Try/With with a single clause

[nojaf]

Issue created from fantomas-online

Code

// OK
try
    persistState currentState
with ex ->
    printfn "Something went wrong: %A" ex

// OK
try
    persistState currentState
with :? System.ApplicationException as ex ->
    printfn "Something went wrong: %A" ex

Result

// OK
try
    persistState currentState
with
| ex -> printfn "Something went wrong: %A" ex

// OK
try
    persistState currentState
with
| :? System.ApplicationException as ex -> printfn "Something went wrong: %A" ex

Problem description

The MS F# style guide was updated recently and Fantomas does no longer adhere to it.

To solve this issue, a new setting will have to be introduced to still adhere to the GR style guide.
The guides diverge on this topic.

//cc @Smaug123 @pbiggar

Extra information

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

Options

Fantomas Master at 09/07/2021 15:59:52 - 7d861f4

Default Fantomas configuration

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

[64J0]

I want to start contributing, do you have any material to understand the code for newbies @nojaf ?

[nojaf]

Hi there @64J0, thank you for your interest in this.

In general, I'd say our Contribution Guidelines cover a lot of good to know topics. You could start there. As for the code itself, I've made some videos over the years which should help you there.

As for the issue you are trying to solve, this will be quite demanding on and your PR will require a high level of finishing.
First of you should target your PR against the 4.6 branch as it has a stylistic impact on the default settings.
I would start with adding new tests (in ControlStructureTests) with the samples of the guide. Focus on that first just so you know that you get the behaviour right.
The changes in CodePrinter will likely be in

fantomas/src/Fantomas/CodePrinter.fs

Lines 2236 to 2248 in 50d1af0

	| TryWith (e, cs) ->
	atCurrentColumn (
	kw TRY !- "try "
	+> indent
	+> sepNln
	+> genExpr astContext e
	+> unindent
	+> kw WITH !+~ "with"
	+> indentOnWith
	+> sepNln
	+> col sepNln cs (genClause astContext true)
	+> unindentOnWith
	)

You want to do something different in the case of a single clause.

Now, there is a twist here, [the G-Research style guide has a different opinion on this](https://github.com/G-Research/fsharp-formatting-conventions#formatting-trywith-expressions), so we will need to introduce a new setting to support this as well. Setting names are hard, so perhaps go with `BarBeforeTryWithClause` for now, until further notice. The default should be false, and when set to true it should always put the bar before the clause. Best to create a new unit test file `BarBeforeTryWithClauseTests` to cover this, similar to [BarBeforeDiscriminatedUnionDeclarationTests](https://github.com/fsprojects/fantomas/blob/7451175fc6dfa84bc40ffd5a70f086afc5d04672/src/Fantomas.Tests/BarBeforeDiscriminatedUnionDeclarationTests.fs) for example.

Please read the contribution guidelines carefully as they do contain a lot of pointers (branch name, unit test names, draft PR, ...) and work test-driven (trust me on this).

I hope this helps, let me know if you have any further questions. Good luck!

[Smaug123]

As the one who speaks for the G-Research style guidelines, I really am not very attached to our difference with Microsoft here. Honestly I think I'd be happy for us to change our style guideline, if it makes the Fantomas change substantially simpler; I don't think any of us has a very strong opinion on it.

[nojaf]

Well, that would simplify things a bit. @Smaug123 could we resolve G-Research/fsharp-formatting-conventions#30 with this new information?

[64J0]

Thank you very much @nojaf.