[interop] add more specific diagnostic when rvalue reference parameter isn't imported

Author: hyp

include/swift/AST/DiagnosticsClangImporter.def

@@ -156,6 +156,7 @@ NOTE(macro_not_imported, none, "macro '%0' unavailable (cannot import)", (String
 
 NOTE(return_type_not_imported, none, "return type unavailable (cannot import)", ())
 NOTE(parameter_type_not_imported, none, "parameter %0 unavailable (cannot import)", (const clang::NamedDecl*))
+NOTE(rvalue_ref_params_not_imported, none, "C++ functions with rvalue reference parameters are unavailable in Swift", ())
 NOTE(incomplete_interface, none, "interface %0 is incomplete", (const clang::NamedDecl*))
 NOTE(incomplete_protocol, none, "protocol %0 is incomplete", (const clang::NamedDecl*))
 NOTE(incomplete_record, none, "record '%0' is not defined (incomplete)", (StringRef))

lib/ClangImporter/ImportType.cpp

@@ -2362,7 +2362,7 @@ ClangImporter::Implementation::importParameterType(
 
       // We don't support rvalue reference types, just bail.
       if (paramTy->isRValueReferenceType()) {
-        // FIXME: add import diagnostic.
+        addImportDiagnosticFn(Diagnostic(diag::rvalue_ref_params_not_imported));
         return None;
       }
 

test/Interop/Cxx/reference/reference-cannot-import-diagnostic.swift

@@ -0,0 +1,24 @@
+// RUN: rm -rf %t
+// RUN: split-file %s %t
+// RUN: not %target-swift-frontend -typecheck -I %t/Inputs  %t/test.swift  -enable-experimental-cxx-interop 2>&1 | %FileCheck %s
+
+//--- Inputs/module.modulemap
+module Test {
+    header "test.h"
+    requires cplusplus
+}
+
+//--- Inputs/test.h
+
+void acceptRValueRef(int &&);
+
+//--- test.swift
+
+import Test
+
+public func test() {
+  var x: CInt = 2
+  acceptRValueRef(x)
+  // CHECK: note: function 'acceptRValueRef' unavailable (cannot import)
+  // CHECK: note: C++ functions with rvalue reference parameters are unavailable in Swift
+}