treesitter: allow to iterate over node children

runtime/doc/lua.txt

@@ -622,6 +622,12 @@ Node methods						*lua-treesitter-node*
 tsnode:parent()						*tsnode:parent()*
 	Get the node's immediate parent.
 
+tsnode:iter_children()					*tsnode:iter_children()*
+	Iterates over all the direct children of {tsnode}, regardless of
+	wether they are named or not.
+	Returns the child node plus the eventual field name corresponding to
+	this child node.
+
 tsnode:child_count()					*tsnode:child_count()*
 	Get the node's number of children.
 

src/nvim/lua/treesitter.c

@@ -73,6 +73,7 @@ static struct luaL_Reg node_meta[] = {
   { "descendant_for_range", node_descendant_for_range },
   { "named_descendant_for_range", node_named_descendant_for_range },
   { "parent", node_parent },
+  { "iter_children", node_iter_children },
   { "_rawquery", node_rawquery },
   { NULL, NULL }
 };
@@ -84,12 +85,17 @@ static struct luaL_Reg query_meta[] = {
   { NULL, NULL }
 };
 
-// cursor is not exposed, but still needs garbage collection
+// cursors are not exposed, but still needs garbage collection
 static struct luaL_Reg querycursor_meta[] = {
   { "__gc", querycursor_gc },
   { NULL, NULL }
 };
 
+static struct luaL_Reg treecursor_meta[] = {
+  { "__gc", treecursor_gc },
+  { NULL, NULL }
+};
+
 static PMap(cstr_t) *langs;
 
 static void build_meta(lua_State *L, const char *tname, const luaL_Reg *meta)
@@ -116,6 +122,7 @@ void tslua_init(lua_State *L)
   build_meta(L, "treesitter_node", node_meta);
   build_meta(L, "treesitter_query", query_meta);
   build_meta(L, "treesitter_querycursor", querycursor_meta);
+  build_meta(L, "treesitter_treecursor", treecursor_meta);
 }
 
 int tslua_has_language(lua_State *L)
@@ -746,6 +753,74 @@ static int node_named_descendant_for_range(lua_State *L)
   return 1;
 }
 
+static int node_next_child(lua_State *L)
+{
+  TSTreeCursor *ud = luaL_checkudata(
+      L, lua_upvalueindex(1), "treesitter_treecursor");
+  if (!ud) {
+    return 0;
+  }
+
+  TSNode source;
+  if (!node_check(L, lua_upvalueindex(2), &source)) {
+    return 0;
+  }
+
+  // First call should return first child
+  if (ts_node_eq(source, ts_tree_cursor_current_node(ud))) {
+    if (ts_tree_cursor_goto_first_child(ud)) {
+      goto push;
+    } else {
+      goto end;
+    }
+  }
+
+  if (ts_tree_cursor_goto_next_sibling(ud)) {
+push:
+      push_node(
+          L,
+          ts_tree_cursor_current_node(ud),
+          lua_upvalueindex(2));  // [node]
+
+      const char * field = ts_tree_cursor_current_field_name(ud);
+
+      if (field != NULL) {
+        lua_pushstring(L, ts_tree_cursor_current_field_name(ud));
+      } else {
+        lua_pushnil(L);
+      }  // [node, field_name_or_nil]
+      return 2;
+  }
+
+end:
+  return 0;
+}
+
+static int node_iter_children(lua_State *L)
+{
+  TSNode source;
+  if (!node_check(L, 1, &source)) {
+    return 0;
+  }
+
+  TSTreeCursor *ud = lua_newuserdata(L, sizeof(TSTreeCursor));  // [udata]
+  *ud = ts_tree_cursor_new(source);
+
+  lua_getfield(L, LUA_REGISTRYINDEX, "treesitter_treecursor");  // [udata, mt]
+  lua_setmetatable(L, -2);  // [udata]
+  lua_pushvalue(L, 1);  // [udata, source_node]
+  lua_pushcclosure(L, node_next_child, 2);
+
+  return 1;
+}
+
+static int treecursor_gc(lua_State *L)
+{
+  TSTreeCursor *ud = luaL_checkudata(L, 1, "treesitter_treecursor");
+  ts_tree_cursor_delete(ud);
+  return 0;
+}
+
 static int node_parent(lua_State *L)
 {
   TSNode node;

test/functional/lua/treesitter_spec.lua

@@ -127,6 +127,30 @@ void ui_refresh(void)
   }
 }]]
 
+  it('allows to iterate over nodes children', function()
+    if not check_parser() then return end
+
+    insert(test_text);
+
+    local res = exec_lua([[
+      parser = vim.treesitter.get_parser(0, "c")
+
+      func_node = parser:parse():root():child(0)
+
+      res = {}
+      for node, field in func_node:iter_children() do
+        table.insert(res, {node:type(), field})
+      end
+      return res
+    ]])
+
+    eq({
+      {"primitive_type", "type"},
+      {"function_declarator", "declarator"},
+      {"compound_statement", "body"}
+    }, res)
+  end)
+
   local query = [[
     ((call_expression function: (identifier) @minfunc (argument_list (identifier) @min_id)) (eq? @minfunc "MIN"))
     "for" @keyword