IMO it’s high time to reconsider the default setting for this flag. This MSVC compatibility is regularly causing more issues than it solves. It most recently came up in this code review in 2021, which as I understand it did not land:
https://reviews.llvm.org/D103772
Previously it was mentioned in an issue in 2019:
https://github.com/llvm/llvm-project/issues/42377
As I understand it, flipping the default here would be inconsistent with MSVC. Some people look at this issue and say, “MSVC uses /Zc:twoPhase- by default, so clang-cl should follow MSVC”. However, Clang’s -fdelayed-template-parsing setting isn’t really the same thing as /Zc:twoPhase-, and I think if we can address the build failure from last time, users will get more value from a more C+±conforming default compiler behavior. So, I think we should go ahead and make the change anyway.