config.errorHandler should capture user wathcer errors too (ref #3142)

src/core/observer/watcher.js

@@ -188,7 +188,24 @@ export default class Watcher {
         // set new value
         const oldValue = this.value
         this.value = value
-        this.cb.call(this.vm, value, oldValue)
+        if (this.user) {
+          try {
+            this.cb.call(this.vm, value, oldValue)
+          } catch (e) {
+            process.env.NODE_ENV !== 'production' && warn(
+              `Error in watcher "${this.expression}"`,
+              this.vm
+            )
+            /* istanbul ignore else */
+            if (config.errorHandler) {
+              config.errorHandler.call(null, e, this.vm)
+            } else {
+              throw e
+            }
+          }
+        } else {
+          this.cb.call(this.vm, value, oldValue)
+        }
       }
     }
   }

test/unit/features/global-api/config.spec.js

@@ -33,6 +33,25 @@ describe('Global config', () => {
       expect(spy).toHaveBeenCalledWith(err, vm)
       Vue.config.errorHandler = null
     })
+
+    it('should capture user watcher callback errors', done => {
+      const spy = jasmine.createSpy('errorHandler')
+      Vue.config.errorHandler = spy
+      const err = new Error()
+      const vm = new Vue({
+        data: { a: 1 },
+        watch: {
+          a: () => {
+            throw err
+          }
+        }
+      }).$mount()
+      vm.a = 2
+      waitForUpdate(() => {
+        expect(spy).toHaveBeenCalledWith(err, vm)
+        Vue.config.errorHandler = null
+      }).then(done)
+    })
   })
 
   describe('optionMergeStrategies', () => {