Provide a protocol for GPBExtensionRegistry's lookup support.

This allows some to use an alternative registry if they have a different
implementation.

This is really just wiring though the change to use the GPBExtensionRegistry
protocol vs the concrete GPBExtensionRegistry through the other apis.

objectivec/GPBCodedInputStream.h

@@ -31,7 +31,7 @@
 #import <Foundation/Foundation.h>
 
 @class GPBMessage;
-@class GPBExtensionRegistry;
+@protocol GPBExtensionRegistry;
 
 NS_ASSUME_NONNULL_BEGIN
 
@@ -184,7 +184,7 @@ CF_EXTERN_C_END
  *                          extensions for message.
  **/
 - (void)readMessage:(GPBMessage *)message
-  extensionRegistry:(nullable GPBExtensionRegistry *)extensionRegistry;
+  extensionRegistry:(nullable id<GPBExtensionRegistry>)extensionRegistry;
 
 /**
  * Reads and discards a single field, given its tag value.

objectivec/GPBCodedInputStream.m

@@ -434,7 +434,7 @@ void GPBCodedInputStreamCheckLastTagWas(GPBCodedInputStreamState *state,
 
 - (void)readGroup:(int32_t)fieldNumber
               message:(GPBMessage *)message
-    extensionRegistry:(GPBExtensionRegistry *)extensionRegistry {
+    extensionRegistry:(id<GPBExtensionRegistry>)extensionRegistry {
   CheckRecursionLimit(&state_);
   ++state_.recursionDepth;
   [message mergeFromCodedInputStream:self extensionRegistry:extensionRegistry];
@@ -454,7 +454,7 @@ void GPBCodedInputStreamCheckLastTagWas(GPBCodedInputStreamState *state,
 }
 
 - (void)readMessage:(GPBMessage *)message
-    extensionRegistry:(GPBExtensionRegistry *)extensionRegistry {
+    extensionRegistry:(id<GPBExtensionRegistry>)extensionRegistry {
   CheckRecursionLimit(&state_);
   int32_t length = ReadRawVarint32(&state_);
   size_t oldLimit = GPBCodedInputStreamPushLimit(&state_, length);
@@ -466,7 +466,7 @@ void GPBCodedInputStreamCheckLastTagWas(GPBCodedInputStreamState *state,
 }
 
 - (void)readMapEntry:(id)mapDictionary
-    extensionRegistry:(GPBExtensionRegistry *)extensionRegistry
+    extensionRegistry:(id<GPBExtensionRegistry>)extensionRegistry
                 field:(GPBFieldDescriptor *)field
         parentMessage:(GPBMessage *)parentMessage {
   CheckRecursionLimit(&state_);

objectivec/GPBCodedInputStream_PackagePrivate.h

@@ -61,7 +61,7 @@ typedef struct GPBCodedInputStreamState {
 // support for older data.
 - (void)readGroup:(int32_t)fieldNumber
               message:(GPBMessage *)message
-    extensionRegistry:(GPBExtensionRegistry *)extensionRegistry;
+    extensionRegistry:(id<GPBExtensionRegistry>)extensionRegistry;
 
 // Reads a group field value from the stream and merges it into the given
 // UnknownFieldSet.
@@ -70,7 +70,7 @@ typedef struct GPBCodedInputStreamState {
 
 // Reads a map entry.
 - (void)readMapEntry:(id)mapDictionary
-    extensionRegistry:(GPBExtensionRegistry *)extensionRegistry
+    extensionRegistry:(id<GPBExtensionRegistry>)extensionRegistry
                 field:(GPBFieldDescriptor *)field
         parentMessage:(GPBMessage *)parentMessage;
 @end

objectivec/GPBDictionary.m

@@ -386,7 +386,7 @@ BOOL GPBDictionaryIsInitializedInternalHelper(NSDictionary *dict, GPBFieldDescri
 static void ReadValue(GPBCodedInputStream *stream,
                       GPBGenericValue *valueToFill,
                       GPBDataType type,
-                      GPBExtensionRegistry *registry,
+                      id<GPBExtensionRegistry>registry,
                       GPBFieldDescriptor *field) {
   switch (type) {
     case GPBDataTypeBool:
@@ -454,7 +454,7 @@ static void ReadValue(GPBCodedInputStream *stream,
 
