Avoid fatal panic on stale config-retainer project paths in project rebuild flow

internal/project/projectcollectionbuilder.go

@@ -612,7 +612,10 @@ func (b *ProjectCollectionBuilder) markProjectsAffectedByConfigChanges(
 	for projectPath := range configChangeResult.affectedProjects {
 		project, ok := b.configuredProjects.Load(projectPath)
 		if !ok {
-			panic(fmt.Sprintf("project %s affected by config change not found", projectPath))
+			if logger != nil {
+				logger.Logf("Skipping stale project %s affected by config change (project may have been removed)", projectPath)
+			}
+			continue
 		}
 		project.ChangeIf(
 			func(p *Project) bool { return !p.dirty || p.dirtyFilePath != "" },

internal/project/projectcollectionbuilder_panic_repro_test.go

@@ -0,0 +1,70 @@
+package project
+
+import (
+	"context"
+	"testing"
+
+	"github.com/microsoft/typescript-go/internal/bundled"
+	"github.com/microsoft/typescript-go/internal/lsp/lsproto"
+	"github.com/microsoft/typescript-go/internal/project/logging"
+	"github.com/microsoft/typescript-go/internal/tspath"
+	"github.com/microsoft/typescript-go/internal/vfs/vfstest"
+)
+
+func TestProjectCollectionBuilder_HandlesStaleConfigRetainer(t *testing.T) {
+	t.Parallel()
+
+	if !bundled.Embedded {
+		t.Skip("bundled files are not embedded")
+	}
+
+	files := map[string]any{
+		"/src/tsconfig.json": `{"compilerOptions": {"strict": true}}`,
+		"/src/index.ts":      `export const x = 1;`,
+	}
+
+	fs := bundled.WrapFS(vfstest.FromMap(files, false /*useCaseSensitiveFileNames*/))
+	session := NewSession(&SessionInit{
+		BackgroundCtx: context.Background(),
+		Options: &SessionOptions{
+			CurrentDirectory:   "/",
+			DefaultLibraryPath: bundled.LibPath(),
+			TypingsLocation:    "/home/src/Library/Caches/typescript",
+			PositionEncoding:   lsproto.PositionEncodingKindUTF8,
+			WatchEnabled:       false,
+			LoggingEnabled:     false,
+		},
+		FS:          fs,
+		Client:      noopClient{},
+		Logger:      logging.NewTestLogger(),
+		NpmExecutor: nil,
+	})
+
+	session.DidOpenFile(
+		context.Background(),
+		lsproto.DocumentUri("file:///src/index.ts"),
+		1,
+		files["/src/index.ts"].(string),
+		lsproto.LanguageKindTypeScript,
+	)
+
+	snapshot := session.Snapshot()
+	configPath := session.toPath("/src/tsconfig.json")
+	entry := snapshot.ConfigFileRegistry.configs[configPath]
+	if entry == nil {
+		t.Fatal("expected /src/tsconfig.json config entry to exist")
+	}
+	if entry.retainingProjects == nil {
+		entry.retainingProjects = make(map[tspath.Path]struct{})
+	}
+	entry.retainingProjects[session.toPath("/stale/tsconfig.json")] = struct{}{}
+
+	session.DidChangeWatchedFiles(context.Background(), []*lsproto.FileEvent{
+		{
+			Uri:  lsproto.DocumentUri("file:///src/tsconfig.json"),
+			Type: lsproto.FileChangeTypeChanged,
+		},
+	})
+
+	_, _ = session.GetLanguageService(context.Background(), lsproto.DocumentUri("file:///src/index.ts"))
+}