cgen: fix assigning option of array index (fix #23451) (#23455)

vlib/v/gen/c/cgen.v

@@ -6718,6 +6718,12 @@ fn (mut g Gen) gen_or_block_stmts(cvar_name string, cast_typ string, stmts []ast
 								if expr_stmt.expr.is_return_used {
 									g.write('*(${cast_typ}*) ${cvar_name}.data = ')
 								}
+							} else if g.inside_opt_or_res && return_is_option && g.inside_assign {
+								g.write('_option_ok(&(${cast_typ}[]) { ')
+								g.expr_with_cast(expr_stmt.expr, expr_stmt.typ, return_type.clear_option_and_result())
+								g.writeln(' }, (${option_name}*)&${cvar_name}, sizeof(${cast_typ}));')
+								g.indent--
+								return
 							} else {
 								g.write('*(${cast_typ}*) ${cvar_name}.data = ')
 							}

vlib/v/gen/c/index.v

@@ -342,7 +342,11 @@ fn (mut g Gen) index_of_array(node ast.IndexExpr, sym ast.TypeSymbol) {
 				g.or_block(tmp_opt, node.or_expr, elem_type)
 			}
 			if !g.is_amp {
-				g.write('\n${cur_line}(*(${elem_type_str}*)${tmp_opt}.data)')
+				if g.inside_opt_or_res && elem_type.has_flag(.option) && g.inside_assign {
+					g.write('\n${cur_line}(*(${elem_type_str}*)&${tmp_opt})')
+				} else {
+					g.write('\n${cur_line}(*(${elem_type_str}*)${tmp_opt}.data)')
+				}
 			} else {
 				g.write('\n${cur_line}*${tmp_opt_ptr}')
 			}

vlib/v/tests/assign/assign_option_of_array_index_test.v

@@ -0,0 +1,9 @@
+fn make_option() ?string {
+	return none
+}
+
+fn test_assign_option_of_array_index() {
+	arr := [make_option()]
+	unwrapped := arr[99] or { 'unknown' } // <- out of bounds access!
+	assert '${unwrapped}' == "Option('unknown')"
+}