[clang] [Clang] Warn about `[[noreturn]]` on coroutines (PR #127623)

[via cfe-commits]

================
@@ -3910,8 +3910,13 @@ StmtResult Sema::BuildReturnStmt(SourceLocation ReturnLoc, Expr *RetValExp,
     FnRetType = FD->getReturnType();
     if (FD->hasAttrs())
       Attrs = &FD->getAttrs();
-    if (FD->isNoReturn())
-      Diag(ReturnLoc, diag::warn_noreturn_function_has_return_expr) << FD;
+    if (FD->isNoReturn()) {
+      const FunctionScopeInfo *Scope = getEnclosingFunction();
+      if (Scope && Scope->isCoroutine())
+        Diag(ReturnLoc, diag::warn_noreturn_coroutine) << FD;
+      else
+        Diag(ReturnLoc, diag::warn_noreturn_function_has_return_expr) << FD;
+    }
----------------
Sirraide wrote:

Also, looking at the AST, I think the only way for us to end up in `BuildReturnStmt` in a coroutine is for the `ReturnStmt` that the compiler implicitly generates for the call to `get_return_object()` since `return` is disallowed in coroutines; I don’t think we really care to diagnose that (because seriously, if e.g. `get_return_object()` is `noreturn`, then witw is the user trying to accomplish with that...)

https://github.com/llvm/llvm-project/pull/127623