internal error: entered unreachable code: parse_dot_or_call_expr_with_ shouldn't produce this

[dwrensha]

I'm seeing an internal compiler error on the following input (found by fuzz-rustc):

type T = [(String, [String; u:b ()(:)])];

$ rustc main.rs
error: expected expression, found `:`
 --> main.rs:1:36
  |
1 | type T = [(String, [String; u:b ()(:)])];
  |                                    ^ expected expression

thread 'rustc' panicked at 'internal error: entered unreachable code: parse_dot_or_call_expr_with_ shouldn't produce this', src/librustc_parse/parser/expr.rs:641:26
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/blob/master/CONTRIBUTING.md#bug-reports

note: rustc 1.44.0-nightly (699f83f52 2020-03-29) running on x86_64-unknown-linux-gnu

error: aborting due to previous error

[dwrensha]

Report from cargo bisect-rustc:

searched nightlies: from nightly-2020-01-09 to nightly-2020-03-30
regressed nightly: nightly-2020-03-08
searched commits: from 2890b37 to 823ff8c
regressed commit: a039217

[Centril]

#68985 is the cause.

Reduced to:

type T = [_; u:b ()(:)];

clarified to:

fn main() {
    expr : fun()(:);
}

clarified further to:

expr as fun()(:);