checker: add more checks for operator overloading (#8030)

vlib/v/checker/checker.v

@@ -5114,7 +5114,8 @@ fn (mut c Checker) fn_decl(mut node ast.FnDecl) {
 			c.error('.str() methods should have 0 arguments', node.pos)
 		}
 	}
-	if node.language == .v && node.is_method && node.name in ['+', '-', '*', '%', '/', '<', '>', '==', '!='] {
+	if node.language == .v && node.is_method && node.name in
+		['+', '-', '*', '%', '/', '<', '>', '==', '!=', '>=', '<='] {
 		if node.params.len != 2 {
 			c.error('operator methods should have exactly 1 argument', node.pos)
 		} else {
@@ -5124,7 +5125,11 @@ fn (mut c Checker) fn_decl(mut node ast.FnDecl) {
 				c.error('operator methods are only allowed for struct and type alias',
 					node.pos)
 			} else {
-				if node.receiver.typ != node.params[1].typ {
+				if node.rec_mut {
+					c.error('receiver cannot be `mut` for operator overloading', node.receiver_pos)
+				} else if node.params[1].is_mut {
+					c.error('argument cannot be `mut` for operator overloading', node.pos)
+				} else if node.receiver.typ != node.params[1].typ {
 					c.error('both sides of an operator must be the same type', node.pos)
 				} else if node.name in ['<', '>', '==', '!=', '>=', '<='] &&
 					node.return_type != table.bool_type {

vlib/v/checker/tests/method_op_err.out

@@ -19,23 +19,37 @@ vlib/v/checker/tests/method_op_err.vv:18:1: error: operator comparison methods s
       | ~~~~~~~~~~~~~~~~~~~~~~~~~~~~
    19 |     return User{}
    20 | }
-vlib/v/checker/tests/method_op_err.vv:24:24: error: infix expr: cannot use `Foo` (right expression) as `User`
+vlib/v/checker/tests/method_op_err.vv:22:9: error: receiver cannot be `mut` for operator overloading
-   22 | fn main() {
+   20 | }
-   23 |     println(User{3, 4})
+   21 | 
-   24 |     println(User{3, 4} - Foo{3, 3})
+   22 | fn (mut u User) * (u1 User) User {
+      |         ~~~~~~
+   23 |     return User{}
+   24 | }
+vlib/v/checker/tests/method_op_err.vv:26:1: error: argument cannot be `mut` for operator overloading
+   24 | }
+   25 | 
+   26 | fn (u User) / (mut u1 User) User {
+      | ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+   27 |     return User{}
+   28 | }
+vlib/v/checker/tests/method_op_err.vv:32:24: error: infix expr: cannot use `Foo` (right expression) as `User`
+   30 | fn main() {
+   31 |     println(User{3, 4})
+   32 |     println(User{3, 4} - Foo{3, 3})
       |                        ^
-   25 |     println(User{3, 2} < User{2, 4})
+   33 |     println(User{3, 2} < User{2, 4})
-   26 |     println(User{3, 4} < Foo{3, 4})
+   34 |     println(User{3, 4} < Foo{3, 4})
-vlib/v/checker/tests/method_op_err.vv:25:24: error: operation `User` < `User` does not exist, please define it
+vlib/v/checker/tests/method_op_err.vv:33:24: error: operation `User` < `User` does not exist, please define it
-   23 |     println(User{3, 4})
+   31 |     println(User{3, 4})
-   24 |     println(User{3, 4} - Foo{3, 3})
+   32 |     println(User{3, 4} - Foo{3, 3})
-   25 |     println(User{3, 2} < User{2, 4})
+   33 |     println(User{3, 2} < User{2, 4})
       |                        ^
-   26 |     println(User{3, 4} < Foo{3, 4})
+   34 |     println(User{3, 4} < Foo{3, 4})
-   27 | }
+   35 | }
-vlib/v/checker/tests/method_op_err.vv:26:24: error: mismatched types `User` and `Foo`
+vlib/v/checker/tests/method_op_err.vv:34:24: error: mismatched types `User` and `Foo`
-   24 |     println(User{3, 4} - Foo{3, 3})
+   32 |     println(User{3, 4} - Foo{3, 3})
-   25 |     println(User{3, 2} < User{2, 4})
+   33 |     println(User{3, 2} < User{2, 4})
-   26 |     println(User{3, 4} < Foo{3, 4})
+   34 |     println(User{3, 4} < Foo{3, 4})
       |                        ^
-   27 | }
+   35 | }

vlib/v/checker/tests/method_op_err.vv

@@ -19,6 +19,14 @@ fn (u User) > (u1 User) User {
     return User{}
 }
 
+fn (mut u User) * (u1 User) User {
+    return User{}
+}
+
+fn (u User) / (mut u1 User) User {
+    return User{}
+}
+
 fn main() {
     println(User{3, 4})
     println(User{3, 4} - Foo{3, 3})