Move msg.gas to global function gasleft(). Closes #2971.

libsolidity/analysis/GlobalContext.cpp

@@ -39,6 +39,7 @@ m_magicVariables(vector<shared_ptr<MagicVariableDeclaration const>>{
 	make_shared<MagicVariableDeclaration>("assert", make_shared<FunctionType>(strings{"bool"}, strings{}, FunctionType::Kind::Assert, false, StateMutability::Pure)),
 	make_shared<MagicVariableDeclaration>("block", make_shared<MagicType>(MagicType::Kind::Block)),
 	make_shared<MagicVariableDeclaration>("ecrecover", make_shared<FunctionType>(strings{"bytes32", "uint8", "bytes32", "bytes32"}, strings{"address"}, FunctionType::Kind::ECRecover, false, StateMutability::Pure)),
+	make_shared<MagicVariableDeclaration>("gasleft", make_shared<FunctionType>(strings(), strings{"uint256"}, FunctionType::Kind::GasLeft, false, StateMutability::View)),
 	make_shared<MagicVariableDeclaration>("keccak256", make_shared<FunctionType>(strings(), strings{"bytes32"}, FunctionType::Kind::SHA3, true, StateMutability::Pure)),
 	make_shared<MagicVariableDeclaration>("log0", make_shared<FunctionType>(strings{"bytes32"}, strings{}, FunctionType::Kind::Log0)),
 	make_shared<MagicVariableDeclaration>("log1", make_shared<FunctionType>(strings{"bytes32", "bytes32"}, strings{}, FunctionType::Kind::Log1)),

libsolidity/ast/Types.cpp

@@ -3000,8 +3000,10 @@ bool MagicType::operator==(Type const& _other) const
 	return other.m_kind == m_kind;
 }
 
-MemberList::MemberMap MagicType::nativeMembers(ContractDefinition const*) const
+MemberList::MemberMap MagicType::nativeMembers(ContractDefinition const *_contract) const
 {
+	solAssert(_contract, "");
+	const bool v050 = _contract->sourceUnit().annotation().experimentalFeatures.count(ExperimentalFeature::V050);
 	switch (m_kind)
 	{
 	case Kind::Block:
@@ -3014,13 +3016,17 @@ MemberList::MemberMap MagicType::nativeMembers(ContractDefinition const*) const
 			{"gaslimit", make_shared<IntegerType>(256)}
 		});
 	case Kind::Message:
-		return MemberList::MemberMap({
+	{
+		std::vector<MemberList::Member> members = {
 			{"sender", make_shared<IntegerType>(160, IntegerType::Modifier::Address)},
-			{"gas", make_shared<IntegerType>(256)},
 			{"value", make_shared<IntegerType>(256)},
 			{"data", make_shared<ArrayType>(DataLocation::CallData)},
 			{"sig", make_shared<FixedBytesType>(4)}
-		});
+		};
+		if (!v050)
+			members.emplace_back("gas", make_shared<IntegerType>(256));
+		return MemberList::MemberMap(members);
+	}
 	case Kind::Transaction:
 		return MemberList::MemberMap({
 			{"origin", make_shared<IntegerType>(160, IntegerType::Modifier::Address)},

libsolidity/ast/Types.h

@@ -902,7 +902,8 @@ public:
 		ByteArrayPush, ///< .push() to a dynamically sized byte array in storage
 		ObjectCreation, ///< array creation using new
 		Assert, ///< assert()
-		Require ///< require()
+		Require, ///< require()
+		GasLeft ///< gasleft()
 	};
 
 	virtual Category category() const override { return Category::Function; }

libsolidity/codegen/ExpressionCompiler.cpp

@@ -906,6 +906,9 @@ bool ExpressionCompiler::visit(FunctionCall const& _functionCall)
 			m_context << success;
 			break;
 		}
+		case FunctionType::Kind::GasLeft:
+			m_context << Instruction::GAS;
+			break;
 		default:
 			solAssert(false, "Invalid function type.");
 		}
@@ -921,6 +924,8 @@ bool ExpressionCompiler::visit(NewExpression const&)
 
 bool ExpressionCompiler::visit(MemberAccess const& _memberAccess)
 {
+	const bool v050 = m_context.experimentalFeatureActive(ExperimentalFeature::V050);
+
 	CompilerContext::LocationSetter locationSetter(m_context, _memberAccess);
 	// Check whether the member is a bound function.
 	ASTString const& member = _memberAccess.memberName();
@@ -1135,7 +1140,7 @@ bool ExpressionCompiler::visit(MemberAccess const& _memberAccess)
 			m_context << Instruction::CALLVALUE;
 		else if (member == "origin")
 			m_context << Instruction::ORIGIN;
-		else if (member == "gas")
+		else if (!v050 && member == "gas")
 			m_context << Instruction::GAS;
 		else if (member == "gasprice")
 			m_context << Instruction::GASPRICE;