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

11 files changed, 102 insertions, 9 deletions

diff --git a/docs/contracts.rst b/docs/contracts.rst
index 967eb2c8..5754b734 100644
--- a/docs/contracts.rst
+++ b/docs/contracts.rst
@@ -402,7 +402,7 @@ State variables can be declared as ``constant``. In this case, they have to be
 assigned from an expression which is a constant at compile time. Any expression
 that accesses storage, blockchain data (e.g. ``now``, ``this.balance`` or
 ``block.number``) or
-execution data (``msg.gas``) or make calls to external contracts are disallowed. Expressions
+execution data (``msg.value``) or make calls to external contracts are disallowed. Expressions
 that might have a side-effect on memory allocation are allowed, but those that
 might have a side-effect on other memory objects are not. The built-in functions
 ``keccak256``, ``sha256``, ``ripemd160``, ``ecrecover``, ``addmod`` and ``mulmod``
diff --git a/docs/miscellaneous.rst b/docs/miscellaneous.rst
index 70ed6201..7d3d058b 100644
--- a/docs/miscellaneous.rst
+++ b/docs/miscellaneous.rst
@@ -315,8 +315,9 @@ Global Variables
 - ``block.gaslimit`` (``uint``): current block gaslimit
 - ``block.number`` (``uint``): current block number
 - ``block.timestamp`` (``uint``): current block timestamp
+- ``gasleft() returns (uint256)``: remaining gas
 - ``msg.data`` (``bytes``): complete calldata
-- ``msg.gas`` (``uint``): remaining gas
+- ``msg.gas`` (``uint``): remaining gas - deprecated in version 0.4.21 and to be replaced by ``gasleft()``
 - ``msg.sender`` (``address``): sender of the message (current call)
 - ``msg.value`` (``uint``): number of wei sent with the message
 - ``now`` (``uint``): current block timestamp (alias for ``block.timestamp``)
diff --git a/docs/units-and-global-variables.rst b/docs/units-and-global-variables.rst
index cc4d4446..1b58b1e8 100644
--- a/docs/units-and-global-variables.rst
+++ b/docs/units-and-global-variables.rst
@@ -58,8 +58,9 @@ Block and Transaction Properties
 - ``block.gaslimit`` (``uint``): current block gaslimit
 - ``block.number`` (``uint``): current block number
 - ``block.timestamp`` (``uint``): current block timestamp as seconds since unix epoch
+- ``gasleft() returns (uint256)``: remaining gas
 - ``msg.data`` (``bytes``): complete calldata
-- ``msg.gas`` (``uint``): remaining gas
+- ``msg.gas`` (``uint``): remaining gas - deprecated in version 0.4.21 and to be replaced by ``gasleft()``
 - ``msg.sender`` (``address``): sender of the message (current call)
 - ``msg.sig`` (``bytes4``): first four bytes of the calldata (i.e. function identifier)
 - ``msg.value`` (``uint``): number of wei sent with the message
diff --git a/libsolidity/analysis/GlobalContext.cpp b/libsolidity/analysis/GlobalContext.cpp
index fd39d860..34cb61d8 100644
--- a/libsolidity/analysis/GlobalContext.cpp
+++ b/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)),
diff --git a/libsolidity/ast/Types.cpp b/libsolidity/ast/Types.cpp
index 771ae643..bde0dd6e 100644
--- a/libsolidity/ast/Types.cpp
+++ b/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)},
diff --git a/libsolidity/ast/Types.h b/libsolidity/ast/Types.h
index 7985521e..c20a025f 100644
--- a/libsolidity/ast/Types.h
+++ b/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; }
diff --git a/libsolidity/codegen/ExpressionCompiler.cpp b/libsolidity/codegen/ExpressionCompiler.cpp
index 61920592..d3599367 100644
--- a/libsolidity/codegen/ExpressionCompiler.cpp
+++ b/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;
diff --git a/test/libsolidity/SolidityEndToEndTest.cpp b/test/libsolidity/SolidityEndToEndTest.cpp
index c352a2c2..e61afb0e 100644
--- a/test/libsolidity/SolidityEndToEndTest.cpp
+++ b/test/libsolidity/SolidityEndToEndTest.cpp
@@ -2481,6 +2481,25 @@ BOOST_AUTO_TEST_CASE(gas_and_value_basic)
 	BOOST_REQUIRE(callContractFunction("checkState()") == encodeArgs(false, 20 - 5));
 }
 
