[LLVMbugs] [Bug 17669] New: Attribute for "arc-retain-cycles" check in addition to "add" and "set" method selector prefix convention

[bugzilla-daemon at llvm.org]

http://llvm.org/bugs/show_bug.cgi?id=17669

            Bug ID: 17669
           Summary: Attribute for "arc-retain-cycles" check in addition to
                    "add" and "set" method selector prefix convention
           Product: clang
           Version: unspecified
          Hardware: Macintosh
                OS: MacOS X
            Status: NEW
          Severity: enhancement
          Priority: P
         Component: -New Bugs
          Assignee: unassignedclangbugs at nondot.org
          Reporter: fortinmike at gmail.com
                CC: llvmbugs at cs.uiuc.edu
    Classification: Unclassified

This enhancement request pertains to Objective-C warnings generated by clang.

I am implementing a few methods in a library that take block arguments and
store them for later, repeated execution. However, those methods do not benefit
from the "arc-retain-cycles" warning because their signature doesn't begin with
"add" nor "set"; it’s pretty easy to create a retain cycle by accident,
particularly for novice Objective-C devs. I would like to annotate the methods
I know can lead to cycles for inclusion in this check to save others (and
myself) from introducing leaks in the future.

I’m proposing adding an Objective-C-specific attribute (if that’s the
appropriate construct) to indicate that a method’s usages should be checked for
potential retain cycles without requiring the method to begin with “add” or
“set". Something like:

- (void)doSomethingWithObject:(id)anObject andBlock:(void (^)())aBlock
__attribute__((check_retain_cycles));

In addition, it would probably be nice to offer the complementary ability to
exclude some “add” and “set”-prefixed methods from the retain cycle check if we
know it’s not relevant in a specific case, like the NSOperationQueue
“addOperationWithBlock” exclusion that’s currently hard-coded in the
isSetterLikeSelector() function (SemaChecking.cpp:6620) but in a dynamic way
using an attribute:

- (void)addOperationWithBlock:(void (^)(void))block
__attribute__((dont_check_retain_cycles));

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