Disallow conversion between unrelated contract types.

16 files changed, 99 insertions, 16 deletions

diff --git a/Changelog.md b/Changelog.md
index da287000..bcd55955 100644
--- a/Changelog.md
+++ b/Changelog.md
@@ -40,6 +40,7 @@ Breaking Changes:
  * Type Checker: Disallow arithmetic operations for boolean variables.
  * Type Checker: Disallow tight packing of literals. This was already the case in the experimental 0.5.0 mode.
  * Type Checker: Disallow conversions between ``bytesX`` and ``uintY`` of different size.
+ * Type Checker: Disallow conversions between unrelated contract types. Explicit conversion via ``address`` can still achieve it.
  * Type Checker: Disallow empty tuple components. This was partly already the case in the experimental 0.5.0 mode.
  * Type Checker: Disallow multi-variable declarations with mismatching number of values. This was already the case in the experimental 0.5.0 mode.
  * Type Checker: Disallow specifying base constructor arguments multiple times in the same inheritance hierarchy. This was already the case in the experimental 0.5.0 mode.
diff --git a/docs/contracts.rst b/docs/contracts.rst
index e78c3ff7..e87c8a67 100644
--- a/docs/contracts.rst
+++ b/docs/contracts.rst
@@ -1,5 +1,7 @@
 .. index:: ! contract
 
+.. _contracts:
+
 ##########
 Contracts
 ##########
diff --git a/docs/types.rst b/docs/types.rst
index d6767b54..3aad413d 100644
--- a/docs/types.rst
+++ b/docs/types.rst
@@ -192,6 +192,23 @@ The ``.gas()`` option is available on all three methods, while the ``.value()``
 .. note::
     The use of ``callcode`` is discouraged and will be removed in the future.
 
+Contract Types
+--------------
+
+Every :ref:`contract<contracts>` defines its own type. Contracts can be implicitly converted
+to contracts they inherit from. They can be explicitly converted from and to ``address`` types.
+
+The data representation of a contract is identical to that of the ``address`` type and
+this type is also used in the :ref:`ABI<ABI>`.
+
+Contracts do not support any operators.
+
+The members of contract types are the external functions of the contract including
+public state variables.
+
+.. note::
+    Starting with version 0.5.0 contracts do not derive from the address type, but can still be explicitly converted to address.
+
 .. index:: byte array, bytes32
 
 
diff --git a/libsolidity/ast/Types.cpp b/libsolidity/ast/Types.cpp
index 2c2d3b68..7b079f45 100644
--- a/libsolidity/ast/Types.cpp
+++ b/libsolidity/ast/Types.cpp
@@ -1403,15 +1403,15 @@ bool ContractType::isImplicitlyConvertibleTo(Type const& _convertTo) const
 {
 	if (*this == _convertTo)
 		return true;
-	if (_convertTo.category() == Category::Integer)
-		return dynamic_cast<IntegerType const&>(_convertTo).isAddress();
 	if (_convertTo.category() == Category::Contract)
 	{
 		auto const& bases = contractDefinition().annotation().linearizedBaseContracts;
 		if (m_super && bases.size() <= 1)
 			return false;
-		return find(m_super ? ++bases.begin() : bases.begin(), bases.end(),
-					&dynamic_cast<ContractType const&>(_convertTo).contractDefinition()) != bases.end();
+		return find(
+			m_super ? ++bases.begin() : bases.begin(), bases.end(),
+			&dynamic_cast<ContractType const&>(_convertTo).contractDefinition()
+		) != bases.end();
 	}
 	return false;
 }
@@ -1420,8 +1420,7 @@ bool ContractType::isExplicitlyConvertibleTo(Type const& _convertTo) const
 {
 	return
 		isImplicitlyConvertibleTo(_convertTo) ||
-		_convertTo.category() == Category::Integer ||
-		_convertTo.category() == Category::Contract;
+		_convertTo == IntegerType(160, IntegerType::Modifier::Address);
 }
 
