From 0f0e466d36a3e09c4c5873998b5dd32dbe8025d6 Mon Sep 17 00:00:00 2001
From: chriseth <chris@ethereum.org>
Date: Thu, 22 Nov 2018 15:04:43 +0100
Subject: [PATCH 1/2] Allow visibility change from external to public.

---
 libsolidity/analysis/TypeChecker.cpp | 15 ++++++---------
 1 file changed, 6 insertions(+), 9 deletions(-)

diff --git a/libsolidity/analysis/TypeChecker.cpp b/libsolidity/analysis/TypeChecker.cpp
index a6c23ada7..d503b9ec9 100644
--- a/libsolidity/analysis/TypeChecker.cpp
+++ b/libsolidity/analysis/TypeChecker.cpp
@@ -413,16 +413,14 @@ void TypeChecker::checkFunctionOverride(FunctionDefinition const& _function, Fun
 
 	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 &&
+		// Visibility change from external to public is fine.
+		// Any other change is disallowed.
+		if (!(
+			_super.visibility() == FunctionDefinition::Visibility::External &&
 			_function.visibility() == FunctionDefinition::Visibility::Public
-		)
-			return;
-		overrideError(_function, _super, "Overriding function visibility differs.");
+		))
+			overrideError(_function, _super, "Overriding function visibility differs.");
 	}
-
 	else if (_function.stateMutability() != _super.stateMutability())
 		overrideError(
 			_function,
@@ -433,7 +431,6 @@ void TypeChecker::checkFunctionOverride(FunctionDefinition const& _function, Fun
 			stateMutabilityToString(_function.stateMutability()) +
 			"\"."
 		);
-
 	else if (functionType != superType)
 		overrideError(_function, _super, "Overriding function return types differ.");
 }

From ac5803bf3e5dc43adf8bf64c1041603259e8a16f Mon Sep 17 00:00:00 2001
From: chriseth <chris@ethereum.org>
Date: Thu, 22 Nov 2018 17:38:12 +0100
Subject: [PATCH 2/2] Changelog entry and tests.

---
 Changelog.md                                      |  1 +
 test/libsolidity/SolidityEndToEndTest.cpp         | 15 +++++++++++++++
 .../override/external_turns_public_no_params.sol  |  7 +++++++
 .../syntaxTests/inheritance/super_on_external.sol | 10 ++++++++++
 .../nameAndTypeResolution/182_equal_overload.sol  |  1 -
 5 files changed, 33 insertions(+), 1 deletion(-)
 create mode 100644 test/libsolidity/syntaxTests/inheritance/override/external_turns_public_no_params.sol
 create mode 100644 test/libsolidity/syntaxTests/inheritance/super_on_external.sol

diff --git a/Changelog.md b/Changelog.md
index ff26882d8..e6f015537 100644
--- a/Changelog.md
+++ b/Changelog.md
@@ -1,6 +1,7 @@
 ### 0.5.1 (unreleased)
 
 Language Features:
+ * Allow public functions to override external functions.
 
 
 Compiler Features:
diff --git a/test/libsolidity/SolidityEndToEndTest.cpp b/test/libsolidity/SolidityEndToEndTest.cpp
index e591432a3..e9667483f 100644
--- a/test/libsolidity/SolidityEndToEndTest.cpp
+++ b/test/libsolidity/SolidityEndToEndTest.cpp
@@ -14062,6 +14062,21 @@ BOOST_AUTO_TEST_CASE(flipping_sign_tests)
 	ABI_CHECK(callContractFunction("f()"), encodeArgs(true));
 }
 
+BOOST_AUTO_TEST_CASE(external_public_override)
+{
+	char const* sourceCode = R"(
+		contract A {
+			function f() external returns (uint) { return 1; }
+		}
+		contract B is A {
+			function f() public returns (uint) { return 2; }
+			function g() public returns (uint) { return f(); }
+		}
+	)";
+	compileAndRun(sourceCode);
+	ABI_CHECK(callContractFunction("f()"), encodeArgs(2));
+	ABI_CHECK(callContractFunction("g()"), encodeArgs(2));
+}
 BOOST_AUTO_TEST_SUITE_END()
 
 }
diff --git a/test/libsolidity/syntaxTests/inheritance/override/external_turns_public_no_params.sol b/test/libsolidity/syntaxTests/inheritance/override/external_turns_public_no_params.sol
new file mode 100644
index 000000000..3d0394f5e
--- /dev/null
+++ b/test/libsolidity/syntaxTests/inheritance/override/external_turns_public_no_params.sol
@@ -0,0 +1,7 @@
+contract A {
+    function f() external pure {}
+}
+contract B is A {
+    function f() public pure {
+    }
+}
diff --git a/test/libsolidity/syntaxTests/inheritance/super_on_external.sol b/test/libsolidity/syntaxTests/inheritance/super_on_external.sol
new file mode 100644
index 000000000..21f3b1c2e
--- /dev/null
+++ b/test/libsolidity/syntaxTests/inheritance/super_on_external.sol
@@ -0,0 +1,10 @@
+contract A {
+    function f() external pure {}
+}
+contract B is A {
+    function f() public pure {
+        super.f();
+    }
+}
+// ----
+// TypeError: (106-113): Member "f" not found or not visible after argument-dependent lookup in contract super B.
diff --git a/test/libsolidity/syntaxTests/nameAndTypeResolution/182_equal_overload.sol b/test/libsolidity/syntaxTests/nameAndTypeResolution/182_equal_overload.sol
index cb9eb3fa8..6f0c7df79 100644
--- a/test/libsolidity/syntaxTests/nameAndTypeResolution/182_equal_overload.sol
+++ b/test/libsolidity/syntaxTests/nameAndTypeResolution/182_equal_overload.sol
@@ -4,4 +4,3 @@ contract C {
 }
 // ----
 // DeclarationError: (17-66): Function with same name and arguments defined twice.
-// TypeError: (17-66): Overriding function visibility differs.