feat(bazel): add stream_bazel_logs option to tee stderr to os.Stderr (#124)

Adds a per-repository `stream_bazel_logs` config flag (default false).
When enabled, Bazel query stderr is tee'd to os.Stderr via
io.MultiWriter while still being captured in the existing stderrBuf for
error reporting. Threaded through bazel.Params.StreamLogs and wired in
nativeOrchestrator from RepositoryConfig.StreamBazelLogs. This way
consumers can surface the bazel log as is and know what's going on in
the queries live

StreamBazelLogs forwards Bazel's stderr to the Tango process's stderr in
real time instead of buffering it. When true, operators see query
progress live as Bazel runs; the trade-off is that stderr is no longer
captured, so query-failure errors will not include it. When false
(default) stderr is buffered and folded into the returned error if the
query fails.

Author: xytan0056

config/repository_config.go

@@ -25,6 +25,7 @@ type RepositoryConfig struct {
 	BazelCommand           string   `yaml:"bazel_command"`
 	QueryTimeout           int64    `yaml:"query_timeout"` // in seconds
 	BazelExtraArgs         []string `yaml:"bazel_extra_args"`
+	StreamBazelLogs        bool     `yaml:"stream_bazel_logs"`
 }
 
 // RepositoryConfigProvider looks up per-repository configuration by remote.

core/bazel/bazel.go

@@ -56,6 +56,7 @@ type BazelClient struct {
 	logger             *zap.SugaredLogger
 	execCommandContext func(ctx context.Context, name string, arg ...string) commander
 	queryTimeout       time.Duration
+	streamLogs         bool
 }
 
 type Params struct {
@@ -65,6 +66,7 @@ type Params struct {
 	Logger             *zap.SugaredLogger
 	ExecCommandContext func(ctx context.Context, name string, arg ...string) commander
 	QueryTimeout       time.Duration
+	StreamLogs         bool
 }
 
 func NewBazelClient(ctx context.Context, p Params) (*BazelClient, error) {
@@ -97,6 +99,7 @@ func NewBazelClient(ctx context.Context, p Params) (*BazelClient, error) {
 		logger:             p.Logger,
 		execCommandContext: execCmd,
 		queryTimeout:       timeout,
+		streamLogs:         p.StreamLogs,
 	}, nil
 }
 

core/bazel/query.go

@@ -67,6 +67,13 @@ func (b *BazelClient) executeQueryInternal(ctx context.Context, query string, st
 	if err != nil {
 		return nil, err
 	}
+	// In streamLogs mode, stderr goes straight to os.Stderr so operators see
+	// bazel progress live; otherwise it's captured for inclusion in failure
+	// errors (see wrapQueryFailure).
+	stderrSink := io.Writer(&stderrBuf)
+	if b.streamLogs {
+		stderrSink = os.Stderr
+	}
 	// orchestrate `allOfFailFast`
 	// create a `g` group and a new `gCtx` derived from our 15 minute timeout `ctx`.
 	g, gCtx := errgroup.WithContext(cmdCtx)
@@ -83,24 +90,33 @@ func (b *BazelClient) executeQueryInternal(ctx context.Context, query string, st
 	})
 	// stream stderr
 	g.Go(func() error {
-		return streamOutput(gCtx, stderr, &stderrBuf)
+		return streamOutput(gCtx, stderr, stderrSink)
 	})
 	waitErr := cmd.Wait()
 	streamErr := g.Wait()
-	// The command itself failed.
 	if waitErr != nil {
-		b.logger.Errorf("Bazel query failed: %v\nstderr:\n%s", waitErr, stderrBuf.String())
-		return queryResults, fmt.Errorf("bazel query failed: %w\nstderr:\n%s", waitErr, stderrBuf.String())
+		return queryResults, b.wrapQueryFailure("bazel query failed", waitErr, &stderrBuf)
 	}
-	// The command succeeded, but there was an error in the stream processing.
 	if streamErr != nil {
-		b.logger.Errorf("Error in stream processing: %v\nstderr:\n%s", streamErr, stderrBuf.String())
-		return nil, fmt.Errorf("stream processing failed: %w\nstderr:\n%s", streamErr, stderrBuf.String())
+		return nil, b.wrapQueryFailure("stream processing failed", streamErr, &stderrBuf)
 	}
 	b.logger.Debugf("Parsed %d targets from bazel query", len(queryResults.Target))
 	return queryResults, nil
 }
 
+// wrapQueryFailure logs the failure and returns a wrapped error. When stderr
+// was captured (streamLogs off), its contents are appended so the failure is
+// self-contained. When streamLogs is on the operator has already seen stderr
+// live, so it's omitted.
+func (b *BazelClient) wrapQueryFailure(msg string, cause error, stderrBuf *bytes.Buffer) error {
+	tail := ""
+	if !b.streamLogs {
+		tail = "\nstderr:\n" + stderrBuf.String()
+	}
+	b.logger.Errorf("%s: %v%s", msg, cause, tail)
+	return fmt.Errorf("%s: %w%s", msg, cause, tail)
+}
+
 // FromFile reads a proto file generated by bazel query.
 func FromFile(path string) (*buildpb.QueryResult, error) {
 	var f io.ReadCloser

orchestrator/native_orchestrator.go

@@ -196,6 +196,7 @@ func (b *nativeOrchestrator) GetTargetGraph(ctx context.Context, param GetTarget
 			Logger:        b.logger,
 			BazelCommand:  repoCfg.BazelCommand,
 			QueryTimeout:  time.Duration(repoCfg.QueryTimeout) * time.Second,
+			StreamLogs:    repoCfg.StreamBazelLogs,
 		})
 		if err != nil {
 			logger.Errorw("GetTargetGraph: Error creating bazel client", zap.Error(err))