[ObjC] Add the concept of a closed enum.

- FieldDescriptor:
  - Add a new flag to mark when the enum on the field is closed (vs open).
  - Support computing the state for when generated sources predate the support.
- EnumDescriptor:
  - Support passing flags to the descriptor creation, currently closed is the
    only new flag.
  - Add an isClosed property to expose the state of the enum.

This does NOT update generation yet, allows things to be tested before the
generation support is added.

PiperOrigin-RevId: 488671606

Author: protobuf-github-bot

objectivec/GPBDescriptor.h

@@ -235,6 +235,18 @@ typedef NS_ENUM(uint8_t, GPBFieldType) {
 @property(nonatomic, readonly, copy) NSString *name;
 /** Function that validates that raw values are valid enum values. */
 @property(nonatomic, readonly) GPBEnumValidationFunc enumVerifier;
+/**
+ * Is this a closed enum, meaning that it:
+ * - Has a fixed set of named values.
+ * - Encountering values not in this set causes them to be treated as unknown
+ *   fields.
+ * - The first value (i.e., the default) may be nonzero.
+ *
+ * NOTE: This is only accurate if the generate sources for a proto file were
+ * generated with a protobuf release after the v21.9 version, as the ObjC
+ * generator wasn't capturing this information.
+ */
+@property(nonatomic, readonly) BOOL isClosed;
 
 /**
  * Returns the enum value name for the given raw enum.

objectivec/GPBDescriptor.m

@@ -51,7 +51,8 @@ - (instancetype)initWithFieldDescription:(void *)description
                                     file:(GPBFileDescriptor *)file
                          includesDefault:(BOOL)includesDefault
                            usesClassRefs:(BOOL)usesClassRefs
-                     proto3OptionalKnown:(BOOL)proto3OptionalKnown;
+                     proto3OptionalKnown:(BOOL)proto3OptionalKnown
+                  closedEnumSupportKnown:(BOOL)closedEnumSupportKnown;
 
 @end
 
@@ -60,7 +61,8 @@ - (instancetype)initWithName:(NSString *)name
                   valueNames:(const char *)valueNames
                       values:(const int32_t *)values
                        count:(uint32_t)valueCount
-                enumVerifier:(GPBEnumValidationFunc)enumVerifier;
+                enumVerifier:(GPBEnumValidationFunc)enumVerifier
+                       flags:(GPBEnumDescriptorInitializationFlags)flags;
 @end
 
 // Direct access is use for speed, to avoid even internally declaring things
@@ -150,6 +152,8 @@ + (instancetype)allocDescriptorForClass:(Class)messageClass
   BOOL fieldsIncludeDefault = (flags & GPBDescriptorInitializationFlag_FieldsWithDefault) != 0;
   BOOL usesClassRefs = (flags & GPBDescriptorInitializationFlag_UsesClassRefs) != 0;
   BOOL proto3OptionalKnown = (flags & GPBDescriptorInitializationFlag_Proto3OptionalKnown) != 0;
+  BOOL closedEnumSupportKnown =
+      (flags & GPBDescriptorInitializationFlag_ClosedEnumSupportKnown) != 0;
 
   void *desc;
   for (uint32_t i = 0; i < fieldCount; ++i) {
@@ -164,7 +168,8 @@ + (instancetype)allocDescriptorForClass:(Class)messageClass
                                                         file:file
                                              includesDefault:fieldsIncludeDefault
                                                usesClassRefs:usesClassRefs
-                                         proto3OptionalKnown:proto3OptionalKnown];
+                                         proto3OptionalKnown:proto3OptionalKnown
+                                      closedEnumSupportKnown:closedEnumSupportKnown];
     [fields addObject:fieldDescriptor];
     [fieldDescriptor release];
   }
@@ -475,7 +480,8 @@ - (instancetype)initWithFieldDescription:(void *)description
                                     file:(GPBFileDescriptor *)file
                          includesDefault:(BOOL)includesDefault
                            usesClassRefs:(BOOL)usesClassRefs
-                     proto3OptionalKnown:(BOOL)proto3OptionalKnown {
+                     proto3OptionalKnown:(BOOL)proto3OptionalKnown
+                  closedEnumSupportKnown:(BOOL)closedEnumSupportKnown {
   if ((self = [super init])) {
     GPBMessageFieldDescription *coreDesc;
     if (includesDefault) {
@@ -506,6 +512,21 @@ - (instancetype)initWithFieldDescription:(void *)description
       }
     }
 
