Add more warnings to for the ObjC runtime build

Working on https://github.com/google/protobuf/issues/1599, specifically:
- Turn on more warnings that the Xcode UI calls out with individual controls.
- Manually add:
  -Wundef
  -Wswitch-enum
- Manually add and then diable in the unittests because of XCTest's headers:
  -Wreserved-id-macro
  -Wdocumentation-unknown-command
- Manually add -Wdirect-ivar-access, but disable it for the unittests and in
  the library code (via #pragmas to suppress it). This is done so proto users
  can enable the warning.

1 files changed, 9 insertions, 1 deletions

diff --git a/objectivec/GPBUnknownFieldSet.m b/objectivec/GPBUnknownFieldSet.m
index 4ddc0d2a..af08556e 100644
--- a/objectivec/GPBUnknownFieldSet.m
+++ b/objectivec/GPBUnknownFieldSet.m
@@ -93,6 +93,12 @@ static void CopyWorker(const void *key, const void *value, void *context) {
   [copied release];
 }
 
+// Direct access is use for speed, to avoid even internally declaring things
+// read/write, etc. The warning is enabled in the project to ensure code calling
+// protos can turn on -Wdirect-ivar-access without issues.
+#pragma clang diagnostic push
+#pragma clang diagnostic ignored "-Wdirect-ivar-access"
+
 - (id)copyWithZone:(NSZone *)zone {
   GPBUnknownFieldSet *result = [[GPBUnknownFieldSet allocWithZone:zone] init];
   if (fields_) {
@@ -148,7 +154,7 @@ static void CopyWorker(const void *key, const void *value, void *context) {
 }
 
 - (NSArray *)sortedFields {
-  if (!fields_) return nil;
+  if (!fields_) return [NSArray array];
   size_t count = CFDictionaryGetCount(fields_);
   ssize_t keys[count];
   GPBUnknownField *values[count];
@@ -420,4 +426,6 @@ static void GPBUnknownFieldSetMergeUnknownFields(const void *key,
   }
 }
 
+#pragma clang diagnostic pop
+
 @end