Parse errors not reported sometimes inside `--cfg` option

[mwkmwkmwk]

I tried this command:

rustc --cfg "abc\""

(note the lone stray quote passed at the end of the argument)

I expected to see this happen:

error: invalid `--cfg` argument: `abc"` (expected `key` or `key="value"`)

Instead, this happened: rustc exits with code 1, but with no output on stderr or stdout

Meta

rustc --version --verbose:

rustc 1.55.0 (c8dfcfe04 2021-09-06)
binary: rustc
commit-hash: c8dfcfe046a7680554bf4eb612bad840e7631c4b
commit-date: 2021-09-06
host: x86_64-unknown-linux-gnu
release: 1.55.0
LLVM version: 12.0.1

(but, same on current nightly)