+    // If the ClosedEnum flag wasn't known (i.e. generated code from an older
+    // version), compute the flag for the rest of the runtime.
+    if (!closedEnumSupportKnown) {
+      // NOTE: This isn't correct, it is using the syntax of the file that
+      // declared the field, not the syntax of the file that declared the
+      // enum; but for older generated code, that's all we have and that happens
+      // to be what the runtime was doing (even though it was wrong). This is
+      // only wrong in the rare cases an enum is declared in a proto3 syntax
+      // file but used for a field in the proto2 syntax file.
+      BOOL isClosedEnum = (dataType == GPBDataTypeEnum && file.syntax != GPBFileSyntaxProto3);
+      if (isClosedEnum) {
+        coreDesc->flags |= GPBFieldClosedEnum;
+      }
+    }
+
     if (isMapOrArray) {
       // map<>/repeated fields get a *Count property (inplace of a has*) to
       // support checking if there are any entries without triggering
@@ -535,9 +556,14 @@ - (instancetype)initWithFieldDescription:(void *)description
         NSAssert(msgClass_, @"Class %s not defined", className);
       }
     } else if (dataType == GPBDataTypeEnum) {
+      enumDescriptor_ = coreDesc->dataTypeSpecific.enumDescFunc();
+#if defined(DEBUG) && DEBUG
       NSAssert((coreDesc->flags & GPBFieldHasEnumDescriptor) != 0,
                @"Field must have GPBFieldHasEnumDescriptor set");
-      enumDescriptor_ = coreDesc->dataTypeSpecific.enumDescFunc();
+      NSAssert(!closedEnumSupportKnown ||
+                   (((coreDesc->flags & GPBFieldClosedEnum) != 0) == enumDescriptor_.isClosed),
+               @"Internal error, ClosedEnum flag doesn't agree with EnumDescriptor");
+#endif  // DEBUG
     }
 
     // Non map<>/repeated fields can have defaults in proto2 syntax.
@@ -740,6 +766,7 @@ @implementation GPBEnumDescriptor {
   const uint8_t *extraTextFormatInfo_;
   uint32_t *nameOffsets_;
   uint32_t valueCount_;
+  uint32_t flags_;
 }
 
 @synthesize name = name_;
@@ -749,12 +776,14 @@ + (instancetype)allocDescriptorForName:(NSString *)name
                             valueNames:(const char *)valueNames
                                 values:(const int32_t *)values
                                  count:(uint32_t)valueCount
-                          enumVerifier:(GPBEnumValidationFunc)enumVerifier {
+                          enumVerifier:(GPBEnumValidationFunc)enumVerifier
+                                 flags:(GPBEnumDescriptorInitializationFlags)flags {
   GPBEnumDescriptor *descriptor = [[self alloc] initWithName:name
                                                   valueNames:valueNames
                                                       values:values
                                                        count:valueCount
-                                                enumVerifier:enumVerifier];
+                                                enumVerifier:enumVerifier
+                                                       flags:flags];
   return descriptor;
 }
 
@@ -763,29 +792,61 @@ + (instancetype)allocDescriptorForName:(NSString *)name
                                 values:(const int32_t *)values
                                  count:(uint32_t)valueCount
                           enumVerifier:(GPBEnumValidationFunc)enumVerifier
+                                 flags:(GPBEnumDescriptorInitializationFlags)flags
                    extraTextFormatInfo:(const char *)extraTextFormatInfo {
   // Call the common case.
   GPBEnumDescriptor *descriptor = [self allocDescriptorForName:name
                                                     valueNames:valueNames
                                                         values:values
                                                          count:valueCount
-                                                  enumVerifier:enumVerifier];
+                                                  enumVerifier:enumVerifier
+                                                         flags:flags];
   // Set the extra info.
   descriptor->extraTextFormatInfo_ = (const uint8_t *)extraTextFormatInfo;
   return descriptor;
 }
 
