feat: exception with useful message if $ref cannot be resolved

keywords/add_keyword.js

@@ -21,9 +21,12 @@ module.exports = function (ajv, keyword, jsonPatch, patchSchema) {
       return source;
 
       function getSchema($ref) {
-        if (it.baseId && it.baseId != '#')
-          $ref = url.resolve(it.baseId, $ref);
-        return ajv.getSchema($ref).schema;
+        var id = it.baseId && it.baseId != '#'
+                  ? url.resolve(it.baseId, $ref)
+                  : $ref;
+        var validate = ajv.getSchema(id);
+        if (validate) return validate.schema;
+        throw new Error('can\'t resolve reference ' + $ref + ' from id ' + it.baseId);
       }
     },
     metaSchema: {

spec/errors.spec.js

@@ -0,0 +1,57 @@
+'use strict';
+
+var Ajv = require('ajv');
+var addKeywords = require('..');
+var addMerge = require('../keywords/merge');
+var addPatch = require('../keywords/patch');
+var assert = require('assert');
+
+describe('errors', function() {
+  var ajv;
+
+  describe('no v5 option', function() {
+    beforeEach(function() {
+      ajv = new Ajv;
+    });
+
+    it('adding $merge and $patch should throw without v5 option', function() {
+      assert.throws(function() {
+        addKeywords(ajv);
+      });
+    });
+
+    it('adding $merge only should throw without v5 option', function() {
+      assert.throws(function() {
+        addMerge(ajv);
+      });
+    });
+
+    it('adding $patch only should throw without v5 option', function() {
+      assert.throws(function() {
+        addPatch(ajv);
+      });
+    });
+  });
+
+  describe('missing $ref', function() {
+    beforeEach(function() {
+      ajv = new Ajv({ v5: true });
+      addKeywords(ajv);
+    });
+
+    it('should throw exception if cannot resolve $ref', function() {
+      var schema = {
+        "$merge": {
+          "source": { "$ref": "obj.json#" },
+          "with": {
+            "properties": { "q": { "type": "number" } }
+          }
+        }
+      };
+
+      assert.throws(function() {
+        ajv.compile(schema);
+      });
+    });
+  });
+});