x/exp/trace, internal/trace/v2: region end without region start panics #64878
Description
Producing a trace with the following program:
func main() {
trace.Start(io.Discard)
r := trace.StartRegion(context.Background(), "my region")
trace.Stop()
trace.Start(os.Stdout)
r.End()
trace.Stop()
}
and trying to parse it results in
panic: runtime error: index out of range [-1]
goroutine 1 [running]:
internal/trace/v2.(*gState).endRegion(0x851e60?, {0x0, {0xc000013200, 0x9}})
/home/dominikh/prj/go/src/internal/trace/v2/order.go:920 +0x191
internal/trace/v2.(*ordering).advance(0xc000206050, 0xc0000382f0, 0xc0000e5900, 0x1a1a0c, 0x2)
/home/dominikh/prj/go/src/internal/trace/v2/order.go:659 +0x6bd1
internal/trace/v2.(*Reader).ReadEvent(0xc000206000)
/home/dominikh/prj/go/src/internal/trace/v2/reader.go:161 +0x74a
cmd/trace/v2.debugProcessedEvents({0xc20aa0?, 0xc0000b2960?})
/home/dominikh/prj/go/src/cmd/trace/v2/main.go:166 +0xf8
cmd/trace/v2.Main({0x7fff3054ca86?, 0xc0000222b0?}, {0x8c5dcb, 0xb}, {0xc00010fe10?, 0x7fa1ac?}, 0x1)
/home/dominikh/prj/go/src/cmd/trace/v2/main.go:34 +0x11f8
main.main()
/home/dominikh/prj/go/src/cmd/trace/main.go:87 +0xa4
/cc @mknyszek