Invalid code when formatting `matches!()` expressions with leading pipe also for the first alternative

[tsdh]

When I format the following code using rustfmt src/cmds.rs (with rustfmt 1.5.2-stable (8ede3aa 2023-07-12)) I get invalid code.

Original valid code:

impl SwayrCommand {
    fn is_scripting_command(&self) -> bool {
        matches!(
            self,
            | SwayrCommand::GetWindowsAsJson { .. }
            | SwayrCommand::ForEachWindow { .. }
        )
    }
}

Invalid code after formatting:

impl SwayrCommand {
    fn is_scripting_command(&self) -> bool {
        matches!(self, |SwayrCommand::GetWindowsAsJson { .. }| {
            SwayrCommand::ForEachWindow { .. }
        })
    }
}

The issue seems to be caused by the pipe | before the first alternative which is probably uncommon but legal.

---

I hoped I could fix the subjectively strange indentation of matches!() where the 2nd to last alternative are indented much more than the first that way. I.e., that's what I get now

impl SwayrCommand {
    fn is_scripting_command(&self) -> bool {
        matches!(
            self,
            SwayrCommand::GetWindowsAsJson { .. }
                | SwayrCommand::ForEachWindow { .. }
                | SwayrCommand::ForEachWindow2 { .. }
                | SwayrCommand::ForEachWindow4 { .. }
        )
    }
}

and what would please me more would be

impl SwayrCommand {
    fn is_scripting_command(&self) -> bool {
        matches!(
            self,
            SwayrCommand::GetWindowsAsJson { .. }
            | SwayrCommand::ForEachWindow { .. }
            | SwayrCommand::ForEachWindow2 { .. }
            | SwayrCommand::ForEachWindow4 { .. }
        )
    }
}

and by prefixing even the first alternative with a pipe, I would get

impl SwayrCommand {
    fn is_scripting_command(&self) -> bool {
        matches!(
            self,
            | SwayrCommand::GetWindowsAsJson { .. }
            | SwayrCommand::ForEachWindow { .. }
            | SwayrCommand::ForEachWindow2 { .. }
            | SwayrCommand::ForEachWindow4 { .. }
        )
    }
}

which is as aesthetically pleasing as the wished-for version.

[ytmimi]

I hoped I could fix the subjectively strange indentation of matches!() where the 2nd to last alternative are indented much more than the first that way. I.e., that's what I get now

Support for matches isn't perfect. see #5547 and the other linked issues.

For what it's worth, I've already started work to improve matches! formatting in #5554. I started working on that before the formation of the official style team, so I'll likely need to work with them to make sure the formatting is correct before we move forward.

I also just double checked and the code changes proposed in #5554 produce the following with your first input snippet:

impl SwayrCommand {
    fn is_scripting_command(&self) -> bool {
        matches!(self, SwayrCommand::GetWindowsAsJson { .. } | SwayrCommand::ForEachWindow { .. })
    }
}

The larger input snippet is formatted as:

impl SwayrCommand {
    fn is_scripting_command(&self) -> bool {
        matches!(
            self,
            SwayrCommand::GetWindowsAsJson { .. }
            | SwayrCommand::ForEachWindow { .. }
            | SwayrCommand::ForEachWindow2 { .. }
            | SwayrCommand::ForEachWindow4 { .. }
        )
    }
}