ICE: `TyKind::CVarArgs` should have been handled elsewhere

[matthiaskrgr]

auto-reduced (treereduce-rust):

trait Trait<Input> {}

async fn walk2<F: 'static>(filter: F)
where
    for<'a> F: Trait<&'a u32> + 'a,
    for<'a> ...: 'a,
{
}

fn main() {}

original:

//@ edition:2018
//@ check-pass

trait Trait<Input> {
    type Output;
}

async fn walk<F>(filter: F)
where
    for<'a> F: Trait<&'a u32> + 'a,
    for<'a> <F as Trait<&'a u32>>::Output: 'a,
{
}

async fn walk2<F: 'static>(filter: F)
where
    for<'a> F: Trait<&'a u32> + 'a,
    for<'a> ...: 'a,
{
}

fn main() {}

Version information

rustc 1.80.0-nightly (20be84a7e 2024-05-31)
binary: rustc
commit-hash: 20be84a7e62af0a623af4bfb75df6d30cb39d6d0
commit-date: 2024-05-31
host: x86_64-unknown-linux-gnu
release: 1.80.0-nightly
LLVM version: 18.1.6

Command:
/home/matthias/.rustup/toolchains/master/bin/rustc -Zunstable-options --edition=2024

Program output

warning: unused variable: `filter`
 --> /tmp/icemaker_global_tempdir.rDpA1ZHdMkLV/rustc_testrunner_tmpdir_reporting.yF5KcAa0ogWF/mvce.rs:3:28
  |
3 | async fn walk2<F: 'static>(filter: F)
  |                            ^^^^^^ help: if this is intentional, prefix it with an underscore: `_filter`
  |
  = note: `#[warn(unused_variables)]` on by default

warning: trait `Trait` is never used
 --> /tmp/icemaker_global_tempdir.rDpA1ZHdMkLV/rustc_testrunner_tmpdir_reporting.yF5KcAa0ogWF/mvce.rs:1:7
  |
1 | trait Trait<Input> {}
  |       ^^^^^
  |
  = note: `#[warn(dead_code)]` on by default

warning: function `walk2` is never used
 --> /tmp/icemaker_global_tempdir.rDpA1ZHdMkLV/rustc_testrunner_tmpdir_reporting.yF5KcAa0ogWF/mvce.rs:3:10
  |
3 | async fn walk2<F: 'static>(filter: F)
  |          ^^^^^

warning: 3 warnings emitted

note: no errors encountered even though delayed bugs were created

note: those delayed bugs will now be shown as internal compiler errors

error: internal compiler error: `TyKind::CVarArgs` should have been handled elsewhere
 --> /tmp/icemaker_global_tempdir.rDpA1ZHdMkLV/rustc_testrunner_tmpdir_reporting.yF5KcAa0ogWF/mvce.rs:6:13
  |
6 |     for<'a> ...: 'a,
  |             ^^^
  |
note: delayed at compiler/rustc_ast_lowering/src/lib.rs:1471:39 - disabled backtrace
 --> /tmp/icemaker_global_tempdir.rDpA1ZHdMkLV/rustc_testrunner_tmpdir_reporting.yF5KcAa0ogWF/mvce.rs:6:13
  |
6 |     for<'a> ...: 'a,
  |             ^^^

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: please make sure that you have updated to the latest nightly

note: rustc 1.80.0-nightly (20be84a7e 2024-05-31) running on x86_64-unknown-linux-gnu

note: compiler flags: -Z unstable-options -Z dump-mir-dir=dir

query stack during panic:
end of query stack

[matthiaskrgr]

also repros with --edition=2018

or with 2015 if you remove the async :)

[matthiaskrgr]

Regression in nightly-2020-12-20
fetching (via remote github) commits from max(f745834, 2020-12-17) to 1f5bc17
ending github query because we found starting sha: f745834
get_commits_between returning commits, len: 9
commit[0] 2020-12-18: Auto merge of #80081 - ehuss:update-cargo, r=Mark-Simulacrum
commit[1] 2020-12-18: Auto merge of #80154 - GuillaumeGomez:str-to-symbol, r=jyn514
commit[2] 2020-12-19: Auto merge of #77035 - mibac138:fn-fat-arrow-return, r=davidtwco
commit[3] 2020-12-19: Auto merge of #79073 - davidtwco:issue-78957-const-param-attrs, r=lcnr
commit[4] 2020-12-19: Auto merge of #80180 - JohnTitor:rollup-a31s996, r=JohnTitor
commit[5] 2020-12-19: Auto merge of #80106 - jackh726:binder-refactor-part-2, r=lcnr
commit[6] 2020-12-19: Auto merge of #79342 - CDirkx:ipaddr-const, r=oli-obk
commit[7] 2020-12-19: Auto merge of #80132 - matthewjasper:revert-eval-order, r=nikomatsakis
commit[8] 2020-12-19: Auto merge of #80104 - Nadrieril:usefulness-merging, r=varkor

[matthiaskrgr]

This is also kinda bad because rustc does not tell you what you did wrong (theres no error shown)

mvce:

fn walk2<F: 'static>()
where
    for<'a> ...:,
{
}

fn main() {}

[fmease]

fn f() where for<> ...: {}
fn main() {}

[fmease]

very likely #77035