From 315dff328518f5003bbbfcf6934e3edcb26e7be4 Mon Sep 17 00:00:00 2001
From: Max Brunsfeld <maxbrunsfeld@gmail.com>
Date: Tue, 9 Jan 2018 12:33:51 -0800
Subject: [PATCH] Add an API for getting a node's child index

---
 include/tree_sitter/runtime.h |  1 +
 src/runtime/node.c            | 19 +++++++++++++++++++
 test/runtime/node_test.cc     | 12 ++++++++++++
 3 files changed, 32 insertions(+)

diff --git a/include/tree_sitter/runtime.h b/include/tree_sitter/runtime.h
index 9f51b549..c4dde4fe 100644
--- a/include/tree_sitter/runtime.h
+++ b/include/tree_sitter/runtime.h
@@ -92,6 +92,7 @@ TSNode ts_node_child(TSNode, uint32_t);
 TSNode ts_node_named_child(TSNode, uint32_t);
 uint32_t ts_node_child_count(TSNode);
 uint32_t ts_node_named_child_count(TSNode);
+uint32_t ts_node_child_index(TSNode);
 TSNode ts_node_next_sibling(TSNode);
 TSNode ts_node_next_named_sibling(TSNode);
 TSNode ts_node_prev_sibling(TSNode);
diff --git a/src/runtime/node.c b/src/runtime/node.c
index cec988cf..e4353e5b 100644
--- a/src/runtime/node.c
+++ b/src/runtime/node.c
@@ -329,6 +329,25 @@ TSNode ts_node_parent(TSNode self) {
   return result;
 }
 
+uint32_t ts_node_child_index(TSNode self) {
+  const Tree *tree = ts_node__tree(self);
+  uint32_t result = 0;
+
+  for (;;) {
+    const Tree *parent = tree->context.parent;
+    uint32_t index = tree->context.index;
+    if (!parent) return UINT32_MAX;
+    for (uint32_t i = 0; i < index; i++) {
+      Tree *child = parent->children[i];
+      result += child->visible ? 1 : child->visible_child_count;
+    }
+    if (parent->visible) break;
+    tree = parent;
+  }
+
+  return result;
+}
+
 TSNode ts_node_child(TSNode self, uint32_t child_index) {
   return ts_node__child(self, child_index, true);
 }
diff --git a/test/runtime/node_test.cc b/test/runtime/node_test.cc
index fcc7552d..bb620244 100644
--- a/test/runtime/node_test.cc
+++ b/test/runtime/node_test.cc
@@ -243,6 +243,18 @@ describe("Node", [&]() {
     });
   });
 
+  describe("child_index()", [&]() {
+    it("returns the index of the node within its parent", [&]() {
+      AssertThat(ts_node_child_index(ts_node_child(root_node, 0)), Equals(0u));
+      AssertThat(ts_node_child_index(ts_node_child(root_node, 1)), Equals(1u));
+      AssertThat(ts_node_child_index(ts_node_child(root_node, 2)), Equals(2u));
+      AssertThat(ts_node_child_index(ts_node_child(root_node, 3)), Equals(3u));
+      AssertThat(ts_node_child_index(ts_node_child(root_node, 4)), Equals(4u));
+      AssertThat(ts_node_child_index(ts_node_child(root_node, 5)), Equals(5u));
+      AssertThat(ts_node_child_index(ts_node_child(root_node, 6)), Equals(6u));
+    });
+  });
+
   describe("symbols()", [&]() {
     it("returns an iterator that yields each of the node's symbols", [&]() {
       const TSLanguage *language = ts_document_language(document);