Runtime tracing, flight recording by jakebailey · Pull Request #3627 · microsoft/typescript-go

jakebailey · 2026-04-27T21:26:04Z

This adds Go runtime/trace support, including flight recording. Traces are integrated into the VS Code extension, similarly to pprof profiling.

I've added trace points in various places, and plumbed context around a bit.

Copilot

Pull request overview

Adds Go runtime/trace integration (including a flight recorder) to tsgo, and wires capture/control into the LSP + the preview VS Code extension to make runtime tracing accessible similarly to existing pprof tooling.

Changes:

Introduces internal/runtimetrace to manage process-lifetime runtime tracing and flight-recorder snapshots (env-driven + SIGUSR1 on Unix).
Plumbs context.Context through checker/program APIs and adds trace regions/log events across compiler, parser, resolver, project system, and LSP request handling.
Adds new LSP custom requests + VS Code extension commands to start/snapshot/stop the flight recorder.

Reviewed changes

Copilot reviewed 31 out of 31 changed files in this pull request and generated 5 comments.

Show a summary per file

File	Description
internal/transformers/tstransforms/importelision_test.go	Updates test program stub + checker creation to pass `context.Context`.
internal/testrunner/compiler_runner.go	Passes `t.Context()` into `ForEachCheckerParallel` for tracing-friendly APIs.
internal/runtimetrace/runtimetrace.go	New session management for runtime trace + flight recorder via env vars, snapshot-on-stop, Unix signal hook.
internal/runtimetrace/recorder.go	New `FlightRecorder` wrapper around `runtime/trace` flight recorder APIs (start/snapshot/stop).
internal/runtimetrace/api.go	New helpers for trace regions/tasks and safe/unsafe logging conventions.
internal/runtimetrace/signal_unix.go	Unix SIGUSR1 handler to trigger a flight snapshot.
internal/runtimetrace/signal_other.go	Non-Unix no-op signal handler implementation.
internal/project/snapshot.go	Adds trace region around snapshot cloning.
internal/project/session.go	Adds trace region around snapshot updates.
internal/project/project.go	Adapts program binding call to new context-aware `BindSourceFiles`.
internal/project/checkerpool.go	Threads `ctx` into checker creation in the project checker pool.
internal/parser/parser.go	Adds trace region + trace log events to parsing entrypoint.
internal/module/resolver.go	Adds trace region + trace log events to module resolution entrypoint.
internal/lsp/server.go	Adds per-request trace tasks/logging and new handlers for flight recorder control.
internal/lsp/lsproto/lsp_generated.go	Generated protocol additions for flight recorder requests/params/results.
internal/lsp/lsproto/_generate/generate.mts	Adds generator specs for flight recorder protocol structures/requests.
internal/ls/autoimport/util.go	Makes checker pool acquisition context-aware and threads ctx into checker creation.
internal/ls/autoimport/registry.go	Updates checker creation/usage to pass ctx and handle canceled acquisition.
internal/ls/autoimport/aliasresolver.go	Updates `BindSourceFiles` signature for ctx-aware checker.Program.
internal/execute/tsc.go	Adds trace regions around compilation entrypoints.
internal/compiler/program.go	Adds trace regions/logging in binding/diagnostics/emit, and threads ctx through checker pool APIs.
internal/compiler/fileloader.go	Adds trace region around program file processing.
internal/compiler/emitter.go	Adds trace region/logging for emit and adds additional transformer regions.
internal/compiler/checkerpool.go	Threads ctx into checker creation and adds trace region/logging around checker pool init.
internal/checker/checker_test.go	Updates tests/bench to new ctx-aware `BindSourceFiles`/`NewChecker`.
internal/checker/checker.go	Makes `Program.BindSourceFiles` ctx-aware and adds trace regions/logging in checker creation + file checking.
cmd/tsgo/main.go	Starts/stops runtime tracing session for the tsgo process lifetime.
_extension/src/session.ts	Adds VS Code commands for start/snapshot/stop flight recorder and context key wiring.
_extension/src/client.ts	Adds client methods to call new custom LSP flight recorder requests.
_extension/package.json	Registers new extension commands and enablement conditions.
.golangci.yml	Updates depguard rules to forbid direct `runtime/trace` usage outside `internal/runtimetrace` and adjusts linter exclusions.

Copilot · 2026-04-27T21:31:56Z

+func (s *Server) handleSnapshotFlightRecorder(_ context.Context, params *lsproto.ProfileParams, _ *lsproto.RequestMessage) (*lsproto.ProfileResult, error) {
+	filePath, err := s.flightRecorder.Snapshot(params.Dir)
+	if err != nil {
+		return nil, err


handleSnapshotFlightRecorder dereferences params.Dir without checking whether params is nil. Since the generated handler signature accepts *ProfileParams, a malformed/null params payload would panic the server. Consider validating params != nil (and returning an InvalidRequest-style error) before using it.

