Require !!omap keys to be unique

__tests__/types.js

@@ -410,6 +410,17 @@ date (00:00:00Z): 2002-12-14\n`)
         expect(String(doc)).toBe(src)
       })
 
+    test('require unique keys', () => {
+      const src = `!!omap\n- a: 1\n- b: 2\n- b: 9\n`
+      const doc = YAML.parseDocument(src, { version: '1.1' })
+      expect(doc.errors).toMatchObject([
+        {
+          name: 'YAMLSemanticError',
+          message: 'Ordered maps must not include duplicate keys'
+        }
+      ])
+    })
+
     test('stringify', () => {
       const map = new Map([['a', 1], ['b', 2], ['c', 3]])
       const str = YAML.stringify(map, { version: '1.1' })

src/schema/_omap.js

@@ -17,7 +17,7 @@ export class YAMLOMap extends YAMLSeq {
         key = toJSON(pair, '', opt)
       }
       if (map.has(key))
-        throw new Error('Ordered maps must not include duplicate values')
+        throw new Error('Ordered maps must not include duplicate keys')
       map.set(key, value)
     }
     return map
@@ -26,6 +26,17 @@ export class YAMLOMap extends YAMLSeq {
 
 function parseOMap(doc, cst) {
   const pairs = parsePairs(doc, cst)
+  const seenKeys = []
+  for (const { key } of pairs.items) {
+    if (key instanceof Scalar) {
+      if (seenKeys.includes(key.value)) {
+        const msg = 'Ordered maps must not include duplicate keys'
+        throw new YAMLSemanticError(cst, msg)
+      } else {
+        seenKeys.push(key.value)
+      }
+    }
+  }
   return Object.assign(new YAMLOMap(), pairs)
 }