tuple with match formats to invalid code

[ThisFunctionalTom]

Issue created from fantomas-online

Code

let a = "Hello"
match a with
    | "first" -> 1
    | "second" -> 2
    , []

Result

let a = "Hello"

match a with
| "first" -> 1
| "second" -> 2,
[]

Problem description

When formatting a tuple with pattern match as first element fantomas puts comma in the wrong place and generates not compilable code.

Expected formatting:

let a = "Hello"

match a with
| "first" -> 1
| "second" -> 2
,[]

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 4.2.0

Default Fantomas configuration

[nojaf]

Hello Tom,

Thank you for reporting this issue. It appears that Fantomas joins every synExpr of a tuple with a comma and a new line (if the whole expression is multiline).

So in pseudo code:

let myTuple = a, b

If a, b is multiline it will go like

let myTuple =
    a,
    b

See genTuple. In the case of SynExpr.Match, this leads to different code that what you originally had.

Would you be interested in submitting a pull request?

[ThisFunctionalTom]

I'll give it a try.

[ThisFunctionalTom]

Hi Florian,

thank you so much for explaining the issue and pointing to the right place.

I wrote some unit tests and fixed this issue, or at least I hope I fixed it 😅 .

One thing I am not sure if it's important.

If I have a long tuple and the match is the last element in it should it also be formatted with commas at the beginning of the line?

Here two examples.

This

match "Hello" with 
| "first" -> 1 
| "second" -> 2 
| _ -> 3
, 1
, "Hello"  

must be formatted like it is, I think, because of the semantics.

But this

1
, "Hello"
, match "Hello" with 
  | "first" -> 1 
  | "second" -> 2 
  | _ -> 3

can be formatted like this

1, 
"Hello", 
match "Hello" with 
| "first" -> 1 
| "second" -> 2 
| _ -> 3

with my current implementation it will be formatted with commas at the beginning of the line.
I am not sure if it is OK. What do you think?

Also, I think that maybe it is not important. One should not write code like this 😁

[c-rindi]

@ThisFunctionalTom Thanks for submitting the PR (and humour)!