Make tree node handle names visible in context user fields

spec/test_context_field_handle.cpp

@@ -0,0 +1,36 @@
+#include "testparser.h"
+#include <cassert>
+#include <cstring>
+#include "testutils.h"
+
+int main()
+{
+    char input[128];
+
+    /* Enough tokens that the tree node arena is reallocated during the parse. */
+    memset(input, 0, sizeof(input));
+    for (size_t i = 0u; i < 40u; i++)
+    {
+        input[i] = 'a';
+    }
+
+    p_context_t * context = p_context_new((uint8_t const *)input, strlen(input));
+    assert_eq(P_SUCCESS, p_parse(context));
+
+    /* The handle was stored in a context user field during the parse, before
+     * the remaining nodes were created. It still refers to the same node. */
+    assert_eq(1u, context->have_first);
+    assert(context->first_item.valid());
+    Token token = context->first_item.pToken1();
+    assert(token.valid());
+    assert_eq(TOKEN_a, token.token());
+    assert_eq(7u, token.pvalue());
+
+    /* The stored handle refers to the first Item, which starts at column 1. */
+    assert_eq(1u, context->first_item.position().row);
+    assert_eq(1u, context->first_item.position().col);
+
+    p_context_delete(context);
+
+    return 0;
+}