markused: fix generic map index (fix #25012) (#25022)

vlib/v/markused/walker.v

@@ -628,7 +628,7 @@ fn (mut w Walker) expr(node_ ast.Expr) {
 			w.expr(node.expr)
 			w.mark_by_type(node.expr_type)
 			w.uses_guard = true
-			if node.expr_type != 0 && !w.uses_str_index_check
+			if node.expr_type != 0 && !w.uses_str_index_check && node.expr is ast.IndexExpr
 				&& w.table.final_sym(node.expr_type).kind in [.u8, .string] {
 				w.uses_str_index_check = true
 			}
@@ -1296,9 +1296,6 @@ fn (mut w Walker) mark_resource_dependencies() {
 	if w.uses_mem_align {
 		w.fn_by_name('memdup_align')
 	}
-	if w.uses_guard || w.uses_check_index {
-		w.fn_by_name('error')
-	}
 	if w.uses_spawn {
 		w.fn_by_name('malloc')
 		w.fn_by_name('tos3')
@@ -1407,6 +1404,9 @@ fn (mut w Walker) mark_resource_dependencies() {
 			continue
 		}
 	}
+	if w.uses_guard || w.uses_check_index {
+		w.fn_by_name('error')
+	}
 	if w.uses_append {
 		ref_array_idx_str := int(ast.array_type.ref()).str()
 		w.fn_by_name(ref_array_idx_str + '.push')

vlib/v/tests/generics/struct_generic_map_index_test.v

@@ -0,0 +1,21 @@
+pub struct Set[T] {
+mut:
+	elements map[T]u8
+}
+
+pub fn (l Set[T]) == (r Set[T]) bool {
+	if l.elements.len != r.elements.len {
+		return false
+	}
+	for key, l_val in l.elements {
+		r_val := r.elements[key] or { return false }
+		if l_val != r_val {
+			return false
+		}
+	}
+	return true
+}
+
+fn test_main() {
+	_ := Set[int]{}
+}