reflect: add Method.IsExported and StructField.IsExported methods

The IsExported method is a more intuitive helper for checking whether
the method or field is exported than checking whether PkgPath is empty.

In the same CL, modify the standard library to make use of this helper.

Fixes #41563

Change-Id: Iaacfb3b74449501f98e2707aa32095a32bd3c3c1
Reviewed-on: https://go-review.googlesource.com/c/go/+/266197
Trust: Joe Tsai <joetsai@digital-static.net>
Run-TryBot: Joe Tsai <thebrokentoaster@gmail.com>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: Ian Lance Taylor <iant@golang.org>

1 files changed, 46 insertions, 9 deletions

diff --git a/src/reflect/all_test.go b/src/reflect/all_test.go
index 1225d6177d..35cc469d74 100644
--- a/src/reflect/all_test.go
+++ b/src/reflect/all_test.go
@@ -2900,6 +2900,7 @@ func TestFieldPkgPath(t *testing.T) {
 		index    []int
 		pkgPath  string
 		embedded bool
+		exported bool
 	}
 
 	checkPkgPath := func(name string, s []pkgpathTest) {
@@ -2911,27 +2912,63 @@ func TestFieldPkgPath(t *testing.T) {
 			if got, want := f.Anonymous, test.embedded; got != want {
 				t.Errorf("%s: Field(%d).Anonymous = %v, want %v", name, test.index, got, want)
 			}
+			if got, want := f.IsExported(), test.exported; got != want {
+				t.Errorf("%s: Field(%d).IsExported = %v, want %v", name, test.index, got, want)
+			}
 		}
 	}
 
 	checkPkgPath("testStruct", []pkgpathTest{
-		{[]int{0}, "", false},             // Exported
-		{[]int{1}, "reflect_test", false}, // unexported
-		{[]int{2}, "", true},              // OtherPkgFields
-		{[]int{2, 0}, "", false},          // OtherExported
-		{[]int{2, 1}, "reflect", false},   // otherUnexported
-		{[]int{3}, "reflect_test", true},  // int
-		{[]int{4}, "reflect_test", true},  // *x
+		{[]int{0}, "", false, true},              // Exported
+		{[]int{1}, "reflect_test", false, false}, // unexported
+		{[]int{2}, "", true, true},               // OtherPkgFields
+		{[]int{2, 0}, "", false, true},           // OtherExported
+		{[]int{2, 1}, "reflect", false, false},   // otherUnexported
+		{[]int{3}, "reflect_test", true, false},  // int
+		{[]int{4}, "reflect_test", true, false},  // *x
 	})
 
 	type localOtherPkgFields OtherPkgFields
 	typ = TypeOf(localOtherPkgFields{})
 	checkPkgPath("localOtherPkgFields", []pkgpathTest{
-		{[]int{0}, "", false},        // OtherExported
-		{[]int{1}, "reflect", false}, // otherUnexported
+		{[]int{0}, "", false, true},         // OtherExported
+		{[]int{1}, "reflect", false, false}, // otherUnexported
 	})
 }
 
+func TestMethodPkgPath(t *testing.T) {
+	type I interface {
+		x()
+		X()
+	}
+	typ := TypeOf((*interface {
+		I
+		y()
+		Y()
+	})(nil)).Elem()
+
+	tests := []struct {
+		name     string
+		pkgPath  string
+		exported bool
+	}{
+		{"X", "", true},
+		{"Y", "", true},
+		{"x", "reflect_test", false},
+		{"y", "reflect_test", false},
+	}
+
+	for _, test := range tests {
+		m, _ := typ.MethodByName(test.name)
+		if got, want := m.PkgPath, test.pkgPath; got != want {
+			t.Errorf("MethodByName(%q).PkgPath = %q, want %q", test.name, got, want)
+		}
+		if got, want := m.IsExported(), test.exported; got != want {
+			t.Errorf("MethodByName(%q).IsExported = %v, want %v", test.name, got, want)
+		}
+	}
+}
+
 func TestVariadicType(t *testing.T) {
 	// Test example from Type documentation.
 	var f func(x int, y ...float64)