Feature request: Support full-path PAGER on native Windows

[kit-ty-kate]

Currently setting the PAGER environment variable on Windows to the full-path to the binary (e.g. C:\cygwin64\bin\groff.exe) does not work as cmdliner uses the where cmd.exe command which does not support full-paths unlike command -v used on Unix.

Discussed in ocaml/opam#5797

[dbuenzli]

So what I'm supposed to do ? First check Filename.is_relative on the value and if false use where ?

[kit-ty-kate]

I would personally do something like:

if String.equal (Filename.basename value) value then
  Sys.command "where ..."
else if Sys.file_exists value then
  0
else
  1

to emulate the command -v behaviour but I'm a Windows beginner and I'm not too picky anyway.

[dbuenzli]

Tried something. Tell me if it doesn't work.

[kit-ty-kate]

I've done some tests:

• Paging now works out of the box in Cygwin terminal (when Sys.win32 = true)
• Paging doesn't work out of the box on Cmd and Powershell because TERM is not set by default (in which case cmdliner bypass the pager check entirely and always render things in plain text)
• When forcing a non-plain mode (with --help=pager) with PAGER=C:\Cygwin64\bin\less.exe it works on both Cmd and Powershell
• However there is a slight glitch on Cmd where the UTF8 … is not rendered correctly. It displays ÔÇa (with a underlined, small and above other letters) instead.

[dbuenzli]

Thanks for the tests. 5292a8c tweaks the logic to always page on Sys.win32 = true and `Auto.

It displays ÔÇa

Ô ça j'en sais rien. IIRC I don't think cmd.exe actually supports UTF-8 by default. Random stackexchange answer.

[dbuenzli]

Ah but wait Sys.win32 is also true on cygwin we may want to still have the TERM lookup there.

[kit-ty-kate]

Ô ça j'en sais rien. IIRC I don't think cmd.exe actually supports UTF-8 by default. Random stackexchange answer.

From a discussion with @dra27 this is apparently related to ocaml/ocaml#1408

Ah but wait Sys.win32 is also true on cygwin we may want to still have the TERM lookup there.

I agree

[dbuenzli]

Now that Windowzing is all the rage, are we subtle enough ?

[kit-ty-kate]

I haven't had time to test cmdliner master, I'll do that right now, give me a second

[kit-ty-kate]

So after testing, before and after, paging now works perfectly out of the box with Cygwin Terminal/bash, Windows Terminal/PowerShell and Command Prompt/cmd with cmdliner master (paged by less on Cygwin and by more.com on Windows Terminal and cmd)

However on both Windows Terminal/PowerShell and Command Prompt/cmd we do get the weird UTF-8 characters still.
Looking a bit into the matter, executing chcp 65001 (found both in the above stackexchange and this stackoverflow thread) seems to fix the issue for both cmd and powershell. I'm not sure if there is anything we can do anything in cmdliner while waiting for ocaml/ocaml#1408 but at least opam could add the command in our release announcement.

I think we'd be happy to get a release of cmdliner that we can use before the release of opam 2.2.0~beta3 next week or before 2.2.0~rc1, but it's absolutely not critical so no rush ^^

Sorry for the delay on this.

[dbuenzli]

Thanks for feedback. Will do a release, I'm eager to use d203fb4 in my code bases.