Breaking behavior change for TokenStream containing trailing joint token #76399
Labels
A-proc-macros
Area: Procedural macros
P-critical
Critical priority
regression-from-stable-to-nightly
Performance or correctness regression from stable to nightly.
T-compiler
Relevant to the compiler team, which will review and decide on the PR/issue.
Between nightly-2020-09-05 and nightly-2020-09-06, libproc_macro stopped preserving the jointness of a trailing joint punctuation token in a TokenStream (likely #76285; @matklad @petrochenkov).
Cargo.toml:
src/lib.rs:
src/main.rs
This breaks some real-world code such as the following, though only with old versions of some libraries as far as I have found. I don't know which behavior above is correct but I would like it to be intentionally decided so that we know what behavior to implement in proc-macro2.
fails to compile since nightly-2020-09-06:
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