[all-commits] [llvm/llvm-project] bfd643: Fix merging of two arity-only pack deductions.

[Richard Smith via All-commits]

  Branch: refs/heads/master
  Home:   https://github.com/llvm/llvm-project
  Commit: bfd643353e6b7ca7b89c0f983ff6a24c36aed276
      https://github.com/llvm/llvm-project/commit/bfd643353e6b7ca7b89c0f983ff6a24c36aed276
  Author: Richard Smith <richard at metafoo.co.uk>
  Date:   2020-07-14 (Tue, 14 Jul 2020)

  Changed paths:
    M clang/lib/Sema/SemaTemplateDeduction.cpp
    M clang/test/SemaTemplate/deduction.cpp

  Log Message:
  -----------
  Fix merging of two arity-only pack deductions.

If we deduced the arity of a pack in two different ways, but didn't
deduce an element of the pack in either of those deductions, we'd merge
that element to produce a null template argument, which we'd incorrectly
interpret as the merge having failed.

Testcase based on one supplied by Hubert Tong.