Type checking for pure expressions.

5 files changed, 88 insertions, 28 deletions

diff --git a/libsolidity/analysis/TypeChecker.cpp b/libsolidity/analysis/TypeChecker.cpp
index fbff6865..38da9b14 100644
--- a/libsolidity/analysis/TypeChecker.cpp
+++ b/libsolidity/analysis/TypeChecker.cpp
@@ -467,27 +467,20 @@ bool TypeChecker::visit(VariableDeclaration const& _variable)
 	// TypeChecker at the VariableDeclarationStatement level.
 	TypePointer varType = _variable.annotation().type;
 	solAssert(!!varType, "Failed to infer variable type.");
+	if (_variable.value())
+		expectType(*_variable.value(), *varType);
 	if (_variable.isConstant())
 	{
-		if (!dynamic_cast<ContractDefinition const*>(_variable.scope()))
+		if (!_variable.isStateVariable())
 			typeError(_variable.location(), "Illegal use of \"constant\" specifier.");
 		if (!_variable.value())
 			typeError(_variable.location(), "Uninitialized \"constant\" variable.");
-		if (!varType->isValueType())
-		{
-			bool constImplemented = false;
-			if (auto arrayType = dynamic_cast<ArrayType const*>(varType.get()))
-				constImplemented = arrayType->isByteArray();
-			if (!constImplemented)
-				typeError(
-					_variable.location(),
-					"Illegal use of \"constant\" specifier. \"constant\" "
-					"is not yet implemented for this type."
-				);
-		}
+		else if (!_variable.value()->annotation().isPure)
+			typeError(
+				_variable.value()->location(),
+				"Initial value for constant variable has to be compile-time constant."
+			);
 	}
-	if (_variable.value())
-		expectType(*_variable.value(), *varType);
 	if (!_variable.isStateVariable())
 	{
 		if (varType->dataStoredIn(DataLocation::Memory) || varType->dataStoredIn(DataLocation::CallData))
@@ -928,6 +921,10 @@ bool TypeChecker::visit(Conditional const& _conditional)
 	}
 
 	_conditional.annotation().type = commonType;
+	_conditional.annotation().isPure =
+		_conditional.condition().annotation().isPure &&
+		_conditional.trueExpression().annotation().isPure &&
+		_conditional.falseExpression().annotation().isPure;
 
 	if (_conditional.annotation().lValueRequested)
 		typeError(
@@ -1009,6 +1006,7 @@ bool TypeChecker::visit(TupleExpression const& _tuple)
 	}
 	else
 	{
+		bool isPure = true;
 		TypePointer inlineArrayType;
 		for (size_t i = 0; i < components.size(); ++i)
 		{
@@ -1031,10 +1029,13 @@ bool TypeChecker::visit(TupleExpression const& _tuple)
 					else if (inlineArrayType)
 						inlineArrayType = Type::commonType(inlineArrayType, types[i]);
 				}
+				if (!components[i]->annotation().isPure)
+					isPure = false;
 			}
 			else
 				types.push_back(TypePointer());
 		}
+		_tuple.annotation().isPure = isPure;
 		if (_tuple.isInlineArray())
 		{
 			if (!inlineArrayType) 
@@ -1061,7 +1062,8 @@ bool TypeChecker::visit(UnaryOperation const& _operation)
 {
 	// Inc, Dec, Add, Sub, Not, BitNot, Delete
 	Token::Value op = _operation.getOperator();
-	if (op == Token::Value::Inc || op == Token::Value::Dec || op == Token::Value::Delete)
+	bool const modifying = (op == Token::Value::Inc || op == Token::Value::Dec || op == Token::Value::Delete);
+	if (modifying)
 		requireLValue(_operation.subExpression());
 	else
 		_operation.subExpression().accept(*this);
@@ -1079,6 +1081,7 @@ bool TypeChecker::visit(UnaryOperation const& _operation)
 		t = subExprType;
 	}
 	_operation.annotation().type = t;
+	_operation.annotation().isPure = !modifying && _operation.subExpression().annotation().isPure;
 	return false;
 }
 
@@ -1105,6 +1108,10 @@ void TypeChecker::endVisit(BinaryOperation const& _operation)
 		Token::isCompareOp(_operation.getOperator()) ?
 		make_shared<BoolType>() :
 		commonType;
+	_operation.annotation().isPure =
+		_operation.leftExpression().annotation().isPure &&
+		_operation.rightExpression().annotation().isPure;
+
 	if (_operation.getOperator() == Token::Exp)
 	{
 		if (
@@ -1133,6 +1140,8 @@ bool TypeChecker::visit(FunctionCall const& _functionCall)
 	vector<ASTPointer<Expression const>> arguments = _functionCall.arguments();
 	vector<ASTPointer<ASTString>> const& argumentNames = _functionCall.names();
 
