internal/trace: add "command" to convert text traces to raw

This is primarily helpful for parsing traces dumped via CI.

cmd/dist doesn't like commands in std which are not actually part of the
Go distribution. So rather than using a real command, this is actually a
test which does the conversion.

Change-Id: I6a6a636c829a4acc0bce8cf7548105ad59d83c67
Reviewed-on: https://go-review.googlesource.com/c/go/+/716882
Reviewed-by: Michael Knyszek <mknyszek@google.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>

src/internal/trace/testtrace/helpers.go

@@ -37,6 +37,7 @@ func Dump(t *testing.T, testName string, traceBytes []byte, forceToFile bool) {
 			t.Logf("text trace too large to dump (%d bytes)", len(s))
 		} else {
 			t.Log(s)
+			t.Log("Convert this to a raw trace with `go test internal/trace/testtrace -covert in.tracetxt -out out.trace`")
 		}
 	} else {
 		// We asked to dump the trace or failed. Write the trace to a file.

src/internal/trace/testtrace/helpers_test.go

@@ -0,0 +1,79 @@
+// Copyright 2025 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package testtrace
+
+import (
+	"flag"
+	"fmt"
+	"io"
+	"internal/trace/raw"
+	"os"
+	"testing"
+)
+
+var (
+	convert = flag.String("convert", "", "Path to trace text file to convert to binary format")
+	output = flag.String("out", "", "Output path for converted trace")
+)
+
+// TestConvertDump is not actually a test, it is a tool for converting trace
+// text dumps generated by Dump into the binary trace format. Set -convert and
+// -o to perform a converison.
+//
+//  go test internal/trace/testtrace -convert in.tracetxt -out out.trace
+//
+// This would be cleaner as a dedicated internal command rather than a test,
+// but cmd/dist does not handle internal (non-distributed) commands in std
+// well.
+func TestConvertDump(t *testing.T) {
+	if *convert == "" {
+		t.Skip("Set -convert to convert a trace text file")
+	}
+	if *output == "" {
+		t.Fatal("Set -o to specify conversion output")
+	}
+
+	if err := convertDump(*convert, *output); err != nil {
+		t.Error(err)
+	}
+}
+
+func convertDump(inPath, outPath string) error {
+	in, err := os.Open(inPath)
+	if err != nil {
+		return fmt.Errorf("error opening input: %v", err)
+	}
+	defer in.Close()
+
+	out, err := os.Create(outPath)
+	if err != nil {
+		return fmt.Errorf("error creating output: %v", err)
+	}
+	defer out.Close()
+
+	tr, err := raw.NewTextReader(in)
+	if err != nil {
+		return fmt.Errorf("error creating text reader: %v", err)
+	}
+	tw, err := raw.NewWriter(out, tr.Version())
+	if err != nil {
+		return fmt.Errorf("error creating raw writer: %v", err)
+	}
+
+	for {
+		ev, err := tr.ReadEvent()
+		if err == io.EOF {
+			break
+		}
+		if err != nil {
+			return fmt.Errorf("bad trace file: %v", err)
+		}
+		if err := tw.WriteEvent(ev); err != nil {
+			return fmt.Errorf("failed to write trace bytes: %v", err)
+		}
+	}
+
+	return nil
+}