[C++ Patch] PR 84588 ("[8 Regression] internal compiler error: Segmentation fault (contains_struct_check())")

[Paolo Carlini]

Hi,

On 08/05/2018 19:15, Jason Merrill wrote:
> On Fri, Apr 20, 2018 at 1:46 PM, Paolo Carlini <paolo.carlini@oracle.com> wrote:
>> Hi,
>>
>> in this error-recovery regression, after sensible diagnostic about "two or
>> more data types in declaration..." we get confused, we issue a cryptic -
>> but useful hint to somebody working on the present bug ;) - "template
>> definition of non-template" error and we finally crash. I think the issue
>> here is that we want to use abort_fully_implicit_template as part of the
>> error recovery done by cp_parser_parameter_declaration_list, when the loop
>> is exited early after a cp_parser_parameter_declaration internally called
>> synthesize_implicit_template_parm. Indeed, if we do that we get the same
>> error recovery behavior we get for the same testcase modified to not use an
>> auto parameter (likewise for related testcases):
>>
>> struct a {
>>    void b() {}
>>     void c(auto = [] {
>>      if (a a(int int){})
>>        ;
>>    }) {}
>> };
> Hmm, the erroneous declaration is within the lambda body, so messing
> with whether c is a template seems wrong.
I'm sorry, I don't follow: why you think the issue has to do with c? The 
issue happens while we are parsing:

 Â Â Â  a a(int auto)

in the original testcase, in particular the parameters. We set 
parser->fully_implicit_function_template_p in 
synthesize_implicit_template_parm, which in turn is called by 
cp_parser_simple_type_specifier when it sees the auto. As I said, we 
don't have the bug for the snippet you quote above, which is identical 
to that attached in the bug but for the auto in the declaration of a:

struct a {
 Â  void b() {}
 Â  void c(void (*) () = [] {
 Â Â Â Â Â  if (a a(int auto){})
 Â Â Â Â Â  ;
 Â  }) {}
};

Paolo.