'assertion failed' after error

[m-hugo]

Code

use std::result::Result;
fn main() -> Ok {Ok}

Meta

rustc --version --verbose:

note: rustc 1.52.0-nightly (3f5aee2d5 2021-02-12) running on x86_64-unknown-linux-gnu

Error output

error[E0573]: expected type, found variant `Ok`
 --> ./out.rs:2:14
  |
2 | fn main() -> Ok {Ok}
  |              ^^ not a type
  |

thread 'rustc' panicked at 'assertion failed: !self.substitutions.is_empty()', compiler/rustc_errors/src/lib.rs:189:9

Backtrace

stack backtrace:
   0: rust_begin_unwind
             at /rustc/3f5aee2d5241139d808f4fdece0026603489afd1/library/std/src/panicking.rs:493:5
   1: core::panicking::panic_fmt
             at /rustc/3f5aee2d5241139d808f4fdece0026603489afd1/library/core/src/panicking.rs:92:14
   2: core::panicking::panic
             at /rustc/3f5aee2d5241139d808f4fdece0026603489afd1/library/core/src/panicking.rs:50:5
   3: rustc_errors::CodeSuggestion::splice_lines
   4: <rustc_errors::emitter::EmitterWriter as rustc_errors::emitter::Emitter>::emit_diagnostic
   5: rustc_errors::HandlerInner::emit_diagnostic
   6: rustc_errors::diagnostic_builder::DiagnosticBuilder::emit
   7: rustc_resolve::Resolver::report_errors
   8: rustc_session::utils::<impl rustc_session::session::Session>::time
   9: rustc_resolve::Resolver::resolve_crate
  10: rustc_interface::passes::configure_and_expand_inner
  11: rustc_interface::passes::configure_and_expand::{{closure}}
  12: rustc_data_structures::box_region::PinnedGenerator<I,A,R>::new
  13: rustc_interface::queries::Queries::expansion
  14: rustc_interface::queries::<impl rustc_interface::interface::Compiler>::enter
  15: rustc_span::with_source_map
  16: scoped_tls::ScopedKey<T>::set

[osa1]

There could be multiple ways of fixing this, but I think it would be good to fix this by fixing this function:

rust/compiler/rustc_resolve/src/late/diagnostics.rs

Lines 92 to 106 in b86674e

	/// Gets the stringified path for an enum from an `ImportSuggestion` for an enum variant.
	fn import_candidate_to_enum_paths(suggestion: &ImportSuggestion) -> (String, String) {
	let variant_path = &suggestion.path;
	let variant_path_string = path_names_to_string(variant_path);
	let path_len = suggestion.path.segments.len();
	let enum_path = ast::Path {
	span: suggestion.path.span,
	segments: suggestion.path.segments[0..path_len - 1].to_vec(),
	tokens: None,
	};
	let enum_path_string = path_names_to_string(&enum_path);
	(variant_path_string, enum_path_string)
	}

Given something like std::prelude::v1::Ok, this function returns std::prelude::v1 as the enum path. Instead it should return std::prelude::v1::Result. More generally, for variant path like x::y::V it will return x::y (a module path, instead of a variant path), which is not how this function is supposed to work.

I don't know if this is easy to fix though. Perhaps there's an easier fix at the call site of this function and we could avoid calling this function altogether.

[tmiasko]

cc #82087

[osa1]

#82087 should fix this issue, without generating a suggestion.

[m-hugo]

i didn't see #78651, closing as duplicate