/x.ts"))
 
 				service.CloseFile("/home/projects/TS/p1/src/x.ts")
 				assert.Check(t, service.GetScriptInfo("/home/projects/TS/p1/src/x.ts") == nil)
 				assert.Check(t, service.Projects()[0].GetProgram().GetSourceFile("/home/projects/TS/p1/src/x.ts") == nil)
 				assert.Equal(t, service.SourceFileCount(), 1)
 
-				files["/home/projects/TS/p1/src/x.ts"] = ``
-				service.OpenFile("/home/projects/TS/p1/src/x.ts", files["/home/projects/TS/p1/src/x.ts"].(string), core.ScriptKindTS, "")
+				err := host.FS().WriteFile("/home/projects/TS/p1/src/x.ts", "", false)
+				assert.NilError(t, err)
+
+				service.OpenFile("/home/projects/TS/p1/src/x.ts", "", core.ScriptKindTS, "")
 				assert.Equal(t, service.GetScriptInfo("/home/projects/TS/p1/src/x.ts").Text(), "")
 				assert.Check(t, service.Projects()[0].GetProgram().GetSourceFile("/home/projects/TS/p1/src/x.ts") != nil)
 				assert.Equal(t, service.Projects()[0].GetProgram().GetSourceFile("/home/projects/TS/p1/src/x.ts").Text(), "")
@@ -296,18 +303,22 @@ func TestService(t *testing.T) {
 				t.Parallel()
 				files := maps.Clone(defaultFiles)
 				delete(files, "/home/projects/TS/p1/tsconfig.json")
-				service, _ := projecttestutil.Setup(files)
+				service, host := projecttestutil.Setup(files)
 				service.OpenFile("/home/projects/TS/p1/src/x.ts", files["/home/projects/TS/p1/src/x.ts"].(string), core.ScriptKindTS, "")
 				service.OpenFile("/home/projects/TS/p1/src/index.ts", files["/home/projects/TS/p1/src/index.ts"].(string), core.ScriptKindTS, "")
+				files = nil // Avoid using initial file set after this point
 
-				delete(files, "/home/projects/TS/p1/src/x.ts")
+				err := host.FS().Remove("/home/projects/TS/p1/src/x.ts")
+				assert.NilError(t, err)
 
 				service.CloseFile("/home/projects/TS/p1/src/x.ts")
 				assert.Check(t, service.GetScriptInfo("/home/projects/TS/p1/src/x.ts") == nil)
 				assert.Check(t, service.Projects()[0].GetProgram().GetSourceFile("/home/projects/TS/p1/src/x.ts") == nil)
 
-				files["/home/projects/TS/p1/src/x.ts"] = ``
-				service.OpenFile("/home/projects/TS/p1/src/x.ts", files["/home/projects/TS/p1/src/x.ts"].(string), core.ScriptKindTS, "")
+				err = host.FS().WriteFile("/home/projects/TS/p1/src/x.ts", "", false)
+				assert.NilError(t, err)
+
+				service.OpenFile("/home/projects/TS/p1/src/x.ts", "", core.ScriptKindTS, "")
 				assert.Equal(t, service.GetScriptInfo("/home/projects/TS/p1/src/x.ts").Text(), "")
 				assert.Check(t, service.Projects()[0].GetProgram().GetSourceFile("/home/projects/TS/p1/src/x.ts") != nil)
 				assert.Equal(t, service.Projects()[0].GetProgram().GetSourceFile("/home/projects/TS/p1/src/x.ts").Text(), "")
@@ -333,6 +344,7 @@ func TestService(t *testing.T) {
 			service.OpenFile("/home/projects/TS/p1/src/index.ts", files["/home/projects/TS/p1/src/index.ts"].(string), core.ScriptKindTS, "")
 			service.OpenFile("/home/projects/TS/p2/src/index.ts", files["/home/projects/TS/p2/src/index.ts"].(string), core.ScriptKindTS, "")
 			assert.Equal(t, len(service.Projects()), 2)
+			files = nil // Avoid using initial file set after this point
 			_, p1 := service.EnsureDefaultProjectForFile("/home/projects/TS/p1/src/index.ts")
 			_, p2 := service.EnsureDefaultProjectForFile("/home/projects/TS/p2/src/index.ts")
 			assert.Equal(
@@ -356,6 +368,7 @@ func TestService(t *testing.T) {
 			service.OpenFile("/home/projects/TS/p1/src/index.ts", files["/home/projects/TS/p1/src/index.ts"].(string), core.ScriptKindTS, "")
 			service.OpenFile("/home/projects/TS/p2/src/index.ts", files["/home/projects/TS/p2/src/index.ts"].(string), core.ScriptKindTS, "")
 			assert.Equal(t, len(service.Projects()), 2)
+			files = nil // Avoid using initial file set after this point
 			_, p1 := service.EnsureDefaultProjectForFile("/home/projects/TS/p1/src/index.ts")
 			_, p2 := service.EnsureDefaultProjectForFile("/home/projects/TS/p2/src/index.ts")
 			x1 := p1.GetProgram().GetSourceFile("/home/projects/TS/p1/src/x.ts")
@@ -371,13 +384,16 @@ func TestService(t *testing.T) {
 		t.Run("change open file", func(t *testing.T) {
 			t.Parallel()
 			files := maps.Clone(defaultFiles)
-			service, _ := projecttestutil.Setup(files)
+			service, host := projecttestutil.Setup(files)
 			service.OpenFile("/home/projects/TS/p1/src/x.ts", files["/home/projects/TS/p1/src/x.ts"].(string), core.ScriptKindTS, "")
 			service.OpenFile("/home/projects/TS/p1/src/index.ts", files["/home/projects/TS/p1/src/index.ts"].(string), core.ScriptKindTS, "")
 			_, project := service.EnsureDefaultProjectForFile("/home/projects/TS/p1/src/index.ts")
 			programBefore := project.GetProgram()
+			files = nil // Avoid using initial file set after this point
+
+			err := host.FS().WriteFile("/home/projects/TS/p1/src/x.ts", `export const x = 2;`, false)
+			assert.NilError(t, err)
 
