[cxx-interop] Bail on dependent reference types. We don't know how to handle those yet.

Author: zoecarver

lib/ClangImporter/ImportType.cpp

@@ -546,6 +546,12 @@ namespace {
         return importFunctionPointerLikeType(*type, pointeeType);
       }
 
+      // Currently, we can't generate thunks for references to dependent types
+      // because there's no way to cast without a copy (without writing the SIL
+      // manually).
+      if (pointeeQualType->isDependentType())
+        return Type();
+
       if (Impl.isOverAligned(pointeeQualType)) {
         return importOverAlignedFunctionPointerLikeType(*type, Impl);
       }

test/Interop/Cxx/reference/Inputs/reference.h

@@ -16,6 +16,12 @@ void setConstStaticIntRvalueRef(const int &&);
 auto getFuncRef() -> int (&)();
 auto getFuncRvalueRef() -> int (&&)();
 
+template<class T>
+struct ClassTemplate {};
+
+template<class T>
+const ClassTemplate<T> &refToDependent() { return ClassTemplate<T>(); }
+
 // We cannot import "_Atomic" types. Make sure we fail gracefully instead of
 // crashing when we have an "_Atomic" type or a reference to one.
 void dontImportAtomicRef(_Atomic(int)&) { }

test/Interop/Cxx/reference/reference-module-interface.swift

@@ -13,4 +13,5 @@
 // CHECK: func getFuncRef() -> @convention(c) () -> Int32
 // CHECK: func getFuncRvalueRef() -> @convention(c) () -> Int32
 
+// CHECK-NOT: refToDependent
 // CHECK-NOT: dontImportAtomicRef