[coroutines] Fix fallthrough diagnostics for coroutines

Summary:
This patch fixes a number of issues with the analysis warnings emitted when a coroutine may reach the end of the function w/o returning.

* Fix bug where coroutines with `return_value` are incorrectly diagnosed as missing `co_return`'s.
* Rework diagnostic message to no longer say "non-void coroutine", because that implies the coroutine doesn't have a void return type, which it might. In this case a non-void coroutine is one who's promise type does not contain `return_void()`

As a side-effect of this patch, coroutine bodies that contain an invalid coroutine promise objects are marked as invalid.

Reviewers: GorNishanov, rsmith, aaron.ballman, majnemer

Reviewed By: GorNishanov

Subscribers: cfe-commits

Differential Revision: https://reviews.llvm.org/D33532

llvm-svn: 303831

1 files changed, 5 insertions, 2 deletions

diff --git a/clang/lib/Sema/SemaCoroutine.cpp b/clang/lib/Sema/SemaCoroutine.cpp
index 8f7011c985e..45b3a48d158 100644
--- a/clang/lib/Sema/SemaCoroutine.cpp
+++ b/clang/lib/Sema/SemaCoroutine.cpp
@@ -719,13 +719,16 @@ static FunctionDecl *findDeleteForPromise(Sema &S, SourceLocation Loc,
 
 void Sema::CheckCompletedCoroutineBody(FunctionDecl *FD, Stmt *&Body) {
   FunctionScopeInfo *Fn = getCurFunction();
-  assert(Fn && Fn->CoroutinePromise && "not a coroutine");
-
+  assert(Fn && Fn->isCoroutine() && "not a coroutine");
   if (!Body) {
     assert(FD->isInvalidDecl() &&
            "a null body is only allowed for invalid declarations");
     return;
   }
+  // We have a function that uses coroutine keywords, but we failed to build
+  // the promise type.
+  if (!Fn->CoroutinePromise)
+    return FD->setInvalidDecl();
 
   if (isa<CoroutineBodyStmt>(Body)) {
     // Nothing todo. the body is already a transformed coroutine body statement.