Update tests after code review

libsolidity/parsing/Parser.cpp

@@ -989,11 +989,16 @@ ASTPointer<UsingForDirective> Parser::parseUsingDirective()
 					Token::BitNot
 				};
 				if (!util::contains(overridable, operator_))
+				{
 					parserError(
 						4403_error,
-						("The operator " + string{TokenTraits::toString(operator_)} + " cannot be user-implemented. This is only possible for the following operators: ") +
+						(
+							"The operator " + (TokenTraits::toString(operator_) ? string(TokenTraits::toString(operator_)) + " " : "")
+							+ "cannot be user-implemented. This is only possible for the following operators: "
+						) +
 						util::joinHumanReadable(overridable | ranges::views::transform([](Token _t) { return string{TokenTraits::toString(_t)}; }))
 					);
+				}
 				operators.emplace_back(operator_);
 				advance();
 			}

test/libsolidity/syntaxTests/operators/custom/operator_bound_to_error.sol

@@ -0,0 +1,10 @@
+using {add as +} for E;
+
+error E();
+
+function add(E, E) pure returns (E) {
+    return E.E1;
+}
+
+// ----
+// TypeError 5172: (21-22): Name has to refer to a user-defined value type, struct, enum or contract.

test/libsolidity/syntaxTests/operators/custom/operator_not_user_implementable.sol

@@ -1,10 +1,14 @@
 using {
-    shiftL as <<, shiftR as >>,
-    exp as **, neg as !
+    shiftL as <<,
+    shiftR as >>,
+    exp as **,
+    neg as !,
+    f as x
 } for int256;
 
 // ----
 // ParserError 4403: (22-24): The operator << cannot be user-implemented. This is only possible for the following operators: |, &, ^, +, -, *, /, %, ==, !=, <, >, <=, >=, ~
-// ParserError 4403: (36-38): The operator >> cannot be user-implemented. This is only possible for the following operators: |, &, ^, +, -, *, /, %, ==, !=, <, >, <=, >=, ~
-// ParserError 4403: (51-53): The operator ** cannot be user-implemented. This is only possible for the following operators: |, &, ^, +, -, *, /, %, ==, !=, <, >, <=, >=, ~
-// ParserError 4403: (62-63): The operator ! cannot be user-implemented. This is only possible for the following operators: |, &, ^, +, -, *, /, %, ==, !=, <, >, <=, >=, ~
+// ParserError 4403: (40-42): The operator >> cannot be user-implemented. This is only possible for the following operators: |, &, ^, +, -, *, /, %, ==, !=, <, >, <=, >=, ~
+// ParserError 4403: (55-57): The operator ** cannot be user-implemented. This is only possible for the following operators: |, &, ^, +, -, *, /, %, ==, !=, <, >, <=, >=, ~
+// ParserError 4403: (70-71): The operator ! cannot be user-implemented. This is only possible for the following operators: |, &, ^, +, -, *, /, %, ==, !=, <, >, <=, >=, ~
+// ParserError 4403: (82-83): The operator cannot be user-implemented. This is only possible for the following operators: |, &, ^, +, -, *, /, %, ==, !=, <, >, <=, >=, ~

test/libsolidity/syntaxTests/operators/custom/operator_with_calldata_parameters.sol

@@ -0,0 +1,11 @@
+using {add as +} for S;
+
+struct S {
+    uint x;
+} 
+
+function add(S calldata, S calldata) pure returns (S calldata r) {
+    assembly {
+        r := 0
+    }
+}

test/libsolidity/syntaxTests/operators/custom/operator_with_storage_parameters.sol

@@ -0,0 +1,18 @@
+using {add as +} for S;
+
+struct S {
+    uint x;
+}
+
+function add(S storage a, S storage) pure returns (S storage) {
+    return a;
+}
+
+contract C {
+    S a;
+    S b;
+
+    function test() public view {
+        a + b;
+    }
+}