thread_local!{static mut x: y = 0;} produces very bad error messages

Code

thread_local! {
    /// hello
    /// world
    pub static mut tables: i32 = 0;
}

Current output

error: no rules expected `vis` metavariable
   --> src/lib.rs:3:1
    |
  3 | / thread_local! {
  4 | |     /// hello
  5 | |     /// world
  6 | |     pub static mut tables: i32 = 0;
  7 | | }
    | |_^ no rules expected this token in macro call
    |
note: while trying to match `@`
   --> /playground/.rustup/toolchains/stable-x86_64-unknown-linux-gnu/lib/rustlib/src/rust/library/std/src/thread/local.rs:152:9
    |
152 |         @processing_cfg_attr { pred: ($($predicate:tt)*), rhs: [] };
    |         ^
    = note: captured metavariables except for `:tt`, `:ident` and `:lifetime` cannot be compared to other tokens
    = note: see <https://doc.rust-lang.org/nightly/reference/macros-by-example.html#forwarding-a-matched-fragment> for more information
    = note: this error originates in the macro `$crate::thread::local_impl::thread_local_process_attrs` which comes from the expansion of the macro `thread_local` (in Nightly builds, run with -Z macro-backtrace for more info)

error: could not compile `playground` (lib) due to 1 previous error

Desired output

error: no rules expected `mut`
   --> src/lib.rs:3:1
    |
  6 |    pub static mut tables: i32 = 0;
    |               ^^^ no rules expected this token in macro call
    |
note: [...]

Rationale and extra context

It took me way too long to find out that, oh, right, I'm supposed to use Cell here, not mut. :)

Other cases

Rust Version

rust playground

Anything else?

No response

Start with the thread_local! macro definitions in std/src/thread/local.rs, especially the attribute-processing entry point shown in the diagnostic, and reproduce the supplied static mut example. Trace why the macro reports the forwarded vis metavariable instead of mut; done means the diagnostic points at mut and matches the desired output, with coverage for this example.