[verifier] [cxx-interop] Remove empty return result from constructors.

Set the synthesized constructor's return result to nullptr and add an ASTVerifier check that the constructor's return statement does not contain a result.

Author: zoecarver

lib/AST/ASTVerifier.cpp

@@ -988,6 +988,14 @@ class Verifier : public ASTWalker {
       }
 
       if (S->hasResult()) {
+        if (isa<ConstructorDecl>(func)) {
+          Out << "Expected ReturnStmt not to have a result. A constructor "
+                 "should not return a result. Returned expression: ";
+          S->getResult()->dump(Out);
+          Out << "\n";
+          abort();
+        }
+
         auto result = S->getResult();
         auto returnType = result->getType();
         // Make sure that the return has the same type as the function.

lib/ClangImporter/ImportDecl.cpp

@@ -502,9 +502,7 @@ synthesizeEnumRawValueConstructorBody(AbstractFunctionDecl *afd,
                                      /*implicit*/ true);
   assign->setType(TupleType::getEmpty(ctx));
 
-  auto result = TupleExpr::createEmpty(ctx, SourceLoc(), SourceLoc(),
-                                       /*Implicit=*/true);
-  auto ret = new (ctx) ReturnStmt(SourceLoc(), result, /*Implicit=*/true);
+  auto ret = new (ctx) ReturnStmt(SourceLoc(), nullptr, /*Implicit=*/true);
 
   auto body = BraceStmt::create(ctx, SourceLoc(), {assign, ret}, SourceLoc(),
                                 /*implicit*/ true);
@@ -1366,11 +1364,7 @@ synthesizeValueConstructorBody(AbstractFunctionDecl *afd, void *context) {
     }
   }
 
-  auto result = TupleExpr::createEmpty(ctx, SourceLoc(), SourceLoc(),
-                                       /*Implicit=*/true);
-  result->setType(TupleType::getEmpty(ctx));
-
-  auto ret = new (ctx) ReturnStmt(SourceLoc(), result, /*Implicit=*/true);
+  auto ret = new (ctx) ReturnStmt(SourceLoc(), nullptr, /*Implicit=*/true);
   stmts.push_back(ret);
 
   // Create the function body.
@@ -1567,9 +1561,7 @@ synthesizeRawValueBridgingConstructorBody(AbstractFunctionDecl *afd,
                                      /*Implicit=*/true);
   assign->setType(TupleType::getEmpty(ctx));
 
-  auto result = TupleExpr::createEmpty(ctx, SourceLoc(), SourceLoc(),
-                                       /*Implicit=*/true);
-  auto ret = new (ctx) ReturnStmt(SourceLoc(), result, /*Implicit=*/true);
+  auto ret = new (ctx) ReturnStmt(SourceLoc(), nullptr, /*Implicit=*/true);
 
   auto body = BraceStmt::create(ctx, SourceLoc(), {assign, ret}, SourceLoc());
   return { body, /*isTypeChecked=*/true };