[ObjC] Introduce the new GPBUnknownFields type.

`GPBUnknownFields` will be the eventually replacement for `GPBUnknownFieldSet`. This
introduces the type and the changes to `GPBUnknownField`.

The new api will preserve the wire ordering of unknown fields. This is now checked
in conformance tests.

While this adds the type changes and tests them, it does not yet wire the changes
in to the rest of the Runtime, so the conformance tests still done pass.
`GPBUnknownFieldSet` also hasn't been deprecated yet, that will come in later with
the wiring in to the runtime.

PiperOrigin-RevId: 648361455

objectivec/BUILD.bazel

@@ -84,6 +84,7 @@ objc_library(
         "GPBRootObject.h",
         "GPBRuntimeTypes.h",
         "GPBUnknownField.h",
+        "GPBUnknownFields.h",
         "GPBUnknownFieldSet.h",
         "GPBUtilities.h",
         "GPBWellKnownTypes.h",
@@ -138,6 +139,7 @@ objc_library(
         "GPBType.pbobjc.m",
         "GPBUnknownField.m",
         "GPBUnknownFieldSet.m",
+        "GPBUnknownFields.m",
         "GPBUtilities.m",
         "GPBWellKnownTypes.m",
         "GPBWireFormat.m",

objectivec/GPBProtocolBuffers.h

@@ -19,6 +19,7 @@
 #import "GPBRootObject.h"
 #import "GPBUnknownField.h"
 #import "GPBUnknownFieldSet.h"
+#import "GPBUnknownFields.h"
 #import "GPBUtilities.h"
 #import "GPBWellKnownTypes.h"
 #import "GPBWireFormat.h"

objectivec/GPBProtocolBuffers.m

@@ -26,6 +26,7 @@
 #import "GPBRootObject.m"
 #import "GPBUnknownField.m"
 #import "GPBUnknownFieldSet.m"
+#import "GPBUnknownFields.m"
 #import "GPBUtilities.m"
 #import "GPBWellKnownTypes.m"
 #import "GPBWireFormat.m"

objectivec/GPBUnknownField.h

@@ -11,8 +11,25 @@
 @class GPBUInt32Array;
 @class GPBUInt64Array;
 @class GPBUnknownFieldSet;
+@class GPBUnknownFields;
 
 NS_ASSUME_NONNULL_BEGIN
+
+typedef NS_ENUM(uint8_t, GPBUnknownFieldType) {
+  GPBUnknownFieldTypeVarint,
+  GPBUnknownFieldTypeFixed32,
+  GPBUnknownFieldTypeFixed64,
+  GPBUnknownFieldTypeLengthDelimited,  // Length prefixed
+  GPBUnknownFieldTypeGroup,            // Tag delimited
+
+  /**
+   * This type is only used with fields from `GPBUnknownFieldsSet`. Some methods
+   * only work with instances with this type and other apis require the other
+   * type(s). It is a programming error to use the wrong methods.
+   **/
+  GPBUnknownFieldTypeLegacy,
+};
+
 /**
  * Store an unknown field. These are used in conjunction with
  * GPBUnknownFieldSet.
@@ -26,48 +43,127 @@ __attribute__((objc_subclassing_restricted))
 /** The field number the data is stored under. */
 @property(nonatomic, readonly, assign) int32_t number;
 
-/** An array of varint values for this field. */
+/** The type of the field. */
+@property(nonatomic, readonly, assign) GPBUnknownFieldType type;
+
+/**
+ * Fetch the varint value.
+ *
+ * It is a programming error to call this when the `type` is not a varint.
+ */
+@property(nonatomic, readonly, assign) uint64_t varint;
+
+/**
+ * Fetch the fixed32 value.
+ *
+ * It is a programming error to call this when the `type` is not a fixed32.
+ */
+@property(nonatomic, readonly, assign) uint32_t fixed32;
+
+/**
+ * Fetch the fixed64 value.
+ *
+ * It is a programming error to call this when the `type` is not a fixed64.
+ */
+@property(nonatomic, readonly, assign) uint64_t fixed64;
+
+/**
+ * Fetch the length delimited (length prefixed) value.
+ *
+ * It is a programming error to call this when the `type` is not a length
+ * delimited.
+ */
+@property(nonatomic, readonly, strong, nonnull) NSData *lengthDelimited;
+
+/**
+ * Fetch the group (tag delimited) value.
+ *
+ * It is a programming error to call this when the `type` is not a group.
+ */
+@property(nonatomic, readonly, strong, nonnull) GPBUnknownFields *group;
+
+/**
+ * An array of varint values for this field.
+ *
+ * Only valid for type == GPBUnknownFieldTypeLegacy, it is a programming error
+ * to use with any other type.
+ */
 @property(nonatomic, readonly, strong) GPBUInt64Array *varintList;
 
-/** An array of fixed32 values for this field. */
+/**
+ * An array of fixed32 values for this field.
+ *
+ * Only valid for type == GPBUnknownFieldTypeLegacy, it is a programming error
+ * to use with any other type.
+ */
 @property(nonatomic, readonly, strong) GPBUInt32Array *fixed32List;
 
-/** An array of fixed64 values for this field. */
+/**
+ * An array of fixed64 values for this field.
+ *
+ * Only valid for type == GPBUnknownFieldTypeLegacy, it is a programming error
+ * to use with any other type.
+ */
 @property(nonatomic, readonly, strong) GPBUInt64Array *fixed64List;
 
-/** An array of data values for this field. */
+/**
+ * An array of data values for this field.
+ *
+ * Only valid for type == GPBUnknownFieldTypeLegacy, it is a programming error
+ * to use with any other type.
+ */
 @property(nonatomic, readonly, strong) NSArray<NSData *> *lengthDelimitedList;
 
-/** An array of groups of values for this field. */
+/**
+ * An array of groups of values for this field.
+ *
+ * Only valid for type == GPBUnknownFieldTypeLegacy, it is a programming error
+ * to use with any other type.
+ */
 @property(nonatomic, readonly, strong) NSArray<GPBUnknownFieldSet *> *groupList;
 
 /**
  * Add a value to the varintList.
  *
+ * Only valid for type == GPBUnknownFieldTypeLegacy, it is a programming error
+ * to use with any other type.
+ *
  * @param value The value to add.
  **/
 - (void)addVarint:(uint64_t)value;
 /**
  * Add a value to the fixed32List.
  *
+ * Only valid for type == GPBUnknownFieldTypeLegacy, it is a programming error
+ * to use with any other type.
+ *
  * @param value The value to add.
  **/
 - (void)addFixed32:(uint32_t)value;
 /**
  * Add a value to the fixed64List.
  *
+ * Only valid for type == GPBUnknownFieldTypeLegacy, it is a programming error
+ * to use with any other type.
+ *
  * @param value The value to add.
  **/
 - (void)addFixed64:(uint64_t)value;
 /**
  * Add a value to the lengthDelimitedList.
  *
+ * Only valid for type == GPBUnknownFieldTypeLegacy, it is a programming error
+ * to use with any other type.
+ *
  * @param value The value to add.
  **/
 - (void)addLengthDelimited:(NSData *)value;
 /**
  * Add a value to the groupList.
  *
+ * Only valid for type == GPBUnknownFieldTypeLegacy, it is a programming error
+ * to use with any other type.
+ *
  * @param value The value to add.
  **/
 - (void)addGroup:(GPBUnknownFieldSet *)value;