Add p_set_input_index()

spec/test_set_position.c

@@ -77,5 +77,33 @@ int main()
         p_context_delete(context);
     }
 
+    /* p_set_input_index() rewinds the lexer's byte cursor. Combined with
+     * p_set_position(), it re-reads an earlier section of the input: both
+     * tokens are lexed, then the cursor and text position are rewound to the
+     * start so that the same tokens are produced again with the same reported
+     * positions. */
+    {
+        char const * input = "ab";
+        p_context_t * context = p_context_new((uint8_t const *)input, strlen(input));
+        p_token_info_t token_info;
+        size_t start_index = p_input_index(context);
+        p_position_t start_position = p_position(context);
+        assert_eq(0u, start_index);
+        assert(p_lex(context, &token_info) == P_SUCCESS);
+        assert_eq((size_t)TOKEN_a, (size_t)token_info.token);
+        assert(p_lex(context, &token_info) == P_SUCCESS);
+        assert_eq((size_t)TOKEN_b, (size_t)token_info.token);
+        assert_eq(2u, p_input_index(context));
+        /* Rewind and re-read from the start. */
+        p_set_input_index(context, start_index);
+        p_set_position(context, start_position);
+        assert_eq(0u, p_input_index(context));
+        assert(p_lex(context, &token_info) == P_SUCCESS);
+        assert_eq((size_t)TOKEN_a, (size_t)token_info.token);
+        assert_eq(1u, (size_t)token_info.position.row);
+        assert_eq(1u, (size_t)token_info.position.col);
+        p_context_delete(context);
+    }
+
     return 0;
 }