Change nightly Rust version? - rust

Question

I tried to build rls by the command cargo +nightly build --release -Z unstable-options, but got the following errors:
error[E0599]: no method named `expect_none` found for enum `Option<Fingerprint>` in the current scope
--> /Users/cjw/.cargo/registry/src/github.com-1ecc6299db9ec823/rustc-ap-rustc_span-705.0.0/src/lib.rs:2003:48
|
2003 | cache[index].replace(sub_hash).expect_none("Cache slot was filled");
| ^^^^^^^^^^^ method not found in `Option<Fingerprint>`
After searching it, I found that expect_none is a nightly feature and seemingly has been removed.
So I think maybe I should change the rust compiler version to fix the compilation problem. If this is the correct solution, how could I do it? Can anyone provide some detail suggestions?

Answer 1

Using rustup you can manage different nightly versions. See The Edition Guide for more.
As Option::expect_none was removed on March 25th, we can get the nightly for March 24th in the following way:
rustup toolchain install nightly-2021-03-24 --force
Note: the --force option was used as the components rustfmt and clippy might be missing.
Switch to the newly downloaded toolchain:
rustup default nightly-2021-03-24
The following main.rs should now panic, as expected:
#![feature(option_expect_none)]
fn main() {
let value = Some(42);
value.expect_none("The answer");
}
If you're curious, you could try this with nightly-2021-03-26 and you'll find that it will give you the expected error, indicating it was indeed removed:
error[E0599]: no method named `expect_none` found for enum `Option<{integer}>` in the current scope
--> src/main.rs:5:11
|
5 | value.expect_none("Expected none!");
| ^^^^^^^^^^^ method not found in `Option<{integer}>`