+BOOST_AUTO_TEST_CASE(gas_left)
+{
+	char const* sourceCode = R"(
+		contract test {
+			function getGasLeft() public returns (uint256 val) { return msg.gas; }
+		}
+	)";
+	compileAndRun(sourceCode);
+	BOOST_REQUIRE(callContractFunction("getGasLeft()") == encodeArgs(99978604));
+
+	sourceCode = R"(
+		contract test {
+			function getGasLeft() public returns (uint256 val) { return gasleft(); }
+		}
+	)";
+	compileAndRun(sourceCode);
+	BOOST_REQUIRE(callContractFunction("getGasLeft()") == encodeArgs(99978604));
+}
+
 BOOST_AUTO_TEST_CASE(value_complex)
 {
 	char const* sourceCode = R"(
diff --git a/test/libsolidity/SolidityExpressionCompiler.cpp b/test/libsolidity/SolidityExpressionCompiler.cpp
index e2a0c3cd..83129ba1 100644
--- a/test/libsolidity/SolidityExpressionCompiler.cpp
+++ b/test/libsolidity/SolidityExpressionCompiler.cpp
@@ -515,6 +515,39 @@ BOOST_AUTO_TEST_CASE(blockhash)
 	BOOST_CHECK_EQUAL_COLLECTIONS(code.begin(), code.end(), expectation.begin(), expectation.end());
 }
 
+BOOST_AUTO_TEST_CASE(gas_left)
+{
+	char const* sourceCode = R"(
+		contract test {
+			function f() returns (uint256 val) {
+				return msg.gas;
+			}
+		}
+	)";
+	bytes code = compileFirstExpression(
+		sourceCode, {}, {},
+		{make_shared<MagicVariableDeclaration>("msg", make_shared<MagicType>(MagicType::Kind::Message))}
+	);
+
+	bytes expectation({byte(Instruction::GAS)});
+	BOOST_CHECK_EQUAL_COLLECTIONS(code.begin(), code.end(), expectation.begin(), expectation.end());
+
+	sourceCode = R"(
+		contract test {
+			function f() returns (uint256 val) {
+				return gasleft();
+			}
+		}
+	)";
+	code = compileFirstExpression(
+		sourceCode, {}, {},
+		{make_shared<MagicVariableDeclaration>("gasleft", make_shared<FunctionType>(strings(), strings{"uint256"}, FunctionType::Kind::GasLeft))}
+	);
+
+	expectation = bytes({byte(Instruction::GAS)});
+	BOOST_CHECK_EQUAL_COLLECTIONS(code.begin(), code.end(), expectation.begin(), expectation.end());
+}
+
 BOOST_AUTO_TEST_SUITE_END()
 
 }
diff --git a/test/libsolidity/SolidityNameAndTypeResolution.cpp b/test/libsolidity/SolidityNameAndTypeResolution.cpp
index eeefe818..469211d3 100644
--- a/test/libsolidity/SolidityNameAndTypeResolution.cpp
+++ b/test/libsolidity/SolidityNameAndTypeResolution.cpp
@@ -7409,6 +7409,31 @@ BOOST_AUTO_TEST_CASE(builtin_reject_gas)
 	CHECK_ERROR(text, TypeError, "Member \"gas\" not found or not visible after argument-dependent lookup");
 }
 
+BOOST_AUTO_TEST_CASE(gas_left)
+{
+	char const* text = R"(
+		contract C {
+			function f() public returns (uint256 val) { return msg.gas; }
+		}
+	)";
+	CHECK_SUCCESS(text);
+
+	text = R"(
+		contract C {
+			function f() public returns (uint256 val) { return gasleft(); }
+		}
+	)";
+	CHECK_SUCCESS(text);
+
+	text = R"(
+		pragma experimental "v0.5.0";
+		contract C {
+			function f() public returns (uint256 val) { return msg.gas; }
+		}
+	)";
+	CHECK_ERROR(text, TypeError, "Member \"gas\" not found or not visible after argument-dependent lookup in msg");
+}
+
 BOOST_AUTO_TEST_CASE(builtin_reject_value)
 {
 	char const* text = R"(
diff --git a/test/libsolidity/ViewPureChecker.cpp b/test/libsolidity/ViewPureChecker.cpp
index 2599ca28..609a0154 100644
--- a/test/libsolidity/ViewPureChecker.cpp
+++ b/test/libsolidity/ViewPureChecker.cpp
@@ -109,6 +109,7 @@ BOOST_AUTO_TEST_CASE(environment_access)
 		"block.difficulty",
 		"block.number",
 		"block.gaslimit",
+		"gasleft()",
 		"msg.gas",
 		"msg.value",
 		"msg.sender",