treesitter: add node:id()

runtime/doc/treesitter.txt

@@ -136,6 +136,15 @@ tsnode:has_error()					*tsnode:has_error()*
 tsnode:sexpr()						*tsnode:sexpr()*
 	Get an S-expression representing the node as a string.
 
+tsnode:id()							*tsnode:id()*
+	Get an unique identier for the node inside its own tree.
+
+	No guarantees are made about this identifer's internal representation,
+	except for being a primitive lua type with value equality (so not a table).
+	Presently it is a (non-printable) string.
+
+	NB: the id is not guaranteed to be unique for nodes from different trees.
+
 tsnode:descendant_for_range({start_row}, {start_col}, {end_row}, {end_col})
 						*tsnode:descendant_for_range()*
 	Get the smallest node within this node that spans the given range of

runtime/lua/vim/treesitter/highlighter.lua

@@ -157,7 +157,7 @@ local function on_line_impl(self, buf, line)
       a.nvim_buf_set_extmark(buf, ns, start_row, start_col,
                              { end_line = end_row, end_col = end_col,
                                hl_group = hl,
-                               ephemeral = true
+                               ephemeral = true,
                               })
     end
     if start_row > line then

src/nvim/lua/treesitter.c

@@ -58,6 +58,7 @@ static struct luaL_Reg node_meta[] = {
   { "__tostring", node_tostring },
   { "__eq", node_eq },
   { "__len", node_child_count },
+  { "id", node_id },
   { "range", node_range },
   { "start", node_start },
   { "end_", node_end },
@@ -621,6 +622,17 @@ static int node_eq(lua_State *L)
   return 1;
 }
 
+static int node_id(lua_State *L)
+{
+  TSNode node;
+  if (!node_check(L, 1, &node)) {
+    return 0;
+  }
+
+  lua_pushlstring(L, (const char *)&node.id, sizeof node.id);
+  return 1;
+}
+
 static int node_range(lua_State *L)
 {
   TSNode node;

test/functional/lua/treesitter_spec.lua

@@ -80,13 +80,6 @@ describe('treesitter API with C parser', function()
     eq({1,2,1,12}, exec_lua("return {descendant:range()}"))
     eq("(declaration type: (primitive_type) declarator: (init_declarator declarator: (identifier) value: (number_literal)))", exec_lua("return descendant:sexpr()"))
 
-    eq(true, exec_lua("return child == child"))
-    -- separate lua object, but represents same node
-    eq(true, exec_lua("return child == root:child(0)"))
-    eq(false, exec_lua("return child == descendant2"))
-    eq(false, exec_lua("return child == nil"))
-    eq(false, exec_lua("return child == tree"))
-
     feed("2G7|ay")
     exec_lua([[
       tree2 = parser:parse()
@@ -98,6 +91,21 @@ describe('treesitter API with C parser', function()
     eq("<node declaration>", exec_lua("return tostring(descendant2)"))
     eq({1,2,1,13}, exec_lua("return {descendant2:range()}"))
 
+    eq(true, exec_lua("return child == child"))
+    -- separate lua object, but represents same node
+    eq(true, exec_lua("return child == root:child(0)"))
+    eq(false, exec_lua("return child == descendant2"))
+    eq(false, exec_lua("return child == nil"))
+    eq(false, exec_lua("return child == tree"))
+
+    eq("string", exec_lua("return type(child:id())"))
+    eq(true, exec_lua("return child:id() == child:id()"))
+    -- separate lua object, but represents same node
+    eq(true, exec_lua("return child:id() == root:child(0):id()"))
+    eq(false, exec_lua("return child:id() == descendant2:id()"))
+    eq(false, exec_lua("return child:id() == nil"))
+    eq(false, exec_lua("return child:id() == tree"))
+
     -- orginal tree did not change
     eq({1,2,1,12}, exec_lua("return {descendant:range()}"))