Unknown feature proc_macro_span_shrink

[rohit123sinha456]

proc-macro2 is a dependent library of the anchor framework. Whenever I am doing a anchor build, the build fails showing the following error :-

If somebody can please help with this..

error[E0635]: unknown feature proc_macro_span_shrink
--> /Users/rohitsinha/.cargo/registry/src/github.com-1ecc6299db9ec823/proc-macro2-1.0.46/src/lib.rs:92:30
|
92 | feature(proc_macro_span, proc_macro_span_shrink)
| ^^^^^^^^^^^^^^^^^^^^^^

For more information about this error, try rustc --explain E0635.
error: could not compile proc-macro2 due to previous error
warning: build failed, waiting for other jobs to finish...
error: build failed

P.S Thanks in advance for any help.

[taiki-e]

See #348 (comment) and subsequent comments.

[ericcornelissen]

For your information, wanted to raise that I'm seeing this ~exact error on the nightly toolchain (specifically rust version 1.72.0-nightly (330727467 2023-06-29)) while not seeing it on the latest stable version (reference builds):

error[E0635]: unknown feature `proc_macro_span_shrink`
  --> /home/runner/.cargo/registry/src/index.crates.io-6f17d22bba15001f/proc-macro2-1.0.58/src/lib.rs:92:30
   |
92 |     feature(proc_macro_span, proc_macro_span_shrink)
   |                              ^^^^^^^^^^^^^^^^^^^^^^

For more information about this error, try `rustc --explain E0635`.
error: could not compile `proc-macro2` (lib) due to previous error
warning: build failed, waiting for other jobs to finish...

I'm not quite sure what to make of it because this project's daily scheduled CI also runs tests on the nightly build, but I figured you might want to know (or, if it's preventable, this might help others as well).

[taiki-e]

@ericcornelissen The problem you are seeing is different from the problem that was originally reported here.
AFAIK, you need to upgrade proc-macro2 to 1.0.60+, downgrade proc-macro2 to 1.0.43 or before, downgrade the nightly toolchain to nightly-2023-06-28 or before, or use a non-nightly toolchain.
See also rust-lang/rust#113152.