Provide gas stipend manually for send(0).

Changelog.md

@@ -42,6 +42,7 @@ Bugfixes:
  * Why3 translator: crash fix for exponentiation
  * Type Checker: Fallback function cannot return data anymore.
  * Code Generator: Fix crash when sha3() was used on unsupported types.
+ * Code Generator: Manually set gas stipend for .send(0).
 
 Lots of changes to the documentation mainly by voluntary external contributors.
 

libsolidity/codegen/ExpressionCompiler.cpp

@@ -568,12 +568,17 @@ bool ExpressionCompiler::visit(FunctionCall const& _functionCall)
 			break;
 		case Location::Send:
 			_functionCall.expression().accept(*this);
-			m_context << u256(0); // do not send gas (there still is the stipend)
+			// Provide the gas stipend manually at first because we may send zero ether.
+			// Will be zeroed if we send more than zero ether.
+			m_context << u256(eth::GasCosts::callStipend);
 			arguments.front()->accept(*this);
 			utils().convertType(
 				*arguments.front()->annotation().type,
 				*function.parameterTypes().front(), true
 			);
+			// gas <- gas * !value
+			m_context << Instruction::SWAP1 << Instruction::DUP2;
+			m_context << Instruction::ISZERO << Instruction::MUL << Instruction::SWAP1;
 			appendExternalFunctionCall(
 				FunctionType(
 					TypePointers{},

test/libsolidity/SolidityEndToEndTest.cpp

@@ -4625,6 +4625,26 @@ BOOST_AUTO_TEST_CASE(failing_send)
 	BOOST_REQUIRE(callContractFunction("callHelper(address)", c_helperAddress) == encodeArgs(true, 20));
 }
 
+BOOST_AUTO_TEST_CASE(send_zero_ether)
+{
+	// Sending zero ether to a contract should still invoke the fallback function
+	// (it previously did not because the gas stipend was not provided by the EVM)
+	char const* sourceCode = R"(
+		contract Receiver {
+			function () payable {
+			}
+		}
+		contract Main {
+			function s() returns (bool) {
+				var r = new Receiver();
+				return r.send(0);
+			}
+		}
+	)";
+	compileAndRun(sourceCode, 20, "Main");
+	BOOST_REQUIRE(callContractFunction("s()") == encodeArgs(true));
+}
+
 BOOST_AUTO_TEST_CASE(reusing_memory)
 {
 	// Invoke some features that use memory and test that they do not interfere with each other.