internal/trace: refactor Stack.Frames to return iter.Seq

The Frames function is almost an iter.Seq, except for its bool return
value.

Since none of the callers in the Go tree rely on the bool, we can remove
it. However, doing so might still obscure the intended usage as an iterator.

This refactor changes the API to return iter.Seq, making the intended
usage explicit. Refactoring the existing callers to take advantage of
the new interface will be done in a follow-up CL.

Change-Id: I03e4d6d762910e418cc37d59a6c519eb7f39b3b0
Reviewed-on: https://go-review.googlesource.com/c/go/+/608855
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Reviewed-by: Dmitri Shuralyov <dmitshur@google.com>
Reviewed-by: Michael Knyszek <mknyszek@google.com>

src/cmd/trace/gstate.go

@@ -364,7 +364,7 @@ func (gs *gState[R]) rangeEnd(ts trace.Time, name string, stack trace.Stack, ctx
 
 func lastFunc(s trace.Stack) string {
 	var last trace.StackFrame
-	s.Frames(func(f trace.StackFrame) bool {
+	s.Frames()(func(f trace.StackFrame) bool {
 		last = f
 		return true
 	})

src/cmd/trace/pprof.go

@@ -307,7 +307,7 @@ func (m *stackMap) profile() []traceviewer.ProfileRecord {
 	for stack, record := range m.stacks {
 		rec := *record
 		i := 0
-		stack.Frames(func(frame trace.StackFrame) bool {
+		stack.Frames()(func(frame trace.StackFrame) bool {
 			rec.Stack = append(rec.Stack, &trace.Frame{
 				PC:   frame.PC,
 				Fn:   frame.Func,
@@ -327,7 +327,7 @@ func (m *stackMap) profile() []traceviewer.ProfileRecord {
 // pcsForStack extracts the first pprofMaxStack PCs from stack into pcs.
 func pcsForStack(stack trace.Stack, pcs *[pprofMaxStack]uint64) {
 	i := 0
-	stack.Frames(func(frame trace.StackFrame) bool {
+	stack.Frames()(func(frame trace.StackFrame) bool {
 		pcs[i] = frame.PC
 		i++
 		return i < len(pcs)

src/cmd/trace/regions.go

@@ -72,7 +72,7 @@ func fingerprintRegion(r *trace.UserRegionSummary) regionFingerprint {
 func regionTopStackFrame(r *trace.UserRegionSummary) trace.StackFrame {
 	var frame trace.StackFrame
 	if r.Start != nil && r.Start.Stack() != trace.NoStack {
-		r.Start.Stack().Frames(func(f trace.StackFrame) bool {
+		r.Start.Stack().Frames()(func(f trace.StackFrame) bool {
 			frame = f
 			return false
 		})

src/cmd/trace/viewer.go

@@ -15,7 +15,7 @@ import (
 // used to store the frames to reduce allocations.
 func viewerFrames(stk trace.Stack) []*trace.Frame {
 	var frames []*trace.Frame
-	stk.Frames(func(f trace.StackFrame) bool {
+	stk.Frames()(func(f trace.StackFrame) bool {
 		frames = append(frames, &trace.Frame{
 			PC:   f.PC,
 			Fn:   f.Func,

src/internal/trace/event.go

@@ -6,6 +6,7 @@ package trace
 
 import (
 	"fmt"
+	"iter"
 	"math"
 	"strings"
 	"time"
@@ -265,24 +266,25 @@ type Stack struct {
 }
 
 // Frames is an iterator over the frames in a Stack.
-func (s Stack) Frames(yield func(f StackFrame) bool) bool {
-	if s.id == 0 {
-		return true
-	}
-	stk := s.table.stacks.mustGet(s.id)
-	for _, pc := range stk.pcs {
-		f := s.table.pcs[pc]
-		sf := StackFrame{
-			PC:   f.pc,
-			Func: s.table.strings.mustGet(f.funcID),
-			File: s.table.strings.mustGet(f.fileID),
-			Line: f.line,
+func (s Stack) Frames() iter.Seq[StackFrame] {
+	return func(yield func(StackFrame) bool) {
+		if s.id == 0 {
+			return
 		}
-		if !yield(sf) {
-			return false
+		stk := s.table.stacks.mustGet(s.id)
+		for _, pc := range stk.pcs {
+			f := s.table.pcs[pc]
+			sf := StackFrame{
+				PC:   f.pc,
+				Func: s.table.strings.mustGet(f.funcID),
+				File: s.table.strings.mustGet(f.fileID),
+				Line: f.line,
+			}
+			if !yield(sf) {
+				return
+			}
 		}
 	}
-	return true
 }
 
