Unable to specify `edition2021` in order to use unstable packages in Rust

Question

I want to run an example via Cargo but I am facing an error:

error: failed to parse manifest at `/Users/aviralsrivastava/dev/subxt/Cargo.toml`

The full stacktrace is:

error: failed to parse manifest at `/Users/aviralsrivastava/dev/subxt/Cargo.toml`

Caused by:
  feature `edition2021` is required

  The package requires the Cargo feature called `edition2021`, but that feature is not stabilized in this version of Cargo (1.56.0-nightly (b51439fd8 2021-08-09)).
  Consider adding `cargo-features = ["edition2021"]` to the top of Cargo.toml (above the [package] table) to tell Cargo you are opting in to use this unstable feature.
  See https://doc.rust-lang.org/nightly/cargo/reference/unstable.html#edition-2021 for more information about the status of this feature.

Based on the suggestion, I go ahead and modify the Cargo.toml:

  Consider adding `cargo-features = ["edition2021"]` to the top of Cargo.toml (above the [package] table) to tell Cargo you are opting in to use this unstable feature.
diff --git a/Cargo.toml b/Cargo.toml
index 26a02c7..186d09b 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -1,6 +1,6 @@
 [workspace]
 members = [".", "cli", "codegen", "macro"]
-
+cargo-features = ["edition2021"]
 [package]
 name = "subxt"
 version = "0.15.0"
(END)

I still face the same error as if nothing was changed in the toml file.

How do I resolve the above error in order to use unstable packages?

Answer 1

Try:

curl --proto '=https' --tlsv1.2 -sSf https://sh.rustup.rs | sh -s -- -y
source $HOME/.cargo/env && rustup default nightly && rustup update

Answer 2

Edition 2021 is now part of the stable channel.

As what happened to me, you probably just need to update your stable version by running rustup update stable.

That should fix the issue, and not require you to switch over to the nightly channel.