Merge pull request #8994 from ethereum/fixInvertedBinaryOp

Fix type inversion for shift and exp operators.

Changelog.md

@@ -6,6 +6,7 @@ Breaking changes:
  * Deprecated the identifier `now`.
  * JSON AST: Removes members with ``null`` value from JSON output.
  * Type Checker: Disallow shifts by signed types.
+ * Type Checker: Exponentiation and shifts of literals by non-literals will always use ``uint256`` or ``int256`` as a type.
 
 Language Features:
  * Yul: Disallow EVM instruction `pc()`.

docs/types/value-types.rst

@@ -444,6 +444,11 @@ long as the operands are integers. If any of the two is fractional, bit operatio
 and exponentiation is disallowed if the exponent is fractional (because that might result in
 a non-rational number).
 
+Shifts and exponentiation with literal numbers as left (or base) operand and integer types
+as the right (exponent) operand are always performed
+in the ``uint256`` (for non-negative literals) or ``int256`` (for a negative literals) type,
+regardless of the type of the right (exponent) operand.
+
 .. warning::
     Division on integer literals used to truncate in Solidity prior to version 0.4.0, but it now converts into a rational number, i.e. ``5 / 2`` is not equal to ``2``, but to ``2.5``.
 

libsolidity/ast/TypeProvider.h

@@ -96,6 +96,7 @@ public:
 	static IntegerType const* uint(unsigned _bits) { return integer(_bits, IntegerType::Modifier::Unsigned); }
 
 	static IntegerType const* uint256() { return uint(256); }
+	static IntegerType const* int256() { return integer(256, IntegerType::Modifier::Signed); }
 
 	static FixedPointType const* fixedPoint(unsigned m, unsigned n, FixedPointType::Modifier _modifier);
 

libsolidity/ast/Types.cpp

@@ -965,10 +965,38 @@ TypeResult RationalNumberType::binaryOperatorResult(Token _operator, Type const*
 {
 	if (_other->category() == Category::Integer || _other->category() == Category::FixedPoint)
 	{
-		auto commonType = Type::commonType(this, _other);
+		if (isFractional())
-		if (!commonType)
+			return TypeResult::err("Fractional literals not supported.");
-			return nullptr;
+		else if (!integerType())
-		return commonType->binaryOperatorResult(_operator, _other);
+			return TypeResult::err("Literal too large.");
+
+		// Shift and exp are not symmetric, so it does not make sense to swap
+		// the types as below. As an exception, we always use uint here.
+		if (TokenTraits::isShiftOp(_operator))
+		{
+			if (!isValidShiftAndAmountType(_operator, *_other))
+				return nullptr;
+			return isNegative() ? TypeProvider::int256() : TypeProvider::uint256();
+		}
+		else if (Token::Exp == _operator)
+		{
+			if (auto const* otherIntType = dynamic_cast<IntegerType const*>(_other))
+			{
+				if (otherIntType->isSigned())
+					return TypeResult::err("Exponentiation power is not allowed to be a signed integer type.");
+			}
+			else if (dynamic_cast<FixedPointType const*>(_other))
+				return TypeResult::err("Exponent is fractional.");
+
+			return isNegative() ? TypeProvider::int256() : TypeProvider::uint256();
+		}
+		else
+		{
+			auto commonType = Type::commonType(this, _other);
+			if (!commonType)
+				return nullptr;
+			return commonType->binaryOperatorResult(_operator, _other);
+		}
 	}
 	else if (_other->category() != category())
 		return nullptr;

test/libsolidity/semanticTests/cleanup/exp_cleanup.sol

@@ -1,5 +1,5 @@
 contract C {
-    function f() public pure returns (uint8 x) {
+    function f() public pure returns (uint x) {
         uint8 y = uint8(2)**uint8(8);
         return 0**y;
     }

test/libsolidity/semanticTests/exponentiation/literal_base.sol

@@ -0,0 +1,16 @@
+contract test {
+    function f(uint x) public pure returns (uint, int) {
+        uint a = 2 ** x;
+        int b = -2 ** x;
+        return (a, b);
+    }
+}
+// ----
+// f(uint256): 0 -> 1, 1
+// f(uint256): 1 -> 2, -2
+// f(uint256): 2 -> 4, 4
+// f(uint256): 13 -> 0x2000, -8192
+// f(uint256): 113 -> 0x020000000000000000000000000000, -10384593717069655257060992658440192
+// f(uint256): 114 -> 0x040000000000000000000000000000, 20769187434139310514121985316880384
+// f(uint256): 1113 -> 0x00, 0
+// f(uint256): 1114 -> 0x00, 0

test/libsolidity/syntaxTests/nameAndTypeResolution/113_exp_warn_literal_base_1.sol

@@ -5,4 +5,3 @@ contract test {
     }
 }
 // ----
-// Warning: (99-104): Result of exponentiation has type uint8 and thus might overflow. Silence this warning by converting the literal to the expected type.

test/libsolidity/syntaxTests/nameAndTypeResolution/116_shift_warn_literal_base_1.sol

@@ -5,4 +5,3 @@ contract test {
     }
 }
 // ----
-// Warning: (99-106): Result of shift has type uint8 and thus might overflow. Silence this warning by converting the literal to the expected type.

test/libsolidity/syntaxTests/nameAndTypeResolution/333_fixed_point_casting_exponents_15.sol

@@ -4,4 +4,4 @@ contract test {
     }
 }
 // ----
-// TypeError: (61-77): Operator ** not compatible with types int_const 3 and ufixed128x18
+// TypeError: (61-77): Operator ** not compatible with types int_const 3 and ufixed128x18. Exponent is fractional.

test/libsolidity/syntaxTests/nameAndTypeResolution/334_fixed_point_casting_exponents_neg.sol

@@ -4,4 +4,4 @@ contract test {
     }
 }
 // ----
-// TypeError: (61-78): Operator ** not compatible with types int_const 42 and fixed128x18
+// TypeError: (61-78): Operator ** not compatible with types int_const 42 and fixed128x18. Exponent is fractional.

test/libsolidity/syntaxTests/nameAndTypeResolution/shift_warn_literal_large_shift_amount.sol

@@ -0,0 +1,7 @@
+contract test {
+    function f() pure public returns(uint) {
+        uint x = 100;
+        return 10 << x;
+    }
+}
+// ----

test/libsolidity/syntaxTests/signed_rational_modulus.sol

@@ -7,4 +7,4 @@ contract test {
     }
 }
 // ----
-// UnimplementedFeatureError: Not yet implemented - FixedPointType.
+// TypeError: (117-123): Operator % not compatible with types rational_const 1 / 2 and fixed128x18. Fractional literals not supported.