Return attribute deleted on reformatting

[sadgit]

Issue created from fantomas-online

Please describe here fantomas problem you encountered

Fantomas has deleted the return attribute - this breaks the code

Code

let function1     x : [<return: MyCustomAttributeThatWorksOnReturns>] int = x + 1

Result

let function1 x: int = x + 1

Options

Fantomas Next - 4.0.0-alpha-001-1/1/1990

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
StrictMode	false

[nojaf]

Hello, this is an AST bug.

The attributes of the return type are stored in SynBinding -> SynValInfo -> SynArgInfo -> SynAttributes.

So the LetBinding active pattern should be extended to also capture the synValData.

And then the attributes can be generated in genLetBinding.
I believe the additional attributes should be passed to genPatWithReturnType.

The attributes themselves can be printed with genAttributes.

Could I persuade you to tackle this issue yourself?
Check out this video if you are less familiar with AST.

[kontomondo]

@nojaf From what I could tell, the genPatWithReturnType is never called in this case, under getLetBinding, the below code is hit:

       +> leadingExpressionIsMultiline
               (afterLetKeyword +> genPat +> enterNodeTokenByName rangeBetweenBindingPatternAndExpression "EQUALS")
               (genExprSepEqPrependType astContext p e)

and in turn in: genExprSepEqPrependType:

        (addExtraSpaceBeforeGenericType
         +> genCommentBeforeColon
         +> sepColon
         +> genType astContext false t

since this is called from a number of places, I tried introducing an option valInfo in there:
and genExprSepEqPrependType astContext (pat:SynPat) (e: SynExpr) (valInfo:SynValInfo option) (isPrefixMultiline: bool) ctx =

and pass it from getLetBinding, then I added:

        let genMetadataAttributes ctx =
            match valInfo with
            | Some(SynValInfo(_, SynArgInfo(attributes, _, _))) -> genAttributes astContext attributes ctx
            | None -> sepNone ctx

and

        (addExtraSpaceBeforeGenericType
         +> genCommentBeforeColon
         +> sepColon
         +> genMetadataAttributes
         +> genType astContext false t

when formatting let f x: [<return: MyCustomAttributeThatWorksOnReturns>] int = x the result is :

let f x: [<``return``:MyCustomAttributeThatWorksOnReturns>]
int = x

note the extra new line and the return in quotes, am I on the right path here ?

[nojaf]

I think you are on the right track but again this is hard to read.
It is really encouraged to make a (draft) PR, by correct linking you are letting other people know that you are working on this. As for the extra `` I think I know where those are coming from.

[sadgit]

That looks proimising - now we have to fix the back-tcks on the reserved word return

…

On Sat, 16 May 2020 at 10:08, Florian Verdonck ***@***.***> wrote: I think you are on the right track but again this is hard to read. It is really encouraged to make a (draft) PR, by correct linking you are letting other people know that you are working on this. As for the extra `` I think I know where those are coming from. — You are receiving this because you authored the thread. Reply to this email directly, view it on GitHub <#800 (comment)>, or unsubscribe <https://github.com/notifications/unsubscribe-auth/AAFJ5S3GVBH4VCQRTJLFH4TRRZJZJANCNFSM4MXCE4XQ> .

[kontomondo]

@nojaf @sadgit this can be closed as the fix has been merged in