enforce interface-functions to be external-declared

- libsolidity: Enforce interface-functions must be external-declared.
- Changelog adapted to reflect changes wrt. functions in interfaces.
- test: Adjustments according to prior interface-function changes.
- tests: Adapting SolidityEndToEndTest to interface-function change.
- docs: Adapted documentation to interface-function change.

Changelog.md

@@ -44,6 +44,7 @@ Breaking Changes:
  * Type Checker: Disallow uninitialized storage variables. This was already the case in the experimental 0.5.0 mode.
  * Type Checker: Only accept a single ``bytes`` type for ``.call()`` (and family), ``keccak256()``, ``sha256()`` and ``ripemd160()``.
  * Type Checker: Fallback function must be external. This was already the case in the experimental 0.5.0 mode.
+ * Type Checker: Interface functions must be declared external. This was already the case in the experimental 0.5.0 mode.
  * Remove obsolete ``std`` directory from the Solidity repository. This means accessing ``https://github.com/ethereum/soldity/blob/develop/std/*.sol`` (or ``https://github.com/ethereum/solidity/std/*.sol`` in Remix) will not be possible.
  * References Resolver: Turn missing storage locations into an error. This was already the case in the experimental 0.5.0 mode.
  * Syntax Checker: Named return values in function types are an error.

docs/contracts.rst

@@ -1150,6 +1150,7 @@ Interfaces
 Interfaces are similar to abstract contracts, but they cannot have any functions implemented. There are further restrictions:
 
 - Cannot inherit other contracts or interfaces.
+- All declared functions must be external.
 - Cannot define constructor.
 - Cannot define variables.
 - Cannot define structs.
@@ -1167,7 +1168,7 @@ Interfaces are denoted by their own keyword:
     pragma solidity ^0.4.11;
 
     interface Token {
-        function transfer(address recipient, uint amount) public;
+        function transfer(address recipient, uint amount) external;
     }
 
 Contracts can inherit interfaces as they would inherit other contracts.

docs/security-considerations.rst

@@ -203,7 +203,7 @@ Now someone tricks you into sending ether to the address of this attack wallet:
     pragma solidity >0.4.24;
 
     interface TxUserWallet {
-        function transferTo(address dest, uint amount) public;
+        function transferTo(address dest, uint amount) external;
     }
 
     contract TxAttackWallet {

libsolidity/analysis/TypeChecker.cpp

@@ -671,18 +671,10 @@ bool TypeChecker::visit(FunctionDefinition const& _function)
 	{
 		if (_function.isImplemented())
 			m_errorReporter.typeError(_function.location(), "Functions in interfaces cannot have an implementation.");
-		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.");
-			else if (_function.visibility() != FunctionDefinition::Visibility::External)
-				m_errorReporter.warning(_function.location(), "Functions in interfaces should be declared external.");
-		}
+
+		if (_function.visibility() != FunctionDefinition::Visibility::External)
+			m_errorReporter.typeError(_function.location(), "Functions in interfaces must be declared external.");
+
 		if (_function.isConstructor())
 			m_errorReporter.typeError(_function.location(), "Constructor cannot be defined in interfaces.");
 	}

test/libsolidity/SolidityEndToEndTest.cpp

@@ -11649,7 +11649,7 @@ BOOST_AUTO_TEST_CASE(interface_contract)
 	char const* sourceCode = R"(
 		interface I {
 			event A();
-			function f() public returns (bool);
+			function f() external returns (bool);
 			function() external payable;
 		}
 

test/libsolidity/syntaxTests/constructor/interface_constructor_new.sol

@@ -2,6 +2,6 @@ interface I {
 	constructor() public;
 }
 // ----
-// Warning: (15-36): Functions in interfaces should be declared external.
+// TypeError: (15-36): Functions in interfaces must be declared external.
 // TypeError: (15-36): Constructor cannot be defined in interfaces.
 // TypeError: (15-36): Constructor must be implemented if declared.

test/libsolidity/syntaxTests/constructor/interface_constructor_old.sol

@@ -3,6 +3,6 @@ interface I {
 }
 // ----
 // Warning: (15-35): Defining constructors as functions with the same name as the contract is deprecated. Use "constructor(...) { ... }" instead.
-// Warning: (15-35): Functions in interfaces should be declared external.
+// TypeError: (15-35): Functions in interfaces must be declared external.
 // TypeError: (15-35): Constructor cannot be defined in interfaces.
 // TypeError: (15-35): Constructor must be implemented if declared.

test/libsolidity/syntaxTests/nameAndTypeResolution/416_interface_function_bodies.sol

@@ -1,7 +1,6 @@
 interface I {
-    function f() public {
+    function f() external pure {
     }
 }
 // ----
-// TypeError: (18-45): Functions in interfaces cannot have an implementation.
-// Warning: (18-45): Functions in interfaces should be declared external.
+// TypeError: (18-52): Functions in interfaces cannot have an implementation.

test/libsolidity/syntaxTests/nameAndTypeResolution/421_interface_function_parameters.sol

@@ -1,5 +1,4 @@
 interface I {
-    function f(uint a) public returns (bool);
+    function f(uint a) external returns (bool);
 }
 // ----
-// Warning: (18-59): Functions in interfaces should be declared external.

test/libsolidity/syntaxTests/parsing/interface_basic.sol

@@ -1,5 +1,4 @@
 interface Interface {
-	function f() public;
+	function f() external;
 }
 // ----
-// Warning: (23-43): Functions in interfaces should be declared external.

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

@@ -2,5 +2,4 @@ interface I {
 	function f();
 }
 // ----
-// Warning: (15-28): Functions in interfaces should be declared external.
-// Warning: (15-28): No visibility specified. Defaulting to "public". In interfaces it defaults to external.
+// TypeError: (15-28): Functions in interfaces must be declared external.

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

@@ -2,4 +2,4 @@ interface I {
 	function f() internal;
 }
 // ----
-// TypeError: (15-37): Functions in interfaces cannot be internal or private.
+// TypeError: (15-37): Functions in interfaces must be declared external.

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

@@ -2,4 +2,4 @@ interface I {
 	function f() private;
 }
 // ----
-// TypeError: (15-36): Functions in interfaces cannot be internal or private.
+// TypeError: (15-36): Functions in interfaces must be declared external.

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

@@ -2,4 +2,4 @@ interface I {
 	function f() public;
 }
 // ----
-// Warning: (15-35): Functions in interfaces should be declared external.
+// TypeError: (15-35): Functions in interfaces must be declared external.