improve smart indentation

[smoothdeveloper]

Repro steps

1. define a function which spans several lines
2. move carret on last line
3. press Enter, and then Backspace, then Enter

Expected behavior

The cursor remains indented to the same level as the one obtained after pressing Backspace

Actual behavior

The indentation jumps back to the indeted level corresponding to last line of the function, the way it works in VS2015.

Known workarounds

None

Related information

The way it behaves in VS2015:

The way it behaves in VS2017:

In both, I have this Tabs settings:

The change in behaviour is rather annoying with muscle memory, and if it was unintended, this might be considered as a bug.

Provide any related information

• Win 7 pro 64
• using latest VS2017 F# nightly 15.4.1.17032701 (but it doesn't matter, it behaves this way since any version of VS2017)

[cartermp]

@dungpa Had made a change to improve indentation in vs2017 a while back. I suspect there was a regression from the beginning (not @dungpa's changes), and that it hasn't quite been picked up yet.

[smoothdeveloper]

The implementation: https://github.com/Microsoft/visualfsharp/blob/427318deda16d340e9e61db6af220fee6e81bb78/vsintegration/src/FSharp.Editor/Formatting/IndentationService.fs

I believe we would need further information to provide to implement the logic, I'm thinking we should pass the current caret location (the column) because if user deindented, the caret location will be in a column less indented.

Any idea how I can obtain that information from the context of this class?

Any idea where to look for the way it was implemented before we migrated to rely Microsoft.CodeAnalysis?