Template deduction succeeds despite qualifier mismatch

[zygoloid]

Bugzilla Link	9233
Resolution	FIXED
Resolved on	Jun 17, 2011 00:32
Version	trunk
OS	Linux
CC	@DougGregor

Extended Description

In this code:

template void f(const T **q);

int main() {
int **p;
f(p);
}

clang deduces T = int, then decides the function is not viable because of the qualifier mismatch. This causes the wrong diagnostic to be issued. [temp.deduct.call]p4, which allows this sort of qualifier mismatch in other cases, says:

"The transformed A can be another pointer or pointer to member type that can be converted to the deduced A via a qualification conversion (4.4)."

But "T **" can't be converted to "const T **" via a qualification conversion.

I noticed this while testing:

int **p;
const auto **q = p;

which also gives the wrong diagnostic, for the same reason.

[DougGregor]

We have a nice big FIXME in DeduceTemplateArguments for this:

  // FIXME: we need to check that the deduced A is the same as A,
  // modulo the various allowed differences.

[DougGregor]

Fixed in Clang r133163.

[zygoloid]

Sadly, we still give the wrong diagnostic for the auto case:

:1:23: error: cannot initialize a variable of type 'const int **' with an lvalue of type 'int **'
int **p; const auto **q = p;
^ ~

[DougGregor]

Fixed this last part in Clang r133239.