[PATCH] D122895: [C89/C2x] Improve diagnostics around strict prototypes in C

[Aaron Ballman via Phabricator via cfe-commits]

aaron.ballman added a comment.

In D122895#3511855 <https://reviews.llvm.org/D122895#3511855>, @aaron.ballman wrote:

> In D122895#3511646 <https://reviews.llvm.org/D122895#3511646>, @dexonsmith wrote:
>
>>   void f1(void (^block)());
>>   
>>   void f2(void) {
>>     f1(^(int x) { /* do something with x */ });
>>   }
>
> Your code example is interesting though as I would expect that to trigger `-Wdeprecated-non-prototype` as well as `-Wstrict-prototypes`. I'd expect the pedantic warning to complain about the block declaration because it specifies no prototype, and I'd expect the changes behavior warning because that code will break in C2x.

I think the current behavior today makes sense but we should see if we can improve it to make *more* sense. With `-Wstrict-prototypes`, we should complain about the block without a prototype, but the use at the call site is not declaring a conflicting declaration nor is it a call to a function without a prototype but passes arguments (both of those are `-Wdeprecated-non-prototype` warnings). Instead, it's a new kind of situation that we may want to consider adding additional coverage for under `-Wdeprecated-non-prototype` based on the same reasoning we used for diagnosing calls to a function without a prototype but pass arguments. This is not specific to blocks, consider:

  void func(void (*fp)());
  void do_it(int i);
  
  int main(void) {
    func(do_it); // It'd be nice to diagnose this too, but we don't today
  }


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