Move function name logic to function package (#106)

Adjust the logic of NameOf for more recent versions of Go.

2 files changed, 91 insertions, 2 deletions

diff --git a/cmp/internal/function/func.go b/cmp/internal/function/func.go
index 4c35ff1..1b4c4c5 100644
--- a/cmp/internal/function/func.go
+++ b/cmp/internal/function/func.go
@@ -2,10 +2,15 @@
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE.md file.
 
-// Package function identifies function types.
+// Package function provides functionality for identifying function types.
 package function
 
-import "reflect"
+import (
+	"reflect"
+	"regexp"
+	"runtime"
+	"strings"
+)
 
 type funcType int
 
@@ -47,3 +52,36 @@ func IsType(t reflect.Type, ft funcType) bool {
 	}
 	return false
 }
+
+var lastIdentRx = regexp.MustCompile(`[_\p{L}][_\p{L}\p{N}]*$`)
+
+// NameOf returns the name of the function value.
+func NameOf(v reflect.Value) string {
+	fnc := runtime.FuncForPC(v.Pointer())
+	if fnc == nil {
+		return "<unknown>"
+	}
+	fullName := fnc.Name() // e.g., "long/path/name/mypkg.(*MyType).(long/path/name/mypkg.myMethod)-fm"
+
+	// Method closures have a "-fm" suffix.
+	fullName = strings.TrimSuffix(fullName, "-fm")
+
+	var name string
+	for len(fullName) > 0 {
+		inParen := strings.HasSuffix(fullName, ")")
+		fullName = strings.TrimSuffix(fullName, ")")
+
+		s := lastIdentRx.FindString(fullName)
+		if s == "" {
+			break
+		}
+		name = s + "." + name
+		fullName = strings.TrimSuffix(fullName, s)
+
+		if i := strings.LastIndexByte(fullName, '('); inParen && i >= 0 {
+			fullName = fullName[:i]
+		}
+		fullName = strings.TrimSuffix(fullName, ".")
+	}
+	return strings.TrimSuffix(name, ".")
+}
diff --git a/cmp/internal/function/func_test.go b/cmp/internal/function/func_test.go
new file mode 100644
index 0000000..61eeccd
--- /dev/null
+++ b/cmp/internal/function/func_test.go
@@ -0,0 +1,51 @@
+// Copyright 2019, The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE.md file.
+
+package function
+
+import (
+	"bytes"
+	"reflect"
+	"testing"
+)
+
+type myType struct{ bytes.Buffer }
+
+func (myType) valueMethod() {}
+func (myType) ValueMethod() {}
+
+func (*myType) pointerMethod() {}
+func (*myType) PointerMethod() {}
+
+func TestNameOf(t *testing.T) {
+	tests := []struct {
+		fnc  interface{}
+		want string
+	}{
+		{TestNameOf, "function.TestNameOf"},
+		{func() {}, "function.TestNameOf.func1"},
+		{(myType).valueMethod, "function.myType.valueMethod"},
+		{(myType).ValueMethod, "function.myType.ValueMethod"},
+		{(myType{}).valueMethod, "function.myType.valueMethod"},
+		{(myType{}).ValueMethod, "function.myType.ValueMethod"},
+		{(*myType).valueMethod, "function.myType.valueMethod"},
+		{(*myType).ValueMethod, "function.myType.ValueMethod"},
+		{(&myType{}).valueMethod, "function.myType.valueMethod"},
+		{(&myType{}).ValueMethod, "function.myType.ValueMethod"},
+		{(*myType).pointerMethod, "function.myType.pointerMethod"},
+		{(*myType).PointerMethod, "function.myType.PointerMethod"},
+		{(&myType{}).pointerMethod, "function.myType.pointerMethod"},
+		{(&myType{}).PointerMethod, "function.myType.PointerMethod"},
+		{(*myType).Write, "function.myType.Write"},
+		{(&myType{}).Write, "bytes.Buffer.Write"},
+	}
+	for _, tt := range tests {
+		t.Run("", func(t *testing.T) {
+			got := NameOf(reflect.ValueOf(tt.fnc))
+			if got != tt.want {
+				t.Errorf("NameOf() = %v, want %v", got, tt.want)
+			}
+		})
+	}
+}