reflect: let StructOf define unexported fields

This was missing from the original StructOf CL because I couldn't
think of a use for it. Now I can: even with types used entirely
by reflect, unexported fields can be set using UnsafeAddr.

Change-Id: I5e7e3d81d16e8817cdd69d85796ce33930ef523b
Reviewed-on: https://go-review.googlesource.com/c/go/+/85661
Run-TryBot: Ian Lance Taylor <iant@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Ian Lance Taylor <iant@golang.org>

2 files changed, 19 insertions, 23 deletions

diff --git a/src/reflect/all_test.go b/src/reflect/all_test.go
index fbb6feb0d9..7c5dd59aa7 100644
--- a/src/reflect/all_test.go
+++ b/src/reflect/all_test.go
@@ -4733,17 +4733,14 @@ func TestStructOfExportRules(t *testing.T) {
 			mustPanic: true,
 		},
 		{
-			field:     StructField{Name: "s2", Type: TypeOf(int(0)), PkgPath: "other/pkg"},
-			mustPanic: true,
+			field: StructField{Name: "s2", Type: TypeOf(int(0)), PkgPath: "other/pkg"},
 		},
 		{
-			field:     StructField{Name: "s2", Type: TypeOf(int(0)), PkgPath: "other/pkg"},
-			mustPanic: true,
+			field: StructField{Name: "s2", Type: TypeOf(int(0)), PkgPath: "other/pkg"},
 		},
 		{
-			field:     StructField{Name: "S", Type: TypeOf(S1{})},
-			mustPanic: false,
-			exported:  true,
+			field:    StructField{Name: "S", Type: TypeOf(S1{})},
+			exported: true,
 		},
 		{
 			field:    StructField{Name: "S", Type: TypeOf((*S1)(nil))},
@@ -4774,20 +4771,16 @@ func TestStructOfExportRules(t *testing.T) {
 			mustPanic: true,
 		},
 		{
-			field:     StructField{Name: "s", Type: TypeOf(S1{}), PkgPath: "other/pkg"},
-			mustPanic: true, // TODO(sbinet): creating a name with a package path
+			field: StructField{Name: "s", Type: TypeOf(S1{}), PkgPath: "other/pkg"},
 		},
 		{
-			field:     StructField{Name: "s", Type: TypeOf((*S1)(nil)), PkgPath: "other/pkg"},
-			mustPanic: true, // TODO(sbinet): creating a name with a package path
+			field: StructField{Name: "s", Type: TypeOf((*S1)(nil)), PkgPath: "other/pkg"},
 		},
 		{
-			field:     StructField{Name: "s", Type: TypeOf(s2{}), PkgPath: "other/pkg"},
-			mustPanic: true, // TODO(sbinet): creating a name with a package path
+			field: StructField{Name: "s", Type: TypeOf(s2{}), PkgPath: "other/pkg"},
 		},
 		{
-			field:     StructField{Name: "s", Type: TypeOf((*s2)(nil)), PkgPath: "other/pkg"},
-			mustPanic: true, // TODO(sbinet): creating a name with a package path
+			field: StructField{Name: "s", Type: TypeOf((*s2)(nil)), PkgPath: "other/pkg"},
 		},
 		{
 			field:     StructField{Name: "", Type: TypeOf(ΦType{})},
diff --git a/src/reflect/type.go b/src/reflect/type.go
index 2cf912cf54..f1f8ba93a4 100644
--- a/src/reflect/type.go
+++ b/src/reflect/type.go
@@ -2731,15 +2731,18 @@ func StructOf(fields []StructField) Type {
 }
 
 func runtimeStructField(field StructField) structField {
-	if field.PkgPath != "" {
-		panic("reflect.StructOf: StructOf does not allow unexported fields")
+	if field.Anonymous && field.PkgPath != "" {
+		panic("reflect.StructOf: field \"" + field.Name + "\" is anonymous but has PkgPath set")
 	}
 
-	// Best-effort check for misuse.
-	// Since PkgPath is empty, not much harm done if Unicode lowercase slips through.
-	c := field.Name[0]
-	if 'a' <= c && c <= 'z' || c == '_' {
-		panic("reflect.StructOf: field \"" + field.Name + "\" is unexported but missing PkgPath")
+	exported := field.PkgPath == ""
+	if exported {
+		// Best-effort check for misuse.
+		// Since this field will be treated as exported, not much harm done if Unicode lowercase slips through.
+		c := field.Name[0]
+		if 'a' <= c && c <= 'z' || c == '_' {
+			panic("reflect.StructOf: field \"" + field.Name + "\" is unexported but missing PkgPath")
+		}
 	}
 
 	offsetEmbed := uintptr(0)
@@ -2749,7 +2752,7 @@ func runtimeStructField(field StructField) structField {
 
 	resolveReflectType(field.Type.common()) // install in runtime
 	return structField{
-		name:        newName(field.Name, string(field.Tag), true),
+		name:        newName(field.Name, string(field.Tag), exported),
 		typ:         field.Type.common(),
 		offsetEmbed: offsetEmbed,
 	}