Fix child count error when documents starts w/ ubiquitous tokens

spec/runtime/language_specs.cc

@@ -1,5 +1,6 @@
 #include "runtime/runtime_spec_helper.h"
 #include <functional>
+#include "runtime/length.h"
 #include "runtime/helpers/read_test_entries.h"
 #include "runtime/helpers/spy_input.h"
 #include "runtime/helpers/log_debugger.h"
@@ -11,6 +12,35 @@ extern "C" const TSLanguage *ts_language_golang();
 extern "C" const TSLanguage *ts_language_c();
 extern "C" const TSLanguage *ts_language_cpp();
 
+void expect_the_correct_tree(TSNode node, TSDocument *doc, string tree_string) {
+  const char *node_string = ts_node_string(node, doc);
+  AssertThat(node_string, Equals(tree_string));
+  free((void *)node_string);
+}
+
+void expect_a_consistent_tree(TSNode node, TSDocument *doc) {
+  TSLength start = ts_node_pos(node);
+  TSLength end = ts_length_add(start, ts_node_size(node));
+  size_t child_count = ts_node_child_count(node);
+
+  bool has_changes = ts_node_has_changes(node);
+  bool some_child_has_changes = false;
+
+  for (size_t i = 0; i < child_count; i++) {
+    TSNode child = ts_node_child(node, i);
+    TSLength child_start = ts_node_pos(child);
+    TSLength child_end = ts_length_add(child_start, ts_node_size(child));
+
+    AssertThat(child_start.chars, IsGreaterThan(start.chars) || Equals(start.chars));
+    AssertThat(child_end.chars, IsLessThan(end.chars) || Equals(end.chars));
+    if (ts_node_has_changes(child))
+      some_child_has_changes = true;
+  }
+
+  if (child_count > 0)
+    AssertThat(has_changes, Equals(some_child_has_changes));
+}
+
 START_TEST
 
 map<string, const TSLanguage *> languages({
@@ -43,18 +73,14 @@ describe("Languages", [&]() {
       for (auto &entry : test_entries_for_language(pair.first)) {
         SpyInput *input;
 
-        auto expect_the_correct_tree = [&](string tree_string) {
-          const char *node_string = ts_node_string(ts_document_root_node(doc), doc);
-          AssertThat(node_string, Equals(tree_string));
-          free((void *)node_string);
-        };
-
         auto it_handles_edit_sequence = [&](string name, std::function<void()> edit_sequence){
           it(("parses " + entry.description + ": " + name).c_str(), [&]() {
             input = new SpyInput(entry.input, 3);
             ts_document_set_input(doc, input->input());
             edit_sequence();
-            expect_the_correct_tree(entry.tree_string);
+            TSNode root_node = ts_document_root_node(doc);
+            expect_the_correct_tree(root_node, doc, entry.tree_string);
+            expect_a_consistent_tree(root_node, doc);
             delete input;
           });
         };

src/runtime/tree.c

@@ -40,6 +40,7 @@ static void ts_tree__set_children(TSTree *self, TSTree **children,
                                   size_t child_count) {
   self->children = children;
   self->child_count = child_count;
+  self->visible_child_count = 0;
   for (size_t i = 0; i < child_count; i++) {
     TSTree *child = children[i];
     ts_tree_retain(child);