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.