Disallow completely empty nodes in flow collections

fix #321

CHANGELOG.md

@@ -31,6 +31,8 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 ### Fixed
 - Astral characters are no longer encoded by dump/safeDump, #587.
 - "duplicate mapping key" exception now points at the correct column, #452.
+- Extra commas in flow collections (e.g. `[foo,,bar]`) now throw an exception
+  instead of producing null, #321.
 - Removed `bower.json`.
 
 

lib/loader.js

@@ -723,6 +723,9 @@ function readFlowCollection(state, nodeIndent) {
       return true;
     } else if (!readNext) {
       throwError(state, 'missed comma between flow collection entries');
+    } else if (ch === 0x2C/* , */) {
+      // "flow collection entries can never be completely empty", as per YAML 1.2, section 7.4
+      throwError(state, "expected the node content, but found ','");
     }
 
     keyTag = keyNode = valueNode = null;

test/issues/0321.js

@@ -0,0 +1,19 @@
+'use strict';
+
+
+const assert = require('assert');
+const yaml   = require('../../');
+
+
+it('Should throw exception on extra comma in flow mappings', function () {
+  assert.throws(function () {
+    yaml.load('[foo, bar,, baz]');
+  }, /expected the node content, but found ','/);
+
+  assert.throws(function () {
+    yaml.load('{foo, bar,, baz}');
+  }, /expected the node content, but found ','/);
+
+  // empty key is allowed here
+  assert.deepStrictEqual(yaml.load('{foo,: bar}'), { foo: null, null: 'bar' });
+});