Make rustc --explain compatible with BusyBox less

[omnivagant]

busybox less does not support the -r flag and less(1) says:

USE OF THE -r OPTION IS NOT RECOMMENDED.

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[nnethercote]

USE OF THE -r OPTION IS NOT RECOMMENDED.

I see this text in the man page for GNU less, which is used on my Linux machine (unsurprising) and on my Mac laptop (huh?)

less is used as the pager on non-Windows sytems if PAGER isn't set. I guess the question is whether any versions of less (other than busybox's) have -R/-r that don't mean the same things as the GNU version.

https://man.freebsd.org/cgi/man.cgi?query=less shows that freebsd less is also the GNU one. Maybe that explains my Mac result above? Similar story with openbsd: https://man.openbsd.org/less.1. And netbsd: https://man.netbsd.org/less.1.

So, changing to -R seems ok for a lot of the popular non-Windows platforms, and fixes busybox, but I'm worried that I might be overlooking some other platform. Any suggestions how to overcome that worry?

[omnivagant]

It was introduced in #112697 but I cannot find any trace of why -r was chosen isntead of -R, perhaps out of habit? I can see situations where you would want to use less -r, but I don't think this is one.

With your additions, I cannot think of any other popular implementation of less.

It was discoevered in Alpine Linux https://gitlab.alpinelinux.org/alpine/aports/-/issues/16598

[nnethercote]

I tried out less -R on my Linux box, the output is identical to less -r.

To summarize:

• rustc currently uses less -r for paging --explain output.
• GNU less supports both -r and -R, and -R is strongly preferred according to the man page.
• The relevant-to-rustc behaviour of GNU less is identical with -r and -R
• GNU less is used on most(?) Linuxes and also BSDs, including macOS.
• busybox less only supports -R.

Based on all that, changing from less -r to less -R seems ok to me.

@tgross35: you added the less -r invocation in #112697. Was there a reason for using -r instead of -R? Any objections to changing to less -R?

[tgross35]

@tgross35: you added the less -r invocation in #112697. Was there a reason for using -r instead of -R? Any objections to changing to less -R?

Just habit as suggested above, I didn't know -R existed and pretty strongly preferred. So +1 to this change.

[tgross35]

Assuming you're on board here @nnethercote

@bors r+ rollup

[bors]

📌 Commit 6f8fe79 has been approved by tgross35

It is now in the queue for this repository.