Disallow comparison operators on contracts

Changelog.md

@@ -2,8 +2,9 @@
 
 Breaking changes:
  * Disallow ``.pop()`` on arrays containing nested mappings.
- * Disallow ``delete`` on types that contain nested mappings.
  * Disallow ``codecopy`` and ``codesize`` in ``pure`` functions.
+ * Disallow ``delete`` on types that contain nested mappings.
+ * Disallow all comparison operators on contract types.
  * Inline Assembly: Consider functions, function parameters and return variables for shadowing checks.
  * Commandline Interface: Remapping targets are not automatically added to allowed paths.
  * Commandline Interface: Assembler mode no longer enables all outputs by default.

libsolidity/ast/Types.h

@@ -927,6 +927,11 @@ public:
 	BoolResult isImplicitlyConvertibleTo(Type const& _convertTo) const override;
 	/// Contracts can only be explicitly converted to address types and base contracts.
 	BoolResult isExplicitlyConvertibleTo(Type const& _convertTo) const override;
+	/// Contracts do not support any comparison operators
+	TypeResult binaryOperatorResult(Token, Type const*) const override
+	{
+		return TypeResult::err("No arithmetic or comparison operations are allowed on contract types. Consider converting to \"address\".");
+	}
 	TypeResult unaryOperatorResult(Token _operator) const override;
 	std::string richIdentifier() const override;
 	bool operator==(Type const& _other) const override;

test/libsolidity/ABIDecoderTests.cpp

@@ -48,7 +48,7 @@ BOOST_AUTO_TEST_CASE(value_types)
 				if (d != 4) return 4;
 				if (x != "abc") return 5;
 				if (e != true) return 6;
-				if (g != this) return 7;
+				if (address(g) != address(this)) return 7;
 				return 20;
 			}
 		}

test/libsolidity/semanticTests/salted_create/salted_create.sol

@@ -6,7 +6,7 @@ contract A {
     function different_salt() public returns (bool) {
         B x = new B{salt: "abc"}();
         B y = new B{salt: "abcef"}();
-        return x != y;
+        return address(x) != address(y);
     }
     function same_salt() public returns (bool) {
         B x = new B{salt: "xyz"}();

test/libsolidity/smtCheckerTests/functions/getters/contract.sol

@@ -5,11 +5,11 @@ contract C {
 
 	function f() public view {
 		D e = this.d();
-		assert(e == d); // should hold
+		assert(address(e) == address(d)); // should hold
 		assert(address(e) == address(this)); // should fail
 	}
 }
 // ====
 // SMTEngine: all
 // ----
-// Warning 6328: (123-158): CHC: Assertion violation happens here.\nCounterexample:\nd = 0\ne = 0\n\nTransaction trace:\nC.constructor()\nState: d = 0\nC.f()
+// Warning 6328: (141-176): CHC: Assertion violation happens here.\nCounterexample:\nd = 0\ne = 0\n\nTransaction trace:\nC.constructor()\nState: d = 0\nC.f()

test/libsolidity/smtCheckerTests/functions/getters/struct_4.sol

@@ -11,7 +11,7 @@ contract C {
 
 	function test() public view {
 		(D d, function () external returns (uint) f) = this.s();
-		assert(d == s.d); // should hold
+		assert(address(d) == address(s.d)); // should hold
 		assert(address(d) == address(this)); // should fail
 	}
 }
@@ -19,4 +19,4 @@ contract C {
 // SMTEngine: all
 // ----
 // Warning 2072: (146-183): Unused local variable.
-// Warning 6328: (234-269): CHC: Assertion violation happens here.\nCounterexample:\ns = {d: 0, f: 0}\nd = 0\nf = 0\n\nTransaction trace:\nC.constructor()\nState: s = {d: 0, f: 0}\nC.test()
+// Warning 6328: (252-287): CHC: Assertion violation happens here.\nCounterexample:\ns = {d: 0, f: 0}\nd = 0\nf = 0\n\nTransaction trace:\nC.constructor()\nState: s = {d: 0, f: 0}\nC.test()

test/libsolidity/smtCheckerTests/types/contract.sol

@@ -1,11 +1,11 @@
 contract C
 {
 	function f(C c, C d) public pure {
-		assert(c == d);
+		assert(address(c) == address(d));
 	}
 }
 // ====
 // SMTEngine: all
 // SMTIgnoreCex: yes
 // ----
-// Warning 6328: (51-65): CHC: Assertion violation happens here.
+// Warning 6328: (51-83): CHC: Assertion violation happens here.