-			files["/home/projects/TS/p1/src/x.ts"] = `export const x = 2;`
 			assert.NilError(t, service.OnWatchedFilesChanged(t.Context(), []*lsproto.FileEvent{
 				{
 					Type: lsproto.FileChangeTypeChanged,
@@ -391,12 +407,15 @@ func TestService(t *testing.T) {
 		t.Run("change closed program file", func(t *testing.T) {
 			t.Parallel()
 			files := maps.Clone(defaultFiles)
-			service, _ := projecttestutil.Setup(files)
+			service, host := projecttestutil.Setup(files)
 			service.OpenFile("/home/projects/TS/p1/src/index.ts", files["/home/projects/TS/p1/src/index.ts"].(string), core.ScriptKindTS, "")
 			_, project := service.EnsureDefaultProjectForFile("/home/projects/TS/p1/src/index.ts")
 			programBefore := project.GetProgram()
+			files = nil // Avoid using initial file set after this point
+
+			err := host.FS().WriteFile("/home/projects/TS/p1/src/x.ts", `export const x = 2;`, false)
+			assert.NilError(t, err)
 
-			files["/home/projects/TS/p1/src/x.ts"] = `export const x = 2;`
 			assert.NilError(t, service.OnWatchedFilesChanged(t.Context(), []*lsproto.FileEvent{
 				{
 					Type: lsproto.FileChangeTypeChanged,
@@ -422,18 +441,20 @@ func TestService(t *testing.T) {
 					let y: number = x;`,
 			}
 
-			service, _ := projecttestutil.Setup(files)
+			service, host := projecttestutil.Setup(files)
 			service.OpenFile("/home/projects/TS/p1/src/index.ts", files["/home/projects/TS/p1/src/index.ts"].(string), core.ScriptKindTS, "")
 			_, project := service.EnsureDefaultProjectForFile("/home/projects/TS/p1/src/index.ts")
 			program := project.GetProgram()
 			assert.Equal(t, len(program.GetSemanticDiagnostics(projecttestutil.WithRequestID(t.Context()), program.GetSourceFile("/home/projects/TS/p1/src/index.ts"))), 0)
 
-			files["/home/projects/TS/p1/tsconfig.json"] = `{
+			err := host.FS().WriteFile("/home/projects/TS/p1/tsconfig.json", `{
 				"compilerOptions": {
 					"noLib": false,
 					"strict": true
 				}
-			}`
+			}`, false)
+			assert.NilError(t, err)
+
 			assert.NilError(t, service.OnWatchedFilesChanged(t.Context(), []*lsproto.FileEvent{
 				{
 					Type: lsproto.FileChangeTypeChanged,
@@ -457,13 +478,15 @@ func TestService(t *testing.T) {
 				"/home/projects/TS/p1/src/x.ts":     `export declare const x: number | undefined;`,
 				"/home/projects/TS/p1/src/index.ts": `import { x } from "./x";`,
 			}
-			service, _ := projecttestutil.Setup(files)
+			service, host := projecttestutil.Setup(files)
 			service.OpenFile("/home/projects/TS/p1/src/index.ts", files["/home/projects/TS/p1/src/index.ts"].(string), core.ScriptKindTS, "")
 			_, project := service.EnsureDefaultProjectForFile("/home/projects/TS/p1/src/index.ts")
 			program := project.GetProgram()
 			assert.Equal(t, len(program.GetSemanticDiagnostics(projecttestutil.WithRequestID(t.Context()), program.GetSourceFile("/home/projects/TS/p1/src/index.ts"))), 0)
 
-			delete(files, "/home/projects/TS/p1/src/x.ts")
+			err := host.FS().Remove("/home/projects/TS/p1/src/x.ts")
+			assert.NilError(t, err)
+
 			assert.NilError(t, service.OnWatchedFilesChanged(t.Context(), []*lsproto.FileEvent{
 				{
 					Type: lsproto.FileChangeTypeDeleted,
@@ -488,13 +511,15 @@ func TestService(t *testing.T) {
 				"/home/projects/TS/p1/src/index.ts": `let x = 2;`,
 				"/home/projects/TS/p1/src/x.ts":     `let y = x;`,
 			}
-			service, _ := projecttestutil.Setup(files)
+			service, host := projecttestutil.Setup(files)
 			service.OpenFile("/home/projects/TS/p1/src/x.ts", files["/home/projects/TS/p1/src/x.ts"].(string), core.ScriptKindTS, "")
 			_, project := service.EnsureDefaultProjectForFile("/home/projects/TS/p1/src/x.ts")
 			program := project.GetProgram()
 			assert.Equal(t, len(program.GetSemanticDiagnostics(projecttestutil.WithRequestID(t.Context()), program.GetSourceFile("/home/projects/TS/p1/src/x.ts"))), 0)
 