++ (instancetype)allocDescriptorForName:(NSString *)name
+                            valueNames:(const char *)valueNames
+                                values:(const int32_t *)values
+                                 count:(uint32_t)valueCount
+                          enumVerifier:(GPBEnumValidationFunc)enumVerifier {
+  return [self allocDescriptorForName:name
+                           valueNames:valueNames
+                               values:values
+                                count:valueCount
+                         enumVerifier:enumVerifier
+                                flags:GPBEnumDescriptorInitializationFlag_None];
+}
+
++ (instancetype)allocDescriptorForName:(NSString *)name
+                            valueNames:(const char *)valueNames
+                                values:(const int32_t *)values
+                                 count:(uint32_t)valueCount
+                          enumVerifier:(GPBEnumValidationFunc)enumVerifier
+                   extraTextFormatInfo:(const char *)extraTextFormatInfo {
+  return [self allocDescriptorForName:name
+                           valueNames:valueNames
+                               values:values
+                                count:valueCount
+                         enumVerifier:enumVerifier
+                                flags:GPBEnumDescriptorInitializationFlag_None
+                  extraTextFormatInfo:extraTextFormatInfo];
+}
+
 - (instancetype)initWithName:(NSString *)name
                   valueNames:(const char *)valueNames
                       values:(const int32_t *)values
                        count:(uint32_t)valueCount
-                enumVerifier:(GPBEnumValidationFunc)enumVerifier {
+                enumVerifier:(GPBEnumValidationFunc)enumVerifier
+                       flags:(GPBEnumDescriptorInitializationFlags)flags {
   if ((self = [super init])) {
     name_ = [name copy];
     valueNames_ = valueNames;
     values_ = values;
     valueCount_ = valueCount;
     enumVerifier_ = enumVerifier;
+    flags_ = flags;
   }
   return self;
 }
@@ -796,6 +857,10 @@ - (void)dealloc {
   [super dealloc];
 }
 
+- (BOOL)isClosed {
+  return (flags_ & GPBEnumDescriptorInitializationFlag_IsClosed) != 0;
+}
+
 - (void)calcValueNameOffsets {
   @synchronized(self) {
     if (nameOffsets_ != NULL) {

objectivec/GPBDescriptor_PackagePrivate.h

@@ -73,6 +73,18 @@ typedef NS_OPTIONS(uint16_t, GPBFieldFlags) {
   GPBFieldMapKeySFixed64 = 10 << 8,
   GPBFieldMapKeyBool = 11 << 8,
   GPBFieldMapKeyString = 12 << 8,
+
+  // If the enum for this field is "closed", meaning that it:
+  // - Has a fixed set of named values.
+  // - Encountering values not in this set causes them to be treated as unknown
+  //   fields.
+  // - The first value (i.e., the default) may be nonzero.
+  // NOTE: This could be tracked just on the GPBEnumDescriptor, but to support
+  // previously generated code, there would be not data to get the behavior
+  // correct, so instead it is tracked on the field. If old source compatibility
+  // is removed, this could be removed and the GPBEnumDescription fetched from
+  // the GPBFieldDescriptor instead.
+  GPBFieldClosedEnum = 1 << 12,
 };
 
 // NOTE: The structures defined here have their members ordered to minimize
@@ -173,6 +185,12 @@ typedef NS_OPTIONS(uint32_t, GPBDescriptorInitializationFlags) {
   // at startup. This allows older generated code to still work with the
   // current runtime library.
   GPBDescriptorInitializationFlag_Proto3OptionalKnown = 1 << 3,
+
+  // This flag is used to indicate that the generated sources already contain
+  // the `GPBFieldCloseEnum` flag and it doesn't have to be computed at startup.
+  // This allows the older generated code to still work with the current runtime
+  // library.
+  GPBDescriptorInitializationFlag_ClosedEnumSupportKnown = 1 << 4,
 };
 