 // NoStack is a sentinel value that can be compared against any Stack value, indicating
@@ -796,7 +798,7 @@ func (e Event) String() string {
 		if s.Stack != NoStack {
 			fmt.Fprintln(&sb)
 			fmt.Fprintln(&sb, "TransitionStack=")
-			s.Stack.Frames(func(f StackFrame) bool {
+			s.Stack.Frames()(func(f StackFrame) bool {
 				fmt.Fprintf(&sb, "\t%s @ 0x%x\n", f.Func, f.PC)
 				fmt.Fprintf(&sb, "\t\t%s:%d\n", f.File, f.Line)
 				return true
@@ -809,7 +811,7 @@ func (e Event) String() string {
 	if stk := e.Stack(); stk != NoStack {
 		fmt.Fprintln(&sb)
 		fmt.Fprintln(&sb, "Stack=")
-		stk.Frames(func(f StackFrame) bool {
+		stk.Frames()(func(f StackFrame) bool {
 			fmt.Fprintf(&sb, "\t%s @ 0x%x\n", f.Func, f.PC)
 			fmt.Fprintf(&sb, "\t\t%s:%d\n", f.File, f.Line)
 			return true

src/internal/trace/summary.go

@@ -394,7 +394,7 @@ func (s *Summarizer) Event(ev *Event) {
 				if stk != NoStack {
 					var frame StackFrame
 					var ok bool
-					stk.Frames(func(f StackFrame) bool {
+					stk.Frames()(func(f StackFrame) bool {
 						frame = f
 						ok = true
 						return true

src/internal/trace/testtrace/validation.go

@@ -351,7 +351,7 @@ func (v *Validator) getOrCreateThread(e *errAccumulator, ev trace.Event, m trace
 func checkStack(e *errAccumulator, stk trace.Stack) {
 	// Check for non-empty values, but we also check for crashes due to incorrect validation.
 	i := 0
-	stk.Frames(func(f trace.StackFrame) bool {
+	stk.Frames()(func(f trace.StackFrame) bool {
 		if i == 0 {
 			// Allow for one fully zero stack.
 			//

src/internal/trace/trace_test.go

@@ -148,7 +148,7 @@ func TestTraceCPUProfile(t *testing.T) {
 				if hogRegion != nil && ev.Goroutine() == hogRegion.Goroutine() {
 					traceSamples++
 					var fns []string
-					ev.Stack().Frames(func(frame trace.StackFrame) bool {
+					ev.Stack().Frames()(func(frame trace.StackFrame) bool {
 						if frame.Func != "runtime.goexit" {
 							fns = append(fns, fmt.Sprintf("%s:%d", frame.Func, frame.Line))
 						}
@@ -438,7 +438,7 @@ func TestTraceStacks(t *testing.T) {
 		stackMatches := func(stk trace.Stack, frames []frame) bool {
 			i := 0
 			match := true
-			stk.Frames(func(f trace.StackFrame) bool {
+			stk.Frames()(func(f trace.StackFrame) bool {
 				if f.Func != frames[i].fn {
 					match = false
 					return false

src/runtime/trace_cgo_test.go

@@ -94,7 +94,7 @@ func mustFindLogV2(t *testing.T, trc io.Reader, category string) trace.Event {
 // dumpStack returns e.Stack() as a string.
 func dumpStackV2(e *trace.Event) string {
 	var buf bytes.Buffer
-	e.Stack().Frames(func(f trace.StackFrame) bool {
+	e.Stack().Frames()(func(f trace.StackFrame) bool {
 		file := strings.TrimPrefix(f.File, runtime.GOROOT())
 		fmt.Fprintf(&buf, "%s\n\t%s:%d\n", f.Func, file, f.Line)
 		return true