rustc --explain: automatically use `less` on *nix systems

[stelcheck]

Ref: https://twitter.com/stelcheck/status/715502560891637760

Since many of the descriptions are rather lengthy, it would be nice to pipe to less by default on OS X, Linux and other *nix systems. Should stdout be piped to another process, this can be detected and disabled fairly easily.

[brson]

If we're going to consider a pager for this we should consider how pages fit into rustc output more generally. @nikomatsakis and I have talked a lot about wanting a pager for rustc.

[sanmai-NL]

Please do let any command line utilities default to the value of the environment variable PAGER instead of e.g. less.

[nikomatsakis]

Please do let any command line utilities default to the value of the environment variable `PAGER` instead of e.g. `less`.

Seems like we should do whatever git does.

[stelcheck]

git seems to be using less.

@sanmai-NL didn't know about PAGER, but agree with you.

edit To clarify: git uses less by default, but is sensitive to the PAGER environment variable.

[nikomatsakis]

From the git man page:

  -p, --paginate
      Pipe all output into less (or if set, $PAGER) if standard

output is a terminal. This overrides the pager. configuration options
(see the
"Configuration Mechanism" section below).

On Mon, Apr 4, 2016 at 10:45 PM, Marc Trudel notifications@github.com
wrote:

git seems to be using less.

@sanmai-NL https://github.com/sanmai-NL didn't know about PAGER, but
agree with you.

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#32665 (comment)

[cengiz-io]

Hello.

If it's ok, I'd like to take this issue on me. Do some research and provide options that we can implement.

[Mark-Simulacrum]

@cengizio Any progress? If not, could someone else take this issue on, or do you still want it?

[cengiz-io]

Hello @Mark-Simulacrum

Thanks for reminding this! This has slipped from my mind. 😱

I'm already working on another issue that involves our UI tests, so yes, if someone else can pick this up, it'd be a faster resolution.

And I'd be happy to re-pick this if there are no takers.

[cengiz-io]

Hello again @Mark-Simulacrum,

I couldn't help myself and I've implemented this for *nix systems. I can send a PR whenever I solve the Windows part.

[Mark-Simulacrum]

Sounds good!

[cengiz-io]

Hello! This is currently blocked due to #42553