 @interface GPBDescriptor () {
@@ -236,14 +254,36 @@ typedef NS_OPTIONS(uint32_t, GPBDescriptorInitializationFlags) {
 }
 @end
 
+typedef NS_OPTIONS(uint32_t, GPBEnumDescriptorInitializationFlags) {
+  GPBEnumDescriptorInitializationFlag_None = 0,
+
+  // Marks this enum as a closed enum.
+  GPBEnumDescriptorInitializationFlag_IsClosed = 1 << 1,
+};
+
 @interface GPBEnumDescriptor ()
 // valueNames, values and extraTextFormatInfo have to be long lived, they are
 // held as raw pointers.
++ (instancetype)allocDescriptorForName:(NSString *)name
+                            valueNames:(const char *)valueNames
+                                values:(const int32_t *)values
+                                 count:(uint32_t)valueCount
+                          enumVerifier:(GPBEnumValidationFunc)enumVerifier
+                                 flags:(GPBEnumDescriptorInitializationFlags)flags;
++ (instancetype)allocDescriptorForName:(NSString *)name
+                            valueNames:(const char *)valueNames
+                                values:(const int32_t *)values
+                                 count:(uint32_t)valueCount
+                          enumVerifier:(GPBEnumValidationFunc)enumVerifier
+                                 flags:(GPBEnumDescriptorInitializationFlags)flags
+                   extraTextFormatInfo:(const char *)extraTextFormatInfo;
+// Deprecated. Calls above with `flags = 0`
 + (instancetype)allocDescriptorForName:(NSString *)name
                             valueNames:(const char *)valueNames
                                 values:(const int32_t *)values
                                  count:(uint32_t)valueCount
                           enumVerifier:(GPBEnumValidationFunc)enumVerifier;
+// Deprecated. Calls above with `flags = 0`
 + (instancetype)allocDescriptorForName:(NSString *)name
                             valueNames:(const char *)valueNames
                                 values:(const int32_t *)values
@@ -297,6 +337,10 @@ GPB_INLINE uint32_t GPBFieldNumber(GPBFieldDescriptor *field) {
   return field->description_->number;
 }
 
+GPB_INLINE BOOL GPBFieldIsClosedEnum(GPBFieldDescriptor *field) {
+  return (field->description_->flags & GPBFieldClosedEnum) != 0;
+}
+
 #pragma clang diagnostic pop
 
 uint32_t GPBFieldTag(GPBFieldDescriptor *self);
@@ -307,10 +351,6 @@ uint32_t GPBFieldTag(GPBFieldDescriptor *self);
 // would be the wire type for packed.
 uint32_t GPBFieldAlternateTag(GPBFieldDescriptor *self);
 
-GPB_INLINE BOOL GPBHasPreservingUnknownEnumSemantics(GPBFileSyntax syntax) {
-  return syntax == GPBFileSyntaxProto3;
-}
-
 GPB_INLINE BOOL GPBExtensionIsRepeated(GPBExtensionDescription *description) {
   return (description->options & GPBExtensionRepeated) != 0;
 }

objectivec/GPBDictionary.m

@@ -501,8 +501,7 @@ void GPBDictionaryReadEntry(id mapDictionary, GPBCodedInputStream *stream,
       [(NSMutableDictionary *)mapDictionary setObject:value.valueString forKey:key.valueString];
     } else {
       if (valueDataType == GPBDataTypeEnum) {
-        if (GPBHasPreservingUnknownEnumSemantics([parentMessage descriptor].file.syntax) ||
-            [field isValidEnumValue:value.valueEnum]) {
+        if (!GPBFieldIsClosedEnum(field) || [field isValidEnumValue:value.valueEnum]) {
           [mapDictionary setGPBGenericValue:&value forGPBGenericValueKey:&key];
         } else {
           NSData *data = [mapDictionary serializedDataForUnknownValue:value.valueEnum