LexError when upgrading from 0.21 to 0.22

[TyberiusPrime]

Bug Description

I'm using pyo3's #[pyclass] #[pymodule] etc to export a very limited number of items, and when trying to ugprade to 0.22 I receive error messages like

--> src/lib.rs:478:1
    |
478 | #[pymethods]
    | ^^^^^^^^^^^^
    |
    = help: message: called `Result::unwrap()` on an `Err` value: LexError

Steps to Reproduce

1. git clone https://github.com/TyberiusPrime/pypipegraph2
2. sed -i s/0.21/0.22/ Cargo.toml
3. cargo check

Backtrace

argo check
    Updating crates.io index
    Checking once_cell v1.16.0
   Compiling pyo3-build-config v0.22.1
   Compiling pyo3-ffi v0.22.1
   Compiling pyo3-macros-backend v0.22.1
   Compiling pyo3 v0.22.1
   Compiling pyo3-macros v0.22.1
    Checking pypipegraph2 v3.0.9 (/home/finkernagel/upstream/ppg2_rust)
error: custom attribute panicked
   --> src/lib.rs:467:1
    |
467 | #[pyclass(name = "PPG2Evaluator")]
    | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
    |
    = help: message: called `Result::unwrap()` on an `Err` value: LexError

error: custom attribute panicked
   --> src/lib.rs:478:1
    |
478 | #[pymethods]
    | ^^^^^^^^^^^^
    |
    = help: message: called `Result::unwrap()` on an `Err` value: LexError

error: custom attribute panicked
   --> src/lib.rs:601:1
    |
601 | #[pyfunction]
    | ^^^^^^^^^^^^^
    |
    = help: message: called `Result::unwrap()` on an `Err` value: LexError

error: custom attribute panicked
   --> src/lib.rs:608:1
    |
608 | #[pyfunction]
    | ^^^^^^^^^^^^^
    |
    = help: message: called `Result::unwrap()` on an `Err` value: LexError

error: custom attribute panicked
   --> src/lib.rs:616:1
    |
616 | #[pymodule]
    | ^^^^^^^^^^^
    |
    = help: message: called `Result::unwrap()` on an `Err` value: LexError

warning: unused imports: `PyKeyError`, `PyTypeError`
 --> src/lib.rs:4:24
  |
4 | use pyo3::exceptions::{PyKeyError, PyTypeError, PyValueError};
  |                        ^^^^^^^^^^  ^^^^^^^^^^^
  |
  = note: `#[warn(unused_imports)]` on by default

warning: unused import: `pyo3::types::PyDict`
 --> src/lib.rs:5:5
  |
5 | use pyo3::types::PyDict;
  |     ^^^^^^^^^^^^^^^^^^^

warning: `pypipegraph2` (lib) generated 2 warnings
error: could not compile `pypipegraph2` (lib) due to 5 previous errors; 2 warnings emitted

Your operating system and version

nixos 24.05

Your Python version (python --version)

3.11.9

Your Rust version (rustc --version)

1.78.0

Your PyO3 version

0.22.2

How did you install python? Did you use a virtualenv?

nix flake

Additional Info

No response

[birkenfeld]

Can reproduce, it's gone with 1.79.0 though.

[Icxolu]

This seems to origin from the c-string literals (#4269)

It seems that proc-macro only supports c-string literal from 1.79 (1) and proc-macro2 will try to use a fallback for these until 1.79 (2, 3), which seems to fail for some reason.

So we should probably bump our c_str_lit to only emit on 1.79 and later as well.