5 files changed, 45 insertions, 1 deletions

diff --git a/libsolidity/analysis/ReferencesResolver.cpp b/libsolidity/analysis/ReferencesResolver.cpp
index c49af013..a0768a34 100644
--- a/libsolidity/analysis/ReferencesResolver.cpp
+++ b/libsolidity/analysis/ReferencesResolver.cpp
@@ -96,7 +96,14 @@ void ReferencesResolver::endVisit(FunctionTypeName const& _typeName)
 	}
 
 	if (_typeName.isPayable() && _typeName.visibility() != VariableDeclaration::Visibility::External)
-			fatalTypeError(_typeName.location(), "Only external function types can be payable.");
+		fatalTypeError(_typeName.location(), "Only external function types can be payable.");
+	if (_typeName.visibility() == VariableDeclaration::Visibility::External)
+		for (auto const& t: _typeName.parameterTypes() + _typeName.returnParameterTypes())
+		{
+			solAssert(t->annotation().type, "Type not set for parameter.");
+			if (!t->annotation().type->canBeUsedExternally(false))
+				fatalTypeError(t->location(), "Internal type cannot be used for external function type.");
+		}
 
 	_typeName.annotation().type = make_shared<FunctionType>(_typeName);
 }
diff --git a/libsolidity/analysis/TypeChecker.cpp b/libsolidity/analysis/TypeChecker.cpp
index f934b2c8..8b6d45e2 100644
--- a/libsolidity/analysis/TypeChecker.cpp
+++ b/libsolidity/analysis/TypeChecker.cpp
@@ -574,6 +574,14 @@ bool TypeChecker::visit(EventDefinition const& _eventDef)
 	return false;
 }
 
+void TypeChecker::endVisit(FunctionTypeName const& _funType)
+{
+	FunctionType const& fun = dynamic_cast<FunctionType const&>(*_funType.annotation().type);
+	if (fun.location() == FunctionType::Location::External)
+		if (!fun.canBeUsedExternally(false))
+			typeError(_funType.location(), "External function type uses internal types.");
+}
+
 bool TypeChecker::visit(InlineAssembly const& _inlineAssembly)
 {
 	// Inline assembly does not have its own type-checking phase, so we just run the
diff --git a/libsolidity/analysis/TypeChecker.h b/libsolidity/analysis/TypeChecker.h
index be1e02be..5874bb50 100644
--- a/libsolidity/analysis/TypeChecker.h
+++ b/libsolidity/analysis/TypeChecker.h
@@ -87,6 +87,7 @@ private:
 	/// case this is a base constructor call.
 	void visitManually(ModifierInvocation const& _modifier, std::vector<ContractDefinition const*> const& _bases);
 	virtual bool visit(EventDefinition const& _eventDef) override;
+	virtual void endVisit(FunctionTypeName const& _funType) override;
 	virtual bool visit(InlineAssembly const& _inlineAssembly) override;
 	virtual bool visit(IfStatement const& _ifStatement) override;
 	virtual bool visit(WhileStatement const& _whileStatement) override;
diff --git a/libsolidity/ast/Types.cpp b/libsolidity/ast/Types.cpp
index e18735d9..c1ae183e 100644
--- a/libsolidity/ast/Types.cpp
+++ b/libsolidity/ast/Types.cpp
@@ -1265,6 +1265,7 @@ TypePointer ArrayType::decodingType() const
 
 TypePointer ArrayType::interfaceType(bool _inLibrary) const
 {
+	// Note: This has to fulfill canBeUsedExternally(_inLibrary) ==  !!interfaceType(_inLibrary)
 	if (_inLibrary && location() == DataLocation::Storage)
 		return shared_from_this();
 
@@ -1282,6 +1283,21 @@ TypePointer ArrayType::interfaceType(bool _inLibrary) const
 		return make_shared<ArrayType>(DataLocation::Memory, baseExt, m_length);
 }
 
+bool ArrayType::canBeUsedExternally(bool _inLibrary) const
+{
+	// Note: This has to fulfill canBeUsedExternally(_inLibrary) ==  !!interfaceType(_inLibrary)
+	if (_inLibrary && location() == DataLocation::Storage)
+		return true;
+	else if (m_arrayKind != ArrayKind::Ordinary)
+		return true;
+	else if (!m_baseType->canBeUsedExternally(_inLibrary))
+		return false;
+	else if (m_baseType->category() == Category::Array && m_baseType->isDynamicallySized())
+		return false;
+	else
+		return true;
+}
+
 u256 ArrayType::memorySize() const
 {
 	solAssert(!isDynamicallySized(), "");
@@ -1815,11 +1831,19 @@ FunctionType::FunctionType(FunctionTypeName const& _typeName):
 	for (auto const& t: _typeName.parameterTypes())
 	{
 		solAssert(t->annotation().type, "Type not set for parameter.");
+		solAssert(
+			m_location != Location::External || t->annotation().type->canBeUsedExternally(false),
+			"Internal type used as parameter for external function."
+		);
 		m_parameterTypes.push_back(t->annotation().type);
 	}
 	for (auto const& t: _typeName.returnParameterTypes())
 	{
 		solAssert(t->annotation().type, "Type not set for return parameter.");
+		solAssert(
+			m_location != Location::External || t->annotation().type->canBeUsedExternally(false),
+			"Internal type used as return parameter for external function."
+		);
 		m_returnParameterTypes.push_back(t->annotation().type);
 	}
 }
diff --git a/libsolidity/ast/Types.h b/libsolidity/ast/Types.h
index 9831bc42..84e56663 100644
--- a/libsolidity/ast/Types.h
+++ b/libsolidity/ast/Types.h
@@ -254,6 +254,9 @@ public:
 	/// @param _inLibrary if set, returns types as used in a library, e.g. struct and contract types
 	/// are returned without modification.
 	virtual TypePointer interfaceType(bool /*_inLibrary*/) const { return TypePointer(); }
+	/// @returns true iff this type can be passed on via calls (to libraries if _inLibrary is true),
+	/// should be have identical to !!interfaceType(_inLibrary) but might do optimizations.
+	virtual bool canBeUsedExternally(bool _inLibrary) const { return !!interfaceType(_inLibrary); }
 
 private:
 	/// @returns a member list containing all members added to this type by `using for` directives.
@@ -580,6 +583,7 @@ public:
 	virtual TypePointer encodingType() const override;
 	virtual TypePointer decodingType() const override;
 	virtual TypePointer interfaceType(bool _inLibrary) const override;
+	virtual bool canBeUsedExternally(bool _inLibrary) const override;
 
 	/// @returns true if this is a byte array or a string
 	bool isByteArray() const { return m_arrayKind != ArrayKind::Ordinary; }