[clang] [clang-tools-extra] [clang] Implement CWG2413 (implicit `typename` in conversion operators) (PR #195207)

[Vlad Serebrennikov via cfe-commits]

https://github.com/Endilll requested changes to this pull request.

Sorry, Core issues closed by P1787R6 are not free lunch. The only thing the filing of such Core issues gives you is the scope of the issue, but not the intent of CWG nor the exact wording that addressed it. You need to dive into paper and come back with something along the lines of what I did in the description of e.g. #91765.

https://github.com/llvm/llvm-project/pull/195207