msw@ any idea who would be a good person for this one?

A bisect would help; I can repro on 65.0.3293.0 and 65.0.3310.0, but haven't touched this area in a while.
I don't see any suspicious recent changes to ChromeLauncherController or chrome/browser/ui/extensions/application_launch.cc, etc.
Perhaps this is related to  Issue 781496 ? This particular defect seems more severe.

Is this really a regression? Which version of hangouts were you testing with -- the app or the extension?

nckgahadagoaajjgafhacjanaoiihapd is the extension, which on 64 has the same behavior described in this bug.

This was tested with an extension, not the hangouts ARC or ChromeOS Apps.

It may not be a recent regression, but I assume it used to work (open the actual extension app window/tab). Feel free to change the type. I did indeed repro with the extension: nckgahadagoaajjgafhacjanaoiihapd

Sounds like the same suspect as  issue 781496 , then: the extension doesn't have a launch URL so we don't know what URL to load, and thus fall back to chrome://extensions.

Is there a reason we even allow pinning an extension?  It seems like a bit of an odd thing to do, and I can't think of many use cases (or good fallbacks, since many extensions won't have a reasonable page to open)... should we just prevent it?

 +toddhausman (cros UX researcher)

Some extensions (hangouts is the first that comes to mind) are useful to pin, I wouldn't discount the usefulness of it without a lot of data.

Hmm... are they useful to pin in the current state (where it opens chrome://extensions or maybe the extension's options page), or would they be useful to pin as a hypothetical feature?  To be clear, I don't think this is a regression - I think this behavior has always been the same for extensions.  This is different than hosted apps and v1/v2 packaged apps.  We don't currently have any mechanism by which an extension can specify a page to open when launched from the toolbar, and adding one would be a new feature, rather than a bug fix.

The Hangouts extension looks and feels like an app. It would be handy to be able to launch it as an app, instead of having to open a Chrome browser window and then click the Hangouts icon in the extensions toolbar.

I agree that many extensions wouldn't have a reasonable page to open -- that's why I suggested a manifest entry or browser action-related feature. Whether we want to add a feature like that, however, depends on whether we want to support this sort of app-like use case for extensions.

Still seeing this issue here which is becoming more and annoying.

The problem is that Chrome apps are deprecated outside of Chrome OS so you have to install the extension on Mac OS or Windows instead of the app.

This way it syncs over to Chrome OS where you then run into this issue.

As https://hangouts.google.com/ still is more of a joke than looking like a PWA alternative there should be a solution here for the extension.

 Issue 781496  has been merged into this issue.