 bool ContractType::isPayable() const
diff --git a/libsolidity/ast/Types.h b/libsolidity/ast/Types.h
index 1a676b42..474a6f33 100644
--- a/libsolidity/ast/Types.h
+++ b/libsolidity/ast/Types.h
@@ -692,9 +692,9 @@ public:
 	virtual Category category() const override { return Category::Contract; }
 	explicit ContractType(ContractDefinition const& _contract, bool _super = false):
 		m_contract(_contract), m_super(_super) {}
-	/// Contracts can be implicitly converted to super classes and to addresses.
+	/// Contracts can be implicitly converted only to base contracts.
 	virtual bool isImplicitlyConvertibleTo(Type const& _convertTo) const override;
-	/// Contracts can be converted to themselves and to integers.
+	/// Contracts can only be explicitly converted to address types and base contracts.
 	virtual bool isExplicitlyConvertibleTo(Type const& _convertTo) const override;
 	virtual TypePointer unaryOperatorResult(Token::Value _operator) const override;
 	virtual std::string richIdentifier() const override;
diff --git a/test/libsolidity/SolidityEndToEndTest.cpp b/test/libsolidity/SolidityEndToEndTest.cpp
index 223250fa..f52d270d 100644
--- a/test/libsolidity/SolidityEndToEndTest.cpp
+++ b/test/libsolidity/SolidityEndToEndTest.cpp
@@ -9420,7 +9420,7 @@ BOOST_AUTO_TEST_CASE(failed_create)
 		contract C {
 			uint public x;
 			constructor() public payable {}
-			function f(uint amount) public returns (address) {
+			function f(uint amount) public returns (D) {
 				x++;
 				return (new D).value(amount)();
 			}
@@ -12524,10 +12524,10 @@ BOOST_AUTO_TEST_CASE(staticcall_for_view_and_pure)
 				return (new C()).f();
 			}
 			function fview() public returns (uint) {
-				return (CView(new C())).f();
+				return (CView(address(new C()))).f();
 			}
 			function fpure() public returns (uint) {
-				return (CPure(new C())).f();
+				return (CPure(address(new C()))).f();
 			}
 		}
 	)";
diff --git a/test/libsolidity/syntaxTests/constructor/inconstructible_internal_constructor_inverted.sol b/test/libsolidity/syntaxTests/constructor/inconstructible_internal_constructor_inverted.sol
index 2a199b3a..ea2ec8f6 100644
--- a/test/libsolidity/syntaxTests/constructor/inconstructible_internal_constructor_inverted.sol
+++ b/test/libsolidity/syntaxTests/constructor/inconstructible_internal_constructor_inverted.sol
@@ -3,11 +3,10 @@
 contract B {
 	A a;
 	constructor() public {
-		a = new A(this);
+		a = new A(address(this));
 	}
 }
 contract A {
-	constructor(address a) internal {}
+	constructor(address) public {}
 }
 // ----
-// TypeError: (141-146): Contract with internal constructor cannot be created directly.
diff --git a/test/libsolidity/syntaxTests/parsing/constructor_allowed_this.sol b/test/libsolidity/syntaxTests/parsing/constructor_allowed_this.sol
index 9f714aea..b66253e4 100644
--- a/test/libsolidity/syntaxTests/parsing/constructor_allowed_this.sol
+++ b/test/libsolidity/syntaxTests/parsing/constructor_allowed_this.sol
@@ -3,9 +3,9 @@ contract A {
     }
 }
 contract B {
-    constructor(address) public {
+    constructor(C) public {
     }
-    function b(address) public returns (A) {
+    function b(C) public returns (A) {
         return new A();
     }
 }
diff --git a/test/libsolidity/syntaxTests/types/address_to_contract.sol b/test/libsolidity/syntaxTests/types/address_to_contract.sol
new file mode 100644
