[ObjC] Ensure -[GPBCodedOutputStream dealloc] cannot throw exceptions

If `-[GPBCodedOutputStream flush]` failed (e.g., because the filesystem
was out of space), then `-[GPBCodedOutputStream dealloc]` would throw
an exception.

`-dealloc` cannot fail, so the only thing to do in this case is to silently
swallow the exception.

PiperOrigin-RevId: 579916429

objectivec/GPBCodedOutputStream.m

@@ -160,7 +160,14 @@ static void GPBWriteRawLittleEndian64(GPBOutputBufferState *state, int64_t value
 }
 
 - (void)dealloc {
-  [self flush];
+  @try {
+    [self flush];
+  } @catch (NSException *exception) {
+    // -dealloc methods cannot fail, so swallow any exceptions from flushing.
+#if defined(DEBUG) && DEBUG
+    NSLog(@"GPBCodedOutputStream: Exception while flushing in dealloc: %@", exception);
+#endif
+  }
   [state_.output close];
   [state_.output release];
   [buffer_ release];

objectivec/Tests/GPBCodedOutputStreamTests.m

@@ -393,4 +393,27 @@
                                NSException, GPBCodedOutputStreamException_WriteFailed);
 }
 
+- (void)testThatDeallocNeverThrows {
+  uint8_t buffer[1] = {0};
+
+  // Output stream which can write precisely 1 byte of data before it's full.
+  NSOutputStream* output = [[[NSOutputStream alloc] initToBuffer:buffer
+                                                        capacity:sizeof(buffer)] autorelease];
+
+  NSMutableData* outputBuffer = [NSMutableData data];
+  GPBCodedOutputStream* codedOutput =
+      [[GPBCodedOutputStream alloc] initWithOutputStream:output data:outputBuffer];
+
+  [codedOutput writeRawByte:0x23];
+  [codedOutput flush];
+
+  // Put one more byte in the output buffer.
+  [codedOutput writeRawByte:0x42];
+  XCTAssertThrowsSpecificNamed([codedOutput flush], NSException,
+                               GPBCodedOutputStreamException_WriteFailed);
+
+  // -dealloc must not throw when it flushes, even if a previous flush failed.
+  XCTAssertNoThrow([codedOutput release]);
+}
+
 @end