[PATCH] c++: Improve the MVP -Wparentheses diagnostic.

[Jason Merrill]

On 10/28/20 5:14 PM, Marek Polacek wrote:
> I noticed that declarator->parenthesized is, for this warning, only set
> to the opening paren.  But we can easily make it a range and generate
> a nicer diagnostic.  Moreover, we can then offer a fix-it hint.
> 
> TL;DR: This patch changes
> 
> mvp3.C:8:7: warning: unnecessary parentheses in declaration of ‘i’ [-Wparentheses]
>      8 |   int (i);
>        |       ^
> 
> to
> 
> mvp3.C:8:7: warning: unnecessary parentheses in declaration of ‘i’ [-Wparentheses]
>      8 |   int (i);
>        |       ^~~
> mvp3.C:8:7: note: remove parentheses
>      8 |   int (i);
>        |       ^~~
>        |       - -
> 
> Tested by using -fdiagnostics-generate-patch and verifying that the
> generated patch DTRT.

OK.

> gcc/cp/ChangeLog:
> 
> 	* decl.c (grokdeclarator): Offer a fix-it hint for the "unnecessary
> 	parentheses in declaration" warning.
> 	* parser.c (cp_parser_direct_declarator): When setting
> 	declarator->parenthesized, use a location range.
> 
> gcc/testsuite/ChangeLog:
> 
> 	* g++.dg/warn/mvp3.C: New test.
> ---
>   gcc/cp/decl.c                    | 13 +++++++++++--
>   gcc/cp/parser.c                  |  4 +++-
>   gcc/testsuite/g++.dg/warn/mvp3.C | 30 ++++++++++++++++++++++++++++++
>   3 files changed, 44 insertions(+), 3 deletions(-)
>   create mode 100644 gcc/testsuite/g++.dg/warn/mvp3.C
> 
> diff --git a/gcc/cp/decl.c b/gcc/cp/decl.c
> index 2de4e1657fb..ee3c353935d 100644
> --- a/gcc/cp/decl.c
> +++ b/gcc/cp/decl.c
> @@ -12037,8 +12037,17 @@ grokdeclarator (const cp_declarator *declarator,
>   	       && inner_declarator->u.id.qualifying_scope
>   	       && (MAYBE_CLASS_TYPE_P (type)
>   		   || TREE_CODE (type) == ENUMERAL_TYPE)))
> -	warning_at (declarator->parenthesized, OPT_Wparentheses,
> -		    "unnecessary parentheses in declaration of %qs", name);
> +	{
> +	  if (warning_at (declarator->parenthesized, OPT_Wparentheses,
> +			  "unnecessary parentheses in declaration of %qs",
> +			  name))
> +	    {
> +	      gcc_rich_location iloc (declarator->parenthesized);
> +	      iloc.add_fixit_remove (get_start (declarator->parenthesized));
> +	      iloc.add_fixit_remove (get_finish (declarator->parenthesized));
> +	      inform (&iloc, "remove parentheses");
> +	    }
> +	}
>         if (declarator->kind == cdk_id || declarator->kind == cdk_decomp)
>   	break;
>   
> diff --git a/gcc/cp/parser.c b/gcc/cp/parser.c
> index 03780fab0a7..57759fc1882 100644
> --- a/gcc/cp/parser.c
> +++ b/gcc/cp/parser.c
> @@ -21864,7 +21864,9 @@ cp_parser_direct_declarator (cp_parser* parser,
>   	    open_paren = NULL;
>   	}
>         if (open_paren)
> -	declarator->parenthesized = open_paren->location;
> +	declarator->parenthesized = make_location (open_paren->location,
> +						   open_paren->location,
> +						   close_paren->location);
>       }
>   
>     /* If we entered a scope, we must exit it now.  */
> diff --git a/gcc/testsuite/g++.dg/warn/mvp3.C b/gcc/testsuite/g++.dg/warn/mvp3.C
> new file mode 100644
> index 00000000000..4d371c5b093
> --- /dev/null
> +++ b/gcc/testsuite/g++.dg/warn/mvp3.C
> @@ -0,0 +1,30 @@
> +// { dg-do compile }
> +// { dg-options "-Wparentheses -fdiagnostics-show-caret" }
> +// Test fix-it hints for the MVP warning.
> +
> +void
> +g ()
> +{
> +  int (i); // { dg-warning "7:unnecessary parentheses" }
> +/* { dg-begin-multiline-output "" }
> +   int (i);
> +       ^~~
> +   { dg-end-multiline-output "" } */
> +// { dg-message "7:remove parentheses" "" { target *-*-* } 8 }
> +/* { dg-begin-multiline-output "" }
> +   int (i);
> +       ^~~
> +       - -
> +   { dg-end-multiline-output "" } */
> +  int (fn(void)); // { dg-warning "7:unnecessary parentheses" }
> +/* { dg-begin-multiline-output "" }
> +   int (fn(void));
> +       ^~~~~~~~~~
> +   { dg-end-multiline-output "" } */
> +// { dg-message "7:remove parentheses" "" { target *-*-* } 19 }
> +/* { dg-begin-multiline-output "" }
> +   int (fn(void));
> +       ^~~~~~~~~~
> +       -        -
> +   { dg-end-multiline-output "" } */
> +}
> 
> base-commit: a3c13696fd2e18e6e2de52b25ddfe72284335732
>