index 00000000..629a3df0
--- /dev/null
+++ b/test/libsolidity/syntaxTests/types/address_to_contract.sol
@@ -0,0 +1,6 @@
+contract C {
+  function f() public pure returns (C c) {
+    c = C(address(2));
+  }
+}
+// ----
diff --git a/test/libsolidity/syntaxTests/types/address_to_contract_implicitly.sol b/test/libsolidity/syntaxTests/types/address_to_contract_implicitly.sol
new file mode 100644
index 00000000..efab7c27
--- /dev/null
+++ b/test/libsolidity/syntaxTests/types/address_to_contract_implicitly.sol
@@ -0,0 +1,7 @@
+contract C {
+  function f() public view {
+    C c = address(2);
+  }
+}
+// ----
+// TypeError: (46-62): Type address is not implicitly convertible to expected type contract C.
diff --git a/test/libsolidity/syntaxTests/types/contract_to_address.sol b/test/libsolidity/syntaxTests/types/contract_to_address.sol
new file mode 100644
index 00000000..ec2f8184
--- /dev/null
+++ b/test/libsolidity/syntaxTests/types/contract_to_address.sol
@@ -0,0 +1,7 @@
+contract C {
+  function f() public view {
+    address a = address(this);
+    a;
+  }
+}
+// ----
diff --git a/test/libsolidity/syntaxTests/types/contract_to_address_implicitly.sol b/test/libsolidity/syntaxTests/types/contract_to_address_implicitly.sol
new file mode 100644
index 00000000..8be9daac
--- /dev/null
+++ b/test/libsolidity/syntaxTests/types/contract_to_address_implicitly.sol
@@ -0,0 +1,8 @@
+contract C {
+  function f() public view {
+    address a = this;
+    a;
+  }
+}
+// ----
+// TypeError: (46-62): Type contract C is not implicitly convertible to expected type address.
diff --git a/test/libsolidity/syntaxTests/types/contract_to_base.sol b/test/libsolidity/syntaxTests/types/contract_to_base.sol
new file mode 100644
index 00000000..b0a24e62
--- /dev/null
+++ b/test/libsolidity/syntaxTests/types/contract_to_base.sol
@@ -0,0 +1,9 @@
+contract A {}
+contract B is A {}
+contract C {
+  function f() public {
+    A a = new B();
+    a;
+  }
+}
+// ----
diff --git a/test/libsolidity/syntaxTests/types/contract_to_base_base.sol b/test/libsolidity/syntaxTests/types/contract_to_base_base.sol
new file mode 100644
index 00000000..e99e5cdc
--- /dev/null
+++ b/test/libsolidity/syntaxTests/types/contract_to_base_base.sol
@@ -0,0 +1,10 @@
+contract A {}
+contract B is A {}
+contract C is B {}
+contract D {
+  function f() public {
+    A a = new C();
+    a;
+  }
+}
+// ----
diff --git a/test/libsolidity/syntaxTests/types/contract_to_derived.sol b/test/libsolidity/syntaxTests/types/contract_to_derived.sol
new file mode 100644
index 00000000..ac8df5d1
--- /dev/null
+++ b/test/libsolidity/syntaxTests/types/contract_to_derived.sol
@@ -0,0 +1,9 @@
+contract B {}
+contract A is B {}
+contract C {
+  function f() public pure {
+    A a = A(new B());
+  }
+}
+// ----
+// TypeError: (85-95): Explicit type conversion not allowed from "contract B" to "contract A".
diff --git a/test/libsolidity/syntaxTests/types/contract_to_unrelated_contract.sol b/test/libsolidity/syntaxTests/types/contract_to_unrelated_contract.sol
new file mode 100644
index 00000000..b0a4875f
--- /dev/null
+++ b/test/libsolidity/syntaxTests/types/contract_to_unrelated_contract.sol
@@ -0,0 +1,9 @@
+contract A {}
+contract B {}
+contract C {
+  function f() public pure {
+    B b = B(new A());
+  }
+}
+// ----
+// TypeError: (80-90): Explicit type conversion not allowed from "contract A" to "contract B".