Force interface functions as external (0.5.0)

Changelog.md

@@ -9,6 +9,7 @@ Features:
  * Syntax Checker: Unary ``+`` is now a syntax error as experimental 0.5.0 feature.
  * Type Checker: Disallow non-pure constant state variables as experimental 0.5.0 feature.
  * Type Checker: Do not add members of ``address`` to contracts as experimental 0.5.0 feature.
+ * Type Checker: Force interface functions to be external as experimental 0.5.0 feature.
  * Type Checker: Require ``storage`` or ``memory`` keyword for local variables as experimental 0.5.0 feature.
 
 Bugfixes:

libsolidity/analysis/TypeChecker.cpp

@@ -595,8 +595,16 @@ bool TypeChecker::visit(FunctionDefinition const& _function)
 	{
 		if (_function.isImplemented())
 			m_errorReporter.typeError(_function.location(), "Functions in interfaces cannot have an implementation.");
-		if (_function.visibility() < FunctionDefinition::Visibility::Public)
-			m_errorReporter.typeError(_function.location(), "Functions in interfaces cannot be internal or private.");
+		if (_function.sourceUnit().annotation().experimentalFeatures.count(ExperimentalFeature::V050))
+		{
+			if (_function.visibility() != FunctionDefinition::Visibility::External)
+				m_errorReporter.typeError(_function.location(), "Functions in interfaces must be declared external.");
+		}
+		else
+		{
+			if (_function.visibility() < FunctionDefinition::Visibility::Public)
+				m_errorReporter.typeError(_function.location(), "Functions in interfaces cannot be internal or private.");
+		}
 		if (_function.isConstructor())
 			m_errorReporter.typeError(_function.location(), "Constructor cannot be defined in interfaces.");
 	}

test/libsolidity/SolidityNameAndTypeResolution.cpp

@@ -5879,6 +5879,28 @@ BOOST_AUTO_TEST_CASE(interface_function_bodies)
 	CHECK_ERROR(text, TypeError, "Functions in interfaces cannot have an implementation");
 }
 
+BOOST_AUTO_TEST_CASE(interface_function_external)
+{
+	char const* text = R"(
+		pragma experimental "v0.5.0";
+		interface I {
+			function f() external;
+		}
+	)";
+	success(text);
+}
+
+BOOST_AUTO_TEST_CASE(interface_function_public)
+{
+	char const* text = R"(
+		pragma experimental "v0.5.0";
+		interface I {
+			function f() public;
+		}
+	)";
+	CHECK_ERROR(text, TypeError, "Functions in interfaces must be declared external.");
+}
+
 BOOST_AUTO_TEST_CASE(interface_function_internal)
 {
 	char const* text = R"(