ICE: 'assertion failed: !self.substitutions.is_empty()', compiler/rustc_errors/src/lib.rs

[chengniansun]

Code

use std::result;
impl result {
    fn into_future() -> Err {}
}

Meta

rustc --version --verbose:

rustc 1.49.0-nightly (4f7612ac1 2020-10-31)
binary: rustc
commit-hash: 4f7612ac1499258025077f1fd05d2f429f9accfb
commit-date: 2020-10-31
host: x86_64-unknown-linux-gnu
release: 1.49.0-nightly

Error output

error[E0573]: expected type, found module `result`
   --> reduced-mutant.rs:2:6
    |
2   |   impl result {
    |        ^^^^^^ help: an enum with a similar name exists: `Result`

error[E0573]: expected type, found variant `Err`
 --> reduced-mutant.rs:3:25
  |
3 |     fn into_future() -> Err {}
  |                         ^^^ not a type
  |
thread 'rustc' panicked at 'assertion failed: !self.substitutions.is_empty()', compiler/rustc_errors/src/lib.rs:173:9
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 1.49.0-nightly (4f7612ac1 2020-10-31) running on x86_64-unknown-linux-gnu

query stack during panic:
end of query stack
error: aborting due to previous error

For more information about this error, try `rustc --explain E0573`.

Backtrace

error[E0573]: expected type, found module `result`
   --> reduced-mutant.rs:2:6
    |
2   |   impl result {
    |        ^^^^^^ help: an enum with a similar name exists: `Result`

error[E0573]: expected type, found variant `Err`
 --> reduced-mutant.rs:3:25
  |
3 |     fn into_future() -> Err {}
  |                         ^^^ not a type
  |
thread 'rustc' panicked at 'assertion failed: !self.substitutions.is_empty()', compiler/rustc_errors/src/lib.rs:173:9
stack backtrace:
   0: std::panicking::begin_panic
   1: <rustc_errors::emitter::EmitterWriter as rustc_errors::emitter::Emitter>::emit_diagnostic
   2: rustc_errors::HandlerInner::emit_diagnostic
   3: rustc_errors::diagnostic_builder::DiagnosticBuilder::emit
   4: rustc_resolve::Resolver::resolve_crate
   5: rustc_interface::passes::configure_and_expand_inner
   6: rustc_interface::passes::configure_and_expand::{{closure}}
   7: rustc_data_structures::box_region::PinnedGenerator<I,A,R>::new
   8: rustc_interface::passes::configure_and_expand
   9: rustc_interface::queries::Queries::expansion
  10: rustc_interface::queries::<impl rustc_interface::interface::Compiler>::enter
  11: rustc_span::with_source_map
  12: scoped_tls::ScopedKey<T>::set
note: Some details are omitted, run with `RUST_BACKTRACE=full` for a verbose 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 1.49.0-nightly (4f7612ac1 2020-10-31) running on x86_64-unknown-linux-gnu

query stack during panic:
end of query stack
error: aborting due to previous error

For more information about this error, try `rustc --explain E0573`.

NOTE: The bug is found by our work-in-progress compiler testing tool Kira, and the test program is reduced/minimized by Perses

[fanninpm]

Playground link of example

Can you confirm if this still ICEs with the latest nightly?

[chengniansun]

$ rustc --verbose --version
rustc 1.50.0-nightly (f76ecd066 2020-12-15)
binary: rustc
commit-hash: f76ecd0668fcdb289456cdc72a39ad15467cc454
commit-date: 2020-12-15
host: x86_64-unknown-linux-gnu
release: 1.50.0-nightly

$ rustc reduced-mutant.rs
error[E0573]: expected type, found module `result`
   --> reduced-mutant.rs:2:6
    |
2   |   impl result {
    |        ^^^^^^ help: an enum with a similar name exists: `Result`

error[E0573]: expected type, found variant `Err`
 --> reduced-mutant.rs:3:25
  |
3 |     fn into_future() -> Err {}
  |                         ^^^ not a type
  |
thread 'rustc' panicked at 'assertion failed: !self.substitutions.is_empty()', compiler/rustc_errors/src/lib.rs:151:9
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 1.50.0-nightly (f76ecd066 2020-12-15) running on x86_64-unknown-linux-gnu

query stack during panic:
end of query stack
error: aborting due to previous error

For more information about this error, try `rustc --explain E0573`.

$ cat reduced-mutant.rs
use std::result;
impl result {
    fn into_future() -> Err {}
}
$

[fanninpm]

After further review, I can confirm that this does cause an ICE with rustc 1.50.0-nightly (f76ecd066 2020-12-15) on macOS 10.15. However, both the playground, running 1.50.0-nightly (2020-12-03 5be3f9f) as of this comment, and (for some weird reason) running glacier locally do not cause an ICE. I will note this in an upcoming PR to glacier.

[estebank]

I think this regression was introduced in https://github.com/rust-lang/rust/pull/72603/files#diff-7e4444c107c648eec7167c8fd88b2665cf1f6e68e2a77d7992001677c09dca81R534

tool_only_suggestion_with_metadata needs to be reworked to either have actual substitutions or remove the assertion and likely early return higher up to make sure that substitutions are present when emitting the diagnostic.

Edit: it was not introduced there, but I've found where it is coming from. It is because of an invalid suggestion with empty substitutions because we were filtering them away. PR incoming.

[osa1]

I think there's another issue as I describe here: #82092 (comment)

Namely import_candidate_to_enum_paths doesn't work as advertised on paths like std::prelude::v1::Err, but it's still called on such paths.

Fixing that function (or the call site) would also fix this issue.

