Configurable? Fn brace next line except single line definitions

[jwilm]

I'm trying to configure braces for fns to appear on the next line except when the function signature fits on a single line. Is this currently possible? Sorry if this is a duplicate; I looked around a bit and couldn't find anything.

Examples

Single line fn

/// Open brace on same line
fn thing_doer() -> Result<Thing, DoError> {
    // ...
}

Multi-line

/// Open brace always comes on next line independent of return and where clause.
fn thing_doer<S>(
    a: &str,
    b: S
) -> Result<Thing, DoError>
    where S: Into<Potato>
{
    // ...
}

Edits

• Updated multi-line example formatting

[jwilm]

I should add, I've tried with AlwaysNext, but that affects the single line case. PreferSameLine and SameLineWhere don't get this right either.

[nrc]

That is not currently possible. Should be possible to add as an option though

[jwilm]

@nrc I'd be willing to do the work; could you point me in the right direction? Haven't had a chance to work with rustfmt src yet.

Thanks!

[nrc]

@jwilm great! I would start with config.rs, to see what the current options are which give you good search terms for searching the rest of the code base. You can also add your new option here which is a nice easy way to start, and you might get some helpful compiler errors when you do it.

For the actual reformatting look in items.rs, functions are quite a lot of work to format, rewrite_fn is the starting point and looks like it has the brace handling. rewrite_fn_base rewrites the signature of the function and returns some information which affects bracing.

https://github.com/rust-lang-nursery/rustfmt/blob/master/Contributing.md has information about how rustfmt works as well as building, etc.

Please ping me here or on irc with questions!

[jwilm]

Thanks for all that info! I'll probably take a whack at this over the weekend.

[dhardy]

@jwilm still working on this?

It would be nice to have this option for all related uses of braces, e.g. if, while, for, match (both opening and patterns):

match some_enum {
    SomeFrabricatedEnum::SomeStruct { struct_field_1,
        struct_field_2 } =>
    {
        do_something_with(struct_field_1, struct_field_2);
    }
    ...
}

Maybe I should also link a motivating example.

[jwilm]

@dhardy sadly no; I sort of lost interest in this when realizing I didn't like a number of rustfmt things at the time (several months ago now).

Regarding your example, it sounds like rustfmt is moving towards favoring short lines and more vertical. In that case, this example would look like:

match some_enum {
    SomeFrabricatedEnum::SomeStruct {
        struct_field_1,
        struct_field_2
    } => {
        do_something_with(struct_field_1, struct_field_2);
    }
    // ...
}

Where a shorter matcher would have } => { on the same line. Given the extra tokens involved and different context in which this arises, I wonder if items such as match and if should have their own issues discussing brace placement.

This recommendation is based on @ubsan's style guide of which some sections have been accepted through RFC. Note that her guide doesn't cover this particular matching case, but the version above is consistent with the specified long function definition syntax (see "Function Definitions" section of guide).