internal/trace: add generator tests for sync events

Add generator tests that verify the timestamps for the sync events
emitted in the go1.25 trace format and earlier versions.

Add the ability to configure the properties of the per-generation sync
batches in testgen. Also refactor testgen to produce more realistic
timestamps by keeping track of lastTs and using it for structural
batches that don't have their own timestamps. Otherwise they default to
zero which means the minTs of the generation can't be controlled.

For #69869

Change-Id: I92a49b8281bc4169b63e13c030c1de7720cd6f26
Reviewed-on: https://go-review.googlesource.com/c/go/+/653876
Auto-Submit: Michael Knyszek <mknyszek@google.com>
Reviewed-by: David Chase <drchase@google.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Reviewed-by: Michael Knyszek <mknyszek@google.com>

1 files changed, 74 insertions, 0 deletions

diff --git a/src/internal/trace/reader_test.go b/src/internal/trace/reader_test.go
index b395183e0e..222d2dfa82 100644
--- a/src/internal/trace/reader_test.go
+++ b/src/internal/trace/reader_test.go
@@ -13,6 +13,7 @@ import (
 	"path/filepath"
 	"strings"
 	"testing"
+	"time"
 
 	"internal/trace"
 	"internal/trace/raw"
@@ -171,3 +172,76 @@ func dumpTraceToFile(t *testing.T, testName string, stress bool, b []byte) strin
 	}
 	return f.Name()
 }
+
+func TestTraceGenSync(t *testing.T) {
+	type sync struct {
+		Time          trace.Time
+		ClockSnapshot *trace.ClockSnapshot
+	}
+	runTest := func(testName string, wantSyncs []sync) {
+		t.Run(testName, func(t *testing.T) {
+			testPath := "testdata/tests/" + testName
+			r, _, _, err := testtrace.ParseFile(testPath)
+			if err != nil {
+				t.Fatalf("malformed test %s: bad trace file: %v", testPath, err)
+			}
+			tr, err := trace.NewReader(r)
+			if err != nil {
+				t.Fatalf("malformed test %s: bad trace file: %v", testPath, err)
+			}
+			var syncEvents []trace.Event
+			for {
+				ev, err := tr.ReadEvent()
+				if err == io.EOF {
+					break
+				}
+				if err != nil {
+					t.Fatalf("malformed test %s: bad trace file: %v", testPath, err)
+				}
+				if ev.Kind() == trace.EventSync {
+					syncEvents = append(syncEvents, ev)
+				}
+			}
+
+			if got, want := len(syncEvents), len(wantSyncs); got != want {
+				t.Errorf("got %d sync events, want %d", got, want)
+			}
+
+			for i, want := range wantSyncs {
+				got := syncEvents[i]
+				gotSync := syncEvents[i].Sync()
+				if got.Time() != want.Time {
+					t.Errorf("sync=%d got time %d, want %d", i+1, got.Time(), want.Time)
+				}
+				if gotSync.ClockSnapshot == nil && want.ClockSnapshot == nil {
+					continue
+				}
+				if gotSync.ClockSnapshot.Trace != want.ClockSnapshot.Trace {
+					t.Errorf("sync=%d got trace time %d, want %d", i+1, gotSync.ClockSnapshot.Trace, want.ClockSnapshot.Trace)
+				}
+				if !gotSync.ClockSnapshot.Wall.Equal(want.ClockSnapshot.Wall) {
+					t.Errorf("sync=%d got wall time %s, want %s", i+1, gotSync.ClockSnapshot.Wall, want.ClockSnapshot.Wall)
+				}
+				if gotSync.ClockSnapshot.Mono != want.ClockSnapshot.Mono {
+					t.Errorf("sync=%d got mono time %d, want %d", i+1, gotSync.ClockSnapshot.Mono, want.ClockSnapshot.Mono)
+				}
+			}
+		})
+	}
+
+	runTest("go123-sync.test", []sync{
+		{10, nil},
+		{40, nil},
+		// The EvFrequency batch for generation 3 is emitted at trace.Time(80),
+		// but 60 is the minTs of the generation, see b30 in the go generator.
+		{60, nil},
+		{63, nil},
+	})
+
+	runTest("go125-sync.test", []sync{
+		{9, &trace.ClockSnapshot{Trace: 10, Mono: 99, Wall: time.Date(2025, 2, 28, 15, 4, 9, 123, time.UTC)}},
+		{38, &trace.ClockSnapshot{Trace: 40, Mono: 199, Wall: time.Date(2025, 2, 28, 15, 4, 10, 123, time.UTC)}},
+		{58, &trace.ClockSnapshot{Trace: 60, Mono: 299, Wall: time.Date(2025, 2, 28, 15, 4, 11, 123, time.UTC)}},
+		{83, nil},
+	})
+}