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Re: [PATCH]: Fix PR c++/88095, class template argument deduction for literal operator templates per P0732 for C++2a


On 8/2/19 9:59 AM, Tom Honermann wrote:
This patch fixes PR c++/88095:
- Bug 88095 - class nontype template parameter UDL string literals doesn't accepts deduction placeholder
- https://gcc.gnu.org/bugzilla/show_bug.cgi?id=88095.

It also addresses a latent issue; literal operator templates with template parameter packs of literal class type were previously accepted.  The patch corrects this and adds a test (udlit-class-nttp-neg.C).

In the change to gcc/cp/parser.c, it is not clear to me whether the 'TREE_CODE (TREE_TYPE (parm)) == TEMPLATE_TYPE_PARM' comparison is necessary; it might be that 'CLASS_PLACEHOLDER_TEMPLATE' suffices on its own.

template_placeholder_p would be a shorter way to write these, but I think even better would be to just change CLASS_TYPE_P to MAYBE_CLASS_TYPE_P. I'll make that change and commit the patch, since it looks like you don't have commit access yet.

If accepted, I'd like to request this change be applied to gcc 9 as it is needed for one of the char8_t remediation approaches documented in P1423, and may be helpful for existing code bases impacted by the char8_t changes adopted via P0482 for C++20.
- https://wg21.link/p1423#emulate

Seems reasonable.  It may be too late to make 9.2 at this point, though.

Jason


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