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>

4 files changed, 23 insertions, 21 deletions

diff --git a/src/internal/trace/event.go b/src/internal/trace/event.go
index 7d869e885f..90effce653 100644
--- a/src/internal/trace/event.go
+++ b/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
diff --git a/src/internal/trace/summary.go b/src/internal/trace/summary.go
index fa3e3359c7..1cd506ac5a 100644
--- a/src/internal/trace/summary.go
+++ b/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
diff --git a/src/internal/trace/testtrace/validation.go b/src/internal/trace/testtrace/validation.go
index ec492110e2..42a561f1f0 100644
--- a/src/internal/trace/testtrace/validation.go
+++ b/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.
 			//
diff --git a/src/internal/trace/trace_test.go b/src/internal/trace/trace_test.go
index 1929069cc5..dcf9d05fb4 100644
--- a/src/internal/trace/trace_test.go
+++ b/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