[clang] [Clang] Propagate elide safe context through [[clang::coro_must_await]] (PR #108474)

[Adrian Vogelsgesang via cfe-commits]

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@@ -249,7 +249,10 @@ Attribute Changes in Clang
   (#GH106864)
 
 - Introduced a new attribute ``[[clang::coro_await_elidable]]`` on coroutine return types
-  to express elideability at call sites where the coroutine is co_awaited as a prvalue.
+  to express elideability at call sites where the coroutine is invoked under a safe elide context.
+
+- Introduced a new attribute ``[[clang::coro_must_await]]`` on function parameters to
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vogelsgesang wrote:

What do you think about `[[clang::coro_await_elideable_argument]]`? I would slightly prefer this over `[[clang::coro_elideable_await_argument]]` because it is more similar to its sibling argument `[[clang::coro_await_elideable]]`, and the duality between the two arguments becomes more obvious already from their names.

I think we should particularly try to avoid any name with `must` in its name. To me, `must` expresses a guarantee given by the compiler to the programmer (such as for the `[[musttail]]` attribute which will fail compilation in case the call cannot be tail-called), enforced by the compiler. However, this attribute behaves the other way around: It expresses a guarantee given by the programmer to the compiler, the compiler does nothing to check or enforce the correctness of it.

https://github.com/llvm/llvm-project/pull/108474