Allow enums in interfaces

Changelog.md

@@ -69,6 +69,7 @@ Language Features:
  * General: Allow appending ``calldata`` keyword to types, to explicitly specify data location for arguments of external functions.
  * General: Support ``pop()`` for storage arrays.
  * General: Scoping rules now follow the C99-style.
+ * General: Allow ``enum``s in interfaces.
 
 Compiler Features:
  * C API (``libsolc``): Export the ``solidity_license``, ``solidity_version`` and ``solidity_compile`` methods.

libsolidity/analysis/TypeChecker.cpp

@@ -751,13 +751,6 @@ bool TypeChecker::visit(VariableDeclaration const& _variable)
 	return false;
 }
 
-bool TypeChecker::visit(EnumDefinition const& _enum)
-{
-	if (m_scope->contractKind() == ContractDefinition::ContractKind::Interface)
-		m_errorReporter.typeError(_enum.location(), "Enumerable cannot be declared in interfaces.");
-	return false;
-}
-
 void TypeChecker::visitManually(
 	ModifierInvocation const& _modifier,
 	vector<ContractDefinition const*> const& _bases

libsolidity/analysis/TypeChecker.h

@@ -96,7 +96,6 @@ private:
 	virtual bool visit(StructDefinition const& _struct) override;
 	virtual bool visit(FunctionDefinition const& _function) override;
 	virtual bool visit(VariableDeclaration const& _variable) override;
-	virtual bool visit(EnumDefinition const& _enum) override;
 	/// We need to do this manually because we want to pass the bases of the current contract in
 	/// case this is a base constructor call.
 	void visitManually(ModifierInvocation const& _modifier, std::vector<ContractDefinition const*> const& _bases);

test/libsolidity/syntaxTests/nameAndTypeResolution/422_interface_enums.sol

@@ -2,4 +2,3 @@ interface I {
     enum A { B, C }
 }
 // ----
-// TypeError: (18-33): Enumerable cannot be declared in interfaces.