Disallow constructor in interfaces

docs/contracts.rst

@@ -931,6 +931,7 @@ Interfaces
 Interfaces are similar to abstract contracts, but they cannot have any functions implemented. There are further restrictions:
 
 #. Cannot inherit other contracts or interfaces.
+#. Cannot define constructor.
 #. Cannot define variables.
 #. Cannot define structs.
 #. Cannot define enums.

libsolidity/analysis/TypeChecker.cpp

@@ -463,6 +463,9 @@ bool TypeChecker::visit(FunctionDefinition const& _function)
 			typeError(_function.location(), "Functions in interfaces cannot have an implementation.");
 		_function.body().accept(*this);
 	}
+	if (_function.isConstructor())
+		if (m_scope->contractKind() == ContractDefinition::ContractKind::Interface)
+			typeError(_function.location(), "Constructor cannot be defined in interfaces.");
 	return false;
 }
 

test/libsolidity/SolidityNameAndTypeResolution.cpp

@@ -5343,7 +5343,7 @@ BOOST_AUTO_TEST_CASE(interface_constructor)
 			function I();
 		}
 	)";
-	success(text);
+	CHECK_ERROR(text, TypeError, "Constructor cannot be defined in interfaces");
 }
 
 BOOST_AUTO_TEST_CASE(interface_functions)