False positive local ambiguity in macro #154594

MCVE:

macro_rules! mcve {
    ($($my_lft:lifetime)? $($my_ty:ty)?) => {};
}

mcve!('a);

error: local ambiguity when calling macro `mcve`: multiple parsing options: built-in NTs lifetime ('my_lft') or ty ('my_ty').
 --> src/lib.rs:5:7
  |
5 | mcve!('a);
  |       ^^

This piece of code should only be able to match $my_lft, but it complains about being able to reach $my_ty.
To prove that $my_ty cannot be reached, and that this problem happens with lifetime but not with other types such as block, i created the following playground link:

• https://play.rust-lang.org/?version=nightly&mode=debug&edition=2024&gist=837c3d88bb5f00ad8936e3ede274f8f2
• (gist) https://gist.github.com/rust-play/837c3d88bb5f00ad8936e3ede274f8f2

Meta

Tried it in editions 2024, 2021 and 2018, using nightly, 1.94.1, 1.80.1, 1.70.0, 1.60.0, 1.50.0, 1.40.0 and 1.31.0 (i.e. the first version with edition 2018, where the $(...)? operator wasn't even stable).

Similar issues (some probably too old to be relevant, but still included just in case):

• macro_rules: Fragment vis somehow matches token [ despite no visibility modifier starting with/having such token #128915
• meta matches pseudo-identifiers #59881
• PR macro_rules: NtLifetime cannot start with an identifier #70768
  • Closed regression: local ambiguity: multiple parsing options: built-in NTs lifetime  #70446
• PR Enable fall through past $:lifetime matcher #51480
  • Closed Macro rules: using lifetime specifier inside recursion causes local ambiguity #50903
• PR Only match a fragment specifier if it starts with certain tokens. #42913
  • Closed $( #[$attr:meta] )* $var:ident → error: local ambiguity: multiple parsing options #24189
  • Closed Spurious local ambiguity error after empty $($ident),* #34030
  • Closed macro_rules treating ';' as an ident #26444
• Commit fc60797
  • Closed macro with repeating arguments fails with ambiguous parse #5902