-			delete(files, "/home/projects/TS/p1/src/index.ts")
+			err := host.FS().Remove("/home/projects/TS/p1/src/index.ts")
+			assert.NilError(t, err)
+
 			assert.NilError(t, service.OnWatchedFilesChanged(t.Context(), []*lsproto.FileEvent{
 				{
 					Type: lsproto.FileChangeTypeDeleted,
@@ -548,7 +573,9 @@ func TestService(t *testing.T) {
 			})
 
 			// Add the missing file
-			files["/home/projects/TS/p1/src/y.ts"] = `export const y = 1;`
+			err := host.FS().WriteFile("/home/projects/TS/p1/src/y.ts", `export const y = 1;`, false)
+			assert.NilError(t, err)
+
 			assert.NilError(t, service.OnWatchedFilesChanged(t.Context(), []*lsproto.FileEvent{
 				{
 					Type: lsproto.FileChangeTypeCreated,
@@ -587,7 +614,9 @@ func TestService(t *testing.T) {
 			}))
 
 			// Add a new file through failed lookup watch
-			files["/home/projects/TS/p1/src/z.ts"] = `export const z = 1;`
+			err := host.FS().WriteFile("/home/projects/TS/p1/src/z.ts", `export const z = 1;`, false)
+			assert.NilError(t, err)
+
 			assert.NilError(t, service.OnWatchedFilesChanged(t.Context(), []*lsproto.FileEvent{
 				{
 					Type: lsproto.FileChangeTypeCreated,
@@ -612,7 +641,7 @@ func TestService(t *testing.T) {
 				}`,
 				"/home/projects/TS/p1/src/index.ts": `a;`,
 			}
-			service, _ := projecttestutil.Setup(files)
+			service, host := projecttestutil.Setup(files)
 			service.OpenFile("/home/projects/TS/p1/src/index.ts", files["/home/projects/TS/p1/src/index.ts"].(string), core.ScriptKindTS, "")
 			_, project := service.EnsureDefaultProjectForFile("/home/projects/TS/p1/src/index.ts")
 			program := project.GetProgram()
@@ -621,7 +650,10 @@ func TestService(t *testing.T) {
 			assert.Equal(t, len(program.GetSemanticDiagnostics(projecttestutil.WithRequestID(t.Context()), program.GetSourceFile("/home/projects/TS/p1/src/index.ts"))), 1)
 
 			// Add a new file through wildcard watch
-			files["/home/projects/TS/p1/src/a.ts"] = `const a = 1;`
+
+			err := host.FS().WriteFile("/home/projects/TS/p1/src/a.ts", `const a = 1;`, false)
+			assert.NilError(t, err)
+
 			assert.NilError(t, service.OnWatchedFilesChanged(t.Context(), []*lsproto.FileEvent{
 				{
 					Type: lsproto.FileChangeTypeCreated,

From 79459016eb11d3230ebf4f5980c4b8da974a66d4 Mon Sep 17 00:00:00 2001
From: Jake Bailey <5341706+jakebailey@users.noreply.github.com>
Date: Mon, 2 Jun 2025 13:35:42 -0700
Subject: [PATCH 4/9] Hack ATA to not use the cached host

---
 internal/project/ata.go     | 2 +-
 internal/project/project.go | 9 +++++++--
 internal/project/service.go | 4 ++++
 3 files changed, 12 insertions(+), 3 deletions(-)

diff --git a/internal/project/ata.go b/internal/project/ata.go
index a2daf41d0a..06d1278193 100644
--- a/internal/project/ata.go
+++ b/internal/project/ata.go
@@ -261,7 +261,7 @@ func (ti *TypingsInstaller) invokeRoutineToInstallTypings(
 			if success {
 				p.Logf("ATA:: Installed typings %v", packageNames)
 				var installedTypingFiles []string
-				resolver := module.NewResolver(p, &core.CompilerOptions{ModuleResolution: core.ModuleResolutionKindNodeNext}, "", "")
+				resolver := module.NewResolver(p.uncachedHost, &core.CompilerOptions{ModuleResolution: core.ModuleResolutionKindNodeNext}, "", "")
 				for _, packageName := range request.filteredTypings {
 					typingFile := ti.typingToFileName(resolver, packageName)
 					if typingFile == "" {
diff --git a/internal/project/project.go b/internal/project/project.go
index 2486ce80ff..0bf58e45f5 100644
--- a/internal/project/project.go
+++ b/internal/project/project.go
@@ -15,6 +15,7 @@ import (
 	"github.com/microsoft/typescript-go/internal/core"
 	"github.com/microsoft/typescript-go/internal/ls"
 	"github.com/microsoft/typescript-go/internal/lsp/lsproto"
+	"github.com/microsoft/typescript-go/internal/module"
 	"github.com/microsoft/typescript-go/internal/tsoptions"
 	"github.com/microsoft/typescript-go/internal/tspath"
 	"github.com/microsoft/typescript-go/internal/vfs"
@@ -73,6 +74,7 @@ const (
 
 type ProjectHost interface {
 	tsoptions.ParseConfigHost
+	module.ResolutionHost
 	NewLine() string
 	DefaultLibraryPath() string
 	TypingsInstaller() *TypingsInstaller
@@ -121,7 +123,9 @@ func typeAcquisitionChanged(opt1 *core.TypeAcquisition, opt2 *core.TypeAcquisiti
 var _ compiler.CompilerHost = (*Project)(nil)
 
 type Project struct {
-	host *projectHostWithCachedFS
+	// TODO: remove this hack
+	uncachedHost ProjectHost
+	host         *projectHostWithCachedFS
 
 	name string
 	kind Kind
@@ -190,6 +194,7 @@ func NewProject(name string, kind Kind, currentDirectory string, host ProjectHos
 
 	host.Log(fmt.Sprintf("Creating %sProject: %s, currentDirectory: %s", kind.String(), name, currentDirectory))
 	project := &Project{
+		uncachedHost:     host,
 		host:             cachedHost,
 		name:             name,
 		kind:             kind,
@@ -281,7 +286,7 @@ func (p *Project) NewLine() string {
 
