Alt-click recursive expansion much slower than clicking Expand

[philrz]

Repro is with Brim commit b4e6924.

See the attached test data C010DR0HHMF.json.gz which is an archive of some of the public messages from the Brim community Slack. Uncompressed, the JSON is over 3 MB in size and is effectively one big array of deeply nested objects. Due to its nature, I'd not be surprised if it took a while to render all of it. But as shown in the attached video, clicking Expand in the Inspector view seems to quickly expand it, and scrolling through it, it all appears to be there with the link at the bottom to show more data. However, after I click Collapse and then instead Alt-click it to start what I expect would be a functionally equivalent expansion, the app hangs for almost a minute before it shows everything. In the video you can see evidence of the hang when I expand the size of the window and the new parts of it don't get shown until the expand is complete.

Repro.mp4

Even if this one turns out to be a fixable bug, it does get me to wondering if it's possible to add some kind of spinner to make it obvious that the app is working vs. permanently hung. As a user, I know when I find my clicks aren't getting a response and the app seems like it might be hung, I'm pretty quick to be impatient and look to kill it and retry. So knowing that there's always going to be some operations that are going to take a while, it would be great to give the user some visual cue in hopes they won't bail too quickly.

[jameskerr]

Bummer!