Use dialog for external changes

[jeremypw]

Fixes #965
Fixes #1327

Following #1308, use dialog instead of infobar when there are external changes

• Add external change dialog inline
• Connect focus in signal at same time as focus out signal
• Check file status before autosaving
• Set buffer modified state to false after save and after loading external changes
• Remove dependence on autosave setting
• Dialog text reflects whether there are unsaved internal changes
• Fix issue with new documents by opening them the same way as existing documents
• Do not show dialog when no unsaved changes e.g. when git branch changed
• Loading external changes is undoable
• Lose now unused infobar

The next Code release is waiting for this to be merged.

[zeebok]

Code looks good. Gonna give a test over the next day or two for you.

[zeebok]

Trying to test by editing the same file in nano is causing two things:

1. I don't see the dialog appear, it simply refreshes the doc with the new version. If autosave is off it still refreshes but the document tab has a * indicating that it isn't saved.
2. If I get to the scenario of the doc refreshing from an external change and perform an undo, the whole document clears. If I undo again the previous version comes back as would be expected.

[jeremypw]

@zeebok Thanks very much for testing this out. Autoloading of external changes is mention in the comments above and is motivated by the need to change git branches without triggering the dialog unnecessarily. The changes should only autoload if there are no unsaved changes to the document.

There is a small improvement wrt master in that the behaviour is the same regardless of the autosave setting - even if autosave is "off" external changes are loaded immediately if there are no unsaved internal edit and in this case the document is not marked as "unsaved".

There is an open question as to whether there needs to be a toast or something indicating the changes have been loaded. Since the changes were presumably made by the same user not sure this is needed.

Undoing shouldn't clear the document though - I'll look into that.

You should get the dialog if there are conflicting changes made internally and externally which in effect means "autosave" is off.

I used gedit when testing as that has its own conflict warning system.

[jeremypw]

Regarding the undo issue: It seems that setting the buffer text programmatically records two actions in the buffer undo manager - "delete old text" and "insert new text", hence it takes two <Ctrl>Z to get back to the old text. Not sure if there is a way round this.

[jeremypw]

I have achieved single-click undo of autoload by using copy/paste rather than just setting the buffer text. This is at the cost of more code and dealing with the asynchronous nature of pasting. Its not quite perfect because after undo the old text remains selected but selection is not recorded by the undo manager so cannot be undone. Questionable whether this is worth the extra complexity as this would be likely to be used very rarely in practice.

[zeebok]

Would a better path be to clear the undo history so trying to undo doesn't do anything?

[zeebok]

Okay now that I know that I can confirm the detection and dialog work as describe! I would say once we settle on what to do about undo, this is good to merge.

[jeremypw]

It would be simpler to disable undoing changes made by autoloading external changes, if that is acceptable.

[zeebok]

I think it is but I am just a single user

[jeremypw]

@zeebok I agree with you. Most users would probably rarely, if ever, trigger this code anyway.