Show error message from backend

app/assets/javascripts/issue_show/components/app.vue

@@ -250,8 +250,14 @@ export default {
           if (error && error.name === 'SpamError') {
             this.openRecaptcha();
           } else {
+            let errMsg = `Error updating ${this.issuableType}`;
+
+            if (error && error.response && error.response.data && error.response.data.errors) {
+              errMsg = error.response.data.errors;
+            }
+
             eventHub.$emit('close.form');
-            window.Flash(`Error updating ${this.issuableType}`);
+            window.Flash(errMsg);
           }
         });
     },

spec/javascripts/issue_show/components/app_spec.js

@@ -292,8 +292,8 @@ describe('Issuable output', () => {
 
       it('shows error mesage from backend if exists', done => {
         const msg = 'Custom error message from backend';
-        spyOn(vm.service, 'updateIssuable').and.callFake(() =>
-          Promise.reject({ response: { data: { errors: msg } } }), // eslint-disable-line prefer-promise-reject-errors
+        spyOn(vm.service, 'updateIssuable').and.callFake(
+          () => Promise.reject({ response: { data: { errors: msg } } }), // eslint-disable-line prefer-promise-reject-errors
         );
 
         vm.updateIssuable();