Error building synthetic apps

[GinesGarcia]

Hi,
I found this error when trying to compile the synthetic apps on Ubuntu 20.04:

error[E0557]: feature has been removed
 --> /home/ubuntu/.cargo/registry/src/github.com-1ecc6299db9ec823/spin-0.4.10/src/lib.rs:6:43
  |
6 | #![cfg_attr(feature = "const_fn", feature(const_fn))]
  |                                           ^^^^^^^^ feature has been removed
  |
  = note: split into finer-grained feature gates

   Compiling quick-error v1.2.3
     Running `rustc --crate-name quick_error /home/ubuntu/.cargo/registry/src/github.com-1ecc6299db9ec823/quick-error-1.2.3/src/lib.rs --error-format=json --json=diagnostic-rendered-ansi,artifacts --crate-type lib --emit=dep-info,metadata,link -C opt-level=3 -C embed-bitcode=no -C metadata=7d28fc56e23a9b83 -C extra-filename=-7d28fc56e23a9b83 --out-dir /home/ubuntu/shenango/shenango/apps/synthetic/target/release/deps -L dependency=/home/ubuntu/shenango/shenango/apps/synthetic/target/release/deps --cap-lints allow -C link-arg=-T/../../../../../base/base.ld -C link-arg=-no-pie`
error: aborting due to previous error

For more information about this error, try `rustc --explain E0557`.
error: could not compile `spin`

Caused by:
  process didn't exit successfully: `rustc --crate-name spin /home/ubuntu/.cargo/registry/src/github.com-1ecc6299db9ec823/spin-0.4.10/src/lib.rs --error-format=json --json=diagnostic-rendered-ansi,artifacts --crate-type lib --emit=dep-info,metadata,link -C opt-level=3 -C embed-bitcode=no --cfg 'feature="const_fn"' --cfg 'feature="default"' --cfg 'feature="once"' --cfg 'feature="unstable"' -C metadata=b2079781bd608b7d -C extra-filename=-b2079781bd608b7d --out-dir /home/ubuntu/shenango/shenango/apps/synthetic/target/release/deps -L dependency=/home/ubuntu/shenango/shenango/apps/synthetic/target/release/deps --cap-lints allow -C link-arg=-T/../../../../../base/base.ld -C link-arg=-no-pie` (exit status: 1)
warning: build failed, waiting for other jobs to finish...
error: build failed

Any ideas about how to solve it?

PS: README.md contains the wrong url to correctly clone the repository

Regards,
Ginés.

[realChocobi]

An earlier edition of Rust may help. Try rustup default nightly-2020-06-06.

[moonbucks]

Even if i use nightly-2020-06-06, I see other errors that if is not allowed in a const_fn

Does anyone have ideas on how to resolve this?

error[E0658]: if is not allowed in a const fn

[BorisPis]

I was able to overcome this by using rustup default nightly-2021-06-06