[apiraino]

Assigning P-medium as discussed as part of the Prioritization Working Group procedure and removing I-prioritize.

[apiraino]

@rustbot label -I-prioritize +P-medium

[hameerabbasi]

The current nightly doesn't reproduce this:

$ cargo bisect-rustc --test-dir=. --start=2020-01-01 --regress=ice
...
ERROR: the end of the range (nightly-2021-02-17) does not reproduce the regression

I think just a testcase needs adding.

It happens only on Rust 2015.

[osa1]

This still panics with current nightly ee88f46:

$ cat test.rs
use std::result;

impl result {
    fn into_future() -> Err {}
}

$ RUST_BACKTRACE=0 rustc +stage1 test.rs
error[E0573]: expected type, found module `result`
   --> test.rs:3:6
    |
3   | impl result {
    |      ^^^^^^ help: an enum with a similar name exists: `Result`
    |
   ::: /home/omer/rust/rust/library/core/src/result.rs:241:1
    |
241 | pub enum Result<T, E> {
    | --------------------- similarly named enum `Result` defined here

error[E0573]: expected type, found variant `Err`
 --> test.rs:4:25
  |
4 |     fn into_future() -> Err {}
  |                         ^^^ not a type
  |
thread 'rustc' panicked at 'assertion failed: !self.substitutions.is_empty()', compiler/rustc_errors/src/lib.rs:189:9
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 1.52.0-dev running on x86_64-unknown-linux-gnu

query stack during panic:
end of query stack
error: aborting due to previous error

For more information about this error, try `rustc --explain E0573`.

[hameerabbasi]

This is rather strange.

$ cargo bisect-rustc --test-dir=. --end=ee88f46bb5e27c4d9f30326e69ff2298dcbeecb1 --regress=ice
...
ERROR: the commit at the end of the range (ee88f46bb5e27c4d9f30326e69ff2298dcbeecb1) does not reproduce the regression
$ cargo build
   Compiling bisect v0.1.0 (/home/habbasi/bisect)
error[E0573]: expected type, found module `result`
   --> src/main.rs:2:6
    |
2   |   impl result {
    |        ^^^^^^ help: an enum with a similar name exists: `Result`

error[E0573]: expected type, found variant `Err`
 --> src/main.rs:3:25
  |
3 |     fn into_future() -> Err {}
  |                         ^^^ not a type
  |
help: try using the variant's enum
  |
3 |     fn into_future() -> core::result::Result {}
  |                         ^^^^^^^^^^^^^^^^^^^^
3 |     fn into_future() -> crate::result::Result {}
  |                         ^^^^^^^^^^^^^^^^^^^^^
3 |     fn into_future() -> std::result::Result {}
  |                         ^^^^^^^^^^^^^^^^^^^

error[E0601]: `main` function not found in crate `bisect`
 --> src/main.rs:1:1
  |
1 | / use std::result;
2 | | impl result {
3 | |     fn into_future() -> Err {}
4 | | }
  | |_^ consider adding a `main` function to `src/main.rs`

error: aborting due to 3 previous errors

Some errors have detailed explanations: E0573, E0601.
For more information about an error, try `rustc --explain E0573`.
error: could not compile `bisect`

To learn more, run the command again with --verbose.

Edit: It happens only when compiling with Rust 2015 edition.

[hameerabbasi]

As stated in the edited message above, this ICE only happens on Rust 2015 edition.

********************************************************************************
Regression in nightly-2020-06-25
********************************************************************************

fetching https://static.rust-lang.org/dist/2020-06-24/channel-rust-nightly-git-commit-hash.txt
nightly manifest 2020-06-24: 40 B / 40 B [================] 100.00 % 674.64 KB/s converted 2020-06-24 to ff5b446d2fdbd898bc97a751f2f72858de185cf1
fetching https://static.rust-lang.org/dist/2020-06-25/channel-rust-nightly-git-commit-hash.txt
nightly manifest 2020-06-25: 40 B / 40 B [================] 100.00 % 689.42 KB/s converted 2020-06-25 to 67100f61e62a86f2bf9e38552ee138e231eddc74
looking for regression commit between 2020-06-24 and 2020-06-25
opening existing repository at "rust.git"
refreshing repository
fetching (via local git) commits from ff5b446d2fdbd898bc97a751f2f72858de185cf1 to 67100f61e62a86f2bf9e38552ee138e231eddc74
opening existing repository at "rust.git"
refreshing repository
looking up first commit
looking up second commit
checking that commits are by bors and thus have ci artifacts...
finding bors merge commits
found 6 bors merge commits in the specified range
  commit[0] 2020-06-23UTC: Auto merge of #73644 - ollie27:rustdoc_alias_filter, r=GuillaumeGomez
  commit[1] 2020-06-23UTC: Auto merge of #73669 - Manishearth:rollup-0n4u7vq, r=Manishearth
  commit[2] 2020-06-24UTC: Auto merge of #73293 - Aaron1011:feature/macro-rules-arg-capture, r=petrochenkov
  commit[3] 2020-06-24UTC: Auto merge of #73679 - ehuss:update-cargo, r=ehuss
  commit[4] 2020-06-24UTC: Auto merge of #73692 - Dylan-DPC:rollup-ehzsbfw, r=Dylan-DPC
  commit[5] 2020-06-24UTC: Auto merge of #73660 - flip1995:clippyup, r=nikomatsakis
ERROR: no commits between ff5b446d2fdbd898bc97a751f2f72858de185cf1 and 67100f61e62a86f2bf9e38552ee138e231eddc74 within last 167 days

[estebank]

The problem is an empty suggestion, #82087 fixes this.