Merge pull request #3681 from ethereum/interface-external

Allow overriding external functions in interfaces with public in a child

libsolidity/analysis/TypeChecker.cpp

@@ -378,7 +378,16 @@ void TypeChecker::checkFunctionOverride(FunctionDefinition const& function, Func
 		function.annotation().superFunction = &super;
 
 	if (function.visibility() != super.visibility())
+	{
+		// visibility is enforced to be external in interfaces, but a contract can override that with public
+		if (
+			super.inContractKind() == ContractDefinition::ContractKind::Interface &&
+			function.inContractKind() != ContractDefinition::ContractKind::Interface &&
+			function.visibility() == FunctionDefinition::Visibility::Public
+		)
+			return;
 		overrideError(function, super, "Overriding function visibility differs.");
+	}
 
 	else if (function.stateMutability() != super.stateMutability())
 		overrideError(

libsolidity/ast/AST.cpp

@@ -290,6 +290,13 @@ TypeDeclarationAnnotation& EnumDefinition::annotation() const
 	return dynamic_cast<TypeDeclarationAnnotation&>(*m_annotation);
 }
 
+ContractDefinition::ContractKind FunctionDefinition::inContractKind() const
+{
+	auto contractDef = dynamic_cast<ContractDefinition const*>(scope());
+	solAssert(contractDef, "Enclosing Scope of FunctionDefinition was not set.");
+	return contractDef->contractKind();
+}
+
 shared_ptr<FunctionType> FunctionDefinition::functionType(bool _internal) const
 {
 	if (_internal)

libsolidity/ast/AST.h

@@ -624,6 +624,8 @@ public:
 	/// arguments separated by commas all enclosed in parentheses without any spaces.
 	std::string externalSignature() const;
 
+	ContractDefinition::ContractKind inContractKind() const;
+
 	virtual TypePointer type() const override;
 
 	/// @param _internal false indicates external interface is concerned, true indicates internal interface is concerned.