Import less --no-init avoidance from bat

[da-x]

This fixes #88.

[dandavison]

@lzybkr Would you be able to review this change from the Windows point-of-view? The code here is copied from bat. If Delta simply does not work correctly with anything other than your version of less then perhaps this version-checking doesn't make sense on Windows?

[dandavison]

Thanks very much @da-x! This LGTM, since it is what bat is doing, and I've double-checked the diff between this and what I get if I just copy bat's current version of these files. I'll wait for @lzybkr's input if possible before merging since, on Windows, Delta is benefitting from his less fork (see #12 ), but bat currently is not.

Ref #116 which aims to use the bat crate and avoid vendoring bat code entirely; however currently I don't think the bat crate exposes what we need.

[dandavison]

Thanks again @da-x. This is good to have, as --no-init (-X) is really something that should be up to the user without delta mysteriously overriding it. #185 is an issue raised by a Delta user who encountered the old behavior.

I think this is the right thing to do on Windows since bat and delta users are advised to use recent versions of less on Windows which have @lzybkr's patches.

[cohml]

Sorry to bring my personal problems here, but I simply cannot crack this.

When using less with delta, no matter how I configure it (e.g., via .gitconfig, via DELTA_PAGER), less does not respect --no-init. Meanwhile, --no-init works perfectly when using less with bat. I also see that when I add arguments for less via .gitconfig or DELTA_PAGER, they are respected (e.g., -N); only --no-init doesn't seem to work.

As a potentially relevant datapoint, when I do LESS= PAGER= \less some_long_file.txt, the screen is cleared upon exiting less, despite that I'm not obviously passing that in anywhere.

Anyway, can you provide any thoughts as to why --no-init might not be working with delta?

[th1000s]

If you are on Linux, you can check the exact way less is called:

Trace (strace) the bat and delta calls to less, writing it to a log file -o, including full syscall args and strings up to a length of 99 -v -s 99, following (process) forks -f, only looking at successful syscalls for process management -z -e process:

strace -o bat.log -v -s 99 -f -z -e process bat examplefile

vs.

git log -10 --patch | strace -o delta.log -v -s 99 -f -z -e process delta

There should be an execve(..) call to less in both logs, but ignore the one with --version in delta. It has the arguments and the env vars (do NOT post these, they might contain sensitive information), for example:

execve("/usr/bin/less", ["less", "--RAW-CONTROL-CHARS", "--quit-if-one-screen"], ["COLUMNS=165", "SECRET=01234", /* more env vars */ ]

delta will add LESSUTFCHARDEF, LESSCHARSET and LESSANSIENDCHARS env vars.