From ef3595b0001614c19174c61d29d221844ed83a0e Mon Sep 17 00:00:00 2001
From: Alex Beregszaszi <alex@rtfs.hu>
Date: Tue, 27 Feb 2018 12:02:56 +0100
Subject: Allow overriding external functions in interfaces with public in an
 implementing contract

---
 libsolidity/analysis/TypeChecker.cpp | 15 +++++++++++++++
 1 file changed, 15 insertions(+)

(limited to 'libsolidity')

diff --git a/libsolidity/analysis/TypeChecker.cpp b/libsolidity/analysis/TypeChecker.cpp
index 999a2a97..487959c5 100644
--- a/libsolidity/analysis/TypeChecker.cpp
+++ b/libsolidity/analysis/TypeChecker.cpp
@@ -366,6 +366,16 @@ void TypeChecker::checkContractIllegalOverrides(ContractDefinition const& _contr
 	}
 }
 
+namespace {
+
+bool functionIsInInterface(FunctionDefinition const& _function)
+{
+	return dynamic_cast<ContractDefinition const*>(_function.scope()) &&
+		dynamic_cast<ContractDefinition const*>(_function.scope())->contractKind() == ContractDefinition::ContractKind::Interface;
+}
+
+}
+
 void TypeChecker::checkFunctionOverride(FunctionDefinition const& function, FunctionDefinition const& super)
 {
 	FunctionType functionType(function);
@@ -378,7 +388,12 @@ 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 (functionIsInInterface(super) && !functionIsInInterface(function) && function.visibility() == FunctionDefinition::Visibility::Public)
+			return;
 		overrideError(function, super, "Overriding function visibility differs.");
+	}
 
 	else if (function.stateMutability() != super.stateMutability())
 		overrideError(
-- 
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