SQUASH ME: Simplified.

Author: christianparpart

libsolidity/analysis/OverrideChecker.cpp

@@ -573,7 +573,17 @@ void OverrideChecker::checkOverride(OverrideProxy const& _overriding, OverridePr
 			);
 	}
 
-	if (_super.isFunction())
+	if (_super.isModifier())
+	{
+		if (_overriding.unimplemented() && !_super.unimplemented())
+			overrideError(
+				_overriding,
+				_super,
+				4593_error,
+				"Overriding an implemented modifier with an unimplemented modifier is not allowed."
+			);
+	}
+	else if (_super.isFunction())
 	{
 		FunctionType const* functionType = _overriding.functionType();
 		FunctionType const* superType = _super.functionType();

libsolidity/analysis/PostTypeChecker.cpp

@@ -131,6 +131,16 @@ void PostTypeChecker::endVisit(ModifierInvocation const& _modifierInvocation)
 	callEndVisit(_modifierInvocation);
 }
 
+bool PostTypeChecker::visit(FunctionDefinition const& _functionDefinition)
+{
+	return callVisit(_functionDefinition);
+}
+
+void PostTypeChecker::endVisit(FunctionDefinition const& _functionDefinition)
+{
+	callEndVisit(_functionDefinition);
+}
+
 namespace
 {
 struct ConstStateVarCircularReferenceChecker: public PostTypeChecker::Checker
@@ -434,4 +444,5 @@ PostTypeChecker::PostTypeChecker(langutil::ErrorReporter& _errorReporter): m_err
 	m_checkers.push_back(make_shared<EventOutsideEmitErrorOutsideRevertChecker>(_errorReporter));
 	m_checkers.push_back(make_shared<NoVariablesInInterfaceChecker>(_errorReporter));
 	m_checkers.push_back(make_shared<ReservedErrorSelector>(_errorReporter));
+	//m_checkers.push_back(make_shared<ModifierImplementedChecker>(_errorReporter));
 }

libsolidity/analysis/PostTypeChecker.h

@@ -97,6 +97,9 @@ class PostTypeChecker: private ASTConstVisitor
 	bool visit(ModifierInvocation const& _modifierInvocation) override;
 	void endVisit(ModifierInvocation const& _modifierInvocation) override;
 
+	bool visit(FunctionDefinition const& _functionDefinition) override;
+	void endVisit(FunctionDefinition const& _functionDefinition) override;
+
 	template <class T>
 	bool callVisit(T const& _node)
 	{

libsolidity/analysis/TypeChecker.cpp

@@ -639,19 +639,6 @@ void TypeChecker::visitManually(
 						"Can only use modifiers defined in the current contract or in base contracts."
 					);
 			}
-
-		if (!modifierDecl->isImplemented())
-		{
-			SecondarySourceLocation hint;
-			hint.append("Declared here.", modifierDecl->location());
-			m_errorReporter.fatalTypeError(
-				0000_error,
-				_modifier.location(),
-				hint,
-				"Referenced modifier not implemented."
-			);
-		}
-
 	}
 	else
 		// check parameters for Base constructors

test/libsolidity/syntaxTests/modifiers/modifier_abstract_override.sol

@@ -0,0 +1,11 @@
+contract A {
+    modifier m() virtual { _; }
+}
+abstract contract B is A {
+    modifier m() virtual override;
+}
+contract C is B {
+    function f() m public {}
+}
+// ----
+// TypeError 4593: (78-108): Overriding an implemented modifier with an unimplemented modifier is not allowed.