# Behavior traces — microsoft/TypeScript

> Canonical page: https://codevetter.com/unpack/typescript/behavior-traces

# Behavior traces — microsoft/TypeScript

Scanned commit 5f6db9c9148635b4cbf72f1193b821b9c6b42dcc (2026-09-22). Generated by codevetter codevetter 1.12.0 on 2026-09-22.

Three flows were traced end to end. Batch compile: main -> runMain -> execute.CommandLine -> tscCompilation -> tsoptions parse/config discovery -> NewCachedFSCompilerHost -> compiler.NewProgram (processAllProgramFiles -> checker pool) -> EmitAndReportStatistics -> EmitFilesAndReportErrors (bind+check diagnostics, Emit) -> report + exit status. LSP: runLSP -> flag parse -> bundled.WrapFS(osvfs.FS()) -> lsp.NewServer -> Server.Run -> read/dispatch loop -> handlerMap -> project.Session snapshots -> ls.LanguageService. API: runAPI -> StdioServer.Run -> ipc transport accept -> StandaloneSession -> proto method table dispatch. A fourth flow covers watch/incremental rebuilds and a fifth covers VS Code extension activation.
- Startup (compile): main() -> runMain() -> core.ApplyDebugStackLimit() -> osutil.Args() -> execute.CommandLine(ctx, newSystem(), args, nil) -> os.Exit(result.Status); newSystem builds osSys with cwd, bundled.WrapFS(osvfs.FS()), bundled.LibPath(). — [tsc/cmd/tsc/main.go#L14-33](https://github.com/microsoft/TypeScript/blob/5f6db9c9148635b4cbf72f1193b821b9c6b42dcc/tsc/cmd/tsc/main.go#L14-L33) [tsc/cmd/tsc/sys.go#L124-138](https://github.com/microsoft/TypeScript/blob/5f6db9c9148635b4cbf72f1193b821b9c6b42dcc/tsc/cmd/tsc/sys.go#L124-L138)
- Compile flow order: CommandLine -> tscCompilation -> report early errors -> handle --init/--version/--help -> resolve configFileName (-p or findConfigFile ancestor walk) -> tsoptions.GetParsedCommandLineOfConfigFile -> CreateReportErrorSummary -> branch to watcher.start / performIncrementalCompilation / performCompilation. — [tsc/internal/execute/tsc.go#L122-267](https://github.com/microsoft/TypeScript/blob/5f6db9c9148635b4cbf72f1193b821b9c6b42dcc/tsc/internal/execute/tsc.go#L122-L267)
- performCompilation: NewContentMapperHost (gated on RunExternalCode) -> compiler.NewCachedFSCompilerHost -> startTracingIfNeeded -> compiler.NewProgram -> tsc.EmitAndReportStatistics -> stopTracing -> CommandLineResult. — [tsc/internal/execute/tsc.go#L345-392](https://github.com/microsoft/TypeScript/blob/5f6db9c9148635b4cbf72f1193b821b9c6b42dcc/tsc/internal/execute/tsc.go#L345-L392) [tsc/internal/execute/tsc/compile.go#L86-98](https://github.com/microsoft/TypeScript/blob/5f6db9c9148635b4cbf72f1193b821b9c6b42dcc/tsc/internal/execute/tsc/compile.go#L86-L98)
- Inside NewProgram: processAllProgramFiles parses and resolves all root+dependency files (parse tasks -> fileLoader -> module.Resolver), then initCheckerPool, verifyCompilerOptions, collectContentMapperOptionDiagnostics. — [tsc/internal/compiler/program.go#L284-294](https://github.com/microsoft/TypeScript/blob/5f6db9c9148635b4cbf72f1193b821b9c6b42dcc/tsc/internal/compiler/program.go#L284-L294) [tsc/internal/compiler/filesparser.go](https://github.com/microsoft/TypeScript/blob/5f6db9c9148635b4cbf72f1193b821b9c6b42dcc/tsc/internal/compiler/filesparser.go)
- Emit path: EmitAndReportStatistics -> EmitFilesAndReportErrors -> GetDiagnosticsOfAnyProgram(ctx, programLike, ...) with per-file GetBindDiagnostics then GetSemanticDiagnostics -> programLike.Emit(EmitOptions{WriteFile}) -> SortAndDeduplicateDiagnostics -> ReportDiagnostic each -> listFiles -> ReportErrorSummary -> exit-status mapping (EmitSkipped+diagnostics => DiagnosticsPresent_OutputsSkipped). — [tsc/internal/execute/tsc/emit.go#L46-140](https://github.com/microsoft/TypeScript/blob/5f6db9c9148635b4cbf72f1193b821b9c6b42dcc/tsc/internal/execute/tsc/emit.go#L46-L140)
- Incremental compile: performIncrementalCompilation reads oldProgram via incremental.ReadBuildInfoProgram(host) before parsing, then incremental.NewProgram(program, oldProgram, CreateHost(host), sys.Now, testing) computes the change set and EmitAndReportStatistics runs against the incremental program. — [tsc/internal/execute/tsc.go#L287-343](https://github.com/microsoft/TypeScript/blob/5f6db9c9148635b4cbf72f1193b821b9c6b42dcc/tsc/internal/execute/tsc.go#L287-L343)
- LSP startup: `tsc --lsp --stdio` -> runLSP -> flag.Parse (--pprofDir, --clientProcessId; --pipe/--socket parsed but rejected, only stdio supported) -> bundled.WrapFS(osvfs.FS()), osvfs.GetGlobalTypingsCacheLocation() -> lsp.NewServer(ServerOptions{In,Out,Err,Cwd,FS,NpmInstall,Spawn,...}) -> s.Run(ctx). — [tsc/cmd/tsc/lsp.go#L20-74](https://github.com/microsoft/TypeScript/blob/5f6db9c9148635b4cbf72f1193b821b9c6b42dcc/tsc/cmd/tsc/lsp.go#L20-L74)
