[ObjC] Deprecate GPBFieldDescriptor.isOptional.

This also deprecates the internal `GPBFieldOptional` flag, the generator will be
updated to stop using it in the future.

PiperOrigin-RevId: 740378571

Author: thomasvl

objectivec/GPBDescriptor.h

@@ -173,7 +173,8 @@ __attribute__((objc_subclassing_restricted))
 /** Whether this field is required. Only valid for proto2 fields. */
 @property(nonatomic, readonly, getter=isRequired) BOOL required;
 /** Whether this field is optional. */
-@property(nonatomic, readonly, getter=isOptional) BOOL optional;
+@property(nonatomic, readonly, getter=isOptional) BOOL optional DEPRECATED_MSG_ATTRIBUTE(
+    "Check if fieldType is GPBFieldTypeSingle and that it is NOT required.");
 /** Type of field (single, repeated, map). */
 @property(nonatomic, readonly) GPBFieldType fieldType;
 /** Type of the key if the field is a map. The value's type is -dataType. */

objectivec/GPBDescriptor.m

@@ -142,11 +142,14 @@ + (instancetype)allocDescriptorForClass:(Class)messageClass
 #if defined(DEBUG) && DEBUG && !defined(NS_BLOCK_ASSERTIONS)
   // No real value in checking all the fields individually, just check the combined flags at the
   // end.
+#pragma clang diagnostic push
+#pragma clang diagnostic ignored "-Wdeprecated-declarations"
   GPBFieldFlags unknownFieldFlags =
       (GPBFieldFlags)(~(GPBFieldRequired | GPBFieldRepeated | GPBFieldPacked | GPBFieldOptional |
                         GPBFieldHasDefaultValue | GPBFieldClearHasIvarOnZero |
                         GPBFieldTextFormatNameCustom | GPBFieldMapKeyMask));
   NSAssert((mergedFieldFlags & unknownFieldFlags) == 0, @"Internal error: unknown field flags set");
+#pragma clang diagnostic pop
 #endif  // defined(DEBUG) && DEBUG
 
   BOOL wireFormat = (flags & GPBDescriptorInitializationFlag_WireFormat) != 0;
@@ -611,9 +614,12 @@ - (BOOL)isRequired {
   return (description_->flags & GPBFieldRequired) != 0;
 }
 
+#pragma clang diagnostic push
+#pragma clang diagnostic ignored "-Wdeprecated-implementations"
 - (BOOL)isOptional {
-  return (description_->flags & GPBFieldOptional) != 0;
+  return self.fieldType == GPBFieldTypeSingle && !self.isRequired;
 }
+#pragma clang diagnostic pop
 
 - (GPBFieldType)fieldType {
   GPBFieldFlags flags = description_->flags;

objectivec/GPBDescriptor_PackagePrivate.h

@@ -19,7 +19,7 @@ typedef NS_OPTIONS(uint16_t, GPBFieldFlags) {
   GPBFieldRequired = 1 << 0,
   GPBFieldRepeated = 1 << 1,
   GPBFieldPacked = 1 << 2,
-  GPBFieldOptional = 1 << 3,
+  GPBFieldOptional __attribute__((deprecated)) = 1 << 3,
   GPBFieldHasDefaultValue = 1 << 4,
 
   // Indicate that the field should "clear" when set to zero value. This is the

objectivec/GPBMessage.m

@@ -1428,8 +1428,6 @@ - (BOOL)isInitialized {
             return NO;
           }
         } else {
-          NSAssert(field.isOptional, @"%@: Single message field %@ not required or optional?",
-                   [self class], field.name);
           if (GPBGetHasIvarField(self, field)) {
             GPBMessage *message = GPBGetMessageMessageField(self, field);
             if (!message.initialized) {

objectivec/Tests/GPBMessage30007FormatTest.m

@@ -138,6 +138,7 @@ typedef GPB_ENUM(Message30007_SubMessage_FieldNumber) {
 NS_ASSUME_NONNULL_END
 
 #pragma clang diagnostic push
+#pragma clang diagnostic ignored "-Wdeprecated-declarations"
 #pragma clang diagnostic ignored "-Wdollar-in-identifier-extension"
 
 GPBObjCClassDeclaration(Message30007);

objectivec/Tests/GPBMessage40310FormatTest.m

@@ -137,6 +137,7 @@ typedef GPB_ENUM(Message40310_SubMessage_FieldNumber) {
 NS_ASSUME_NONNULL_END
 
 #pragma clang diagnostic push
+#pragma clang diagnostic ignored "-Wdeprecated-declarations"
 #pragma clang diagnostic ignored "-Wdollar-in-identifier-extension"
 
 GPBObjCClassDeclaration(Message40310);