Reorder open statements

[ovatsus]

It would be nice if fantomas reordered the open statements, similar to the reorder usings functionality in C#

[ghost]

Presumably into alphabetical order.

[ovatsus]

Removing unused ones would be a nice extra, but I'm guessing it's much harder to implement, and alphabetical sort would be already very good

[dungpa]

Sorting open statements is easy but removing unused ones is difficult.

The latter requires a type-checking phase which hasn't been implemented in Fantomas yet. I think the feature is in the scope of fsharp-refactor.

[ghost]

Removing duplicates will be useful.

[ovatsus]

This was already done in #51

[ovatsus]

Reopening, as I had to disable this because of #73
@dungpa any ideas how we can do this more safely

[dungpa]

We can add special treatments for open declarations in TokenMatcher module. The module should recognize the whole lines of open declarations and skip them although module names don't match.

[ovatsus]

What if there are comments between the open declarations? Before I disabled this feature, this:

//comment about System.IO
open System.IO
//comment about System
open System

Was being turned to this:

//comment about System.IO
open System
//comment about System
open System.IO

Is this acceptable or should we output this instead?

//comment about System
open System
//comment about System.IO
open System.IO

I'm gessing your proposed solution would output this:

//comment about System.IO
//comment about System
open System
open System.IO

Maybe this case is rare enough that even if we don't get it exactly right it's ok.

[dungpa]

Yes, we are more likely to arrive at the last example. The second one is of course ideal.

I will try to improve TokenMatcher and see how far we can go.

[dungpa]

@dsyme What do you suggest on this? It seems we can't reorder open statements without losing some comments around them.

[ovatsus]

@dungpa any progres on the TokenMatcher changes?

[dungpa]

Not yet. I will work on that tomorrow.