Jason Merrill <ja...@redhat.com> writes:

>> +      /* This can happen for template parms of a template template
>> +        parameter, e.g:
>> +
>> +        template<template<class T, class U> class TT> struct S;
>> +
>> +        Consider the level of the parms of TT; T and U both have
>> +        level 2; TT has no template parm of level 1. So in this case
>> +        the first element of full_template_args is NULL_TREE. If we
>> +        leave it like this TMPL_ARG_DEPTH on args returns 1 instead
>> +        of 2. This will make tsubst wrongly consider that T and U
>> +        have level 1. Instead, let's create a dummy vector as the
>> +        first element of full_template_args so that TMPL_ARG_DEPTH
>> +        returns the correct depth for args.  */
> Hmm, it seems odd that the parms wouldn't have level 1.

Finally, thinking about this a little more, this situation does not seem
completely crazy to me.


 template<class T, template<class U, T> class TT> struct S;

the parms of TT do have a level 1 that contains the parm T.  It seems to
me that we need T and U to have different levels here, so both cannot
have level 1.

>  I wonder if changing that would also avoid needing to use structural
> equality for template template parameters.

What do you mean exactly by "changing that"?  I am getting confused now.


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