internal/impl: remove hack in legacy_extension_hack.go

This hack has now been upstreamed in the v1 codebase;
there is no longer any need to maintain the code in v2.
See https://github.com/golang/protobuf/pull/746

Change-Id: I2c59d11303f5465e65190d893c422c088c647691
Reviewed-on: https://go-review.googlesource.com/c/149659
Reviewed-by: Herbie Ong <herbie@google.com>

internal/impl/legacy_extension.go

@@ -47,7 +47,7 @@ func (p legacyExtensionFields) Has(n pref.FieldNumber) bool {
 	}
 	t := legacyExtensionTypeOf(x.desc)
 	if t.Cardinality() == pref.Repeated {
-		return legacyExtensionValueOf(x.val, t).List().Len() > 0
+		return t.ValueOf(x.val).List().Len() > 0
 	}
 	return true
 }
@@ -63,7 +63,7 @@ func (p legacyExtensionFields) Get(n pref.FieldNumber) pref.Value {
 			// TODO: What is the zero value for Lists?
 			// TODO: This logic is racy.
 			v := t.ValueOf(t.New())
-			x.val = legacyExtensionInterfaceOf(v, t)
+			x.val = t.InterfaceOf(v)
 			p.x.Set(n, x)
 			return v
 		}
@@ -73,7 +73,7 @@ func (p legacyExtensionFields) Get(n pref.FieldNumber) pref.Value {
 		}
 		return t.Default()
 	}
-	return legacyExtensionValueOf(x.val, t)
+	return t.ValueOf(x.val)
 }
 
 func (p legacyExtensionFields) Set(n pref.FieldNumber, v pref.Value) {
@@ -82,7 +82,7 @@ func (p legacyExtensionFields) Set(n pref.FieldNumber, v pref.Value) {
 		panic("no extension descriptor registered")
 	}
 	t := legacyExtensionTypeOf(x.desc)
-	x.val = legacyExtensionInterfaceOf(v, t)
+	x.val = t.InterfaceOf(v)
 	p.x.Set(n, x)
 }
 
@@ -103,10 +103,10 @@ func (p legacyExtensionFields) Mutable(n pref.FieldNumber) pref.Mutable {
 	t := legacyExtensionTypeOf(x.desc)
 	if x.val == nil {
 		v := t.ValueOf(t.New())
-		x.val = legacyExtensionInterfaceOf(v, t)
+		x.val = t.InterfaceOf(v)
 		p.x.Set(n, x)
 	}
-	return legacyExtensionValueOf(x.val, t).Interface().(pref.Mutable)
+	return t.ValueOf(x.val).Interface().(pref.Mutable)
 }
 
 func (p legacyExtensionFields) Range(f func(pref.FieldNumber, pref.Value) bool) {

internal/impl/legacy_extension_hack.go

@@ -141,76 +141,3 @@ type legacyExtensionEntry struct {
 	val  interface{}
 	raw  []byte
 }
-
-// TODO: The legacyExtensionInterfaceOf and legacyExtensionValueOf converters
-// exist since the current storage representation in the v1 data structures use
-// *T for scalars and []T for repeated fields, but the v2 API operates on
-// T for scalars and *[]T for repeated fields.
-//
-// Instead of maintaining this technical debt in the v2 repository,
-// we can offload this into the v1 implementation such that it uses a
-// storage representation that is appropriate for v2, and uses the these
-// functions to present the illusion that that the underlying storage
-// is still *T and []T.
-//
-// See https://github.com/golang/protobuf/pull/746
-const hasPR746 = true
-
-// legacyExtensionInterfaceOf converts a protoreflect.Value to the
-// storage representation used in v1 extension data structures.
-//
-// In particular, it represents scalars (except []byte) a pointer to the value,
-// and repeated fields as the a slice value itself.
-func legacyExtensionInterfaceOf(pv pref.Value, t pref.ExtensionType) interface{} {
-	v := t.InterfaceOf(pv)
-	if !hasPR746 {
-		switch rv := reflect.ValueOf(v); rv.Kind() {
-		case reflect.Bool, reflect.Int32, reflect.Int64, reflect.Uint32, reflect.Uint64, reflect.Float32, reflect.Float64, reflect.String:
-			// Represent primitive types as a pointer to the value.
-			rv2 := reflect.New(rv.Type())
-			rv2.Elem().Set(rv)
-			v = rv2.Interface()
-		case reflect.Ptr:
-			// Represent pointer to slice types as the value itself.
-			switch rv.Type().Elem().Kind() {
-			case reflect.Slice:
-				if rv.IsNil() {
-					v = reflect.Zero(rv.Type().Elem()).Interface()
-				} else {
-					v = rv.Elem().Interface()
-				}
-			}
-		}
-	}
-	return v
-}
-
-// legacyExtensionValueOf converts the storage representation of a value in
-// the v1 extension data structures to a protoreflect.Value.
-//
-// In particular, it represents scalars as the value itself,
-// and repeated fields as a pointer to the slice value.
-func legacyExtensionValueOf(v interface{}, t pref.ExtensionType) pref.Value {
-	if !hasPR746 {
-		switch rv := reflect.ValueOf(v); rv.Kind() {
-		case reflect.Ptr:
-			// Represent slice types as the value itself.
-			switch rv.Type().Elem().Kind() {
-			case reflect.Bool, reflect.Int32, reflect.Int64, reflect.Uint32, reflect.Uint64, reflect.Float32, reflect.Float64, reflect.String:
-				if rv.IsNil() {
-					v = reflect.Zero(rv.Type().Elem()).Interface()
-				} else {
-					v = rv.Elem().Interface()
-				}
-			}
-		case reflect.Slice:
-			// Represent slice types (except []byte) as a pointer to the value.
-			if rv.Type().Elem().Kind() != reflect.Uint8 {
-				rv2 := reflect.New(rv.Type())
-				rv2.Elem().Set(rv)
-				v = rv2.Interface()
-			}
-		}
-	}
-	return t.ValueOf(v)
-}