Disallow conversion between unrelated contract types.

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.

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();
     }
 }

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));
+  }
+}
+// ----

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.

test/libsolidity/syntaxTests/types/contract_to_address.sol

@@ -0,0 +1,7 @@
+contract C {
+  function f() public view {
+    address a = address(this);
+    a;
+  }
+}
+// ----

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.

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;
+  }
+}
+// ----

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;
+  }
+}
+// ----

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".

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".