Expand only one file

[Yamakaky]

Currently, it displays the expansion of the entire crate. For big crates, that's not very practical. Often, you want to see the expansion of only one file.

[TedDriggs]

Being able to get the expansion of one type would also be sufficient, if that's easier to implement (after looking at the code, I'm not sure how much control expand has here).

[dtolnay]

I added support in cargo-expand 0.4 for expanding only one module or item. Check out these examples from the Syn codebase:

$ cargo expand punctuated::printing
    Checking syn v0.15.24
    Finished dev [unoptimized + debuginfo] target(s) in 0.17s

use super::*;
use proc_macro2::TokenStream;
use quote::{ToTokens, TokenStreamExt};
impl<T, P> ToTokens for Punctuated<T, P>
where
    T: ToTokens,
    P: ToTokens,
{
    fn to_tokens(&self, tokens: &mut TokenStream) {
        tokens.append_all(self.pairs())
    }
}
impl<T, P> ToTokens for Pair<T, P>
where
    T: ToTokens,
    P: ToTokens,
{
    fn to_tokens(&self, tokens: &mut TokenStream) {
        match *self {
            Pair::Punctuated(ref a, ref b) => {
                a.to_tokens(tokens);
                b.to_tokens(tokens);
            }
            Pair::End(ref a) => a.to_tokens(tokens),
        }
    }
}

$ cargo expand token::FatArrow
    Checking syn v0.15.24
    Finished dev [unoptimized + debuginfo] target(s) in 0.11s

/// `=>`
///
/// Don't try to remember the name of this type -- use the [`Token!`]
/// macro instead.
///
/// [`Token!`]: index.html
#[rustc_copy_clone_marker]
pub struct FatArrow {
    pub spans: [Span; 2],
}
#[doc(hidden)]
#[allow(non_snake_case)]
pub fn FatArrow<S: IntoSpans<[Span; 2]>>(spans: S) -> FatArrow {
    FatArrow {
        spans: spans.into_spans(),
    }
}

[vedantroy]

Would it be possible to use this to expand code in a test?

[videni]

@dtolnay , do you mean we can expand a specific micro? for example, I am using a micro , lazy_static::static_loader,

then I can expand with cargo expand lazy_static::static_loader, I tried , got

cargo expand lazy_static::static_loader                                                                             

WARNING: no such item: lazy_static::static_loader   

this crate is not usefull for me , be cause it expand lots of micros, it would take hours to find the one I need.