Re: [PATCH 3/3] C: hints for missing stdlib includes for macros and types

[Jeff Law <law at redhat dot com>]

On 05/05/2017 11:51 AM, David Malcolm wrote:
> The C frontend already "knows" about many common functions in
> the C standard library:
> 
>   test.c: In function 'test':
>   test.c:3:3: warning: implicit declaration of function 'printf' [-Wimplicit-function-declaration]
>      printf ("hello world\n");
>      ^~~~~~
>   test.c:3:3: warning: incompatible implicit declaration of built-in function 'printf'
>   test.c:3:3: note: include '<stdio.h>' or provide a declaration of 'printf'
> 
> and which header file they are in.
> 
> However it doesn't know about various types and macros:
> 
> test.c:1:13: error: 'NULL' undeclared here (not in a function)
>  void *ptr = NULL;
>              ^~~~
> 
> This patch uses the name_hint/deferred_diagnostic machinery to
> add hints for missing C standard library headers for some of the
> most common type and macro names.
> 
> For example, the above becomes:
> test.c:1:13: error: 'NULL' undeclared here (not in a function)
>  void *ptr = NULL;
>              ^~~~
> test.c:1:13: note: 'NULL' is defined in header '<stddef.h>'; did you forget to '#include <stddef.h>'?
> 
> If the patch to add fix-it hints for missing #includes is approved:
>   https://gcc.gnu.org/ml/gcc-patches/2017-05/msg00321.html
> then it's trivial to add a fix-it hint to the note.
> 
> gcc/c/ChangeLog:
> 	* c-decl.c (get_c_name_hint): New function.
> 	(class suggest_missing_header): New class.
> 	(lookup_name_fuzzy): Call get_c_name_hint and use it to
> 	suggest missing headers to the user.
> 
> gcc/testsuite/ChangeLog:
> 	* gcc.dg/spellcheck-stdlib.c: New test case.
OK once prereqs are approved.

FWIW, I'm getting a little concerned that we're adding a lot of overhead
to the error paths -- that often doesn't matter.  But sometimes it does
(testcase reduction, errors with machine generated code, etc).
Something to be aware of.


jeff