- LSP request handling: Server.Run reads messages into requestQueue; handleRequestOrNotification consults handlers()[req.Method]; document requests are wrapped by registerLanguageServiceDocumentRequestHandler which resolves session.GetLanguageService(ctx, params.TextDocumentURI()) and returns async work that runs the handler, then EnqueuePublishGlobalDiagnostics. — [tsc/internal/lsp/server.go#L1142-1192](https://github.com/microsoft/TypeScript/blob/5f6db9c9148635b4cbf72f1193b821b9c6b42dcc/tsc/internal/lsp/server.go#L1142-L1192) [tsc/internal/lsp/server.go#L1341-1359](https://github.com/microsoft/TypeScript/blob/5f6db9c9148635b4cbf72f1193b821b9c6b42dcc/tsc/internal/lsp/server.go#L1341-L1359)
- LSP lifecycle: initialize -> handleInitialize creates the project.Session (s.session set; requests before initialize get ErrorCodeServerNotInitialized via the register wrappers); shutdown -> handleShutdown; exit -> handleExit; a parent-process watchdog goroutine polls isProcessAlive(parentPID) every 5s and cancels the server context if the editor dies. — [tsc/internal/lsp/server.go#L1501](https://github.com/microsoft/TypeScript/blob/5f6db9c9148635b4cbf72f1193b821b9c6b42dcc/tsc/internal/lsp/server.go#L1501) [tsc/internal/lsp/server.go#L1317-1339](https://github.com/microsoft/TypeScript/blob/5f6db9c9148635b4cbf72f1193b821b9c6b42dcc/tsc/internal/lsp/server.go#L1317-L1339) [tsc/cmd/tsc/lsp.go#L95-115](https://github.com/microsoft/TypeScript/blob/5f6db9c9148635b4cbf72f1193b821b9c6b42dcc/tsc/cmd/tsc/lsp.go#L95-L115)
- API session startup: `tsc --api` -> runAPI -> parseAPIFlags (--cwd, --pipe, --callbacks, --async, --timing, --runExternalCode) -> api.NewStdioServer -> Run: create pipe or stdio transport -> bundled.WrapFS(osvfs.FS()) optionally wrapped by callbackFS -> project.SessionInit -> NewStandaloneSession -> transport.Accept -> protocol (msgpack sync or JSON-RPC async) -> conn serve loop. — [tsc/cmd/tsc/api.go#L41-82](https://github.com/microsoft/TypeScript/blob/5f6db9c9148635b4cbf72f1193b821b9c6b42dcc/tsc/cmd/tsc/api.go#L41-L82) [tsc/internal/api/server.go#L62-120](https://github.com/microsoft/TypeScript/blob/5f6db9c9148635b4cbf72f1193b821b9c6b42dcc/tsc/internal/api/server.go#L62-L120)
- Watch flow: tscCompilation sees Watch.IsTrue() -> createWatcher(sys, config, commandLineOptions, raw, reporters, testing) -> watcher.start(ctx) -> returns CommandLineResult{Watcher: watcher}; watching is implemented over watchmanager which multiplexes fswatch backends. — [tsc/internal/execute/tsc.go#L233-244](https://github.com/microsoft/TypeScript/blob/5f6db9c9148635b4cbf72f1193b821b9c6b42dcc/tsc/internal/execute/tsc.go#L233-L244) [tsc/internal/execute/watcher.go](https://github.com/microsoft/TypeScript/blob/5f6db9c9148635b4cbf72f1193b821b9c6b42dcc/tsc/internal/execute/watcher.go) [tsc/internal/execute/watchmanager/watchmanager.go](https://github.com/microsoft/TypeScript/blob/5f6db9c9148635b4cbf72f1193b821b9c6b42dcc/tsc/internal/execute/watchmanager/watchmanager.go)
- VS Code flow: extension activate() -> SessionManager.start -> getExe(context) resolves the tsgo binary -> client.start(exe) builds ServerOptions running `[exe, --lsp, ...pprofArgs]` with stdio transport -> NativePreviewLanguageClient (vscode-languageclient) connects; setContext 'typescript.native-preview.serverRunning' toggles command enablement. — [packages/vscode-typescript/src/extension.ts#L33-78](https://github.com/microsoft/TypeScript/blob/5f6db9c9148635b4cbf72f1193b821b9c6b42dcc/packages/vscode-typescript/src/extension.ts#L33-L78) [packages/vscode-typescript/src/client.ts#L233-256](https://github.com/microsoft/TypeScript/blob/5f6db9c9148635b4cbf72f1193b821b9c6b42dcc/packages/vscode-typescript/src/client.ts#L233-L256) [packages/vscode-typescript/src/session.ts#L207-224](https://github.com/microsoft/TypeScript/blob/5f6db9c9148635b4cbf72f1193b821b9c6b42dcc/packages/vscode-typescript/src/session.ts#L207-L224)
- Program reuse on edit: Project updates call Program.UpdateProgram/ReuseProgram, which replaces only the changed SourceFile when safe and bails to a full NewProgram on redirect files, helper/JSX-runtime import requirements, or changed supplemental (content-mapped) files. — [tsc/internal/compiler/program.go#L296-403](https://github.com/microsoft/TypeScript/blob/5f6db9c9148635b4cbf72f1193b821b9c6b42dcc/tsc/internal/compiler/program.go#L296-L403)

Every claim links to its cited files at the pinned commit. Citations identify source evidence; they do not establish runtime correctness. Independent CodeVetter scan — not reviewed by upstream maintainers.

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