+	bool isPure = true;
+
 	// We need to check arguments' type first as they will be needed for overload resolution.
 	shared_ptr<TypePointers> argumentTypes;
 	if (isPositionalCall)
@@ -1140,6 +1149,8 @@ bool TypeChecker::visit(FunctionCall const& _functionCall)
 	for (ASTPointer<Expression const> const& argument: arguments)
 	{
 		argument->accept(*this);
+		if (!argument->annotation().isPure)
+			isPure = false;
 		// only store them for positional calls
 		if (isPositionalCall)
 			argumentTypes->push_back(type(*argument));
@@ -1177,6 +1188,7 @@ bool TypeChecker::visit(FunctionCall const& _functionCall)
 				typeError(_functionCall.location(), "Explicit type conversion not allowed.");
 		}
 		_functionCall.annotation().type = resultType;
+		_functionCall.annotation().isPure = isPure;
 
 		return false;
 	}
@@ -1193,9 +1205,16 @@ bool TypeChecker::visit(FunctionCall const& _functionCall)
 		auto const& structType = dynamic_cast<StructType const&>(*t.actualType());
 		functionType = structType.constructorType();
 		membersRemovedForStructConstructor = structType.membersMissingInMemory();
+		_functionCall.annotation().isPure = isPure;
 	}
 	else
+	{
 		functionType = dynamic_pointer_cast<FunctionType const>(expressionType);
+		_functionCall.annotation().isPure =
+			isPure &&
+			_functionCall.expression().annotation().isPure &&
+			functionType->isPure();
+	}
 
 	if (!functionType)
 	{
@@ -1360,6 +1379,7 @@ void TypeChecker::endVisit(NewExpression const& _newExpression)
 			strings(),
 			FunctionType::Location::ObjectCreation
 		);
+		_newExpression.annotation().isPure = true;
 	}
 	else
 		fatalTypeError(_newExpression.location(), "Contract or array type expected.");
@@ -1445,6 +1465,9 @@ bool TypeChecker::visit(MemberAccess const& _memberAccess)
 			annotation.isLValue = annotation.referencedDeclaration->isLValue();
 	}
 
+	// TODO some members might be pure, but for example `address(0x123).balance` is not pure
+	// although every subexpression is, so leaving this to false for now.
+
 	return false;
 }
 
@@ -1454,6 +1477,7 @@ bool TypeChecker::visit(IndexAccess const& _access)
 	TypePointer baseType = type(_access.baseExpression());
 	TypePointer resultType;
 	bool isLValue = false;
+	bool isPure = _access.baseExpression().annotation().isPure;
 	Expression const* index = _access.indexExpression();
 	switch (baseType->category())
 	{
@@ -1535,6 +1559,9 @@ bool TypeChecker::visit(IndexAccess const& _access)
 	}
 	_access.annotation().type = move(resultType);
 	_access.annotation().isLValue = isLValue;
+	if (index && !index->annotation().isPure)
+		isPure = false;
+	_access.annotation().isPure = isPure;
 
 	return false;
 }
@@ -1589,18 +1616,22 @@ bool TypeChecker::visit(Identifier const& _identifier)
 		!!annotation.referencedDeclaration,
 		"Referenced declaration is null after overload resolution."
 	);
-	auto variableDeclaration = dynamic_cast<VariableDeclaration const*>(annotation.referencedDeclaration);
-	annotation.isConstant = variableDeclaration != nullptr && variableDeclaration->isConstant();
 	annotation.isLValue = annotation.referencedDeclaration->isLValue();
 	annotation.type = annotation.referencedDeclaration->type();
 	if (!annotation.type)
 		fatalTypeError(_identifier.location(), "Declaration referenced before type could be determined.");
+	if (auto variableDeclaration = dynamic_cast<VariableDeclaration const*>(annotation.referencedDeclaration))
+		annotation.isPure = annotation.isConstant = variableDeclaration->isConstant();
+	else if (dynamic_cast<MagicVariableDeclaration const*>(annotation.referencedDeclaration))
+		if (auto functionType = dynamic_cast<FunctionType const*>(annotation.type.get()))
+			annotation.isPure = functionType->isPure();
 	return false;
 }
 
 void TypeChecker::endVisit(ElementaryTypeNameExpression const& _expr)
 {
 	_expr.annotation().type = make_shared<TypeType>(Type::fromElementaryTypeName(_expr.typeName()));
+	_expr.annotation().isPure = true;
 }
 
