Fantomas cuts a long line of code in the middle of a pattern match

[JackMatusiewicz]

Issue created from fantomas-online

The long line of code for the lambda has multiple pattern matches in it. The default configuration settings of fantomas means that when it tries to shorten the length of the line it splits the pattern match over many lines, lead to invalid code

Code

module MyModule =

    let foo : Foo -> Foo =
        BigLongTypee.doStuff<aaaaaaaaaaaaa, bbbbbb, BigLongTypee>
            (fun aaa bbbbbb (CCC ccc) ddddddddddd (EEEE eee) (FFF fff) ggggg ->
                failwith "Not important"
            )

Error

Fantomas was able to format the code but the result appears to be invalid F# code.
Please open an issue.

Formatted result:

module MyModule =

    let foo: Foo -> Foo =
        BigLongTypee.doStuff<aaaaaaaaaaaaa, bbbbbb, BigLongTypee> (fun aaa bbbbbb (CCC ccc) ddddddddddd (EEEE eee) (FFF
                fff) ggggg -> failwith "Not important")

Options

Fantomas Master at 06/02/2020 18:39:46 - eee0f32

Name	Value
IndentSpaceNum	4
PageWidth	120
SemicolonAtEndOfLine	false
SpaceBeforeParameter	true
SpaceBeforeLowercaseInvocation	true
SpaceBeforeUppercaseInvocation	false
SpaceBeforeClassConstructor	false
SpaceBeforeMember	false
SpaceBeforeColon	false
SpaceAfterComma	true
SpaceBeforeSemicolon	false
SpaceAfterSemicolon	true
IndentOnTryWith	false
SpaceAroundDelimiter	true
MaxIfThenElseShortWidth	40
MaxInfixOperatorExpression	50
MaxRecordWidth	40
MaxArrayOrListWidth	40
MaxLetBindingWidth	40
MultilineBlockBracketsOnSameColumn	false
NewlineBetweenTypeDefinitionAndMembers	false
KeepIfThenInSameLine	false
StrictMode	false

[deviousasti]

Linking #842

[nojaf]

Not sure if this is a bug anymore, looks ok now in online tool.

[deviousasti]

That's true. It doesn't seem to be respecting MaxLineLength though.

[nojaf]

True

[nojaf]

Would

module MyModule =

    let foo : Foo -> Foo =
        BigLongTypee.doStuff<aaaaaaaaaaaaa, bbbbbb, BigLongTypee>
            (fun aaa 
                 bbbbbb 
                 (CCC ccc) 
                 ddddddddddd 
                 (EEEE eee) 
                 (FFF fff) 
                 ggggg ->
                failwith "Not important"
            )

be a solution to respect the max line length?

[deviousasti]

This seems fairly readable.
It's more of a best-fit rather than absolute limit?

For e.g., I don't think we can make BigLongTypee.doStuff<aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa> (however unlikely) respect max line length.