Provide generic access to type definition for user-defined types.

libsolidity/ast/Types.cpp

@@ -2341,6 +2341,11 @@ TypeResult StructType::interfaceType(bool _inLibrary) const
 	return *m_interfaceType_library;
 }
 
+Declaration const* StructType::typeDefinition() const
+{
+	return &structDefinition();
+}
+
 BoolResult StructType::validForLocation(DataLocation _loc) const
 {
 	for (auto const& member: m_struct.members())
@@ -2473,6 +2478,11 @@ Type const* EnumType::encodingType() const
 	return TypeProvider::uint(8);
 }
 
+Declaration const* EnumType::typeDefinition() const
+{
+	return &enumDefinition();
+}
+
 TypeResult EnumType::unaryOperatorResult(Token _operator) const
 {
 	return _operator == Token::Delete ? TypeProvider::emptyTuple() : nullptr;
@@ -2541,6 +2551,11 @@ Type const& UserDefinedValueType::underlyingType() const
 	return *type;
 }
 
+Declaration const* UserDefinedValueType::typeDefinition() const
+{
+	return &m_definition;
+}
+
 string UserDefinedValueType::richIdentifier() const
 {
 	return "t_userDefinedValueType" + parenthesizeIdentifier(m_definition.name()) + to_string(m_definition.id());