How to format custom proc macro?

Sorry if anyone has asked about this. I mean, is there a way to make a crate like macro crate make custom proc macro to be formatted by rustfmt?

If you are wanting to turn a proc_macro::TokenStream into formatted source code (e.g. so you can generate code and save it to a file), you can always use std::process::Command to invoke rustfmt and pass it your token_stream.to_string() as stdin.

Otherwise, the prettyplease crate is nice when you want "good enough" formatting to make your generated code readable.

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I'm sorry I misunderstood before. What I want is to format custom syntax inside macro braces, like

custom_lambda! {
    x => {

prettyplease seems unable to format complex custom syntax.
I wonder if there is a way I could "guide" rustfmt to format my custom syntax?

Not as far as I know.