tree 66097cf550c42b76cfecc894d98a4c5343f5aeb9
parent 478bb094b5ac1e164b1ff06034f57fadefdbbb20
author Eric Fiselier <eric@efcs.ca> 1563128475 +0000
committer Eric Fiselier <eric@efcs.ca> 1563128475 +0000

Avoid eager template instantiation caused by the variant narrowing checks.

The standard disallows narrowing conversions when constructing a variant.
This is checked by attempting to perform braced initialization of the
destination type from the argument type. However, braced initialization
can force the compiler (mostly clang) to eagerly instantiate the
constructors of the destintation type -- which can lead to errors in
a non-immediate context.

However, as variant is currently specified, the narrowing checks only
observably apply when the destination type is arithmetic. Meaning we can
skip the check for class types. Hense avoiding the hard errors.

In order to cause fewer build breakages, this patch avoids the narrowing
check except when the destination type is arithmetic.

git-svn-id: https://llvm.org/svn/llvm-project/libcxx/trunk@366022 91177308-0d34-0410-b5e6-96231b3b80d8