[llvm-bugs] [Bug 49109] New: clang incorrectly requires coroutine_handle::from_address to be noexcept

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https://bugs.llvm.org/show_bug.cgi?id=49109

            Bug ID: 49109
           Summary: clang incorrectly requires
                    coroutine_handle::from_address to be noexcept
           Product: clang
           Version: 10.0
          Hardware: PC
                OS: Windows NT
            Status: NEW
          Severity: enhancement
          Priority: P
         Component: C++2a
          Assignee: unassignedclangbugs at nondot.org
          Reporter: redbeard0531 at gmail.com
                CC: blitzrakete at gmail.com, erik.pilkington at gmail.com,
                    llvm-bugs at lists.llvm.org, richard-llvm at metafoo.co.uk

from_address() is not required to be noexcept:
https://eel.is/c++draft/coroutine.handle

However clang will error with a line pointing to (the end of)
coroutine_handle<_Promise>::from_address(), presumably because it is checking
for noexcept as per https://eel.is/c++draft/dcl.fct.def.coroutine#15 after
generating that call as part of its internal lowering. This feels like a
leaking of an implementation detail. In practice, it causes issues when trying
to use libstdc++'s <coroutine> because it doesn't mark that method as noexcept.
I've filed a bug (https://gcc.gnu.org/bugzilla/show_bug.cgi?id=99021) with them
asking to change it, but it would be nice if clang didn't require the noexcept,
both because it isn't required by the standard, and because it will make it
easier to use clang with the already-in-the-wild libstdc++-10 installs.

src/mongo/db/index/columns_index_access_method.cpp:328:28: error: the
expression 'co_await __promise.final_suspend()' is required to be non-throwing
    generator<BSONElement> subcellElements() const {
                           ^
/bin/../lib64/gcc/x86_64-pc-linux-gnu/10.2.0/../../../../include/c++/10.2.0/coroutine:205:5:
note: must be declared with 'noexcept'
    }

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