Use of A | B as c fails to format correctly

[dsyme]

Found this while formatting the F# compiler. It's not a blocker, see workaround below

Issue created from fantomas-online

Code

type T = A | B

let f a  =
    match a with
    | (A | B as bi, x) ->
        1

Result

type T =
    | A
    | B

let f a =
    match a with
    | (A
       | B as bi,
       label1) -> 1

Problem description

Please describe here the Fantomas problem you encountered.
Check out our Contribution Guidelines.

Workaround

The workaround is to parenthesize, e.g.

type T = A | B

let f a  =
    match a with
    | ((A | B) as bi, x) ->
        1

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 master branch at 2022-05-30T18:11:41Z - 5e92752

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?}

[nojaf]

Hello, this rings a bell.
If I recall correctly, the main problem is that we format each SynPat.Or inside a clause slightly differently using ASTContext.
ASTContext is evil, however:

fantomas/src/Fantomas.Core/CodePrinter.fs

Lines 16 to 18 in 5e92752

	/// This type consists of contextual information which is important for formatting
	/// Please avoid using this record as it can be the cause of unexpected behavior when used incorrectly
	type ASTContext =

I think this problem could be solved by removing that record field and trying to format SynPat.Or differently when encountered in the pattern of a clause handler.

Are you interested in submitting a PR for this?

[nojaf]

I believe this problem is addressed due to the refactor of ASTContext in a7f5b3e.