I’m not familiar enough with what you’re trying to do to offer any specific advice. I’ve spent very little time with writing dockerfiles, and have never needed to set up a Rust toolchain in a dockerfile.

I think the first step is figuring out if nightly is really needed. If there aren’t any nightly features needed then the latest stable toolchain should work fine, and worrying about what version of the toolchain to use is a red herring.

You could have just mentioned the project in question since its code is public.

git.joinplu.me/plume/plume

% git grep '#!\[feature'
plume-common/src/lib.rs:#![feature(associated_type_defaults)]
plume-front/src/lib.rs:#![feature(decl_macro, proc_macro_hygiene)]
plume-models/src/lib.rs:#![feature(never_type)]
plume-models/src/lib.rs:#![feature(proc_macro_hygiene)]
plume-models/src/lib.rs:#![feature(box_patterns)]
src/main.rs:#![feature(decl_macro, proc_macro_hygiene)]

% cat rust-toolchain
nightly-2022-07-19

% rm -f rust-toolchain
% cargo check

No errors from plume crates, but we get errors in a couple of locked dependencies:

error[E0422]: cannot find struct, variant or union type `LineColumn` in crate `proc_macro`
   --> /home/user64/.cargo/registry/src/index.crates.io-6f17d22bba15001f/proc-macro2-1.0.49/src/wrapper.rs:479:33
    |
479 |                 let proc_macro::LineColumn { line, column } = s.start();
    |                                 ^^^^^^^^^^ not found in `proc_macro`
    |
help: consider importing one of these items
    |
1   + use crate::LineColumn;
    |
1   + use crate::fallback::LineColumn;
    |
help: if you import `LineColumn`, refer to it directly
    |
479 -                 let proc_macro::LineColumn { line, column } = s.start();
479 +                 let LineColumn { line, column } = s.start();
    |

   Compiling generic-array v0.14.6
error[E0422]: cannot find struct, variant or union type `LineColumn` in crate `proc_macro`
   --> /home/user64/.cargo/registry/src/index.crates.io-6f17d22bba15001f/proc-macro2-1.0.49/src/wrapper.rs:496:33
    |
496 |                 let proc_macro::LineColumn { line, column } = s.end();
    |                                 ^^^^^^^^^^ not found in `proc_macro`
    |
help: consider importing one of these items
    |
1   + use crate::LineColumn;
    |
1   + use crate::fallback::LineColumn;
    |
help: if you import `LineColumn`, refer to it directly
    |
496 -                 let proc_macro::LineColumn { line, column } = s.end();
496 +                 let LineColumn { line, column } = s.end();
    |

    Checking once_cell v1.17.0
error[E0635]: unknown feature `proc_macro_span_shrink`
  --> /home/user64/.cargo/registry/src/index.crates.io-6f17d22bba15001f/proc-macro2-1.0.49/src/lib.rs:92:30
   |
92 |     feature(proc_macro_span, proc_macro_span_shrink)
   |                              ^^^^^^^^^^^^^^^^^^^^^^

Let’s see if a full (semver-compatible) deps update works:

% cargo update
% cargo check

This succeeds.

I will let you pick it from here.
Should be a good learning experience.