Add support for delete operator on UDVT (new branch)

libsolidity/ast/Types.cpp

@@ -2680,6 +2680,11 @@ BoolResult EnumType::isExplicitlyConvertibleTo(Type const& _convertTo) const
 	return false;
 }
 
+TypeResult UserDefinedValueType::unaryOperatorResult(Token _operator) const
+{
+	return _operator == Token::Delete ? TypeProvider::emptyTuple() : nullptr;
+}
+
 unsigned EnumType::memberValue(ASTString const& _member) const
 {
 	unsigned index = 0;

libsolidity/ast/Types.h

@@ -1146,6 +1146,7 @@ class UserDefinedValueType: public Type
 	{}
 
 	Category category() const override { return Category::UserDefinedValueType; }
+	TypeResult unaryOperatorResult(Token _operator) const override;
 	Type const& underlyingType() const;
 	UserDefinedValueTypeDefinition const& definition() const { return m_definition; }
 

test/libsolidity/semanticTests/userDefinedValueType/delete.sol

@@ -0,0 +1,43 @@
+type MyUInt256 is uint256;
+type MyBytes32 is bytes32;
+type MyAddress is address;
+type MyBool is bool;
+
+contract C {
+    MyUInt256 a = MyUInt256.wrap(255);
+
+    function f() external returns(MyUInt256) {
+        delete a;
+        return a;
+    }
+
+    function g(MyUInt256 b) external returns(MyUInt256) {
+        delete b;
+        return b;
+    }
+
+    function h(MyAddress b) external returns(MyAddress) {
+        delete b;
+        return b;
+    }
+
+    function i(MyBytes32 b) external returns(MyBytes32) {
+        delete b;
+        return b;
+    }
+
+    function j(MyBool b) external returns(MyBool) {
+        delete b;
+        return b;
+    }
+}
+// ----
+// f() -> 0
+// g(uint256): 255 -> 0
+// g(uint256): 0 -> 0
+// h(address): 0xffffffffffffffffffffffffffffffffffffffff -> 0x0000000000000000000000000000000000000000
+// h(address): 0x0000000000000000000000000000000000000000 -> 0x0000000000000000000000000000000000000000
+// i(bytes32): 0xffffffffffffffffffffffffffffffffffffffff -> 0x0000000000000000000000000000000000000000
+// i(bytes32): 0x0000000000000000000000000000000000000000 -> 0x0000000000000000000000000000000000000000
+// j(bool): true -> false
+// j(bool): false -> false