 // Trace implements compiler.CompilerHost.
 func (p *Project) Trace(msg string) {
-	p.Log(msg)
+	p.host.Log(msg)
 }
 
 // GetDefaultLibraryPath implements compiler.CompilerHost.
diff --git a/internal/project/service.go b/internal/project/service.go
index 3ec6f02f94..c8190faab0 100644
--- a/internal/project/service.go
+++ b/internal/project/service.go
@@ -108,6 +108,10 @@ func (s *Service) Log(msg string) {
 	s.options.Logger.Info(msg)
 }
 
+func (s *Service) Trace(msg string) {
+	s.Log(msg)
+}
+
 func (s *Service) HasLevel(level LogLevel) bool {
 	return s.options.Logger.HasLevel(level)
 }

From 2f2be30756d44381579ba61576c41d2debee2cc8 Mon Sep 17 00:00:00 2001
From: Jake Bailey <5341706+jakebailey@users.noreply.github.com>
Date: Mon, 2 Jun 2025 13:55:01 -0700
Subject: [PATCH 5/9] fix other impl

---
 internal/api/api.go | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/internal/api/api.go b/internal/api/api.go
index d03df66cd6..95e38fda6e 100644
--- a/internal/api/api.go
+++ b/internal/api/api.go
@@ -115,6 +115,11 @@ func (api *API) Log(s string) {
 	api.options.Logger.Info(s)
 }
 
+// Log implements ProjectHost.
+func (api *API) Trace(s string) {
+	api.options.Logger.Info(s)
+}
+
 // NewLine implements ProjectHost.
 func (api *API) NewLine() string {
 	return api.host.NewLine()

From 71d61543ec863c6f890292256ed240d0fcd06b68 Mon Sep 17 00:00:00 2001
From: Jake Bailey <5341706+jakebailey@users.noreply.github.com>
Date: Mon, 2 Jun 2025 14:30:21 -0700
Subject: [PATCH 6/9] Silence lint

---
 internal/project/service_test.go | 24 ++++++++++++++++--------
 1 file changed, 16 insertions(+), 8 deletions(-)

diff --git a/internal/project/service_test.go b/internal/project/service_test.go
index 9bd83c5f14..350d10ab5c 100644
--- a/internal/project/service_test.go
+++ b/internal/project/service_test.go
@@ -168,7 +168,8 @@ func TestService(t *testing.T) {
 			service, _ := projecttestutil.Setup(files, nil)
 			service.OpenFile("/home/projects/TS/p1/src/index.ts", files["/home/projects/TS/p1/src/index.ts"].(string), core.ScriptKindTS, "")
 			assert.Check(t, service.GetScriptInfo("/home/projects/TS/p1/y.ts") == nil)
-			files = nil // Avoid using initial file set after this point
+			// Avoid using initial file set after this point
+			files = nil //nolint:ineffassign
 
 			err := service.ChangeFile(
 				lsproto.VersionedTextDocumentIdentifier{
@@ -215,7 +216,8 @@ func TestService(t *testing.T) {
 			_, project := service.EnsureDefaultProjectForFile("/home/projects/TS/p1/src/index.ts")
 			programBefore := project.GetProgram()
 			assert.Equal(t, len(programBefore.GetSourceFiles()), 2)
-			files = nil // Avoid using initial file set after this point
+			// Avoid using initial file set after this point
+			files = nil //nolint:ineffassign
 
 			err := service.ChangeFile(
 				lsproto.VersionedTextDocumentIdentifier{
@@ -278,7 +280,8 @@ func TestService(t *testing.T) {
 				service.OpenFile("/home/projects/TS/p1/src/x.ts", files["/home/projects/TS/p1/src/x.ts"].(string), core.ScriptKindTS, "")
 				service.OpenFile("/home/projects/TS/p1/src/index.ts", files["/home/projects/TS/p1/src/index.ts"].(string), core.ScriptKindTS, "")
 				assert.Equal(t, service.SourceFileCount(), 2)
-				files = nil // Avoid using initial file set after this point
+				// Avoid using initial file set after this point
+				files = nil //nolint:ineffassign
 
 				assert.NilError(t, host.FS().Remove("/home/projects/TS/p1/src/x.ts"))
 