 void TypeChecker::endVisit(Literal const& _literal)
@@ -1620,6 +1651,7 @@ void TypeChecker::endVisit(Literal const& _literal)
 			);
 	}
 	_literal.annotation().type = Type::forLiteral(_literal);
+	_literal.annotation().isPure = true;
 	if (!_literal.annotation().type)
 		fatalTypeError(_literal.location(), "Invalid literal value.");
 }
diff --git a/libsolidity/ast/ASTAnnotations.h b/libsolidity/ast/ASTAnnotations.h
index 9c4c3ae8..bd297f9e 100644
--- a/libsolidity/ast/ASTAnnotations.h
+++ b/libsolidity/ast/ASTAnnotations.h
@@ -156,6 +156,8 @@ struct ExpressionAnnotation: ASTAnnotation
 	TypePointer type;
 	/// Whether the expression is a constant variable
 	bool isConstant = false;
+	/// Whether the expression is pure, i.e. compile-time constant.
+	bool isPure = false;
 	/// Whether it is an LValue (i.e. something that can be assigned to).
 	bool isLValue = false;
 	/// Whether the expression is used in a context where the LValue is actually required.
diff --git a/libsolidity/ast/Types.cpp b/libsolidity/ast/Types.cpp
index d2793b6d..0e11c3ec 100644
--- a/libsolidity/ast/Types.cpp
+++ b/libsolidity/ast/Types.cpp
@@ -2456,6 +2456,18 @@ u256 FunctionType::externalIdentifier() const
 	return FixedHash<4>::Arith(FixedHash<4>(dev::keccak256(externalSignature())));
 }
 
+bool FunctionType::isPure() const
+{
+	return
+		m_location == Location::SHA3 ||
+		m_location == Location::ECRecover ||
+		m_location == Location::SHA256 ||
+		m_location == Location::RIPEMD160 ||
+		m_location == Location::AddMod ||
+		m_location == Location::MulMod ||
+		m_location == Location::ObjectCreation;
+}
+
 TypePointers FunctionType::parseElementaryTypeVector(strings const& _types)
 {
 	TypePointers pointers;
diff --git a/libsolidity/ast/Types.h b/libsolidity/ast/Types.h
index 022b67c4..7c8fd429 100644
--- a/libsolidity/ast/Types.h
+++ b/libsolidity/ast/Types.h
@@ -972,6 +972,10 @@ public:
 	}
 	bool hasDeclaration() const { return !!m_declaration; }
 	bool isConstant() const { return m_isConstant; }
+	/// @returns true if the the result of this function only depends on its arguments
+	/// and it does not modify the state.
+	/// Currently, this will only return true for internal functions like keccak and ecrecover.
+	bool isPure() const;
 	bool isPayable() const { return m_isPayable; }
 	/// @return A shared pointer of an ASTString.
 	/// Can contain a nullptr in which case indicates absence of documentation
diff --git a/test/libsolidity/SolidityNameAndTypeResolution.cpp b/test/libsolidity/SolidityNameAndTypeResolution.cpp
index aef93e92..90831ccd 100644
--- a/test/libsolidity/SolidityNameAndTypeResolution.cpp
+++ b/test/libsolidity/SolidityNameAndTypeResolution.cpp
@@ -2180,7 +2180,18 @@ BOOST_AUTO_TEST_CASE(assigning_state_to_const_variable)
 			address constant x = msg.sender;
 		}
 	)";
-	CHECK_ERROR(text, TypeError, "Expression is not compile-time constant.");
+	CHECK_ERROR(text, TypeError, "Initial value for constant variable has to be compile-time constant.");
+}
+
+BOOST_AUTO_TEST_CASE(assign_constant_function_value_to_constant)
+{
+	char const* text = R"(
+		contract C {
+			function () constant returns (uint) x;
+			uint constant y = x();
+		}
+	)";
+	CHECK_ERROR(text, TypeError, "Initial value for constant variable has to be compile-time constant.");
 }
 
 BOOST_AUTO_TEST_CASE(assignment_to_const_var_involving_conversion)
@@ -2197,7 +2208,7 @@ BOOST_AUTO_TEST_CASE(assignment_to_const_var_involving_expression)
 {
 	char const* text = R"(
 		contract C {
-			uint constant x = 0x123 + 9x456;
+			uint constant x = 0x123 + 0x456;
 		}
 	)";
 	CHECK_SUCCESS(text);
@@ -2207,7 +2218,7 @@ BOOST_AUTO_TEST_CASE(assignment_to_const_var_involving_keccak)
 {
 	char const* text = R"(
 		contract C {
-			bytes32 constant x = keccak("abc");
+			bytes32 constant x = keccak256("abc");
 		}
 	)";
 	CHECK_SUCCESS(text);
@@ -2217,22 +2228,21 @@ BOOST_AUTO_TEST_CASE(assignment_to_const_array_vars)
 {
 	char const* text = R"(
 		contract C {
-			uint[3] memory constant x = [1, 2, 3];
+			uint[3] constant x = [uint(1), 2, 3];
 		}
 	)";
 	CHECK_SUCCESS(text);
 }
 
-BOOST_AUTO_TEST_CASE(complex_const_variable)
+BOOST_AUTO_TEST_CASE(constant_struct)
 {
-	//for now constant specifier is valid only for uint bytesXX and enums
 	char const* text = R"(
-		contract Foo {
-			mapping(uint => bool) x;
-			mapping(uint => bool) constant mapVar = x;
+		contract C {
+			struct S { uint x; uint[] y; }
+			S constant x = S(5, new uint[](4));
 		}
 	)";
-	CHECK_ERROR(text, TypeError, "");
+	CHECK_SUCCESS(text);
 }
 
 BOOST_AUTO_TEST_CASE(uninitialized_const_variable)