Merge pull request #10224 from ethereum/strict-literal-to-enum-conversion

[BREAKING] Strict explicit conversion between literals and enums

Changelog.md

@@ -10,6 +10,7 @@ Breaking Changes:
  * Parser: Exponentiation is right associative. ``a**b**c`` is parsed as ``a**(b**c)``.
  * Code Generator: Use ``revert`` with error signature ``Panic(uint256)`` and error codes instead of invalid opcode on failing assertions.
  * Type System: Explicit conversions from literals to integer type is as strict as implicit conversions.
+ * Type System: Explicit conversions from literals to enums are only allowed if the value fits in the enum.
 
 Language Features:
  * Super constructors can now be called using the member notation e.g. ``M.C(123)``.

docs/080-breaking-changes.rst

@@ -35,12 +35,16 @@ the compiler notifying you about it.
 New Restrictions
 ================
 
-* Explicit conversions from negative literals and literals larger than ``type(uint160).max`` to
-  ``address`` are disallowed. Similarly, explicit conversions between literals and an integer type
-  ``T`` are only allowed if the literal lies between ``type(T).min`` and ``type(T).max``. In
-  particular, replace usages of ``uint(-1)`` with ``type(uint).max``.
+* There are new restrictions related to explicit conversion of literals. The previous behaviour in
+  the following cases was likely ambiguous:
 
-  The previous behaviour was likely ambiguous.
+  1. Explicit conversions from negative literals and literals larger than ``type(uint160).max`` to
+     ``address`` are disallowed.
+  2. Explicit conversions between literals and an integer type ``T`` are only allowed if the literal
+     lies between ``type(T).min`` and ``type(T).max``. In particular, replace usages of ``uint(-1)``
+     with ``type(uint).max``.
+  3. Explicit conversions between literals and enums are only allowed if the literal can
+     represent a value in the enum.
 
 * Function call options can only be given once, i.e. ``c.f{gas: 10000}{value: 1}()`` is invalid and has to be changed to ``c.f{gas: 10000, value: 1}()``.
 

libsolidity/ast/Types.cpp

@@ -978,6 +978,9 @@ BoolResult RationalNumberType::isExplicitlyConvertibleTo(Type const& _convertTo)
 	}
 	else if (category == Category::Integer)
 		return false;
+	else if (auto enumType = dynamic_cast<EnumType const*>(&_convertTo))
+		if (isNegative() || isFractional() || m_value >= enumType->numberOfMembers())
+			return false;
 
 	TypePointer mobType = mobileType();
 	return (mobType && mobType->isExplicitlyConvertibleTo(_convertTo));

test/libsolidity/semanticTests/enums/enum_explicit_overflow.sol

@@ -13,8 +13,8 @@ contract test {
         d = uint256(choice);
     }
 
-    function getChoiceFromNegativeLiteral() public returns (uint256 d) {
-        choice = ActionChoices(-1);
+    function getChoiceFromMax() public returns (uint256 d) {
+        choice = ActionChoices(type(uint).max);
         d = uint256(choice);
     }
 
@@ -25,8 +25,9 @@ contract test {
 // compileViaYul: also
 // EVMVersion: >=byzantium
 // ----
+// getChoiceExp(uint256): 2 -> 2
 // getChoiceExp(uint256): 3 -> FAILURE, hex"4e487b71", 33 # These should throw #
 // getChoiceFromSigned(int256): -1 -> FAILURE, hex"4e487b71", 33
-// getChoiceFromNegativeLiteral() -> FAILURE, hex"4e487b71", 33
+// getChoiceFromMax() -> FAILURE, hex"4e487b71", 33
 // getChoiceExp(uint256): 2 -> 2 # These should work #
 // getChoiceExp(uint256): 0 -> 0

test/libsolidity/semanticTests/enums/enum_explicit_overflow_homestead.sol

@@ -13,8 +13,8 @@ contract test {
         d = uint256(choice);
     }
 
-    function getChoiceFromNegativeLiteral() public returns (uint256 d) {
-        choice = ActionChoices(-1);
+    function getChoiceFromMax() public returns (uint256 d) {
+        choice = ActionChoices(type(uint256).max);
         d = uint256(choice);
     }
 
@@ -27,6 +27,6 @@ contract test {
 // ----
 // getChoiceExp(uint256): 3 -> FAILURE # These should throw #
 // getChoiceFromSigned(int256): -1 -> FAILURE
-// getChoiceFromNegativeLiteral() -> FAILURE
+// getChoiceFromMax() -> FAILURE
 // getChoiceExp(uint256): 2 -> 2 # These should work #
 // getChoiceExp(uint256): 0 -> 0

test/libsolidity/syntaxTests/enums/literal_conversion.sol

@@ -0,0 +1,10 @@
+contract C {
+    enum Test { One, Two }
+    function f() public pure {
+        Test a = Test(0);
+        Test b = Test(1);
+        Test c = Test(type(uint).max);
+        a; b; c;
+    }
+}
+// ----

test/libsolidity/syntaxTests/enums/literal_conversion_error.sol

@@ -0,0 +1,16 @@
+contract C {
+    enum Test { One, Two }
+    function f() public {
+        Test(-1);
+        Test(2);
+        Test(13);
+        Test(5/3);
+        Test(0.5);
+    }
+}
+// ----
+// TypeError 9640: (74-82): Explicit type conversion not allowed from "int_const -1" to "enum C.Test".
+// TypeError 9640: (92-99): Explicit type conversion not allowed from "int_const 2" to "enum C.Test".
+// TypeError 9640: (109-117): Explicit type conversion not allowed from "int_const 13" to "enum C.Test".
+// TypeError 9640: (127-136): Explicit type conversion not allowed from "rational_const 5 / 3" to "enum C.Test".
+// TypeError 9640: (146-155): Explicit type conversion not allowed from "rational_const 1 / 2" to "enum C.Test".