@@ -306,7 +309,8 @@ func TestService(t *testing.T) {
 				service, host := projecttestutil.Setup(files, nil)
 				service.OpenFile("/home/projects/TS/p1/src/x.ts", files["/home/projects/TS/p1/src/x.ts"].(string), core.ScriptKindTS, "")
 				service.OpenFile("/home/projects/TS/p1/src/index.ts", files["/home/projects/TS/p1/src/index.ts"].(string), core.ScriptKindTS, "")
-				files = nil // Avoid using initial file set after this point
+				// Avoid using initial file set after this point
+				files = nil //nolint:ineffassign
 
 				err := host.FS().Remove("/home/projects/TS/p1/src/x.ts")
 				assert.NilError(t, err)
@@ -344,7 +348,8 @@ func TestService(t *testing.T) {
 			service.OpenFile("/home/projects/TS/p1/src/index.ts", files["/home/projects/TS/p1/src/index.ts"].(string), core.ScriptKindTS, "")
 			service.OpenFile("/home/projects/TS/p2/src/index.ts", files["/home/projects/TS/p2/src/index.ts"].(string), core.ScriptKindTS, "")
 			assert.Equal(t, len(service.Projects()), 2)
-			files = nil // Avoid using initial file set after this point
+			// Avoid using initial file set after this point
+			files = nil //nolint:ineffassign
 			_, p1 := service.EnsureDefaultProjectForFile("/home/projects/TS/p1/src/index.ts")
 			_, p2 := service.EnsureDefaultProjectForFile("/home/projects/TS/p2/src/index.ts")
 			assert.Equal(
@@ -368,7 +373,8 @@ func TestService(t *testing.T) {
 			service.OpenFile("/home/projects/TS/p1/src/index.ts", files["/home/projects/TS/p1/src/index.ts"].(string), core.ScriptKindTS, "")
 			service.OpenFile("/home/projects/TS/p2/src/index.ts", files["/home/projects/TS/p2/src/index.ts"].(string), core.ScriptKindTS, "")
 			assert.Equal(t, len(service.Projects()), 2)
-			files = nil // Avoid using initial file set after this point
+			// Avoid using initial file set after this point
+			files = nil //nolint:ineffassign
 			_, p1 := service.EnsureDefaultProjectForFile("/home/projects/TS/p1/src/index.ts")
 			_, p2 := service.EnsureDefaultProjectForFile("/home/projects/TS/p2/src/index.ts")
 			x1 := p1.GetProgram().GetSourceFile("/home/projects/TS/p1/src/x.ts")
@@ -389,7 +395,8 @@ func TestService(t *testing.T) {
 			service.OpenFile("/home/projects/TS/p1/src/index.ts", files["/home/projects/TS/p1/src/index.ts"].(string), core.ScriptKindTS, "")
 			_, project := service.EnsureDefaultProjectForFile("/home/projects/TS/p1/src/index.ts")
 			programBefore := project.GetProgram()
-			files = nil // Avoid using initial file set after this point
+			// Avoid using initial file set after this point
+			files = nil //nolint:ineffassign
 
 			err := host.FS().WriteFile("/home/projects/TS/p1/src/x.ts", `export const x = 2;`, false)
 			assert.NilError(t, err)
@@ -411,7 +418,8 @@ func TestService(t *testing.T) {
 			service.OpenFile("/home/projects/TS/p1/src/index.ts", files["/home/projects/TS/p1/src/index.ts"].(string), core.ScriptKindTS, "")
 			_, project := service.EnsureDefaultProjectForFile("/home/projects/TS/p1/src/index.ts")
 			programBefore := project.GetProgram()
-			files = nil // Avoid using initial file set after this point
+			// Avoid using initial file set after this point
+			files = nil //nolint:ineffassign
 
 			err := host.FS().WriteFile("/home/projects/TS/p1/src/x.ts", `export const x = 2;`, false)
 			assert.NilError(t, err)

From 2eff7716a2c1fe48b22502bc18c9995590b09652 Mon Sep 17 00:00:00 2001
From: Jake Bailey <5341706+jakebailey@users.noreply.github.com>
Date: Tue, 3 Jun 2025 13:30:48 -0700
Subject: [PATCH 7/9] Defer it

---
 internal/project/project.go | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/internal/project/project.go b/internal/project/project.go
index 0bf58e45f5..ae45aea8e6 100644
--- a/internal/project/project.go
+++ b/internal/project/project.go
@@ -484,9 +484,10 @@ func (p *Project) updateGraph() bool {
 		return false
 	}
 
+	defer p.host.fs.ClearCache()
+
 	start := time.Now()
 	p.Log("Starting updateGraph: Project: " + p.name)
-	p.host.fs.ClearCache()
 	var writeFileNames bool
 	oldProgram := p.program
 	p.initialLoadPending = false

From fa6df8971cdb1e79df0d74a40c100e48aa8d5157 Mon Sep 17 00:00:00 2001
From: Jake Bailey <5341706+jakebailey@users.noreply.github.com>
Date: Tue, 3 Jun 2025 15:03:56 -0700
Subject: [PATCH 8/9] Only cache during updateGraph

---
 internal/project/ata.go             |  2 +-
 internal/project/project.go         | 12 ++---
 internal/vfs/cachedvfs/cachedvfs.go | 84 +++++++++++++++++++++++------
 3 files changed, 74 insertions(+), 24 deletions(-)

diff --git a/internal/project/ata.go b/internal/project/ata.go
index 4a1ded8925..31dd9b1465 100644
--- a/internal/project/ata.go
+++ b/internal/project/ata.go
@@ -243,7 +243,7 @@ func (ti *TypingsInstaller) invokeRoutineToInstallTypings(
 			if success {
 				p.Logf("ATA:: Installed typings %v", packageNames)
 				var installedTypingFiles []string
-				resolver := module.NewResolver(p.uncachedHost, &core.CompilerOptions{ModuleResolution: core.ModuleResolutionKindNodeNext}, "", "")
+				resolver := module.NewResolver(p, &core.CompilerOptions{ModuleResolution: core.ModuleResolutionKindNodeNext}, "", "")
 				for _, packageName := range request.filteredTypings {
 					typingFile := ti.typingToFileName(resolver, packageName)
 					if typingFile == "" {
diff --git a/internal/project/project.go b/internal/project/project.go
index ae45aea8e6..e2aec93810 100644
--- a/internal/project/project.go
+++ b/internal/project/project.go
@@ -123,9 +123,7 @@ func typeAcquisitionChanged(opt1 *core.TypeAcquisition, opt2 *core.TypeAcquisiti
 var _ compiler.CompilerHost = (*Project)(nil)
 
