Request: add override for @PATHEXT

[zmughal]

As per discussion at PDLPorters/pdl#412 (comment) regarding finding a shell script on MSYS2/MinGW64, it might be useful to use File::Which's logic to find scripts that would be run by sh.exe which do not have any suffix.

This override can be similar in function to $IMPLICIT_CURRENT_DIR.

[plicease]

Another way to handle this would have an option to say "sh mode" which would take these into account. It might make the calling code simpler. It's not really in keeping with the $IMPLICIT_CURRENT_DIR interface tbh, if we did go down this route there should also probably be a "powershell mode".

On the other hand I am tempted by your suggestion because it is less work and it is in keeping with what we have done so far.

[zmughal]

Perhaps this can be simplified by introducing an object that encapsulates all
the external %ENV{qw(PATH PATHEXT)} and options. Then which() would just be
a functional interface to the default object.

The object could control behaviour like

# my $is_msys2 = ...;
my $which = File::Which::Object->new(
    # where `File::Which::Object->default_paths` does what which()
    # currently does from $ENV{PATH}
    paths =>
          $is_msys2
        ? My::Tools->mingw_paths
        : File::Which::Object->default_paths,

    # empty pathexts gets turned into [''] internally
    # (if `allow_empty_pathext_suffix`).
    # Could also have `File::Which::Object->default_pathexts`
    # which does what my @PATHEXT = ... does.
    pathexts => IS_WIN ? [qw(.exe .bat .com)] : [],

    # do not filter out '' from pathexts
    allow_empty_pathext_suffix => $is_msys2
);
my $ls = $which->which('ls');
system($ls);

or have

shell => 'bourne (name from Shell::Guess) on MSWin32 set allow_empty_pathext_suffix => 1
while shell => 'cmd' sets allow_empty_pathext_suffix => 0.

Or maybe allow_empty_pathext_suffix should be an internal option
(_allow_empty_pathext_suffix) with only the shell-type being exposed as part
of the public API.

[plicease]

I like the idea of having an OO interface that doesn't necessarily care about the local operating system, because it will make writing regression tests possible for platforms that we can't easily or regularly test in those real environments. I think the main interface should be something like

# actual names should in no way be considered final or even
# in anyway well thought out.
my $which = File::Which::Object->new(  os => 'msys2_sh' );

So that the each calling code doesn't need to think about the details. I think it is fine to also have overrides for pathext etc for when you need to do that.

I'm not in love with File::Which::Object as the name of the class. File::Which->new might actually work, if we are carefuly to make sure that if File::Which::which is called with just one argument it works in the old way.

[zmughal]

Sounds good! I'll take an initial go at this.