…ulacrum

Fix pretty-printing of `$crate` (take 4)

Pretty-print `$crate` as `crate` or `crate_name` in unstructured tokens like `a $crate c` in `foo!(a $crate c)`, but only if those tokens are printed as a part of AST pretty-printing, rather than as a standalone token stream.

Fixes rust-lang#62325
Previous iterations - rust-lang#56647, rust-lang#57155, rust-lang#57915.

Rollup of 5 pull requests

Successful merges:

 - #61853 (Emit warning when trying to use PGO in conjunction with unwinding on …)
 - #62278 (Add Iterator::partition_in_place() and is_partitioned())
 - #62283 (Target::arch can take more than listed options)
 - #62393 (Fix pretty-printing of `$crate` (take 4))
 - #62474 (Prepare for LLVM 9 update)

Failed merges:

r? @ghost

pretty-print: Do not lose the `$crate` printing flag in `print_tt`

#62393 had this accidental mistake.

Fixes #62562
r? @Mark-Simulacrum

expand: Stop using nonterminals for passing tokens to attribute and derive macros

Make one more step towards fully token-based expansion and fix issues described in rust-lang#72545 (comment).

Now `struct S;` is passed to `foo!(struct S;)` and `#[foo] struct S;` in the same way - as a token stream `struct S ;`, rather than a single non-terminal token `NtItem` which is then broken into parts later.

The cost is making pretty-printing of token streams less pretty.
Some of the pretty-printing regressions will be recovered by keeping jointness with each token, which we will need to do anyway.

Unfortunately, this is not exactly the same thing as rust-lang#73102.
One more observable effect is how `$crate` is printed in the attribute input.
Inside `NtItem` was printed as `crate` or `that_crate`, now as a part of a token stream it's printed as `$crate` (there are good reasons for these differences, see rust-lang#62393 and related PRs).
This may break old proc macros (custom derives) written before the main portion of the proc macro API (macros 1.2) was stabilized, those macros did `input.to_string()` and reparsed the result, now that result can contain `$crate` which cannot be reparsed.

So, I think we should do this regardless, but we need to run crater first.
r? @Aaron1011

expand: Stop using nonterminals for passing tokens to attribute and derive macros

Make one more step towards fully token-based expansion and fix issues described in rust-lang#72545 (comment).

Now `struct S;` is passed to `foo!(struct S;)` and `#[foo] struct S;` in the same way - as a token stream `struct S ;`, rather than a single non-terminal token `NtItem` which is then broken into parts later.

The cost is making pretty-printing of token streams less pretty.
Some of the pretty-printing regressions will be recovered by keeping jointness with each token, which we will need to do anyway.

Unfortunately, this is not exactly the same thing as rust-lang#73102.
One more observable effect is how `$crate` is printed in the attribute input.
Inside `NtItem` was printed as `crate` or `that_crate`, now as a part of a token stream it's printed as `$crate` (there are good reasons for these differences, see rust-lang#62393 and related PRs).
This may break old proc macros (custom derives) written before the main portion of the proc macro API (macros 1.2) was stabilized, those macros did `input.to_string()` and reparsed the result, now that result can contain `$crate` which cannot be reparsed.

So, I think we should do this regardless, but we need to run crater first.
r? @Aaron1011

expand: Stop using nonterminals for passing tokens to attribute and derive macros

Make one more step towards fully token-based expansion and fix issues described in rust-lang#72545 (comment).

Now `struct S;` is passed to `foo!(struct S;)` and `#[foo] struct S;` in the same way - as a token stream `struct S ;`, rather than a single non-terminal token `NtItem` which is then broken into parts later.

The cost is making pretty-printing of token streams less pretty.
Some of the pretty-printing regressions will be recovered by keeping jointness with each token, which we will need to do anyway.

Unfortunately, this is not exactly the same thing as rust-lang#73102.
One more observable effect is how `$crate` is printed in the attribute input.
Inside `NtItem` was printed as `crate` or `that_crate`, now as a part of a token stream it's printed as `$crate` (there are good reasons for these differences, see rust-lang#62393 and related PRs).
This may break old proc macros (custom derives) written before the main portion of the proc macro API (macros 1.2) was stabilized, those macros did `input.to_string()` and reparsed the result, now that result can contain `$crate` which cannot be reparsed.

So, I think we should do this regardless, but we need to run crater first.
r? @Aaron1011

expand: Stop using nonterminals for passing tokens to attribute and derive macros

Make one more step towards fully token-based expansion and fix issues described in rust-lang#72545 (comment).

Now `struct S;` is passed to `foo!(struct S;)` and `#[foo] struct S;` in the same way - as a token stream `struct S ;`, rather than a single non-terminal token `NtItem` which is then broken into parts later.

The cost is making pretty-printing of token streams less pretty.
Some of the pretty-printing regressions will be recovered by keeping jointness with each token, which we will need to do anyway.

Unfortunately, this is not exactly the same thing as rust-lang#73102.
One more observable effect is how `$crate` is printed in the attribute input.
Inside `NtItem` was printed as `crate` or `that_crate`, now as a part of a token stream it's printed as `$crate` (there are good reasons for these differences, see rust-lang#62393 and related PRs).
This may break old proc macros (custom derives) written before the main portion of the proc macro API (macros 1.2) was stabilized, those macros did `input.to_string()` and reparsed the result, now that result can contain `$crate` which cannot be reparsed.

So, I think we should do this regardless, but we need to run crater first.
r? @Aaron1011

expand: Stop using nonterminals for passing tokens to attribute and derive macros

Make one more step towards fully token-based expansion and fix issues described in rust-lang#72545 (comment).

Now `struct S;` is passed to `foo!(struct S;)` and `#[foo] struct S;` in the same way - as a token stream `struct S ;`, rather than a single non-terminal token `NtItem` which is then broken into parts later.

The cost is making pretty-printing of token streams less pretty.
Some of the pretty-printing regressions will be recovered by keeping jointness with each token, which we will need to do anyway.

Unfortunately, this is not exactly the same thing as rust-lang#73102.
One more observable effect is how `$crate` is printed in the attribute input.
Inside `NtItem` was printed as `crate` or `that_crate`, now as a part of a token stream it's printed as `$crate` (there are good reasons for these differences, see rust-lang#62393 and related PRs).
This may break old proc macros (custom derives) written before the main portion of the proc macro API (macros 1.2) was stabilized, those macros did `input.to_string()` and reparsed the result, now that result can contain `$crate` which cannot be reparsed.

So, I think we should do this regardless, but we need to run crater first.
r? @Aaron1011