Start fleshing out RemoteAST's storage-offset API.

include/swift/Remote/Failure.h

@@ -318,14 +318,9 @@ template <> struct Failure::ArgTypesForFailureKind<Failure::KIND##_t> {  \
 };
 #include "swift/Remote/FailureKinds.def"
 
-template <>
-struct Failure::IsAcceptableArgType<Failure::ArgType_String, const char *> {
-  static constexpr bool value = true;
-};
-
-template <>
-struct Failure::IsAcceptableArgType<Failure::ArgType_String, std::string> {
-  static constexpr bool value = true;
+template <class T>
+struct Failure::IsAcceptableArgType<Failure::ArgType_String, T> {
+  static constexpr bool value = std::is_convertible<T, std::string>::value;
 };
 
 template <>

include/swift/Remote/FailureKinds.def

@@ -13,9 +13,16 @@
 // FAILURE(KIND, TEXT, ARGTYS)
 
 FAILURE(Unknown, "an unknown failure occurred", ())
+FAILURE(BadArgument, "the API was called with a bad argument", ())
+
 FAILURE(Memory, "an unknown failure occurred while reading %0 at address %1",
         (String, Address))
 
+FAILURE(DependentArgument,
+        "API was called with a dependent type", ())
+FAILURE(TypeHasNoSuchMember,
+        "type has no member named '%0'", (String))
+
 FAILURE(CouldNotResolveTypeDecl,
         "could not resolve a type with mangled name '%0'", (String))