Add type error when attempting value transfer to a non-payable contract

Changelog.md

@@ -2,6 +2,7 @@
 
 Features:
  * Inline Assembly: Show useful error message if trying to access calldata variables.
+ * Type Checker: Disallow value transfers to contracts without a payable fallback function
 
 Bugfixes:
  * Type Checker: Fix invalid "specify storage keyword" warning for reference members of structs.

libsolidity/analysis/TypeChecker.cpp

@@ -1631,6 +1631,25 @@ bool TypeChecker::visit(MemberAccess const& _memberAccess)
 			annotation.isLValue = annotation.referencedDeclaration->isLValue();
 	}
 
+	if (exprType->category() == Type::Category::Contract)
+	{
+		if (auto callType = dynamic_cast<FunctionType const*>(type(_memberAccess).get()))
+		{
+			auto kind = callType->kind();
+			auto contractType = dynamic_cast<ContractType const*>(exprType.get());
+			solAssert(!!contractType, "Should be contract type.");
+
+			if (
+				(kind == FunctionType::Kind::Send || kind == FunctionType::Kind::Transfer) &&
+				!contractType->isPayable()
+			)
+				m_errorReporter.typeError(
+					_memberAccess.location(),
+					"Value transfer to a contract without a payable fallback function."
+				);
+		}
+	}
+
 	// TODO some members might be pure, but for example `address(0x123).balance` is not pure
 	// although every subexpression is, so leaving this limited for now.
 	if (auto tt = dynamic_cast<TypeType const*>(exprType.get()))

libsolidity/ast/Types.cpp

@@ -1230,6 +1230,12 @@ bool ContractType::isExplicitlyConvertibleTo(Type const& _convertTo) const
 		_convertTo.category() == Category::Contract;
 }
 
+bool ContractType::isPayable() const
+{
+	auto fallbackFunction = m_contract.fallbackFunction();
+	return fallbackFunction && fallbackFunction->isPayable();
+}
+
 TypePointer ContractType::unaryOperatorResult(Token::Value _operator) const
 {
 	return _operator == Token::Delete ? make_shared<TupleType>() : TypePointer();

libsolidity/ast/Types.h

@@ -675,6 +675,10 @@ public:
 	}
 
 	bool isSuper() const { return m_super; }
+
+	// @returns true if and only if the contract has a payable fallback function
+	bool isPayable() const;
+
 	ContractDefinition const& contractDefinition() const { return m_contract; }
 
 	/// Returns the function type of the constructor modified to return an object of the contract's type.

test/libsolidity/SolidityNameAndTypeResolution.cpp

@@ -6146,6 +6146,76 @@ BOOST_AUTO_TEST_CASE(callable_crash)
 	CHECK_ERROR(text, TypeError, "Type is not callable");
 }
 
+BOOST_AUTO_TEST_CASE(error_transfer_non_payable_fallback)
+{
+	char const* text = R"(
+		contract A {
+			function() {}
+		}
+
+		contract B {
+			A a;
+
+			function() {
+				a.transfer(100);
+			}
+		}
+	)";
+	CHECK_ERROR(text, TypeError, "Value transfer to a contract without a payable fallback function.");
+}
+
+BOOST_AUTO_TEST_CASE(error_transfer_no_fallback)
+{
+	char const* text = R"(
+		contract A {}
+
+		contract B {
+			A a;
+
+			function() {
+				a.transfer(100);
+			}
+		}
+	)";
+	CHECK_ERROR(text, TypeError, "Value transfer to a contract without a payable fallback function.");
+}
+
+BOOST_AUTO_TEST_CASE(error_send_non_payable_fallback)
+{
+	char const* text = R"(
+		contract A {
+			function() {}
+		}
+
+		contract B {
+			A a;
+
+			function() {
+				require(a.send(100));
+			}
+		}
+	)";
+	CHECK_ERROR(text, TypeError, "Value transfer to a contract without a payable fallback function.");
+}
+
+BOOST_AUTO_TEST_CASE(does_not_error_transfer_payable_fallback)
+{
+	char const* text = R"(
+		contract A {
+			function() payable {}
+		}
+
+		contract B {
+			A a;
+
+			function() {
+				a.transfer(100);
+			}
+		}
+	)";
+	CHECK_SUCCESS_NO_WARNINGS(text);
+}
+
 BOOST_AUTO_TEST_CASE(returndatacopy_as_variable)
 {
 	char const* text = R"(