 type Project struct {
-	// TODO: remove this hack
-	uncachedHost ProjectHost
-	host         *projectHostWithCachedFS
+	host *projectHostWithCachedFS
 
 	name string
 	kind Kind
@@ -194,7 +192,6 @@ func NewProject(name string, kind Kind, currentDirectory string, host ProjectHos
 
 	host.Log(fmt.Sprintf("Creating %sProject: %s, currentDirectory: %s", kind.String(), name, currentDirectory))
 	project := &Project{
-		uncachedHost:     host,
 		host:             cachedHost,
 		name:             name,
 		kind:             kind,
@@ -223,10 +220,12 @@ type projectHostWithCachedFS struct {
 }
 
 func newProjectHostWithCachedFS(host ProjectHost) *projectHostWithCachedFS {
-	return &projectHostWithCachedFS{
+	newHost := &projectHostWithCachedFS{
 		ProjectHost: host,
 		fs:          cachedvfs.From(host.FS()),
 	}
+	newHost.fs.DisableAndClearCache()
+	return newHost
 }
 
 func (p *projectHostWithCachedFS) FS() vfs.FS {
@@ -484,7 +483,8 @@ func (p *Project) updateGraph() bool {
 		return false
 	}
 
-	defer p.host.fs.ClearCache()
+	p.host.fs.Enable()
+	defer p.host.fs.DisableAndClearCache()
 
 	start := time.Now()
 	p.Log("Starting updateGraph: Project: " + p.name)
diff --git a/internal/vfs/cachedvfs/cachedvfs.go b/internal/vfs/cachedvfs/cachedvfs.go
index 132c67bfaf..0e284fe043 100644
--- a/internal/vfs/cachedvfs/cachedvfs.go
+++ b/internal/vfs/cachedvfs/cachedvfs.go
@@ -1,12 +1,15 @@
 package cachedvfs
 
 import (
+	"sync/atomic"
+
 	"github.com/microsoft/typescript-go/internal/collections"
 	"github.com/microsoft/typescript-go/internal/vfs"
 )
 
 type FS struct {
-	fs vfs.FS
+	fs      vfs.FS
+	enabled atomic.Bool
 
 	directoryExistsCache      collections.SyncMap[string, bool]
 	fileExistsCache           collections.SyncMap[string, bool]
@@ -18,7 +21,19 @@ type FS struct {
 var _ vfs.FS = (*FS)(nil)
 
 func From(fs vfs.FS) *FS {
-	return &FS{fs: fs}
+	fsys := &FS{fs: fs}
+	fsys.enabled.Store(true)
+	return fsys
+}
+
+func (fsys *FS) DisableAndClearCache() {
+	if fsys.enabled.CompareAndSwap(true, false) {
+		fsys.ClearCache()
+	}
+}
+
+func (fsys *FS) Enable() {
+	fsys.enabled.Store(true)
 }
 
 func (fsys *FS) ClearCache() {
@@ -30,29 +45,50 @@ func (fsys *FS) ClearCache() {
 }
 
 func (fsys *FS) DirectoryExists(path string) bool {
-	if ret, ok := fsys.directoryExistsCache.Load(path); ok {
-		return ret
+	if fsys.enabled.Load() {
+		if ret, ok := fsys.directoryExistsCache.Load(path); ok {
+			return ret
+		}
 	}
+
 	ret := fsys.fs.DirectoryExists(path)
-	fsys.directoryExistsCache.Store(path, ret)
+
+	if fsys.enabled.Load() {
+		fsys.directoryExistsCache.Store(path, ret)
+	}
+
 	return ret
 }
 
 func (fsys *FS) FileExists(path string) bool {
-	if ret, ok := fsys.fileExistsCache.Load(path); ok {
-		return ret
+	if fsys.enabled.Load() {
+		if ret, ok := fsys.fileExistsCache.Load(path); ok {
+			return ret
+		}
 	}
+
 	ret := fsys.fs.FileExists(path)
-	fsys.fileExistsCache.Store(path, ret)
+
+	if fsys.enabled.Load() {
+		fsys.fileExistsCache.Store(path, ret)
+	}
+
 	return ret
 }
 
 func (fsys *FS) GetAccessibleEntries(path string) vfs.Entries {
-	if ret, ok := fsys.getAccessibleEntriesCache.Load(path); ok {
-		return ret
+	if fsys.enabled.Load() {
+		if ret, ok := fsys.getAccessibleEntriesCache.Load(path); ok {
+			return ret
+		}
 	}
+
 	ret := fsys.fs.GetAccessibleEntries(path)
-	fsys.getAccessibleEntriesCache.Store(path, ret)
+
+	if fsys.enabled.Load() {
+		fsys.getAccessibleEntriesCache.Store(path, ret)
+	}
+
 	return ret
 }
 
@@ -61,11 +97,18 @@ func (fsys *FS) ReadFile(path string) (contents string, ok bool) {
 }
 
 func (fsys *FS) Realpath(path string) string {
-	if ret, ok := fsys.realpathCache.Load(path); ok {
-		return ret
+	if fsys.enabled.Load() {
+		if ret, ok := fsys.realpathCache.Load(path); ok {
+			return ret
+		}
 	}
+
 	ret := fsys.fs.Realpath(path)
-	fsys.realpathCache.Store(path, ret)
+
+	if fsys.enabled.Load() {
+		fsys.realpathCache.Store(path, ret)
+	}
+
 	return ret
 }
 
