Open Radar

 
Summary:
C++’s `using` keyword makes it much more straight forward to introduce aliases for blocks than a `typedef` does. More importantly than being easier to write, they are much easier to read as well. Unfortunately, parameter names are not picked up by Clang’s documentation parser when declaring an alias name for a block in this way

Steps to Reproduce:
1. Create a file called WarningSign.mm, containing the code between the triple back–ticks:
```
#import <Foundation/Foundation.h>

NS_ASSUME_NONNULL_BEGIN
namespace {
    /**
      Signature of the block to be called if we’ve actually succeeded downloading data.

       @param downloadedFileURL The URL of the temporary file containing the downloaded data. The file must be copied to a different destination if the contents need to be preserved.
     */
    using SuccessHandler = void (^)(NSURL *downloadedFileURL);
    using FailureHandler = void (^)(NSError *error);
}

@protocol SomeDownloader <NSObject>

- (NSProgress *)fetchURL:(NSURL *)remoteURL expectingSHA256:(NSString *)expectedSHASum withSuccessHandler:(SuccessHandler)successHandler failureHandler:(FailureHandler)failureHandler;

@end

NS_ASSUME_NONNULL_END
```
2. Open a new terminal window and type `export DEVELOPER_DIR=${path_to_code_8beta2}`
3. change into the directory containing WarningSign.mm and execute the following command:
clang \
    -x objective-c++ \
    -arch i386 \
    -std=gnu++1y \
    -stdlib=libc++ \
    -isysroot "${DEVELOPER_DIR}/Platforms/iPhoneSimulator.platform/Developer/SDKs/iPhoneSimulator10.0.sdk" \
    -fobjc-arc -fmodules \
    -Wdocumentation \
    -c WarningSign.mm

Expected Results:
The file compiles without warnings or errors.

Actual Results:
The following warning is printed to the console:
WarningSign.mm:8:9: warning: '@param' command used in a comment that is not
      attached to a function declaration [-Wdocumentation]
       @param downloadedFileURL The URL of the temporary file containin...
        ^~~~~
1 warning generated.


Regression:
The same warning occurs on older versions of Xcode as well, but I guess it makes more sense to file this against the most recent version.

Notes:
The only workaround thus far is to replace line 10 in that file with the following:
typedef void (^SuccessHandler)(NSURL * downloadedFileURL);