[PATCH] c++: Fix -Wvexing-parse ICE with omitted int [PR97762]

[Jason Merrill]

On 11/9/20 11:47 AM, Marek Polacek wrote:
> For declarations like
> 
>    long f();
> 
> decl_specifiers->type will be NULL, but I neglected to handle this case,
> therefore we ICE.  So handle this case by pretending we've seen 'int',
> which is good enough for -Wvexing-parse's purposes.
> 
> Bootstrapped/regtested on x86_64-pc-linux-gnu, ok for trunk?

OK.

> gcc/cp/ChangeLog:
> 
> 	PR c++/97762
> 	* parser.c (warn_about_ambiguous_parse): Handle the case when
> 	there is no type in the decl-specifiers.
> 
> gcc/testsuite/ChangeLog:
> 
> 	PR c++/97762
> 	* g++.dg/warn/Wvexing-parse8.C: New test.
> ---
>   gcc/cp/parser.c                            | 23 ++++++++++++++++------
>   gcc/testsuite/g++.dg/warn/Wvexing-parse8.C | 11 +++++++++++
>   2 files changed, 28 insertions(+), 6 deletions(-)
>   create mode 100644 gcc/testsuite/g++.dg/warn/Wvexing-parse8.C
> 
> diff --git a/gcc/cp/parser.c b/gcc/cp/parser.c
> index bbf157eb47f..b14b4c90c92 100644
> --- a/gcc/cp/parser.c
> +++ b/gcc/cp/parser.c
> @@ -20652,13 +20652,24 @@ warn_about_ambiguous_parse (const cp_decl_specifier_seq *decl_specifiers,
>     if (declarator->parenthesized != UNKNOWN_LOCATION)
>       return;
>   
> -  tree type = decl_specifiers->type;
> -  if (TREE_CODE (type) == TYPE_DECL)
> -   type = TREE_TYPE (type);
> +  tree type;
> +  if (decl_specifiers->type)
> +    {
> +      type = decl_specifiers->type;
> +      if (TREE_CODE (type) == TYPE_DECL)
> +	type = TREE_TYPE (type);
>   
> -  /* If the return type is void there is no ambiguity.  */
> -  if (same_type_p (type, void_type_node))
> -    return;
> +      /* If the return type is void there is no ambiguity.  */
> +      if (same_type_p (type, void_type_node))
> +	return;
> +    }
> +  else
> +    {
> +      /* Code like long f(); will have null ->type.  If we have any
> +	 type-specifiers, pretend we've seen int.  */
> +      gcc_checking_assert (decl_specifiers->any_type_specifiers_p);
> +      type = integer_type_node;
> +    }
>   
>     auto_diagnostic_group d;
>     location_t loc = declarator->u.function.parens_loc;
> diff --git a/gcc/testsuite/g++.dg/warn/Wvexing-parse8.C b/gcc/testsuite/g++.dg/warn/Wvexing-parse8.C
> new file mode 100644
> index 00000000000..2d26d22fc4b
> --- /dev/null
> +++ b/gcc/testsuite/g++.dg/warn/Wvexing-parse8.C
> @@ -0,0 +1,11 @@
> +// PR c++/97762
> +// { dg-do compile }
> +
> +void
> +g ()
> +{
> +  long a(); // { dg-warning "empty parentheses" }
> +  signed b(); // { dg-warning "empty parentheses" }
> +  unsigned c(); // { dg-warning "empty parentheses" }
> +  short d(); // { dg-warning "empty parentheses" }
> +}
> 
> base-commit: 4e85ad79a137535393d8dc169359e1730cab3533
>