@@ -74,11 +117,18 @@ func (fsys *FS) Remove(path string) error {
 }
 
 func (fsys *FS) Stat(path string) vfs.FileInfo {
-	if ret, ok := fsys.statCache.Load(path); ok {
-		return ret.(vfs.FileInfo)
+	if fsys.enabled.Load() {
+		if ret, ok := fsys.statCache.Load(path); ok {
+			return ret.(vfs.FileInfo)
+		}
 	}
+
 	ret := fsys.fs.Stat(path)
-	fsys.statCache.Store(path, ret)
+
+	if fsys.enabled.Load() {
+		fsys.statCache.Store(path, ret)
+	}
+
 	return ret
 }
 

From ffcef9f428a5a00e000f925b5863d1c8b3f052b4 Mon Sep 17 00:00:00 2001
From: Jake Bailey <5341706+jakebailey@users.noreply.github.com>
Date: Wed, 4 Jun 2025 18:00:04 -0700
Subject: [PATCH 9/9] Tests

---
 internal/vfs/cachedvfs/cachedvfs_test.go | 140 +++++++++++++++++++++++
 1 file changed, 140 insertions(+)

diff --git a/internal/vfs/cachedvfs/cachedvfs_test.go b/internal/vfs/cachedvfs/cachedvfs_test.go
index f74a42c870..a63b4b359f 100644
--- a/internal/vfs/cachedvfs/cachedvfs_test.go
+++ b/internal/vfs/cachedvfs/cachedvfs_test.go
@@ -34,6 +34,20 @@ func TestDirectoryExists(t *testing.T) {
 
 	cached.DirectoryExists("/other/path")
 	assert.Equal(t, 3, len(underlying.DirectoryExistsCalls()))
+
+	cached.DisableAndClearCache()
+	cached.DirectoryExists("/some/path")
+	assert.Equal(t, 4, len(underlying.DirectoryExistsCalls()))
+
+	cached.DirectoryExists("/some/path")
+	assert.Equal(t, 5, len(underlying.DirectoryExistsCalls()))
+
+	cached.Enable()
+	cached.DirectoryExists("/some/path")
+	assert.Equal(t, 6, len(underlying.DirectoryExistsCalls()))
+
+	cached.DirectoryExists("/some/path")
+	assert.Equal(t, 6, len(underlying.DirectoryExistsCalls()))
 }
 
 func TestFileExists(t *testing.T) {
@@ -54,6 +68,20 @@ func TestFileExists(t *testing.T) {
 
 	cached.FileExists("/other/path/file.txt")
 	assert.Equal(t, 3, len(underlying.FileExistsCalls()))
+
+	cached.DisableAndClearCache()
+	cached.FileExists("/some/path/file.txt")
+	assert.Equal(t, 4, len(underlying.FileExistsCalls()))
+
+	cached.FileExists("/some/path/file.txt")
+	assert.Equal(t, 5, len(underlying.FileExistsCalls()))
+
+	cached.Enable()
+	cached.FileExists("/some/path/file.txt")
+	assert.Equal(t, 6, len(underlying.FileExistsCalls()))
+
+	cached.FileExists("/some/path/file.txt")
+	assert.Equal(t, 6, len(underlying.FileExistsCalls()))
 }
 
 func TestGetAccessibleEntries(t *testing.T) {
@@ -74,6 +102,20 @@ func TestGetAccessibleEntries(t *testing.T) {
 
 	cached.GetAccessibleEntries("/other/path")
 	assert.Equal(t, 3, len(underlying.GetAccessibleEntriesCalls()))
+
+	cached.DisableAndClearCache()
+	cached.GetAccessibleEntries("/some/path")
+	assert.Equal(t, 4, len(underlying.GetAccessibleEntriesCalls()))
+
+	cached.GetAccessibleEntries("/some/path")
+	assert.Equal(t, 5, len(underlying.GetAccessibleEntriesCalls()))
+
+	cached.Enable()
+	cached.GetAccessibleEntries("/some/path")
+	assert.Equal(t, 6, len(underlying.GetAccessibleEntriesCalls()))
+
+	cached.GetAccessibleEntries("/some/path")
+	assert.Equal(t, 6, len(underlying.GetAccessibleEntriesCalls()))
 }
 
 func TestRealpath(t *testing.T) {
@@ -94,6 +136,20 @@ func TestRealpath(t *testing.T) {
 
 	cached.Realpath("/other/path")
 	assert.Equal(t, 3, len(underlying.RealpathCalls()))
+
+	cached.DisableAndClearCache()
+	cached.Realpath("/some/path")
+	assert.Equal(t, 4, len(underlying.RealpathCalls()))
+
+	cached.Realpath("/some/path")
+	assert.Equal(t, 5, len(underlying.RealpathCalls()))
+
+	cached.Enable()
+	cached.Realpath("/some/path")
+	assert.Equal(t, 6, len(underlying.RealpathCalls()))
+
+	cached.Realpath("/some/path")
+	assert.Equal(t, 6, len(underlying.RealpathCalls()))
 }
 