Copilot · 2026-04-27T21:31:57Z

+
+	switch os.Getenv(envRuntimeTraceDetail) {
+	case "", "0", "false", "no", "off":
+		// detail logging disabled


Start only ever sets unsafeLogging to true; it never resets it to false when TSGO_RUNTIME_TRACE_DETAIL is unset/falsey. If Start is called multiple times in-process (tests, multiple entrypoints, etc.), unsafe logging can remain enabled unexpectedly and cause user-data to be emitted even when the env var is off. Consider explicitly storing false in the disabled case (and/or resetting on Stop) so the value always reflects the current configuration.

Suggested change

// detail logging disabled

unsafeLogging.Store(false)

Copilot · 2026-04-27T21:31:57Z

+const (
+	envRuntimeTrace              = "TSGO_RUNTIME_TRACE"
+	envRuntimeTraceFlight        = "TSGO_RUNTIME_TRACE_FLIGHT"
+	envRuntimeTraceFlightMinAge  = "TSGO_RUNTIME_TRACE_FLIGHT_MIN_AGE"
+	envRuntimeTraceFlightMaxByte = "TSGO_RUNTIME_TRACE_FLIGHT_MAX_BYTES"
+	envRuntimeTraceDetail        = "TSGO_RUNTIME_TRACE_DETAIL"
+)


The constant name envRuntimeTraceFlightMaxByte is singular, but it corresponds to TSGO_RUNTIME_TRACE_FLIGHT_MAX_BYTES (plural). Renaming it to ...MaxBytes would avoid confusion and better reflect the actual env var and meaning.

Copilot · 2026-04-27T21:31:58Z

@@ -67,6 +73,7 @@ func (e *emitter) runScriptTransformers(emitContext *printer.EmitContext, source
 }

 func (e *emitter) runDeclarationTransformers(emitContext *printer.EmitContext, sourceFile *ast.SourceFile, declarationFilePath, declarationMapPath string) (*ast.SourceFile, []*ast.Diagnostic) {
+	defer runtimetrace.Region(context.TODO(), "emitter.runDeclarationTransformers")()


runScriptTransformers/runDeclarationTransformers start trace regions with context.TODO(), which breaks nesting/association with the request/task context passed into emit(ctx). Since emit already has a context, consider threading it through to these helpers (e.g., add a ctx parameter) so transformer regions appear under the correct task/region in traces.

Copilot · 2026-04-27T21:31:58Z

@@ -214,11 +216,15 @@ func createCheckerPool(program checker.Program) (getChecker func() (*checker.Che
 				current := created.Load()
 				if current >= maxSize {
 					// At limit, wait for one to become available
-					ch := <-pool
-					return ch, func() { pool <- ch }
+					select {
+					case ch := <-pool:
+						return ch, func() { pool <- ch }
+					case <-ctx.Done():
+						return nil, func() {}
+					}
 				}
 				if created.CompareAndSwap(current, current+1) {
-					ch := core.FirstResult(checker.NewChecker(program, nil))
+					ch := core.FirstResult(checker.NewChecker(ctx, program, nil))
 					return ch, func() { pool <- ch }
 				}
 			}


createCheckerPool returns early on <-ctx.Done() in a couple of places, but if the context is canceled after the initial non-blocking select and before/while the CAS loop runs, it can still spin and/or create a new checker even though cancellation was requested. Consider checking ctx.Err() inside the for { ... } loop (and before creating a new checker) so cancellation reliably stops work.

jakebailey added 6 commits April 27, 2026 14:21

Runtime tracing, flight recording

5b123cd

Trace regions

60682f7

Logging

8bbe19e

More efficient, fixes

3963b24

more trace points

edd2272

Even more trace points and contexts

b57fcef

Copilot AI review requested due to automatic review settings April 27, 2026 21:26

Copilot AI reviewed Apr 27, 2026

View reviewed changes

DanielRosenwasser mentioned this pull request Apr 28, 2026

Elevated CPU usage in --watch mode when idle (compared to tsc) #3611

Open

jakebailey mentioned this pull request Apr 29, 2026

Add TS_GO_DEBUG_STACK_LIMIT to cap goroutine stack size at entry points #3649

Merged

jakebailey added 2 commits May 5, 2026 16:36

Merge branch 'main' into jabaile/go-runtime-trace

b67b2ef

Rename env vars

c88c914

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Runtime tracing, flight recording#3627

Runtime tracing, flight recording#3627
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jabaile/go-runtime-trace

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Pull request overview

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