p_parse_inner: do not consume the follow token

spec/test_parse_inner_shared.c

@@ -50,13 +50,26 @@ int main()
     /* parse_inner_R1("abb", [b]) succeeds: even though `b` is the lookahead
      * that parse_Start uses to select R2 over R1 in the ambiguous state, from
      * R1's start state the reduce to R1 is unconditional, and the follow-
-     * token shift retry at the R1-accepting state completes the parse. */
+     * token shift retry at the R1-accepting state completes the parse.
+     *
+     * The follow token that completed the parse must not be consumed from
+     * the input: p_position() should point to the follow token, and a
+     * subsequent p_lex() should return it. */
     {
         input = "abb";
         context = p_context_new((uint8_t const *)input, strlen(input));
         p_token_t follow_tokens[] = { TOKEN_b };
         assert(p_parse_inner_R1(context, follow_tokens, 1u) == P_SUCCESS);
         assert_eq(11u, (size_t)p_result_R1(context));
+        /* Follow token `b` is at column 3 (1-based). */
+        p_position_t pos = p_position(context);
+        assert_eq(1u, (size_t)pos.row);
+        assert_eq(3u, (size_t)pos.col);
+        p_token_info_t token_info;
+        assert(p_lex(context, &token_info) == P_SUCCESS);
+        assert_eq((size_t)TOKEN_b, (size_t)token_info.token);
+        assert_eq(1u, (size_t)token_info.position.row);
+        assert_eq(3u, (size_t)token_info.position.col);
         p_context_delete(context);
     }
 
@@ -69,6 +82,14 @@ int main()
         p_token_t follow_tokens[] = { TOKEN_a };
         assert(p_parse_inner_R1(context, follow_tokens, 1u) == P_SUCCESS);
         assert_eq(11u, (size_t)p_result_R1(context));
+        /* Follow token `a` is at column 3 (1-based) and remains in the
+         * input. */
+        p_position_t pos = p_position(context);
+        assert_eq(1u, (size_t)pos.row);
+        assert_eq(3u, (size_t)pos.col);
+        p_token_info_t token_info;
+        assert(p_lex(context, &token_info) == P_SUCCESS);
+        assert_eq((size_t)TOKEN_a, (size_t)token_info.token);
         p_context_delete(context);
     }