 func TestStat(t *testing.T) {
@@ -114,6 +170,20 @@ func TestStat(t *testing.T) {
 
 	cached.Stat("/other/path")
 	assert.Equal(t, 3, len(underlying.StatCalls()))
+
+	cached.DisableAndClearCache()
+	cached.Stat("/some/path")
+	assert.Equal(t, 4, len(underlying.StatCalls()))
+
+	cached.Stat("/some/path")
+	assert.Equal(t, 5, len(underlying.StatCalls()))
+
+	cached.Enable()
+	cached.Stat("/some/path")
+	assert.Equal(t, 6, len(underlying.StatCalls()))
+
+	cached.Stat("/some/path")
+	assert.Equal(t, 6, len(underlying.StatCalls()))
 }
 
 func TestReadFile(t *testing.T) {
@@ -131,6 +201,20 @@ func TestReadFile(t *testing.T) {
 	cached.ClearCache()
 	cached.ReadFile("/some/path/file.txt")
 	assert.Equal(t, 3, len(underlying.ReadFileCalls()))
+
+	cached.DisableAndClearCache()
+	cached.ReadFile("/some/path/file.txt")
+	assert.Equal(t, 4, len(underlying.ReadFileCalls()))
+
+	cached.ReadFile("/some/path/file.txt")
+	assert.Equal(t, 5, len(underlying.ReadFileCalls()))
+
+	cached.Enable()
+	cached.ReadFile("/some/path/file.txt")
+	assert.Equal(t, 6, len(underlying.ReadFileCalls()))
+
+	cached.ReadFile("/some/path/file.txt")
+	assert.Equal(t, 7, len(underlying.ReadFileCalls()))
 }
 
 func TestUseCaseSensitiveFileNames(t *testing.T) {
@@ -148,6 +232,20 @@ func TestUseCaseSensitiveFileNames(t *testing.T) {
 	cached.ClearCache()
 	cached.UseCaseSensitiveFileNames()
 	assert.Equal(t, 3, len(underlying.UseCaseSensitiveFileNamesCalls()))
+
+	cached.DisableAndClearCache()
+	cached.UseCaseSensitiveFileNames()
+	assert.Equal(t, 4, len(underlying.UseCaseSensitiveFileNamesCalls()))
+
+	cached.UseCaseSensitiveFileNames()
+	assert.Equal(t, 5, len(underlying.UseCaseSensitiveFileNamesCalls()))
+
+	cached.Enable()
+	cached.UseCaseSensitiveFileNames()
+	assert.Equal(t, 6, len(underlying.UseCaseSensitiveFileNamesCalls()))
+
+	cached.UseCaseSensitiveFileNames()
+	assert.Equal(t, 7, len(underlying.UseCaseSensitiveFileNamesCalls()))
 }
 
 func TestWalkDir(t *testing.T) {
@@ -169,6 +267,20 @@ func TestWalkDir(t *testing.T) {
 	cached.ClearCache()
 	_ = cached.WalkDir("/some/path", walkFn)
 	assert.Equal(t, 3, len(underlying.WalkDirCalls()))
+
+	cached.DisableAndClearCache()
+	_ = cached.WalkDir("/some/path", walkFn)
+	assert.Equal(t, 4, len(underlying.WalkDirCalls()))
+
+	_ = cached.WalkDir("/some/path", walkFn)
+	assert.Equal(t, 5, len(underlying.WalkDirCalls()))
+
+	cached.Enable()
+	_ = cached.WalkDir("/some/path", walkFn)
+	assert.Equal(t, 6, len(underlying.WalkDirCalls()))
+
+	_ = cached.WalkDir("/some/path", walkFn)
+	assert.Equal(t, 7, len(underlying.WalkDirCalls()))
 }
 
 func TestRemove(t *testing.T) {
@@ -186,6 +298,20 @@ func TestRemove(t *testing.T) {
 	cached.ClearCache()
 	_ = cached.Remove("/some/path/file.txt")
 	assert.Equal(t, 3, len(underlying.RemoveCalls()))
+
+	cached.DisableAndClearCache()
+	_ = cached.Remove("/some/path/file.txt")
+	assert.Equal(t, 4, len(underlying.RemoveCalls()))
+
+	_ = cached.Remove("/some/path/file.txt")
+	assert.Equal(t, 5, len(underlying.RemoveCalls()))
+
+	cached.Enable()
+	_ = cached.Remove("/some/path/file.txt")
+	assert.Equal(t, 6, len(underlying.RemoveCalls()))
+
+	_ = cached.Remove("/some/path/file.txt")
+	assert.Equal(t, 7, len(underlying.RemoveCalls()))
 }
 
 func TestWriteFile(t *testing.T) {
@@ -208,4 +334,18 @@ func TestWriteFile(t *testing.T) {
 	assert.Equal(t, "/some/path/file.txt", call.Path)
 	assert.Equal(t, "third content", call.Data)
 	assert.Equal(t, false, call.WriteByteOrderMark)
+
+	cached.DisableAndClearCache()
+	_ = cached.WriteFile("/some/path/file.txt", "fourth content", false)
+	assert.Equal(t, 4, len(underlying.WriteFileCalls()))
+
+	_ = cached.WriteFile("/some/path/file.txt", "fifth content", true)
+	assert.Equal(t, 5, len(underlying.WriteFileCalls()))
+
+	cached.Enable()
+	_ = cached.WriteFile("/some/path/file.txt", "sixth content", false)
+	assert.Equal(t, 6, len(underlying.WriteFileCalls()))
+
+	_ = cached.WriteFile("/some/path/file.txt", "seventh content", true)
+	assert.Equal(t, 7, len(underlying.WriteFileCalls()))
 }