Implement missing read-only checker case for TuplePatternItemsHasRest

gcc/rust/ChangeLog:

	* checks/errors/rust-readonly-check.cc (collect_assignment_tuple): Implement
	read-only checker for tuple patterns with rest pattern.

Signed-off-by: Yap Zhi Heng <[email protected]>

Author: Polygonalr

gcc/rust/checks/errors/rust-readonly-check.cc

@@ -144,14 +144,24 @@ ReadonlyChecker::collect_assignment_tuple (TuplePattern &tuple_pattern,
     {
     case HIR::TuplePatternItems::ItemType::NO_REST:
       {
-	auto &items = static_cast<HIR::TuplePatternItemsNoRest &> (
+	auto &items_no_rest = static_cast<HIR::TuplePatternItemsNoRest &> (
 	  tuple_pattern.get_items ());
-	for (auto &sub : items.get_patterns ())
+	for (auto &sub : items_no_rest.get_patterns ())
 	  {
 	    collect_assignment (*sub, has_init_expr);
 	  }
       }
       break;
+    case HIR::TuplePatternItems::ItemType::HAS_REST:
+      {
+	auto &items_has_rest = static_cast<HIR::TuplePatternItemsHasRest &> (
+	  tuple_pattern.get_items ());
+	for (auto &sub : items_has_rest.get_lower_patterns ())
+	  collect_assignment (*sub, has_init_expr);
+	for (auto &sub : items_has_rest.get_upper_patterns ())
+	  collect_assignment (*sub, has_init_expr);
+      }
+      break;
     default:
       break;
     }

gcc/testsuite/rust/compile/tuplepattern-rest-readonly.rs

@@ -0,0 +1,5 @@
+fn main() {
+    let (a, .., b) = (1, 1);
+    a = 2; // { dg-error "assignment of read-only variable .a." }
+    b = 2; // { dg-error "assignment of read-only variable .b." }
+}