 void GPBDictionaryReadEntry(id mapDictionary,
                             GPBCodedInputStream *stream,
-                            GPBExtensionRegistry *registry,
+                            id<GPBExtensionRegistry>registry,
                             GPBFieldDescriptor *field,
                             GPBMessage *parentMessage) {
   GPBDataType keyDataType = field.mapKeyDataType;

objectivec/GPBDictionary_PackagePrivate.h

@@ -34,7 +34,7 @@
 
 @class GPBCodedInputStream;
 @class GPBCodedOutputStream;
-@class GPBExtensionRegistry;
+@protocol GPBExtensionRegistry;
 @class GPBFieldDescriptor;
 
 @protocol GPBDictionaryInternalsProtocol
@@ -493,7 +493,7 @@ BOOL GPBDictionaryIsInitializedInternalHelper(NSDictionary *dict,
 
 // Helper to read a map instead.
 void GPBDictionaryReadEntry(id mapDictionary, GPBCodedInputStream *stream,
-                            GPBExtensionRegistry *registry,
+                            id<GPBExtensionRegistry>registry,
                             GPBFieldDescriptor *field,
                             GPBMessage *parentMessage);
 

objectivec/GPBExtensionInternals.h

@@ -34,12 +34,12 @@
 
 @class GPBCodedInputStream;
 @class GPBCodedOutputStream;
-@class GPBExtensionRegistry;
+@protocol GPBExtensionRegistry;
 
 void GPBExtensionMergeFromInputStream(GPBExtensionDescriptor *extension,
                                       BOOL isPackedOnStream,
                                       GPBCodedInputStream *input,
-                                      GPBExtensionRegistry *extensionRegistry,
+                                      id<GPBExtensionRegistry>extensionRegistry,
                                       GPBMessage *message);
 
 size_t GPBComputeExtensionSerializedSizeIncludingTag(

objectivec/GPBExtensionInternals.m

@@ -40,7 +40,7 @@
 
 static id NewSingleValueFromInputStream(GPBExtensionDescriptor *extension,
                                         GPBCodedInputStream *input,
-                                        GPBExtensionRegistry *extensionRegistry,
+                                        id<GPBExtensionRegistry>extensionRegistry,
                                         GPBMessage *existingValue)
     __attribute__((ns_returns_retained));
 
@@ -273,7 +273,7 @@ static void WriteArrayIncludingTagsToCodedOutputStream(
 void GPBExtensionMergeFromInputStream(GPBExtensionDescriptor *extension,
                                       BOOL isPackedOnStream,
                                       GPBCodedInputStream *input,
-                                      GPBExtensionRegistry *extensionRegistry,
+                                      id<GPBExtensionRegistry>extensionRegistry,
                                       GPBMessage *message) {
   GPBExtensionDescription *description = extension->description_;
   GPBCodedInputStreamState *state = &input->state_;
@@ -334,7 +334,7 @@ size_t GPBComputeExtensionSerializedSizeIncludingTag(
 // Note that this returns a retained value intentionally.
 static id NewSingleValueFromInputStream(GPBExtensionDescriptor *extension,
                                         GPBCodedInputStream *input,
-                                        GPBExtensionRegistry *extensionRegistry,
+                                        id<GPBExtensionRegistry>extensionRegistry,
                                         GPBMessage *existingValue) {
   GPBExtensionDescription *description = extension->description_;
   GPBCodedInputStreamState *state = &input->state_;

