[cxx-interop] Fix import virtual methods with rvalue ref params

We generate forwarding calls for virutal methods. These forwarding calls
had a type error when the original parameter had an rvalue reference
type. In those scenarios we need to insert a static cast to make the
type checker happy.

rdar://154969620

Author: Gabor Horvath

lib/ClangImporter/SwiftDeclSynthesizer.cpp

@@ -2176,11 +2176,18 @@ clang::CXXMethodDecl *SwiftDeclSynthesizer::synthesizeCXXForwardingMethod(
   for (size_t i = 0; i < newMethod->getNumParams(); ++i) {
     auto *param = newMethod->getParamDecl(i);
     auto type = param->getType();
-    if (type->isReferenceType())
-      type = type->getPointeeType();
-    args.push_back(new (clangCtx) clang::DeclRefExpr(
-        clangCtx, param, false, type, clang::ExprValueKind::VK_LValue,
-        clang::SourceLocation()));
+    clang::Expr *argExpr = new (clangCtx) clang::DeclRefExpr(
+        clangCtx, param, false, type.getNonReferenceType(),
+        clang::ExprValueKind::VK_LValue, clang::SourceLocation());
+    if (type->isRValueReferenceType()) {
+      argExpr = clangSema
+                    .BuildCXXNamedCast(
+                        clang::SourceLocation(), clang::tok::kw_static_cast,
+                        clangCtx.getTrivialTypeSourceInfo(type), argExpr,
+                        clang::SourceRange(), clang::SourceRange())
+                    .get();
+    }
+    args.push_back(argExpr);
   }
   auto memberCall = clangSema.BuildCallExpr(
       nullptr, memberExpr, clang::SourceLocation(), args,

test/Interop/Cxx/reference/Inputs/module.modulemap

@@ -24,3 +24,8 @@ module ConstRefCxxObjCCtorInitParameter {
   requires objc
   requires cplusplus
 }
+
+module VirtMethodWithRvalRef {
+  header "virtual-methods-with-rvalue-reference.h"
+  requires cplusplus
+}

test/Interop/Cxx/reference/Inputs/virtual-methods-with-rvalue-reference.h

@@ -0,0 +1,21 @@
+#pragma once
+
+#include "swift/bridging"
+
+class CxxForeignRef;
+
+void retain(CxxForeignRef * obj);
+void release(CxxForeignRef * obj);
+
+struct NonTrivial {
+    ~NonTrivial();
+};
+
+class CxxForeignRef {
+public:
+    CxxForeignRef(const CxxForeignRef &) = delete;
+    CxxForeignRef() = default;
+    
+    virtual void takesRValRef(NonTrivial&&);
+} SWIFT_SHARED_REFERENCE(retain, release);
+

test/Interop/Cxx/reference/reference-in-virtual-methods.swift

@@ -0,0 +1,7 @@
+// RUN: %target-swift-frontend -typecheck -verify -I %S/Inputs -I %swift_src_root/lib/ClangImporter/SwiftBridging %s -cxx-interoperability-mode=default -disable-availability-checking
+
+import VirtMethodWithRvalRef
+
+func f(_ x: CxxForeignRef, _ y: NonTrivial) {
+    x.takesRValRef(consuming: y)
+}