================
@@ -8281,8 +8288,62 @@ Example:
co_await t;
}
-The behavior is undefined if the caller coroutine is destroyed earlier than the
-callee coroutine.
+Such elision replaces the heap allocated activation frame of the callee
coroutine
+with a local variable within the enclosing braces in the caller's stack frame.
+The local variable, like other variables in coroutines, may be collected into
the
+coroutine frame, which may be allocated on the heap. The behavior is undefined
+if the caller coroutine is destroyed earlier than the callee coroutine.
+
+}];
+}
+
+def CoroMustAwaitDoc : Documentation {
+ let Category = DocCatDecl;
+ let Content = [{
+
+The ``[[clang::coro_must_await]]`` is a function parameter attribute. It works
+in conjunction with ``[[clang::coro_await_elidable]]`` to propagate a safe
elide
+context to a parameter or parameter pack if the function is called under a safe
+elide context.
+
+This is sometimes necessary on utility functions whose role is to compose or
+modify the behavior of a callee coroutine.
+
+Example:
+
+.. code-block:: c++
+
+ template <typename T>
+ class [[clang::coro_await_elidable]] Task { ... };
+
+ template <typename... T>
+ class [[clang::coro_await_elidable]] WhenAll { ... };
+
+ // `when_all` is a utility function that compose coroutines. It does not need
+ // to be a coroutine to propagate.
+ template <typename... T>
+ WhenAll<T...> when_all([[clang::coro_must_await]] Task<T> tasks...);
+
+ Task<int> foo();
+ Task<int> bar();
+ Task<void> example1() {
+ // `when_all``, `foo``, and `bar` are all elide safe because `when_all` is
+ // under a safe elide context and propagated such contexts to foo and bar.
----------------
vogelsgesang wrote:
```suggestion
// under a safe elide context and, thanks to the [[coro_must_await]]
attribute,
// this context is propagated to foo and bar.
```
https://github.com/llvm/llvm-project/pull/108474
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