Disallow variables of library types

Changelog.md

@@ -12,6 +12,7 @@ Compiler Features:
  * SMTChecker: Support inheritance and function overriding.
  * Standard JSON Interface: Output the storage layout of a contract when artifact ``storageLayout`` is requested.
  * TypeChecker: List possible candidates when overload resolution fails.
+ * TypeChecker: Disallow variables of library types.
 
 
 Bugfixes:

libsolidity/analysis/TypeChecker.cpp

@@ -450,6 +450,9 @@ bool TypeChecker::visit(VariableDeclaration const& _variable)
 	TypePointer varType = _variable.annotation().type;
 	solAssert(!!varType, "Variable type not provided.");
 
+	if (auto contractType = dynamic_cast<ContractType const*>(varType))
+		if (contractType->contractDefinition().isLibrary())
+			m_errorReporter.typeError(_variable.location(), "The type of a variable cannot be a library.");
 	if (_variable.value())
 		expectType(*_variable.value(), *varType);
 	if (_variable.isConstant())

test/libsolidity/ABIJson/library_function.sol

@@ -1,9 +1,14 @@
+contract X {}
 library test {
     struct StructType { uint a; }
-    function f(StructType storage b, uint[] storage c, test d) public returns (uint[] memory e, StructType storage f) { f = f; }
+    function f(StructType storage b, uint[] storage c, X d) public returns (uint[] memory e, StructType storage f) { f = f; }
-    function f1(uint[] memory c, test d) public pure returns (uint[] memory e) {  }
+    function f1(uint[] memory c, X d) public pure returns (uint[] memory e) {  }
 }
 // ----
+//     :X
+// []
+//
+//
 //     :test
 // [
 //   {
@@ -16,9 +21,9 @@ library test {
 //         "type": "uint256[]"
 //       },
 //       {
-//         "internalType": "library test",
+//         "internalType": "contract X",
 //         "name": "d",
-//         "type": "test"
+//         "type": "X"
 //       }
 //     ],
 //     "name": "f1",

test/libsolidity/syntaxTests/nameAndTypeResolution/301_library_instances_cannot_be_used.sol

@@ -6,4 +6,5 @@ contract test {
     }
 }
 // ----
+// TypeError: (87-90): The type of a variable cannot be a library.
 // TypeError: (100-103): Member "l" not found or not visible after argument-dependent lookup in library L.

test/libsolidity/syntaxTests/nameAndTypeResolution/typeChecking/library_instances.sol

@@ -0,0 +1,14 @@
+library X { }
+
+contract Y {
+	X abc;
+	function foo(X param) private view
+	{
+		X ofg;
+		ofg = abc;
+	}
+}
+// ----
+// TypeError: (29-34): The type of a variable cannot be a library.
+// TypeError: (50-57): The type of a variable cannot be a library.
+// TypeError: (77-82): The type of a variable cannot be a library.