Adjust default configuration to be more F# idiomatic

[dungpa]

@dsyme's suggestions:

1. Set SpaceBeforeColon = false by default.
2. Set default PageWidth = 120.

Steps to handle:

• Adjust default values in https://github.com/dungpa/fantomas/blob/master/src/Fantomas/FormatConfig.fs#L26
• Fix failing test cases

[ovatsus]

Should we also have a SpaceAfterColon? Or maybe just SpacesAroundColon to control both? And should those options be global? There's at least 4 different situations I can think of where the colon is used, and I don't think they all fit under the same setting:

1. Type declaration in records and abstract members: (usually there's spaces around)

type T = {
    A : int
    B : string }

type IFoo =
    abstract Prop : int

2. Type annotations in return types: (usually there's spaces around)

let xs : int list = []

3. Type annotations in arguments: (I've seen both spaces around, no spaces around, or just spaces after, I think the more common is the first one)

let replace from to (s:string) = s.Replace(from, to)
let replace from to (s: string) = s.Replace(from, to)
let replace from to (s : string) = s.Replace(from, to)

4. Giving names to arguments in type declarations in abstract members: (usually there's no spaces around)

type IFoo =
    abstract Foo : s:string * i:int -> unit

[dungpa]

[I responded a few hours ago, but my comment disappeared]

Should we also have a SpaceAfterColon? Or maybe just SpacesAroundColon to control both?

If we use SpacesAroundColon, we have to implicitly assign value 0, 1, 2 and 3 for it. Using SpaceAfterColon is a bit easier.

And should those options be global?

How do we deal with locality? We may split options into categories e.g.

• Colons in type declarations (case 1 and 4)
• Colons in arguments' type annotations (case 2 and 3)

To be honest, I'm still puzzled about this option.

[dungpa]

My desire is to have something like this https://github.com/icsharpcode/NRefactory/blob/master/ICSharpCode.NRefactory.CSharp/Formatter/FormattingOptionsFactory.cs#L46 where there are at least a few idiomatic styles to choose from.

Unfortunately there is no such style in F# (and functional programming) yet.

[nojaf]

PageWidth is now 120 and SpaceBeforeColon is false, see FormatConfig.