Analysis server doesn't work correctly if a workspace folder/analysis root does not exist

[DanTup]

After pulling latest changes in the SDK, the analysis server didn't work correctly when working on the SDK code. Every request returned:

1700565754126:Res:{"id"::5,"jsonrpc"::"2.0","error"::{"code"::-32007,"data"::"C::\\Dev\\Google\\dart-sdk\\sdk\\pkg\\analysis_server\\lib\\src\\analysis_server.dart","message"::"File is not being analyzed"}}

It seems like this is being triggered by having nnbd_migration in my .code-workspace file (that folder was recently deleted). My guess is that something is going wrong during initialisation that results in no analysis roots being set if one of them does not exist.

[DanTup]

Seems like we're getting stuck here:

https://github.com/dart-lang/sdk/blob/742715e57a65275f4914e33a63df40ae4da89b97/pkg/analysis_server/lib/src/context_manager.dart#L669C78-L669C78

It might be Windows-specific. The FS watcher is not becoming "ready" for a folder that doesn't exist. I thought this had some up/been fixed in the past, but maybe it was non-windows (IIRC each platform might have its own watcher implementation).

There's an existing unit test for this that passes (probably because it's specific to the real watcher) but I can reproduce the failure in an integration test. I'll commit that as failing for now since this might require package:watcher changes to be rolled in to fix.

[DanTup]

While debugging this, I got to the point of just hard-coding some code here that creates a FileWatcher (which is coming from the real FileWatcher in third_party/pkg/watcher with no extra wrapping/abstractions, and DEPs points at the very latest watcher):

However, a near identical test in the pkg:watcher repo passes:

Will need some more investigation 🤷‍♂️

[DanTup]

It turns out there was indeed a bug in watcher, but it was masked because the test setup produced slightly different behaviour in tests to what happened for real.

Working on a fix at dart-archive/watcher#157 and will roll that here once that's done.