rustc panics if outputting help message fails

[vi]

$ rustc --help > /dev/full
error: internal compiler error: unexpected panic

note: the compiler unexpectedly panicked. this is a bug.

I stumbled upon it when tried rustc -Z help | grpe orbit

Version is rustc 1.13.0-nightly (1576de0ce 2016-08-21)

[vi]

Related/dupe:

• Don't panic when println!() fails #24821
• ICE with rustc --version | false #14505
• Panic when piping rustc output to a non existent program #33433
• rustc broken pipe panic when I piped a wrong command #30972

If this bug is WONTFIX then the compiler unexpectedly panicked. this is a bug. we would appreciate a bug report message should be inhibited for this particular case, or dupes will continue flowing.

[Mark-Simulacrum]

So investigating this leads me to believe that we're handling something incorrectly here:

rust/src/libstd/io/stdio.rs

Line 691 in 77f1bec

panic!("failed printing to {}: {}", label, e);

. The panic! seems to still be called despite the error being IO-related:

$ rustc -vV | test
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

thread 'rustc' panicked at 'failed printing to stdout: Broken pipe (os error 32)', src/libstd/io/stdio.rs:691
note: Run with `RUST_BACKTRACE=1` for a backtrace.

[Mark-Simulacrum]

Closing in favor of #34376.