Re: Need suggestion about bug 68425

[David Malcolm <dmalcolm at redhat dot com>]

On Wed, 2016-02-24 at 17:56 +0530, Prasad Ghangal wrote:
> Thanks Prathamesh and Joseph for your suggestions.
> 
> Here is my updated patch :
> 
> for test cases:
> 
>     const int array[5] = {1, 2, 3};
>     const int array1[3] = {1, 2, 3, 6};
>     const int array2[4] = {1, 2, 3, 6, 89};
>     const int array3[5] = {1, 2, 3, 6, 89, 193};
>     const int array4[3] = {1, 2, 3, 6, 89, 193};
>     const int array5[1] = {1, 2, 3, 6, 89, 193};
>     const int array6[3] = {1, 2, 3, 6, 89, 193;
>     const int array7[5] = {1, 2, 3, 6, 89, 193}
>     const int array8[5] = {1, 2, 3, 6, 89, 193
> 
> 
> 
> It gives:
> 
> 68425.c: In function âmainâ:
> 68425.c:4:37: warning: excess elements in array initializer (4
> elements, expected 3)
>      const int array1[3] = {1, 2, 3, 6};
>                                                    ^
> 68425.c:4:37: note: (near initialization for âarray1â)
> 68425.c:5:40: warning: excess elements in array initializer (5
> elements, expected 4)
>      const int array2[4] = {1, 2, 3, 6, 89};
>                                                        ^~
> 68425.c:5:40: note: (near initialization for âarray2â)
> 68425.c:6:44: warning: excess elements in array initializer (6
> elements, expected 5)
>      const int array3[5] = {1, 2, 3, 6, 89, 193};
>                                                              ^~~
> 68425.c:6:44: note: (near initialization for âarray3â)
> 68425.c:7:37: warning: excess elements in array initializer (6
> elements, expected 3)
>      const int array4[3] = {1, 2, 3, 6, 89, 193};
>                                                    ^
> 68425.c:7:37: note: (near initialization for âarray4â)
> 68425.c:8:31: warning: excess elements in array initializer (6
> elements, expected 1)
>      const int array5[1] = {1, 2, 3, 6, 89, 193};
>                                            ^
> 68425.c:8:31: note: (near initialization for âarray5â)
> 68425.c:9:37: warning: excess elements in array initializer (6
> elements, expected 3)
>      const int array6[3] = {1, 2, 3, 6, 89, 193;
>                                                    ^
> 68425.c:9:37: note: (near initialization for âarray6â)
> 68425.c:9:47: error: expected â}â before â;â token
>      const int array6[3] = {1, 2, 3, 6, 89, 193;
>                                                                    ^
> 68425.c:14:1: error: expected declaration or statement at end of
> input
>  }
>  ^

Those caret locations look wrong to me - they don't seem to be
underlining the pertinent source.  Is that what the patched compiler is
printing, or did things get messed up somewhere via email?

(I tried the patch, but it didn't quite apply cleanly against my
working copy)

As mentioned before, I think the ideal behavior would be to underline
*all* of the surplus elements, like this:

68425.c: In function âmainâ:
68425.c:4:37: warning: excess elements in array initializer (4
elements, expected 3)
     const int array1[3] = {1, 2, 3, 6};
                                     ^
68425.c:4:37: note: (near initialization for âarray1â)
68425.c:5:40: warning: excess elements in array initializer (5
elements, expected 4)
     const int array2[4] = {1, 2, 3, 6, 89};
                                        ^~
68425.c:5:40: note: (near initialization for âarray2â)
68425.c:6:44: warning: excess elements in array initializer (6
elements, expected 5)
     const int array3[5] = {1, 2, 3, 6, 89, 193};
                                            ^~~
68425.c:6:44: note: (near initialization for âarray3â)
68425.c:7:37: warning: excess elements in array initializer (6
elements, expected 3)
     const int array4[3] = {1, 2, 3, 6, 89, 193};
                                     ^~~~~~~~~~
68425.c:7:37: note: (near initialization for âarray4â)
68425.c:8:31: warning: excess elements in array initializer (6
elements, expected 1)
     const int array5[1] = {1, 2, 3, 6, 89, 193};
                               ^~~~~~~~~~~~~~~~
68425.c:8:31: note: (near initialization for âarray5â)
68425.c:9:37: warning: excess elements in array initializer (6
elements, expected 3)
     const int array6[3] = {1, 2, 3, 6, 89, 193;
                                     ^~~~~~~~~~
68425.c:9:37: note: (near initialization for âarray6â)
68425.c:9:47: error: expected â}â before â;â token
     const int array6[3] = {1, 2, 3, 6, 89, 193;
                                               ^
68425.c:14:1: error: expected declaration or statement at end of input
 }
 ^

You can use "make_location" to build a range; see e.g. this fragment
from the C++ frontend:

      /* Create a location of the form:
	    type_name{i, f}
	    ^~~~~~~~~~~~~~~
	 with caret == start at the start of the type name,
	 finishing at the closing brace.  */
      location_t finish_loc
	= get_finish (cp_lexer_previous_token (parser->lexer)->location);
      location_t combined_loc = make_location (start_loc, start_loc,
					       finish_loc);

You could do something similar, building a range covering the start of
the first surplus initializer through to the end of the last surplus
initializer.

You can then emit an error_at combined_loc, via error_at.

For an example of how to write a test case for underlines, see the
testsuite part of:
  https://gcc.gnu.org/ml/gcc-patches/2015-12/msg01684.html


For bonus points, it's also possible to add a 2nd location for the
message, by using error_at_richloc, so that you could underline the
array size:

68425.c:9:37: warning: excess elements in array initializer (6
elements,
expected 3)
     const int array6[3] = {1, 2, 3, 6, 89, 193};
           
          ~              ^~~~~~~~~~

Or do that in the followup note, for something like:

68425.c:9:37: warning: excess elements in array initializer (6
elements, expected 3)
     const int array6[3] = {1, 2, 3, 6, 89, 193};
                                     ^~~~~~~~~~
68425.c:9:12: note: (near initialization for âarray6â)
     const int array6[3] = {1, 2, 3, 6, 89, 193;
                      ^

but maybe that's over-ambitious for now.

Hope this is constructive.
Dave