Add TreeCursor.currentFieldName to wasm binding

lib/binding_web/binding.c

@@ -289,6 +289,11 @@ uint32_t ts_tree_cursor_end_index_wasm(const TSTree *tree) {
   return byte_to_code_unit(ts_node_end_byte(node));
 }
 
+uint32_t ts_tree_cursor_current_field_id_wasm(const TSTree *tree) {
+  TSTreeCursor cursor = unmarshal_cursor(TRANSFER_BUFFER, tree);
+  return ts_tree_cursor_current_field_id(&cursor);
+}
+
 void ts_tree_cursor_current_node_wasm(const TSTree *tree) {
   TSTreeCursor cursor = unmarshal_cursor(TRANSFER_BUFFER, tree);
   marshal_node(TRANSFER_BUFFER, ts_tree_cursor_current_node(&cursor));

lib/binding_web/binding.js

@@ -525,6 +525,12 @@ class TreeCursor {
     return unmarshalNode(this.tree);
   }
 
+  currentFieldName() {
+    marshalTreeCursor(this);
+    const fieldId = C._ts_tree_cursor_current_field_id_wasm(this.tree[0]);
+    return this.tree.language.fields[fieldId];
+  }
+
   gotoFirstChild() {
     marshalTreeCursor(this);
     const result = C._ts_tree_cursor_goto_first_child_wasm(this.tree[0]);
@@ -559,6 +565,15 @@ class Language {
         this.types[i] = UTF8ToString(C._ts_language_symbol_name(this[0], i));
       }
     }
+    this.fields = new Array(C._ts_language_field_count(this[0]) + 1);
+    for (let i = 0, n = this.fields.length; i < n; i++) {
+      const fieldName = C._ts_language_field_name_for_id(this[0], i);
+      if (fieldName !== 0) {
+        this.fields[i] = UTF8ToString(fieldName);
+      } else {
+        this.fields[i] = null;
+      }
+    }
   }
 
   get version() {

lib/binding_web/exports.json

@@ -30,6 +30,8 @@
   "abort",
 
   "_ts_init",
+  "_ts_language_field_count",
+  "_ts_language_field_name_for_id",
   "_ts_language_symbol_count",
   "_ts_language_symbol_name",
   "_ts_language_symbol_type",
@@ -64,6 +66,7 @@
   "_ts_parser_new_wasm",
   "_ts_parser_parse_wasm",
   "_ts_parser_set_language",
+  "_ts_tree_cursor_current_field_id_wasm",
   "_ts_tree_cursor_current_node_id_wasm",
   "_ts_tree_cursor_current_node_is_missing_wasm",
   "_ts_tree_cursor_current_node_is_named_wasm",

lib/binding_web/test/tree-test.js

@@ -263,6 +263,34 @@ describe("Tree", () => {
       assert(!cursor.gotoParent());
     });
 
+    it('keeps track of the field name associated with each node', () => {
+      tree = parser.parse('a.b();');
+      cursor = tree.walk();
+      cursor.gotoFirstChild();
+      cursor.gotoFirstChild();
+
+      assert.equal(cursor.currentNode().type, 'call_expression');
+      assert.equal(cursor.currentFieldName(), null);
+
+      cursor.gotoFirstChild();
+      assert.equal(cursor.currentNode().type, 'member_expression');
+      assert.equal(cursor.currentFieldName(), 'function');
+
+      cursor.gotoFirstChild();
+      assert.equal(cursor.currentNode().type, 'identifier');
+      assert.equal(cursor.currentFieldName(), 'object');
+
+      cursor.gotoNextSibling();
+      cursor.gotoNextSibling();
+      assert.equal(cursor.currentNode().type, 'property_identifier');
+      assert.equal(cursor.currentFieldName(), 'property');
+
+      cursor.gotoParent();
+      cursor.gotoNextSibling();
+      assert.equal(cursor.currentNode().type, 'arguments');
+      assert.equal(cursor.currentFieldName(), 'arguments');
+    });
+
     it('returns a cursor that can be reset anywhere in the tree', () => {
       tree = parser.parse('a * b + c / d');
       cursor = tree.walk();