r196296 - Issue diagnostic when constructor or destructor

[jahanian]

On Dec 3, 2013, at 10:31 AM, Arthur O'Dwyer <arthur.j.odwyer at gmail.com> wrote:

> On Tue, Dec 3, 2013 at 9:42 AM, jahanian <fjahanian at apple.com> wrote:
>> On Dec 3, 2013, at 9:35 AM, Jordan Rose <jordan_rose at apple.com> wrote:
>>> On Dec 3, 2013, at 9:10 , Fariborz Jahanian <fjahanian at apple.com> wrote:
>> 
>> Author: fjahanian
>> Date: Tue Dec  3 11:10:08 2013
>> New Revision: 196296
>> 
>> URL: http://llvm.org/viewvc/llvm-project?rev=196296&view=rev
>> Log:
>> Issue diagnostic when constructor or destructor
>> return void expression. // rdar://15366494
>> pr17759.
> [...]
>> +++ cfe/trunk/include/clang/Basic/DiagnosticSemaKinds.td Tue Dec  3 11:10:08
>> 2013
>> @@ -6426,6 +6426,8 @@ def ext_return_has_void_expr : Extension
>> def err_return_init_list : Error<
>> "%select{void function|void method|constructor|destructor}1 %0 "
>> "must not return a value">;
>> +def err_ctor_dtor_returns_void : Error<
>> +  "%select{constructor|destructor}1 %0 must not return void expression">;
> 
> 
> IMO, the diagnostic's wording should be the same for
> 
>    int foo();
>    struct C1 { C1() { return foo(); } };  // error: constructor 'C'
> should not return a value [-Wreturn-type]
> 
> and
> 
>    void bar();
>    struct C2 { C2() { return bar(); } };  // error: constructor 'C'
> must not return void expression [-Wreturn-type]

Problem I faced is that under an extension warning flag, one can return a non-void 
expression in a constructor/destructor. But returning a void expression is always an error.
So, consolidating both cases into one diagnostic is not feasible. Please look at
definition of ext_return_has_expr vs err_ctor_dtor_returns_void

- Fariborz

> 
> I don't see any significant difference between the two cases, and it
> doesn't seem like they should have two different diagnostics issued
> along two different (and convoluted and difficult-to-maintain)
> codepaths. A compromise would be to %select a user-friendly
> clarification in the case that we're about to issue the diagnostic and
> we notice that the returned expression is of type (cv-qualified) void:
> 
>    void bar();
>    struct C2 { C2() { return bar(); } };  // error: constructor 'C'
> should not return a value (not even of type 'void') [-Wreturn-type]
> 
> my $.02,
> –Arthur

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