invalid F# code when pattern matching on exception with long when guard and 2 space indentation

[theimowski]

Issue created from fantomas-online

Code

type A () =
  let b () =
    task {
      if true then
        try
          c ()
        with
        | :? WebSocketException as e when e.WebSocketErrorCode = WebSocketError.ConnectionClosedPrematurely && sourceParty = Agent ->
          ()
    }

Result

type A() =
  let b () =
    task {
      if true then
        try
          c ()
        with :? WebSocketException as e when
          e.WebSocketErrorCode = WebSocketError.ConnectionClosedPrematurely
          && sourceParty = Agent ->
          ()
    }

Problem description

(8,10) (8, 11)Error 10 parse
Incomplete structured construct at or before this point in expression

Extra information

• The formatted result breaks my code.
• The formatted result gives compiler warnings.
• I or my company would be willing to help fix this.

Options

Fantomas v5.2 branch at 1/1/1990

    { config with
                IndentSize = 2 }

_{Did you know that you can ignore files when formatting from fantomas-tool or the FAKE targets by using a .fantomasignore file?}

[nojaf]

Siema! Thank you for reporting this issue.
This looks similar to #2526.

This is an issue rather specific to the indent_size being 2.

I think you can solve this by changing:

fantomas/src/Fantomas.Core/CodePrinter.fs

Lines 1247 to 1249 in 36b7325

	+> optSingle
	(fun e -> !- " when" +> sepSpaceOrIndentAndNlnIfExpressionExceedsPageWidth (genExpr e))
	clauseNode.WhenExpr

into something that along the lines of:

            +> optSingle
                (fun e ->
                    !- " when"
                    +> expressionFitsOnRestOfLine (sepSpace +> genExpr e) (fun ctx ->
                        // See https://github.com/fsprojects/fantomas/issues/2784
                        let doubleIndent = ctx.Config.IndentSize < 4

                        (indent
                         +> onlyIf doubleIndent indent
                         +> sepNln
                         +> genExpr e
                         +> unindent
                         +> onlyIf doubleIndent unindent)
                            ctx))

the idea is to just add a double indent when the indent_size is lower than the default 4 spaces.

Are you interested in submitting a PR for this?

[theimowski]

Siema!

This is an issue rather specific to the indent_size being 2.

We do need to switch back to the default 4 indent size one day - 2 spaces might make the code more concise, but they encourage you to write more nested stuff and they make it harder to notice un-wanted whitespace fuckups like we had recently: by accident we moved a piece of logic after a while loop to the loop itself 🤦

I think you can solve this by changing

I like it how it takes you more time to guide me how to fix it rather than fixing it yourself 😂 But I mean it - it just emphasises how good OSS maintainer you are by encouraging others to contribute! 👍

Are you interested in submitting a PR for this?

There you go! #2785

Side note: I'd consider adding a "fast-track" contributing section in https://fsprojects.github.io/fantomas/docs/contributors for busy dads: I appreciate all the rules and guidelines there are in order to contribute, but on the other hand if you had something like a "5 steps to fix a bug" section for a new comer, it could bring in more eager contributors :)

[nojaf]

Cześć!

Thank you for these kind words 🤗. It may seem strange that I give you a near-working solution instead of just fixing it, but the idea is that we inspire you to save yourself. As this is an open-source project, you will always have the highest stakes in seeing your own problem fixed.

I like the idea of a "fast-track" contributing section. We will give it some thought and see if we can come up with something. Great suggestion!