[PATCH V3] pager: fix the invocation of `more` on Windows

[Augie Fackler]

> On Mar 23, 2017, at 9:57 PM, Matt Harbison <mharbison72 at gmail.com> wrote:
> 
> # HG changeset patch
> # User Matt Harbison <matt_harbison at yahoo.com>
> # Date 1489983573 14400
> #      Mon Mar 20 00:19:33 2017 -0400
> # Node ID d0c2db2d9f13dca534c598de050eb1919ef79059
> # Parent  df82f375fa005b9c71b463182e6b54aa47fa5999
> pager: fix the invocation of `more` on Windows

Queued, thanks much for your work on Windows support.

> 
> After 9335dc6b2a9c, with 'shell' being (mostly) set to False, invoking `more` no
> longer worked.  Instead, a warning was printed and the pager was disabled.
> Invoking `more.com` works.  Since a user may have configured 'pager.pager=more',
> do this substitution at the end.  Surprisingly, `more` does allow for arguments,
> so those are preserved.  This also allows `more` to work in MSYS.
> 
> Setting 'shell=False' runs the executable via CreateProcess(), which has rather
> wonky rules for resolving an executable without an extension [1].  Resolving to
> *.com is not among them.  Since 'shell=True' yields a cryptic error for a bad
> $PAGER, and a *.exe program will work without specifying the extension, sticking
> with current 'shell=False' seems like the right thing to do.  I don't think
> there are any other *.com pagers out there, so this one special case seems OK.
> 
> If somebody wants to do something crazy that requires cmd.exe, I was able to get
> normal paged output with 'pager.pager="cmd.exe /c more"'.  I assume you can
> replace `more` with *.bat, *.vbs or various other creatures listed in $PATHEXT.
> 
> [1] https://msdn.microsoft.com/en-us/library/windows/desktop/ms682425(v=vs.85).aspx
> 
> diff --git a/mercurial/ui.py b/mercurial/ui.py
> --- a/mercurial/ui.py
> +++ b/mercurial/ui.py
> @@ -844,6 +844,15 @@
>         if not pagercmd:
>             return
> 
> +        if pycompat.osname == 'nt':
> +            # `more` cannot be invoked with shell=False, but `more.com` can.
> +            # Hide this implementation detail from the user, so we can also get
> +            # sane bad PAGER behavior.  If args are also given, the space in the
> +            # command line forces shell=True, so that case doesn't need to be
> +            # handled here.
> +            if pagercmd == 'more':
> +                pagercmd = 'more.com'
> +
>         self.debug('starting pager for command %r\n' % command)
>         self.flush()
>         self.pageractive = True
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