rustc_expand: improve diagnostics for non-repeatable metavars

[Unique-Usman]

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[rustbot]

r? @adwinwhite

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[Unique-Usman]

r? @estebank

[rust-log-analyzer]

The job pr-check-2 failed! Check out the build log: (web) (plain enhanced) (plain)

Click to see the possible cause of the failure (guessed by this bot)

    Checking rustc_symbol_mangling v0.0.0 (/checkout/compiler/rustc_symbol_mangling)
error[E0621]: explicit lifetime required in the type of `rules`
   --> compiler/rustc_expand/src/mbe/macro_rules.rs:355:1
    |
355 |   #[instrument(skip(cx, transparency, arg, rules))]
    |   ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
    |   |
    |   lifetime `'cx` required
    |   in this attribute macro expansion
    |
   ::: /cargo/registry/src/index.crates.io-1949cf8c6b5b557f/tracing-attributes-0.1.30/src/lib.rs:566:1
    |
566 | / pub fn instrument(
567 | |     args: proc_macro::TokenStream,
568 | |     item: proc_macro::TokenStream,
569 | | ) -> proc_macro::TokenStream {
    | |____________________________- in this expansion of `#[instrument]`
    |
help: add explicit lifetime `'cx` to the type of `rules`
    |
364 |     rules: &'cx [MacroRule],
    |             +++

For more information about this error, try `rustc --explain E0621`.
[RUSTC-TIMING] rustc_expand test:false 1.445
error: could not compile `rustc_expand` (lib) due to 1 previous error