objectivec/GPBExtensionRegistry.h

@@ -41,6 +41,24 @@ NS_ASSUME_NONNULL_BEGIN
  * GPBExtensionRegistry in which you have registered any extensions that you
  * want to be able to parse. Otherwise, those extensions will just be treated
  * like unknown fields.
+ **/
+@protocol GPBExtensionRegistry <NSObject>
+
+/**
+ * Looks for the extension registered for the given field number on a given
+ * GPBDescriptor.
+ *
+ * @param descriptor  The descriptor to look for a registered extension on.
+ * @param fieldNumber The field number of the extension to look for.
+ *
+ * @return The registered GPBExtensionDescriptor or nil if none was found.
+ **/
+- (nullable GPBExtensionDescriptor *)extensionForDescriptor:(GPBDescriptor *)descriptor
+                                                fieldNumber:(NSInteger)fieldNumber;
+@end
+
+/**
+ * A concrete implementation of `GPBExtensionRegistry`.
  *
  * The *Root classes provide `+extensionRegistry` for the extensions defined
  * in a given file *and* all files it imports. You can also create a
@@ -54,7 +72,7 @@ NS_ASSUME_NONNULL_BEGIN
  * MyMessage *msg = [MyMessage parseData:data extensionRegistry:registry error:&parseError];
  * ```
  **/
-@interface GPBExtensionRegistry : NSObject<NSCopying>
+@interface GPBExtensionRegistry : NSObject<NSCopying, GPBExtensionRegistry>
 
 /**
  * Adds the given GPBExtensionDescriptor to this registry.
@@ -70,18 +88,6 @@ NS_ASSUME_NONNULL_BEGIN
  **/
 - (void)addExtensions:(GPBExtensionRegistry *)registry;
 
-/**
- * Looks for the extension registered for the given field number on a given
- * GPBDescriptor.
- *
- * @param descriptor  The descriptor to look for a registered extension on.
- * @param fieldNumber The field number of the extension to look for.
- *
- * @return The registered GPBExtensionDescriptor or nil if none was found.
- **/
-- (nullable GPBExtensionDescriptor *)extensionForDescriptor:(GPBDescriptor *)descriptor
-                                                fieldNumber:(NSInteger)fieldNumber;
-
 @end
 
 NS_ASSUME_NONNULL_END

objectivec/GPBMessage.h

@@ -36,7 +36,7 @@
 @class GPBCodedInputStream;
 @class GPBCodedOutputStream;
 @class GPBExtensionDescriptor;
-@class GPBExtensionRegistry;
+@protocol GPBExtensionRegistry;
 @class GPBFieldDescriptor;
 @class GPBUnknownFieldSet;
 
@@ -147,7 +147,7 @@ CF_EXTERN_C_END
  * @return A new instance of the generated class.
  **/
 + (nullable instancetype)parseFromData:(NSData *)data
-                     extensionRegistry:(nullable GPBExtensionRegistry *)extensionRegistry
+                     extensionRegistry:(nullable id<GPBExtensionRegistry>)extensionRegistry
                                  error:(NSError **)errorPtr;
 
 /**
@@ -171,7 +171,7 @@ CF_EXTERN_C_END
  **/
 + (nullable instancetype)parseFromCodedInputStream:(GPBCodedInputStream *)input
                                  extensionRegistry:
-                                     (nullable GPBExtensionRegistry *)extensionRegistry
+                                     (nullable id<GPBExtensionRegistry>)extensionRegistry
                                              error:(NSError **)errorPtr;
 
 /**
@@ -196,7 +196,7 @@ CF_EXTERN_C_END
  **/
 + (nullable instancetype)parseDelimitedFromCodedInputStream:(GPBCodedInputStream *)input
                                           extensionRegistry:
-                                              (nullable GPBExtensionRegistry *)extensionRegistry
+                                              (nullable id<GPBExtensionRegistry>)extensionRegistry
                                                       error:(NSError **)errorPtr;
 
 /**
@@ -239,7 +239,7 @@ CF_EXTERN_C_END
  * @return An initialized instance of the generated class.
  **/
 - (nullable instancetype)initWithData:(NSData *)data
