Rustfmt: Allow manually-specifying which macros should be formatted and how

[gnzlbg]

The libc crate has some macros, called s!, f!, etc. which take a series of items:

f! {
    fn foo();
    fn bar();
    // ...
}

I know that formatting macros is very tricky, and that we probably cannot do that by default.

Instead, would it be possible to specify, e.g., in the rustfmt.toml, a list of macros for which rustfmt should try to format the contents as if the contents were a sequence of items ?

E.g. for the case above, rustfmt could format the f! { ... } the contents of ... as if they were items, adding 4 space indentation inside the block.

I think approaches to macros in which users opt-into formatting them, and somehow conveying what the content of the macro is, might be a more viable way forward with respect to macro formatting than trying to do things automatically.

I don't know how to call this, but I could add the following to libc's rustfmt.toml:

format-macro-content-as-items = ["f", "s"]

I think I could use this in other crates that also make heavy use of macros, like packed-simd.

[cphoenix-google]

For many macros, specifying the separator of a list of arguments would be necessary and sufficient. "You're allowed to modify whitespace immediately after this pattern."

Of course this might break in a few special cases, but if it's opt-in that's OK - use it in the other cases.

[cphoenix-google]

Also, rather than specifying it in the .toml, how about a #[rustfmt::] block on the macros you want to format? That would give finer-grained control, more closely linked to the source you want to affect (you don't have to export your .toml to let others format your macro invocations).

// For keyword-args like my_macro!(foo: 5, bar: 6, baz: 7)

[rustfmt::macro_args_separator(",")]

// For the example above with a list of functions

[rustfmt::macro_args_separator(";")]

[Zizico2]

Is there any progress on this? Is there anyway to format macros that just receive regular rust code?