[C++ PATCH,committed] Fix PR17344 (missing tf_error check in coerce_template_parms)

[Mark Mitchell]

Kriang Lerdsuwanakij wrote:

>
> This bug is indeed template argument deduction problem.  For the testcase
> below, we first determine if 'int bar(S)' is a viable candidate by 
> checking if 'A<int>' can be converted to 'S' via the template 
> constructor.  Here
> we can deduce 'X' to 'A' (with current GCC template template parameter
> matching) and proceed to check if 'A<void>' is valid.

Why do we check if "A<void>" is valid as part of SFINAE?  I think that 
if we deduce X = A, whatever happens after that point is just an 
ordinary error, not SFINAE.

> Do you still want me to revert the patch?
>
I don't want to create unncessary churn.  I'd like to hear from Jason 
and Nathan on this issue.

-- 
Mark Mitchell
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