proc,service,terminal: information about stack trace truncation

Add a flag to Stackframe that indicates where the stack frame is the
bottom-most frame of the stack. This allows clients to know whether the
stack trace terminated normally or if it was truncated because the
maximum depth was reached.
Add a truncation message to the 'stack' command.

pkg/proc/stack.go

@@ -47,6 +47,8 @@ type Stackframe struct {
 	SystemStack bool
 	// Inlined is true if this frame is actually an inlined call.
 	Inlined bool
+	// Bottom is true if this is the bottom of the stack
+	Bottom bool
 
 	// lastpc is a memory address guaranteed to belong to the last instruction
 	// executed in this stack frame.
@@ -339,6 +341,7 @@ func (it *stackIterator) switchStack() bool {
 
 // Frame returns the frame the iterator is pointing at.
 func (it *stackIterator) Frame() Stackframe {
+	it.frame.Bottom = it.atend
 	return it.frame
 }
 

pkg/terminal/command.go

@@ -1530,6 +1530,8 @@ func digits(n int) int {
 	return int(math.Floor(math.Log10(float64(n)))) + 1
 }
 
+const stacktraceTruncatedMessage = "(truncated)"
+
 func printStack(stack []api.Stackframe, ind string, offsets bool) {
 	if len(stack) == 0 {
 		return
@@ -1582,6 +1584,10 @@ func printStack(stack []api.Stackframe, ind string, offsets bool) {
 			fmt.Println()
 		}
 	}
+
+	if len(stack) > 0 && !stack[len(stack)-1].Bottom {
+		fmt.Printf("%s"+stacktraceTruncatedMessage+"\n", ind)
+	}
 }
 
 func printcontext(t *Term, state *api.DebuggerState) error {

pkg/terminal/command_test.go

@@ -224,7 +224,7 @@ func TestExecuteFile(t *testing.T) {
 
 func TestIssue354(t *testing.T) {
 	printStack([]api.Stackframe{}, "", false)
-	printStack([]api.Stackframe{{api.Location{PC: 0, File: "irrelevant.go", Line: 10, Function: nil}, nil, nil, 0, 0, nil, ""}}, "", false)
+	printStack([]api.Stackframe{{api.Location{PC: 0, File: "irrelevant.go", Line: 10, Function: nil}, nil, nil, 0, 0, nil, true, ""}}, "", false)
 }
 
 func TestIssue411(t *testing.T) {
@@ -827,3 +827,20 @@ func TestOptimizationCheck(t *testing.T) {
 		})
 	}
 }
+
+func TestTruncateStacktrace(t *testing.T) {
+	withTestTerminal("stacktraceprog", t, func(term *FakeTerminal) {
+		term.MustExec("break main.stacktraceme")
+		term.MustExec("continue")
+		out1 := term.MustExec("stack")
+		t.Logf("untruncated output %q", out1)
+		if strings.Contains(out1, stacktraceTruncatedMessage) {
+			t.Fatalf("stacktrace was truncated")
+		}
+		out2 := term.MustExec("stack 1")
+		t.Logf("truncated output %q", out2)
+		if !strings.Contains(out2, stacktraceTruncatedMessage) {
+			t.Fatalf("stacktrace was not truncated")
+		}
+	})
+}

service/api/types.go

@@ -131,6 +131,8 @@ type Stackframe struct {
 
 	Defers []Defer
 
+	Bottom bool `json:"Bottom,omitempty"` // Bottom is true if this is the bottom frame of the stack
+
 	Err string
 }
 

service/debugger/debugger.go

@@ -932,6 +932,8 @@ func (d *Debugger) convertStacktrace(rawlocs []proc.Stackframe, cfg *proc.LoadCo
 			FramePointerOffset: rawlocs[i].FramePointerOffset(),
 
 			Defers: d.convertDefers(rawlocs[i].Defers),
+
+			Bottom: rawlocs[i].Bottom,
 		}
 		if rawlocs[i].Err != nil {
 			frame.Err = rawlocs[i].Err.Error()

service/rpc2/server.go

@@ -172,11 +172,11 @@ func (s *RPCServer) Stacktrace(arg StacktraceIn, out *StacktraceOut) error {
 	if cfg == nil && arg.Full {
 		cfg = &api.LoadConfig{true, 1, 64, 64, -1}
 	}
-	locs, err := s.debugger.Stacktrace(arg.Id, arg.Depth, arg.Defers, api.LoadConfigToProc(cfg))
+	var err error
+	out.Locations, err = s.debugger.Stacktrace(arg.Id, arg.Depth, arg.Defers, api.LoadConfigToProc(cfg))
 	if err != nil {
 		return err
 	}
-	out.Locations = locs
 	return nil
 }