To involve `macro_rules!` macros, and also a mix of fragment specifiers,
some of which feature the forwaring limitation and some of which don't.

Just some extra sanity checking, making explicit some values not
possible in code working with token trees -- we shouldn't be seeing
explicit delimiter tokens, because they should be represented as
`TokenTree::Delimited`.

This was added (with a different name) to improve an error message. It
is no longer needed -- removing it changes the error message, but overall
I think the new message is no worse:
- the mention of `#` in the first line is a little worse,
- but the extra context makes it very clear what the problem is, perhaps
  even clearer than the old message,
- and the removal of the note about the `expr` fragment (an internal
  detail of `__rust_force_expr`) is an improvement.

Overall I think the error is quite clear and still far better than the
old message that prompted rust-lang#61933, which didn't even mention patterns.

The motivation for this is rust-lang#124141, which will cause pasted
metavariables to be tokenized and reparsed instead of the AST node being
cached. This change in behaviour occasionally has a non-zero perf cost,
and `__rust_force_expr` causes the tokenize/reparse step to occur twice.
Removing `__rust_force_expr` greatly reduces the extra overhead for the
`deep-vector` benchmark.

And remove the `NtPath` and `NtBlock` cases in
`parse_literal_maybe_minus`, because they are unnecessary.

These attributes apply to all enclosed functions/methods/closures, unless
explicitly overridden by another coverage attribute.

…2, r=petrochenkov

Less `maybe_whole_expr`, take 2

I first tried this in rust-lang#107550. I now think it's worth doing again, as a precursor to rust-lang#124141.

r? ```@petrochenkov```

coverage: Make `#[coverage(..)]` apply recursively to nested functions

This PR makes the (currently-unstable) `#[coverage(off)]` and `#[coverage(on)]` attributes apply recursively to all nested functions/closures, instead of just the function they are directly attached to.

Those attributes can now also be applied to modules and to impl/impl-trait blocks, where they have no direct effect, but will be inherited by all enclosed functions/closures/methods that don't override the inherited value.

---

Fixes rust-lang#126625.

Some `Nonterminal` removal precursors

Small things to prepare for rust-lang#124141, more or less.

r? ```@oli-obk```

…r=oli-obk

Remove `__rust_force_expr`.

This was added (with a different name) to improve an error message. It is no longer needed -- removing it changes the error message, but overall I think the new message is no worse:
- the mention of `#` in the first line is a little worse,
- but the extra context makes it very clear what the problem is, perhaps even clearer than the old message,
- and the removal of the note about the `expr` fragment (an internal detail of `__rust_force_expr`) is an improvement.

Overall I think the error is quite clear and still far better than the old message that prompted rust-lang#61933, which didn't even mention patterns.

The motivation for this is rust-lang#124141, which will cause pasted metavariables to be tokenized and reparsed instead of the AST node being cached. This change in behaviour occasionally has a non-zero perf cost, and `__rust_force_expr` causes the tokenize/reparse step to occur twice. Removing `__rust_force_expr` greatly reduces the extra overhead for the `deep-vector` benchmark.

r? ```@oli-obk```

… r=workingjubilee

set self.is_known_utf8 to false in extend_from_slice

try-job: x86_64-msvc

closes rust-lang#126977
Related to rust-lang#126885, rust-lang#126333, and [this conversation](<rust-lang@aa46a33#r143539097>)

Remove `f16` and `f128` ICE paths from smir

Just chasing down some possible ICE paths. ```@compiler-errors``` mentioned in rust-lang#121728 (comment) that it is okay not to support these in smir, but this change seems pretty trivial?

r? ```@celinval``` since you reviewed rust-lang#114607 (review)