error[E0557]: feature has been removed

[jyn514]

When I try to run cargo +nightly test, I get a whole slew of errors:

error[E0557]: feature has been removed
 --> /home/joshua/.cargo/registry/src/github.com-1ecc6299db9ec823/mutagen-plugin-0.1.2/src/lib.rs:1:30
  |
1 | #![feature(plugin_registrar, quote, rustc_private, custom_attribute)]
  |                              ^^^^^ feature has been removed

 error[E0432]: unresolved imports `syntax::fold`, `syntax::fold`
  --> /home/joshua/.cargo/registry/src/github.com-1ecc6299db9ec823/mutagen-plugin-0.1.2/src/lib.rs:23:20
   |
23 | use syntax::fold::{self, Folder, ExpectOne};
   |             ^^^^   ^^^^ no `fold` in the root
   |             |
   |             could not find `fold` in `syntax`

error: cannot find macro `quote_expr!` in this scope
   --> /home/joshua/.cargo/registry/src/github.com-1ecc6299db9ec823/mutagen-plugin-0.1.2/src/lib.rs:431:42
    |
431 |                 let mut mut_expression = quote_expr!(self.cx(), $lit);
    |                                          ^^^^^^^^^^

...
error[E0412]: cannot find type `TypeBinding` in this scope
    --> /home/joshua/.cargo/registry/src/github.com-1ecc6299db9ec823/mutagen-plugin-0.1.2/src/lib.rs:1240:26
     |
1240 | fn ty_bindings_equal(a: &TypeBinding, b: &TypeBinding, inout: bool) -> bool {
     |                          ^^^^^^^^^^^ not found in this scope

error[E0412]: cannot find type `TypeBinding` in this scope
    --> /home/joshua/.cargo/registry/src/github.com-1ecc6299db9ec823/mutagen-plugin-0.1.2/src/lib.rs:1240:43
     |
1240 | fn ty_bindings_equal(a: &TypeBinding, b: &TypeBinding, inout: bool) -> bool {
     |                                           ^^^^^^^^^^^ not found in this scope

error: aborting due to 48 previous errors

Some errors have detailed explanations: E0412, E0432, E0557.
For more information about an error, try `rustc --explain E0412`.
error: Could not compile `mutagen-plugin`.

cargo +nightly --version: cargo 1.37.0-nightly (545f35425 2019-05-23)
rustup run nightly rustc --version: rustc 1.37.0-nightly (d132f544f 2019-06-07)
mutagen-plugin version: v0.1.2

My code in src/main.rs:

#![cfg_attr(test, feature(plugin))]
#![cfg_attr(test, plugin(mutagen_plugin))]
#![feature(custom_attribute)]

#[cfg(test)]
extern crate mutagen;

pub mod lex;
// more code follows

My code in src/lex.rs:

#[cfg_attr(test, mutate)]
// lots of code

[jyn514]

Hmm, I cloned the repo and ran cargo +nightly build and it works fine from there. Not sure why it behaves different when used in a library. I was compiling mutagen, not mutagen-plugin. The plugin shows the same errors.

[jyn514]

https://stackoverflow.com/questions/25561137/how-to-write-a-custom-attribute-that-injects-code-into-a-function#25563608 suggests using the syntax crate instead, not sure if that's a workable solution.

[llogiq]

I have an unfinished rewrite using the syn and quote crates, but stopped working on it due to some architectural discussions with @power-fungus that have not yet been resolved. Guess I should resume working on it.