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

[Aaron Ballman via Phabricator via cfe-commits]

aaron.ballman added inline comments.


================
Comment at: clang/test/CodeGen/2009-06-01-addrofknr.c:8
 
-static int func(f)
+static int func(f) // expected-warning {{this function declaration without a prototype is deprecated in all versions of C and changes behavior in C2x}}
   void *f;
----------------
aaron.ballman wrote:
> jyknight wrote:
> > This message seems vaguer than necessary, since we know _for sure_ this is invalid.
> > 
> > Can we say something like: "K&R-style function definitions are deprecated in all versions of C and not supported in C2x"?
> I'd like to avoid using K&R in the diagnostic text (we're inconsistent about K&R vs prototype, etc already, but I'd like to see us excise `K&R` from diagnostics because it's not particularly descriptive to anyone younger than about 40. :-D
> 
> How about: `function declarations without a prototype are deprecated in all versions of C and not supported in C2x` ?
I went with `a function declaration without a prototype is deprecated in all versions of C and is not supported in C2x`, let me know if you think it needs further adjusting. I also reworded the other diagnostics to sound similar.


================
Comment at: clang/test/Parser/declarators.c:5
 
-void f0();
+void f0(); /* expected-warning {{a function declaration without a prototype is deprecated in all versions of C}} */
 void f1(int [*]);
----------------
aaron.ballman wrote:
> jyknight wrote:
> > Perhaps we should add an explanation to the message like
> >  `(specify '(void)' if you intended to accept no arguments)`
> > to make it clearer to folks who aren't familiar with this weirdness yet?
> They're already offered a fixit for this situation, so I don't know that we need the extra explanation? The user currently gets something like this:
> ```
> C:\Users\aballman\OneDrive - Intel Corporation\Desktop\test.c:2:16: warning: declaration of a function without a prototype is deprecated in all versions of C [-Wstrict-prototypes]
> void other_func();
>                ^
>                 void
> ```
> Do you still think the diagnostic needs to be made longer?
I elected to leave this alone unless you feel strongly.


================
Comment at: clang/test/Sema/knr-def-call.c:15
+void f2(float); // expected-note{{previous declaration is here}} \
+                   expected-warning {{this function declaration with a prototype changes behavior in C2x because it is followed by a function without a prototype}}
+void f2(x) float x; { } // expected-warning{{promoted type 'double' of K&R function parameter is not compatible with the parameter type 'float' declared in a previous prototype}} \
----------------
aaron.ballman wrote:
> jyknight wrote:
> > I think we don't want to emit a warning here. If a declaration with params doesn't match a K&R definition, we already emit a conflicting-types error.
> > 
> > [[Well...except for one case, I've noticed -- we don't current emit any warning when a definition with no parameters fails to match a preceding declaration with params, e.g. `void f(int); void f() { }`. I'm quite surprised -- I'm willing to say that such code is 100% just a bug, not intentional. I note that GCC unconditionally rejects it. I think we should also be emitting an unconditional error in that case.]]]
> > 
> > Anyhow, when you have a K&R style definition with parameters, that -- all by itself -- is definitely invalid in C2x, so we don't need to emit any warning on the declaration.
> > I'm quite surprised -- I'm willing to say that such code is 100% just a bug, not intentional. I note that GCC unconditionally rejects it. I think we should also be emitting an unconditional error in that case.
> 
> I'd rather we be consistent here -- either every mixture of prototype/unprototyped is an error, or they're all a warning. I've added your example as a test case and we warn on it as being a change of behavior in C2x, which I think is defensible.
> 
> > Anyhow, when you have a K&R style definition with parameters, that -- all by itself -- is definitely invalid in C2x, so we don't need to emit any warning on the declaration.
> 
> I tend to agree, let me see what I can do.
I addressed this so we no longer diagnose the function with a prototype in the case where it precedes the function without a prototype.


================
Comment at: clang/test/Sema/warn-deprecated-non-prototype.c:46
+                         strict-note {{this function declaration without a prototype changes behavior in C2x}}
+void order1(int i);   // both-warning {{this function declaration with a prototype changes behavior in C2x because it is preceded by a function without a prototype}}
+
----------------
aaron.ballman wrote:
> jyknight wrote:
> > Maybe something like "this function declaration will conflict with the preceding declaration in C2x, because the preceding declaration does not specify arguments."
> I can see the appeal, but that makes the diagnostic rather long and I'd still like to be consistent in the terminology we use. Given that the old diagnostic was `-Wstrict-prototypes` and the new one is `-Wdeprecated-non-prototype`, I think we don't need to tie ourselves into knots to avoid using the terminology. Do you feel strongly about rewording this?
I've elected to leave this one alone unless you feel strongly.


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  https://reviews.llvm.org/D122895/new/

https://reviews.llvm.org/D122895