-                    extensionRegistry:(nullable GPBExtensionRegistry *)extensionRegistry
+                    extensionRegistry:(nullable id<GPBExtensionRegistry>)extensionRegistry
                                 error:(NSError **)errorPtr;
 
 /**
@@ -264,7 +264,7 @@ CF_EXTERN_C_END
  **/
 - (nullable instancetype)initWithCodedInputStream:(GPBCodedInputStream *)input
                                 extensionRegistry:
-                                    (nullable GPBExtensionRegistry *)extensionRegistry
+                                    (nullable id<GPBExtensionRegistry>)extensionRegistry
                                             error:(NSError **)errorPtr;
 
 /**
@@ -278,7 +278,7 @@ CF_EXTERN_C_END
  *                                         unsuccessful.
  **/
 - (void)mergeFromData:(NSData *)data
-    extensionRegistry:(nullable GPBExtensionRegistry *)extensionRegistry;
+    extensionRegistry:(nullable id<GPBExtensionRegistry>)extensionRegistry;
 
 /**
  * Merges the fields from another message (of the same type) into this

objectivec/GPBMessage.m

@@ -881,7 +881,7 @@ static GPBUnknownFieldSet *GetOrMakeUnknownFields(GPBMessage *self) {
 }
 
 - (instancetype)initWithData:(NSData *)data
-           extensionRegistry:(GPBExtensionRegistry *)extensionRegistry
+           extensionRegistry:(id<GPBExtensionRegistry>)extensionRegistry
                        error:(NSError **)errorPtr {
   if ((self = [self init])) {
     @try {
@@ -912,7 +912,7 @@ static GPBUnknownFieldSet *GetOrMakeUnknownFields(GPBMessage *self) {
 
 - (instancetype)initWithCodedInputStream:(GPBCodedInputStream *)input
                        extensionRegistry:
-                           (GPBExtensionRegistry *)extensionRegistry
+                           (id<GPBExtensionRegistry>)extensionRegistry
                                    error:(NSError **)errorPtr {
   if ((self = [self init])) {
     @try {
@@ -1973,7 +1973,7 @@ static GPBUnknownFieldSet *GetOrMakeUnknownFields(GPBMessage *self) {
 #pragma mark - mergeFrom
 
 - (void)mergeFromData:(NSData *)data
-    extensionRegistry:(GPBExtensionRegistry *)extensionRegistry {
+    extensionRegistry:(id<GPBExtensionRegistry>)extensionRegistry {
   GPBCodedInputStream *input = [[GPBCodedInputStream alloc] initWithData:data];
   [self mergeFromCodedInputStream:input extensionRegistry:extensionRegistry];
   [input checkLastTagWas:0];
@@ -1983,7 +1983,7 @@ static GPBUnknownFieldSet *GetOrMakeUnknownFields(GPBMessage *self) {
 #pragma mark - mergeDelimitedFrom
 
 - (void)mergeDelimitedFromCodedInputStream:(GPBCodedInputStream *)input
-                         extensionRegistry:(GPBExtensionRegistry *)extensionRegistry {
+                         extensionRegistry:(id<GPBExtensionRegistry>)extensionRegistry {
   GPBCodedInputStreamState *state = &input->state_;
   if (GPBCodedInputStreamIsAtEnd(state)) {
     return;
@@ -2003,7 +2003,7 @@ static GPBUnknownFieldSet *GetOrMakeUnknownFields(GPBMessage *self) {
 }
 
 + (instancetype)parseFromData:(NSData *)data
-            extensionRegistry:(GPBExtensionRegistry *)extensionRegistry
+            extensionRegistry:(id<GPBExtensionRegistry>)extensionRegistry
                         error:(NSError **)errorPtr {
   return [[[self alloc] initWithData:data
                    extensionRegistry:extensionRegistry
@@ -2011,7 +2011,7 @@ static GPBUnknownFieldSet *GetOrMakeUnknownFields(GPBMessage *self) {
 }
 
 + (instancetype)parseFromCodedInputStream:(GPBCodedInputStream *)input
-                        extensionRegistry:(GPBExtensionRegistry *)extensionRegistry
+                        extensionRegistry:(id<GPBExtensionRegistry>)extensionRegistry
                                     error:(NSError **)errorPtr {
   return
       [[[self alloc] initWithCodedInputStream:input
