checker: extend check assigning mut reference to immutable var in nested parens (#18442)

vlib/v/checker/assign.v

@@ -733,7 +733,11 @@ fn (mut c Checker) assign_stmt(mut node ast.AssignStmt) {
 			c.inside_ref_lit = old_inside_ref_lit
 			if right_node.op == .amp {
 				expr := if right_node.right is ast.ParExpr {
-					right_node.right.expr
+					mut expr_ := right_node.right.expr
+					for mut expr_ is ast.ParExpr {
+						expr_ = expr_.expr
+					}
+					expr_
 				} else {
 					right_node.right
 				}

vlib/v/checker/tests/assign_immutable_reference_var_with_parenthesis_err.out

@@ -1,7 +1,77 @@
+vlib/v/checker/tests/assign_immutable_reference_var_with_parenthesis_err.vv:11:12: warning: redundant parentheses are used
+    9 | fn foo() {
+   10 |     mut a := &(a_char)
+   11 |     mut b := &((a_char))
+      |               ~~~~~~~~~~
+   12 |     mut c := &((((a_char))))
+   13 |     println(a)
+vlib/v/checker/tests/assign_immutable_reference_var_with_parenthesis_err.vv:11:12: warning: redundant parentheses are used
+    9 | fn foo() {
+   10 |     mut a := &(a_char)
+   11 |     mut b := &((a_char))
+      |               ~~~~~~~~~~
+   12 |     mut c := &((((a_char))))
+   13 |     println(a)
+vlib/v/checker/tests/assign_immutable_reference_var_with_parenthesis_err.vv:12:12: warning: redundant parentheses are used
+   10 |     mut a := &(a_char)
+   11 |     mut b := &((a_char))
+   12 |     mut c := &((((a_char))))
+      |               ~~~~~~~~~~~~~~
+   13 |     println(a)
+   14 |     println(b)
+vlib/v/checker/tests/assign_immutable_reference_var_with_parenthesis_err.vv:12:13: warning: redundant parentheses are used
+   10 |     mut a := &(a_char)
+   11 |     mut b := &((a_char))
+   12 |     mut c := &((((a_char))))
+      |                ~~~~~~~~~~~~
+   13 |     println(a)
+   14 |     println(b)
+vlib/v/checker/tests/assign_immutable_reference_var_with_parenthesis_err.vv:12:14: warning: redundant parentheses are used
+   10 |     mut a := &(a_char)
+   11 |     mut b := &((a_char))
+   12 |     mut c := &((((a_char))))
+      |                 ~~~~~~~~~~
+   13 |     println(a)
+   14 |     println(b)
+vlib/v/checker/tests/assign_immutable_reference_var_with_parenthesis_err.vv:12:12: warning: redundant parentheses are used
+   10 |     mut a := &(a_char)
+   11 |     mut b := &((a_char))
+   12 |     mut c := &((((a_char))))
+      |               ~~~~~~~~~~~~~~
+   13 |     println(a)
+   14 |     println(b)
+vlib/v/checker/tests/assign_immutable_reference_var_with_parenthesis_err.vv:12:13: warning: redundant parentheses are used
+   10 |     mut a := &(a_char)
+   11 |     mut b := &((a_char))
+   12 |     mut c := &((((a_char))))
+      |                ~~~~~~~~~~~~
+   13 |     println(a)
+   14 |     println(b)
+vlib/v/checker/tests/assign_immutable_reference_var_with_parenthesis_err.vv:12:14: warning: redundant parentheses are used
+   10 |     mut a := &(a_char)
+   11 |     mut b := &((a_char))
+   12 |     mut c := &((((a_char))))
+      |                 ~~~~~~~~~~
+   13 |     println(a)
+   14 |     println(b)
 vlib/v/checker/tests/assign_immutable_reference_var_with_parenthesis_err.vv:10:11: error: `a_char` is immutable, cannot have a mutable reference to it
     8 | 
     9 | fn foo() {
-   10 |     mut c := &(a_char)
+   10 |     mut a := &(a_char)
       |              ^
-   11 |     println(c)
+   11 |     mut b := &((a_char))
-   12 | }
+   12 |     mut c := &((((a_char))))
+vlib/v/checker/tests/assign_immutable_reference_var_with_parenthesis_err.vv:11:11: error: `a_char` is immutable, cannot have a mutable reference to it
+    9 | fn foo() {
+   10 |     mut a := &(a_char)
+   11 |     mut b := &((a_char))
+      |              ^
+   12 |     mut c := &((((a_char))))
+   13 |     println(a)
+vlib/v/checker/tests/assign_immutable_reference_var_with_parenthesis_err.vv:12:11: error: `a_char` is immutable, cannot have a mutable reference to it
+   10 |     mut a := &(a_char)
+   11 |     mut b := &((a_char))
+   12 |     mut c := &((((a_char))))
+      |              ^
+   13 |     println(a)
+   14 |     println(b)

vlib/v/checker/tests/assign_immutable_reference_var_with_parenthesis_err.vv

@@ -7,6 +7,10 @@ const a_char = MyChar{
 }
 
 fn foo() {
-	mut c := &(a_char)
+	mut a := &(a_char)
+	mut b := &((a_char))
+	mut c := &((((a_char))))
+	println(a)
+	println(b)
 	println(c)
 }