Disallow conversions between bytesX and uintY of different size.

Changelog.md

@@ -1,6 +1,7 @@
 ### 0.5.0 (unreleased)
 
 Breaking Changes:
+ * Disallow conversions between bytesX and uintY of different size.
  * Type Checker: Disallow arithmetic operations for Boolean variables.
 
 Features:

docs/types.rst

@@ -975,6 +975,15 @@ cut off::
     uint32 a = 0x12345678;
     uint16 b = uint16(a); // b will be 0x5678 now
 
+Since 0.5.0 explicit conversions between integers and fixed-size byte arrays
+are only allowed, if both have the same size. To convert between integers and
+fixed-size byte arrays of different size, they first have to be explicitly
+converted to a matching size. This makes alignment and padding explicit::
+
+    uint16 x = 0xffff;
+    bytes32(uint256(x)); // pad on the left
+    bytes32(bytes2(x)); // pad on the right
+
 .. index:: ! type;deduction, ! var
 
 .. _type-deduction:

libsolidity/ast/Types.cpp

@@ -476,7 +476,7 @@ bool IntegerType::isExplicitlyConvertibleTo(Type const& _convertTo) const
 	return _convertTo.category() == category() ||
 		_convertTo.category() == Category::Contract ||
 		_convertTo.category() == Category::Enum ||
-		_convertTo.category() == Category::FixedBytes ||
+		(_convertTo.category() == Category::FixedBytes && numBits() == dynamic_cast<FixedBytesType const&>(_convertTo).numBytes() * 8) ||
 		_convertTo.category() == Category::FixedPoint;
 }
 
@@ -884,7 +884,10 @@ bool RationalNumberType::isImplicitlyConvertibleTo(Type const& _convertTo) const
 bool RationalNumberType::isExplicitlyConvertibleTo(Type const& _convertTo) const
 {
 	TypePointer mobType = mobileType();
-	return mobType && mobType->isExplicitlyConvertibleTo(_convertTo);
+	return
+		(mobType && mobType->isExplicitlyConvertibleTo(_convertTo)) ||
+		(!isFractional() && _convertTo.category() == Category::FixedBytes)
+	;
 }
 
 TypePointer RationalNumberType::unaryOperatorResult(Token::Value _operator) const
@@ -1281,7 +1284,7 @@ bool FixedBytesType::isImplicitlyConvertibleTo(Type const& _convertTo) const
 
 bool FixedBytesType::isExplicitlyConvertibleTo(Type const& _convertTo) const
 {
-	return _convertTo.category() == Category::Integer ||
+	return (_convertTo.category() == Category::Integer && numBytes() * 8 == dynamic_cast<IntegerType const&>(_convertTo).numBits()) ||
 		_convertTo.category() == Category::FixedPoint ||
 		_convertTo.category() == category();
 }

test/compilationTests/milestonetracker/RLP.sol

@@ -263,7 +263,7 @@ library RLP {
      var (rStartPos, len) = _decode(self);
      if (len != 1)
          throw;
-     uint temp;
+     uint8 temp;
      assembly {
          temp := byte(0, mload(rStartPos))
      }

test/libsolidity/SolidityNameAndTypeResolution.cpp

@@ -3859,19 +3859,6 @@ BOOST_AUTO_TEST_CASE(conditional_with_all_types)
 	CHECK_SUCCESS(text);
 }
 
-BOOST_AUTO_TEST_CASE(index_access_for_bytes)
-{
-	char const* text = R"(
-		contract C {
-			bytes20 x;
-			function f(bytes16 b) public {
-				b[uint(x[2])];
-			}
-		}
-	)";
-	CHECK_SUCCESS(text);
-}
-
 BOOST_AUTO_TEST_CASE(uint7_and_uintM_as_identifier)
 {
 	char const* text = R"(

test/libsolidity/syntaxTests/types/bytes1_to_uint256.sol

@@ -0,0 +1,7 @@
+contract C {
+    function f() public pure returns(uint256) {
+        return uint256(bytes1(''));
+    }
+}
+// ----
+// TypeError: (76-95): Explicit type conversion not allowed from "bytes1" to "uint256".

test/libsolidity/syntaxTests/types/bytes32_to_uint32.sol

@@ -0,0 +1,7 @@
+contract C {
+    function f() public pure returns(uint32) {
+        return uint32(bytes32(''));
+    }
+}
+// ----
+// TypeError: (75-94): Explicit type conversion not allowed from "bytes32" to "uint32".

test/libsolidity/syntaxTests/types/bytes_to_contract.sol

@@ -1,7 +1,7 @@
 contract C {
         function f() public pure {
-                C(bytes20(0x1234));
+                C(bytes20(uint160(0x1234)));
         }
 }
 // ----
-// TypeError: (64-82): Explicit type conversion not allowed from "bytes20" to "contract C".
+// TypeError: (64-91): Explicit type conversion not allowed from "bytes20" to "contract C".

test/libsolidity/syntaxTests/types/bytes_to_uint_same_size.sol

@@ -0,0 +1,20 @@
+contract C {
+    function f() public pure returns (uint256) {
+        return uint256(bytes32(uint256(0)));
+    }
+    function g() public pure returns (uint128) {
+        return uint128(bytes16(uint128(0)));
+    }
+    function h() public pure returns (uint64) {
+        return uint64(bytes8(uint64(0)));
+    }
+    function i() public pure returns (uint32) {
+        return uint32(bytes4(uint32(0)));
+    }
+    function j() public pure returns (uint16) {
+        return uint16(bytes2(uint16(0)));
+    }
+    function k() public pure returns (uint8) {
+        return uint8(bytes1(uint8(0)));
+    }
+}

test/libsolidity/syntaxTests/types/index_access_for_bytes.sol

@@ -0,0 +1,6 @@
+contract C {
+    bytes20 x;
+    function f(bytes16 b) public view {
+        b[uint8(x[2])];
+    }
+}

test/libsolidity/syntaxTests/types/uint256_to_bytes1.sol

@@ -0,0 +1,7 @@
+contract C {
+    function f() public pure returns(bytes1) {
+        return bytes1(uint256(0));
+    }
+}
+// ----
+// TypeError: (75-93): Explicit type conversion not allowed from "uint256" to "bytes1".

test/libsolidity/syntaxTests/types/uint32_to_bytes32.sol

@@ -0,0 +1,7 @@
+contract C {
+    function f() public pure returns(bytes32) {
+        return bytes32(uint32(0));
+    }
+}
+// ----
+// TypeError: (76-94): Explicit type conversion not allowed from "uint32" to "bytes32".