@@ -2023,7 +2023,7 @@ static GPBUnknownFieldSet *GetOrMakeUnknownFields(GPBMessage *self) {
 
 + (instancetype)parseDelimitedFromCodedInputStream:(GPBCodedInputStream *)input
                                  extensionRegistry:
-                                     (GPBExtensionRegistry *)extensionRegistry
+                                     (id<GPBExtensionRegistry>)extensionRegistry
                                              error:(NSError **)errorPtr {
   GPBMessage *message = [[[self alloc] init] autorelease];
   @try {
@@ -2065,7 +2065,7 @@ static GPBUnknownFieldSet *GetOrMakeUnknownFields(GPBMessage *self) {
 }
 
 - (void)parseMessageSet:(GPBCodedInputStream *)input
-      extensionRegistry:(GPBExtensionRegistry *)extensionRegistry {
+      extensionRegistry:(id<GPBExtensionRegistry>)extensionRegistry {
   uint32_t typeId = 0;
   NSData *rawBytes = nil;
   GPBExtensionDescriptor *extension = nil;
@@ -2117,7 +2117,7 @@ static GPBUnknownFieldSet *GetOrMakeUnknownFields(GPBMessage *self) {
 }
 
 - (BOOL)parseUnknownField:(GPBCodedInputStream *)input
-        extensionRegistry:(GPBExtensionRegistry *)extensionRegistry
+        extensionRegistry:(id<GPBExtensionRegistry>)extensionRegistry
                       tag:(uint32_t)tag {
   GPBWireFormat wireType = GPBWireFormatGetTagWireType(tag);
   int32_t fieldNumber = GPBWireFormatGetTagFieldNumber(tag);
@@ -2170,7 +2170,7 @@ static GPBUnknownFieldSet *GetOrMakeUnknownFields(GPBMessage *self) {
 
 static void MergeSingleFieldFromCodedInputStream(
     GPBMessage *self, GPBFieldDescriptor *field, GPBFileSyntax syntax,
-    GPBCodedInputStream *input, GPBExtensionRegistry *extensionRegistry) {
+    GPBCodedInputStream *input, id<GPBExtensionRegistry>extensionRegistry) {
   GPBDataType fieldDataType = GPBGetFieldDataType(field);
   switch (fieldDataType) {
 #define CASE_SINGLE_POD(NAME, TYPE, FUNC_TYPE)                             \
@@ -2306,7 +2306,7 @@ static void MergeRepeatedPackedFieldFromCodedInputStream(
 
 static void MergeRepeatedNotPackedFieldFromCodedInputStream(
     GPBMessage *self, GPBFieldDescriptor *field, GPBFileSyntax syntax,
-    GPBCodedInputStream *input, GPBExtensionRegistry *extensionRegistry) {
+    GPBCodedInputStream *input, id<GPBExtensionRegistry>extensionRegistry) {
   GPBCodedInputStreamState *state = &input->state_;
   id genericArray = GetOrCreateArrayIvarWithField(self, field);
   switch (GPBGetFieldDataType(field)) {
@@ -2371,7 +2371,7 @@ static void MergeRepeatedNotPackedFieldFromCodedInputStream(
 }
 
 - (void)mergeFromCodedInputStream:(GPBCodedInputStream *)input
-                extensionRegistry:(GPBExtensionRegistry *)extensionRegistry {
+                extensionRegistry:(id<GPBExtensionRegistry>)extensionRegistry {
   GPBDescriptor *descriptor = [self descriptor];
   GPBFileSyntax syntax = descriptor.file.syntax;
   GPBCodedInputStreamState *state = &input->state_;

objectivec/GPBMessage_PackagePrivate.h

@@ -78,13 +78,13 @@ typedef struct GPBMessage_Storage *GPBMessage_StoragePtr;
 // or zero for EOF.
 // NOTE: This will throw if there is an error while parsing.
 - (void)mergeFromCodedInputStream:(GPBCodedInputStream *)input
-                extensionRegistry:(GPBExtensionRegistry *)extensionRegistry;
+                extensionRegistry:(id<GPBExtensionRegistry>)extensionRegistry;
 
 // Parses the next delimited message of this type from the input and merges it
 // with this message.
 - (void)mergeDelimitedFromCodedInputStream:(GPBCodedInputStream *)input
                          extensionRegistry:
-                             (GPBExtensionRegistry *)extensionRegistry;
+                             (id<GPBExtensionRegistry>)extensionRegistry;
 
 - (void)addUnknownMapEntry:(int32_t)fieldNum value:(NSData *)data;