Ban custom inner attributes in expressions and statements

[Aaron1011]

Split out from #82608

Custom inner attributes are unstable, so this won't break any stable users.
This allows us to speed up token collection, and avoid a redundant call to collect_tokens_no_attrs when parsing an Expr that has outer attributes.

r? @petrochenkov

[petrochenkov]

One more question - what happens with inner #![cfg]s and #![cfg_attr]s in expressions?
They are stable and cfg_eval and derive still need to know their token ranges to be able to process them.

[Aaron1011]

@petrochenkov: In PR #82608, I plan to implement your earlier suggestion of re-parsing with extra collection when we expand derive/cfg_eval. By banning custom inner attributes (which need token collection in order to remove the attribute from the token stream), we can bail out early during normal parsing of expressions without outer attributes.

[Aaron1011]

@petrochenkov: I've addressed your comments.

[petrochenkov]

@bors r+

[bors]

📌 Commit 7504b9b has been approved by petrochenkov

[bors]

⌛ Testing commit 7504b9b with merge 5e65467...

[bors]

☀️ Test successful - checks-actions
Approved by: petrochenkov
Pushing 5e65467 to master...

[klensy]

This ICE'd in perf: https://perf.rust-lang.org/status.html scroll down to see.

Perf runner don't report ICE's anywhere?
Old syn version from perf pool:

Compiling syn v0.11.11 (/tmp/.tmpnHQAja) ...

thread 'rustc' panicked at 'found unstable fingerprints for evaluate_obligation(e3352ed64d6e2ccd-c82ee1c6b3ce2c20): Ok(EvaluatedToOk)', /rustc/b8719c51e0e44483cff9b6975a830f6e51812a48/compiler/rustc_query_system/src/query/plumbing.rs:593:5
note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace

error: internal compiler error: unexpected panic

note: the compiler unexpectedly panicked. this is a bug.

note: we would appreciate a bug report: https://github.com/rust-lang/rust/issues/new?labels=C-bug%2C+I-ICE%2C+T-compiler&template=ice.md

note: rustc 1.53.0-nightly (b8719c51e 2021-03-26) running on x86_64-unknown-linux-gnu

note: compiler flags: -Z self-profile=/tmp/.tmpnHQAja/self-profile-output -C opt-level=3 -C embed-bitcode=no -C incremental --crate-type lib

note: some of the compiler flags provided by cargo are hidden

query stack during panic:
#0 [evaluate_obligation] evaluating trait selection obligation `quote::Tokens: std::marker::Unpin`
#1 [is_unpin_raw] computing whether `quote::Tokens` is `Unpin`
end of query stack
warning: 49 warnings emitted

thread 'main' panicked at 'assertion failed: status.success()', collector/src/rustc-fake.rs:76:17
note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace
error: could not compile `syn`

[Aaron1011]

It looks like that ICE is actually coming from the current nightly. I thought that #83220 would have fixed that, but it's apparently a different issue (there are no lifetimes involved).

[klensy]

Wait, perf runner started running this pr again.

Last perf run ICE'd on syn too, so this is not this pr root if problem.

[Aaron1011]

Opened #83538 to track resolving the syn crash