Test reentering parser for nested inner parses

spec/test_parse_inner_nested.d

@@ -0,0 +1,64 @@
+import testparser;
+import testutils;
+
+/* Grammar: see test_parse_inner_nested.c. */
+
+size_t mylexfn(p_context_t * context, p_token_info_t * out_token_info)
+{
+    size_t result = p_lex(context, out_token_info);
+    if (result != P_SUCCESS)
+    {
+        return result;
+    }
+    if (out_token_info.token == TOKEN_lparen)
+    {
+        /* Nested parse of the parenthesized sub-expression, stopping at the
+         * closing ')' follow token. This re-enters the parser while the outer
+         * parse is suspended in this lex callback. */
+        p_token_t[] follow_tokens = [TOKEN_rparen];
+        size_t inner_result = p_parse_inner_Start(context, follow_tokens);
+        if (inner_result != P_SUCCESS)
+        {
+            return inner_result;
+        }
+        int value = p_result_Start(context);
+        /* p_parse_inner rewound the input so that ')' was not consumed; consume
+         * it now. */
+        p_token_info_t rparen_info;
+        size_t rparen_result = p_lex(context, &rparen_info);
+        assert(rparen_result == P_SUCCESS);
+        assert(rparen_info.token == TOKEN_rparen);
+        /* Replace the '(' token with a synthesized num carrying the nested
+         * parse result. */
+        out_token_info.token = TOKEN_num;
+        out_token_info.pvalue.v_default = value;
+    }
+    return P_SUCCESS;
+}
+
+int eval(string input)
+{
+    p_context_t * context = p_context_new(input);
+    assert(p_parse(context) == P_SUCCESS);
+    int value = p_result(context);
+    p_context_delete(context);
+    return value;
+}
+
+int main()
+{
+    return 0;
+}
+
+unittest
+{
+    /* No parentheses: plain outer parse. */
+    assert_eq(5, eval("2 + 3"));
+    /* A single group evaluated by the nested parse. */
+    assert_eq(3, eval("(1 + 2)"));
+    /* A group in the middle of an outer expression. */
+    assert_eq(14, eval("2 + (3 + 4) + 5"));
+    /* Nested groups: the nested parse re-enters itself. */
+    assert_eq(37, eval("2 + (10 + (20 + 5))"));
+    assert_eq(15, eval("(1 + 2) + (3 + (4 + 5))"));
+}