runtime: hide <autogenerated> methods from call stack

The compiler generates wrapper methods to forward interface method
calls (which are always pointer-based) to value methods. These
wrappers appear in the call stack even though they are an
implementation detail. This leaves ugly "<autogenerated>" functions in
stack traces and can throw off skip counts for stack traces.

Fix this by considering these runtime frames in printed stack traces
so they will only be printed if runtime frames are being printed, and
by eliding them from the call stack expansion used by CallersFrames
and Caller.

This removes the test for issue 4388 since that was checking that
"<autogenerated>" appeared in the stack trace instead of something
even weirder. We replace it with various runtime package tests.

Fixes #16723.

Change-Id: Ice3f118c66f254bb71478a664d62ab3fc7125819
Reviewed-on: https://go-review.googlesource.com/45412
Run-TryBot: Austin Clements <austin@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Ian Lance Taylor <iant@golang.org>

1 files changed, 58 insertions, 0 deletions

diff --git a/src/runtime/stack_test.go b/src/runtime/stack_test.go
index 25e8f77da4..c9b84be066 100644
--- a/src/runtime/stack_test.go
+++ b/src/runtime/stack_test.go
@@ -5,6 +5,7 @@
 package runtime_test
 
 import (
+	"fmt"
 	. "runtime"
 	"strings"
 	"sync"
@@ -627,3 +628,60 @@ func count23(n int) int {
 	}
 	return 1 + count1(n-1)
 }
+
+type structWithMethod struct{}
+
+func (s structWithMethod) caller() string {
+	_, file, line, ok := Caller(1)
+	if !ok {
+		panic("Caller failed")
+	}
+	return fmt.Sprintf("%s:%d", file, line)
+}
+
+func (s structWithMethod) callers() []uintptr {
+	pc := make([]uintptr, 16)
+	return pc[:Callers(0, pc)]
+}
+
+func (s structWithMethod) stack() string {
+	buf := make([]byte, 4<<10)
+	return string(buf[:Stack(buf, false)])
+}
+
+func TestStackWrapperCaller(t *testing.T) {
+	var d structWithMethod
+	// Force the compiler to construct a wrapper method.
+	wrapper := (*structWithMethod).caller
+	// Check that the wrapper doesn't affect the stack trace.
+	if dc, ic := d.caller(), wrapper(&d); dc != ic {
+		t.Fatalf("direct caller %q != indirect caller %q", dc, ic)
+	}
+}
+
+func TestStackWrapperCallers(t *testing.T) {
+	var d structWithMethod
+	wrapper := (*structWithMethod).callers
+	// Check that <autogenerated> doesn't appear in the stack trace.
+	pcs := wrapper(&d)
+	frames := CallersFrames(pcs)
+	for {
+		fr, more := frames.Next()
+		if fr.File == "<autogenerated>" {
+			t.Fatalf("<autogenerated> appears in stack trace: %+v", fr)
+		}
+		if !more {
+			break
+		}
+	}
+}
+
+func TestStackWrapperStack(t *testing.T) {
+	var d structWithMethod
+	wrapper := (*structWithMethod).stack
+	// Check that <autogenerated> doesn't appear in the stack trace.
+	stk := wrapper(&d)
+	if strings.Contains(stk, "<autogenerated>") {
+		t.Fatalf("<autogenerated> appears in stack trace:\n%s", stk)
+	}
+}