Defaults to external visibility for interfaces.

libsolidity/analysis/StaticAnalyzer.cpp

@@ -50,6 +50,14 @@ void StaticAnalyzer::endVisit(ContractDefinition const&)
 
 bool StaticAnalyzer::visit(FunctionDefinition const& _function)
 {
+	const bool isInterface = m_currentContract->contractKind() == ContractDefinition::ContractKind::Interface;
+	if (_function.noVisibilitySpecified())
+		m_errorReporter.warning(
+			_function.location(),
+			"No visibility specified. Defaulting to \"" +
+			(isInterface ? "external" : Declaration::visibilityToString(_function.visibility())) +
+			"\"."
+		);
 	if (_function.isImplemented())
 		m_currentFunction = &_function;
 	else

libsolidity/analysis/SyntaxChecker.cpp

@@ -214,18 +214,9 @@ bool SyntaxChecker::visit(FunctionDefinition const& _function)
 {
 	bool const v050 = m_sourceUnit->annotation().experimentalFeatures.count(ExperimentalFeature::V050);
 
-	if (_function.noVisibilitySpecified())
-	{
-		if (v050)
-			m_errorReporter.syntaxError(_function.location(), "No visibility specified.");
-		else
-			m_errorReporter.warning(
-				_function.location(),
-				"No visibility specified. Defaulting to \"" +
-				Declaration::visibilityToString(_function.visibility()) +
-				"\"."
-			);
-	}
+	if (v050 && _function.noVisibilitySpecified())
+		m_errorReporter.syntaxError(_function.location(), "No visibility specified.");
+			
 	return true;
 }
 

test/libsolidity/syntaxTests/visibility/interface/function_default.sol

@@ -0,0 +1,6 @@
+interface I {
+	function f();
+}
+// ----
+// Warning: Functions in interfaces should be declared external.
+// Warning: No visibility specified. Defaulting to "external".

test/libsolidity/syntaxTests/visibility/interface/function_default050.sol

@@ -0,0 +1,7 @@
+pragma experimental "v0.5.0";
+interface I {
+	function f();
+}
+// ----
+// SyntaxError: No visibility specified.
+// TypeError: Functions in interfaces must be declared external.