2020-09-05 Nightly type ascription errors on macOS/Linux/Windows

[CleanCut]

Amethyst game engine's CI crashes with type ascription errors on rustc 1.48.0-nightly (cdc8f0606 2020-09-05)

# macOS
cargo test --workspace --features=metal,tiles

# Linux, Windows
cargo test --workspace --features=vulkan,tiles

I expected to see this happen: Relatively the same result as stable/beta.

Instead, nightly failed while both beta and stable passed. See this run

error: expected type, found `:`
  --> C:\Users\runneradmin\.cargo\registry\src\gitpro.ttaallkk.top-1ecc6299db9ec823\rendy-texture-0.4.1\src\format\image.rs:85:10
   |
85 | #[derive(Derivative, Debug, Clone, PartialEq, Eq)]
   |          ^^^^^^^^^^
   |          |
   |          expected type
   |          tried to parse a type due to this type ascription
   |          while parsing this struct
   |
   = note: `#![feature(type_ascription)]` lets you annotate an expression with a type: `<expr>: <type>`
   = note: see issue #23416 <https://github.com/rust-lang/rust/issues/23416> for more information

error: expected expression, found `:`
  --> C:\Users\runneradmin\.cargo\registry\src\gitpro.ttaallkk.top-1ecc6299db9ec823\rendy-texture-0.4.1\src\format\image.rs:85:10
   |
85 | #[derive(Derivative, Debug, Clone, PartialEq, Eq)]
   |          ^^^^^^^^^^
   |          |
   |          expected expression
   |          while parsing this struct

error: proc-macro derive produced unparseable tokens
  --> C:\Users\runneradmin\.cargo\registry\src\gitpro.ttaallkk.top-1ecc6299db9ec823\rendy-texture-0.4.1\src\format\image.rs:85:10
   |
85 | #[derive(Derivative, Debug, Clone, PartialEq, Eq)]
   |          ^^^^^^^^^^

error[E0560]: struct `ImageTextureConfig` has no field named `gfx_hal`
  --> C:\Users\runneradmin\.cargo\registry\src\gitpro.ttaallkk.top-1ecc6299db9ec823\rendy-texture-0.4.1\src\format\image.rs:85:10
   |
85 | #[derive(Derivative, Debug, Clone, PartialEq, Eq)]
   |          ^^^^^^^^^^ `ImageTextureConfig` does not have this field
   |
   = note: available fields are: `format`, `repr`, `kind`, `sampler_info`, `generate_mips`, `premultiply_alpha`

error: aborting due to 4 previous errors

For more information about this error, try `rustc --explain E0560`.
error: could not compile `rendy-texture`.

To learn more, run the command again with --verbose.
warning: build failed, waiting for other jobs to finish...
error: build failed
##[error]Process completed with exit code 1.

[jyn514]

Are you sure this is because of type ascription? It looks like something is going wrong in the proc macro.

Does cargo expand work if the project doesn't compile? I'd be interested to see what changed on nightly.

[CleanCut]

Are you sure this is because of type ascription? It looks like something is going wrong in the proc macro.

No, I'm not at all sure. I'm just pulling that out of the first error: tried to parse a type due to this type ascription.

Does cargo expand work if the project doesn't compile? I'd be interested to see what changed on nightly.

cargo expand run under rustc 1.48.0-nightly (73dc675b9 2020-09-06) appears to fail with the same error (attached).

[jyn514]

Might be related to #76399

[jyn514]

Going to close this as a duplicate of #76399 since it looks like the same issue.