API: Extra events like onPreSaveTextDocument?

[bpasero]

It would be nice to have some extra events I guess. The first one I can think of is onPreSaveTextDocument (or onSaveTextDocument). One that will be invoked right before the document gets saved.

Use Cases

The first one I can think of is my own plugin final-newline that will insert a final newline at the end of the file when the user saves the document. At the moment it is implemented like this: Cmd + s → Save → Insert newline (if necessary) → Save
That last save triggers a new iteration of my plugin which will detect a final newline is already present and will stop the execution. So my loop is triggered twice because the plugin is triggered after the document was saved instead of before.

I think there will be other file manipulation plugins that want to manipulate the file before it gets saved as well.

From Alex:

I agree some sort of onBeforeSave action is indeed needed, we just need more thinking regarding how to expose this without causing any data loss. If we block the save to wait on extensions, I can imagine it possible that the wait could be indefinite, resulting in data loss. Maybe a time ceiling of 10s, after which the file gets saved...

@bpasero What do you think?

[lukehoban]

The top requested feature for the Go extension is a format-on-save option (microsoft/vscode-go#14).

This really begs for being invoked on a pre-save event.

Without it, we have to do some sort of double-save with bookkeeping to make sure the first save doesn't re-trigger the post save event. The best I have managed is this: https://github.com/Microsoft/vscode-go/blob/formatonsave/src/goMain.ts#L99-L118. However, the double-save flashes the (unsaved) marker in the editor and I'm sure there are other issues with this approach.

It would be great to have a pre-save hook to use instead.

[bpasero]

We have a FILE_SAVING event but a) it is not exposed to extensions and b) it currently expects modifications to happen sync and not async, which would be a requirement when we talk from editor to extensions.

[jrieken]

fyi @dbaeumer

[dbaeumer]

@bpasero is this something we can work on. I would like to hook up auto fix support for ESLint and doing this before save would really make a good story.

[bpasero]

Yeah, stretch for April, otherwise May.