[Diagnostics] Don't crash when gathering info about property wrapper in l-value base

Make `TypeBase::getTypeOfMember` more resilient to base type
being either an l-value (which we can look through), or an
error type - in such can it would return immediately.

Resolves: rdar://problem/54184846

Author: xedin

lib/AST/Type.cpp

@@ -3583,6 +3583,14 @@ SubstitutionMap TypeBase::getMemberSubstitutionMap(
 
 Type TypeBase::getTypeOfMember(ModuleDecl *module, const ValueDecl *member,
                                Type memberType) {
+  if (is<ErrorType>())
+    return ErrorType::get(getASTContext());
+
+  if (auto *lvalue = getAs<LValueType>()) {
+    auto objectTy = lvalue->getObjectType();
+    return objectTy->getTypeOfMember(module, member, memberType);
+  }
+
   // If no member type was provided, use the member's type.
   if (!memberType)
     memberType = member->getInterfaceType();

test/decl/var/property_wrappers.swift

@@ -1504,3 +1504,18 @@ struct AllCompositionsStruct {
   }
 }
 
+// rdar://problem/54184846 - crash while trying to retrieve wrapper info on l-value base type
+func test_missing_method_with_lvalue_base() {
+  @propertyWrapper
+  struct Ref<T> {
+    var wrappedValue: T
+  }
+
+  struct S<T> where T: RandomAccessCollection, T.Element: Equatable {
+    @Ref var v: T.Element
+
+    init(items: T, v: Ref<T.Element>) {
+      self.v.binding = v // expected-error {{value of type 'T.Element' has no member 'binding'}}
+    }
+  }
+}