Previously, clang-format detected something like the following as a C++11 attribute specifier.
@[[NSArray class]]
instead of an array with an Objective-C method call inside. In general, when the attribute specifier checking runs, if it sees 2 identifiers in a row, it decides that the square brackets represent an Objective-C method call. However, here, class is tokenized as a keyword instead of an identifier, so this check fails.
To fix this, the attribute specifier first checks whether the first square bracket has an "@" before it. If it does, then that square bracket is not the start of a attribute specifier because it is an Objective-C array literal. (The assumption is that @[[.*]] is not valid C/C++.)