nuxeo-search-form timing with DOM injection causing loading to hang

Search Form hangs with loading spinner

Code bellow depends on method _fetch is called  with the parameter el is not null. Otherwise the loading spinner would be displayed indefinitely.

In real life depending on the timing it often happens that this.$.provider is not injected in DOM yet when _fetch is called and the search form on the screen hangs forever.

Issue is hard to reproduce in a test environment but it happens with client site all the time. It might depend on the responsiveness of the server.

The intermediate solution will be is to check if $.provider is set before going to el.fetch .

A more complete way to address it should be waiting for $.provider injection be complete. 

It might be a part of a bigger issue for templates be injected asynchronously in slots  and there is no confirmation event/callback available to notify when template injection process is complete. Besides this ticket that causes problem with attaching additional logic to UI elements.

https://github.com/nuxeo/nuxeo-web-ui/blob/master/elements/search/nuxeo-search-form.js

_visibleChanged() 
 {    
  if (this.visible) {      
    if (!this._searches) {        
      this.$['saved-searches'].get();        
      if (this.form && this.form.params !== undefined) {         
          this.params = this.form.params;       
      }      
    }      
    if (this.queue) {        
     this.$.list.fetch();      
    } 
    else if (this.auto) {        
     this._fetch(this.$.provider);      //!!!PROBLEM this.$.provider might be undefined
    }    
  }//END: visible  
},


 _fetch(el) {   
    this.loading = true; //SET UNCONDITIONALLY EVEN IF EL IS NULL, PLUS I AM NOT SURE THAT "THIS" IS PROPERLY BOUND ON CALLBACK
    return el.fetch().then(() => {this.loading = false; }).catch((err) => {this.loading = false; throw err;});  
},