test/libsolidity/smtCheckerTests/types/contract_2.sol

@@ -6,11 +6,11 @@ contract D
 contract C
 {
 	function f(D c, D d) public pure {
-		assert(c == d);
+		assert(address(c) == address(d));
 	}
 }
 // ====
 // SMTEngine: all
 // SMTIgnoreCex: yes
 // ----
-// Warning 6328: (76-90): CHC: Assertion violation happens here.
+// Warning 6328: (76-108): CHC: Assertion violation happens here.

test/libsolidity/smtCheckerTests/types/contract_3.sol

@@ -1,9 +1,9 @@
 contract C
 {
 	function f(C c, C d, C e) public pure {
-		require(c == d);
-		require(d == e);
-		assert(c == e);
+		require(address(c) == address(d));
+		require(address(d) == address(e));
+		assert(address(c) == address(e));
 	}
 }
 // ====

test/libsolidity/smtCheckerTests/types/contract_address_conversion_2.sol

@@ -3,7 +3,7 @@ contract C
 	function f(C c, C d) public pure {
 		assert(address(c) == address(c));
 		address a = address(c);
-		require(c == d);
+		require(address(c) == address(d));
 		assert(a == address(d));
 	}
 }

test/libsolidity/syntaxTests/conversion/implicit_conversion_of_super_in_comparison.sol

@@ -20,8 +20,8 @@ contract C {
 }
 // ----
 // TypeError 2271: (144-157): Operator != not compatible with types type(contract super C) and contract C
-// TypeError 2271: (167-180): Operator != not compatible with types contract C and type(contract super C)
+// TypeError 2271: (167-180): Operator != not compatible with types contract C and type(contract super C). No arithmetic or comparison operations are allowed on contract types. Consider converting to "address".
 // TypeError 2271: (254-264): Operator != not compatible with types type(contract super C) and contract C
-// TypeError 2271: (274-284): Operator != not compatible with types contract C and type(contract super C)
+// TypeError 2271: (274-284): Operator != not compatible with types contract C and type(contract super C). No arithmetic or comparison operations are allowed on contract types. Consider converting to "address".
 // TypeError 2271: (349-359): Operator != not compatible with types type(contract super C) and contract D
-// TypeError 2271: (369-379): Operator != not compatible with types contract D and type(contract super C)
+// TypeError 2271: (369-379): Operator != not compatible with types contract D and type(contract super C). No arithmetic or comparison operations are allowed on contract types. Consider converting to "address".

test/libsolidity/syntaxTests/errors/contract_no_comparison.sol

@@ -0,0 +1,21 @@
+contract C {
+	function f(string calldata data) external pure {
+		C c;
+		assert(this == this);
+
+		assert(this == c);
+		assert(this != c);
+		assert(this >= c);
+		assert(this <= c);
+		assert(this < c);
+		assert(this > c);
+	}
+}
+// ----
+// TypeError 2271: (79-91): Operator == not compatible with types contract C and contract C. No arithmetic or comparison operations are allowed on contract types. Consider converting to "address".
+// TypeError 2271: (104-113): Operator == not compatible with types contract C and contract C. No arithmetic or comparison operations are allowed on contract types. Consider converting to "address".
+// TypeError 2271: (125-134): Operator != not compatible with types contract C and contract C. No arithmetic or comparison operations are allowed on contract types. Consider converting to "address".
+// TypeError 2271: (146-155): Operator >= not compatible with types contract C and contract C. No arithmetic or comparison operations are allowed on contract types. Consider converting to "address".
+// TypeError 2271: (167-176): Operator <= not compatible with types contract C and contract C. No arithmetic or comparison operations are allowed on contract types. Consider converting to "address".
+// TypeError 2271: (188-196): Operator < not compatible with types contract C and contract C. No arithmetic or comparison operations are allowed on contract types. Consider converting to "address".
+// TypeError 2271: (208-216): Operator > not compatible with types contract C and contract C. No arithmetic or comparison operations are allowed on contract types. Consider converting to "address".