…down files

We can capture the first identifier with a separate metavariable, and then put it at the end of the enum.

Fixed handling of trailing commas in matcher.

Co-authored-by: Lukas Wirth <lukastw97@gmail.com>

…tensions

It's slower than bit twiddling, but roughly just as fast as slice length
method, usable in const contexts, non-recursive and quite simple to
read.

…r the end of the rule

- It's called `-Zunpretty`, not `-Zpretty`.
- It requires a nightly compiler.
- `-Zunstable-options` is not required.

It contradicts the previous sentence.

About TT munchers, internal rules, and push-down accumulators.

- Use brackets instead of parens in the push-down accumulator.
- Don't use internal rules, especially given that it's now recommended
  against doing so for performance reasons.
- Remove the `@as_expr` rule, it's not necessary. The final output can
  be produced directly from the `0` accumulator rule.
- Reorder the rules so they are in the easiest-to-follow order.
- Generally reformat to improve readability.

I found this example hard to read when I first encountered it. I think
these changes make it much easier to understand.

close #63

This is important because the example on
https://veykril.github.io/tlborm/decl-macros/minutiae/fragment-specifiers.html#pat
is failed due to or-patterns only allowed since 2021 edition.

Co-authored-by: Lukas Wirth <lukastw97@gmail.com>

Co-authored-by: Lukas Wirth <lukastw97@gmail.com>

src: https://doc.rust-lang.org/reference/macros-by-example.html#follow-set-ambiguity-restrictions

The hack example comes from rust-lang/rust#95860.

Better reflects natural ordering of numbers

…ng it I missed this change due to the annotation not being there

For code hidden with `#` there must be a space after the `#`.

I had to do this myself recently and when I looked in this chapter it
was "WIP" so I had to work it out myself. Might as well record it for
the benefit of others.

`mdbook test` reports lots of errors. This commit fixes them, in various
ways.
- Add space after `#` on hidden lines.
- Add `compile_fail` to all examples that are intended to not compile.
- Add `text` to non-code blocks.
- Add `ignore` to examples using `#![feature(...)]`, which requires nightly.
  Unfortunate, but I can't see a better way to handle these.
- Add `edition2021` where necessary.
- Add necessary hidden code.

`mdbook test` isn't run on CI! It should be.

Plus some other CI improvements, based on the equivalent file at
`github.com/nnethercote/perf-book/`:
- Run actions on pull requests, to allow tests to run before merging.
- Add some missing names for steps.
- Update `actions/checkout` from v2 to v3.

this is also seen in the recent stabilization PR attempt: rust-lang/rust#122808 and rust playground confirms it.

a typo