Dialog initial focus when dialog contains a slot element

[josepharhar]

I am (unfortunately) still working on shipping the new dialog initial focus algorithm in chrome, and I am running into breaking changes in chrome's webui (chrome://) pages.

One of the pages has a complex custom element and shadowdom structure that sort of looks like this:

<cr-dialog>
  #shadow-root 
    <dialog>
     <slot></slot>
    </dialog>
  <print-preview-search-box> (slotted)
    #shadow-root 
      <cr-input>
        #shadow-root
          <input autofocus>
      </cr-input>
  </print-preview-search-box>
</cr-dialog>

The page wants <input autofocus> to receive initial focus when the dialog is opened. This currently happens with the old code in chrome because the dialog element just does a flat tree traversal until it finds a descendant with autofocus.

In order to make this work with the new focus delegate spec, I added delegatesFocus to every shadow root and I added the autofocus attribute to every shadow host. However, it still doesn't work, and I think it's because the input we want to autofocus is being slotted into the dialog. @domenic is there any proper way that the input could get initial focus with this structure? Would putting autofocus on the slot make any sense at all? If not, I guess I'll have to find a way to get a hold of the input element in script and focus it manually.

Relevant issues/PRs:
#7079
#7284
#7361
#8174
#8156
#8157
#8199

[domenic]

This basically seems to be a duplicate of #9245. As noted there,

Maybe using a single "focus delegate" algorithm for both cases was too ambitious?

I've lost most of the context here and can no longer help with concrete suggestions for improving the algorithm. But it seems likely we should split "focus delegate" into "shadow host focus delegate" (the current algorithm, although we could remove some of the dialog special stuff) and "dialog focus delegate" (some new algorithm, which uses... the flat tree?? I dunno).

Let's close this and discuss in #9245, although your example is helpful.