internal compiler error: Error constructed but not emitted

[David Renshaw]

I see the following error on the beta and nightly channels, but not on stable:

$ echo "pub t(#" > main.rs

$ rustc main.rs
error: this file contains an un-closed delimiter
 --> main.rs:1:9
  |
1 | pub t(#
  |      -  ^
  |      |
  |      un-closed delimiter

error: internal compiler error: Error constructed but not emitted

thread 'rustc' panicked at 'explicit panic', src/librustc_errors/diagnostic_builder.rs:387:13
note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace.
error: aborting due to 2 previous errors


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/blob/master/CONTRIBUTING.md#bug-reports

note: rustc 1.37.0-beta.2 (74e5a0d47 2019-07-08) running on x86_64-apple-darwin

Found with the help of libfuzzer-sys.

[Felix S Klock II]

triage: P-high, because errors being swallowed, even in the presence of other errors, scares me a bit.

[Niko Matsakis]

Perhaps @estebank might be a good candidate to investigate?

[Esteban Kuber]

The error that is not being emitted is

error: expected `[`, found `)`
 --> file7.rs:1:8
  |
1 | pub t(#
  |        ^ expected `[`

Looking. Found, incoming PR shortly.