[pacman-dev] [PATCH 5/5] meson-make-symlink.sh: Make compatible with non-GNU ln

[Eli Schwartz]

On 4/17/21 2:52 PM, Mark Weiman wrote:
> On Sat, 2021-04-17 at 15:44 +0300, Bjoern Bidar wrote:
>>> The "-T" flag is something available with GNU ln, but on other
>>> implementations of ln, "-T" is not an option. So, to make this script
>>> more portable, a strings check of ln for "GNU coreutils" is done to
>>> determine if "-T" should be used.
>>>
>>> Signed-off-by: Mark Weiman <mark.weiman at markzz.com>
>>> ---
>>>  build-aux/meson-make-symlink.sh | 8 ++++++--
>>>  1 file changed, 6 insertions(+), 2 deletions(-)
>>>
>>> diff --git a/build-aux/meson-make-symlink.sh
>>> b/build-aux/meson-make-symlink.sh index 501cd43d..24a0dd2c 100644
>>> --- a/build-aux/meson-make-symlink.sh
>>> +++ b/build-aux/meson-make-symlink.sh
>>> @@ -4,9 +4,13 @@ set -eu
>>>  # this is needed mostly because $DESTDIR is provided as a variable,
>>>  # and we need to create the target directory...
>>>
>>> +# test if ln is GNU or not
>>> +LN_FLAG="-T"
>>> +strings /bin/ln | grep -q 'GNU coreutils' || LN_FLAG=""
>> No strings needed just do:
>> ln --version|grep GNU
>>
>> Or skip -T even with GNU ln.
> 
> ln --version is not valid on all implementations, but I guess that could be a
> check...
> 
> I can just remove -T altogether as well, also --relative may be an issue.


You are warmly encouraged to rewrite this into something that supports
FreeBSD ln, or any other simple POSIX ln... however, once you have done
so that implementation will work fine even for GNU ln, so you'd better
use it rather than some weird string search of the ln binary (which may
not even be in /bin).

While you're at it, --relative is hardly portable either... but I don't
think we use this side of the logic fork? So that can simply be removed...

A replacement for -T I guess (rather than simply removing it, which is
pointless) would be

if [ -d "${DESTDIR:-}$2" ]; then
    echo "notln: "${DESTDIR:-}$2": cannot overwrite directory"
    exit 1
fi

but on the other hand we could try something really clever by rmdir'ing
it so that the symlink succeeds...

The FreeBSD ln -F "If the target file already exists and is a directory,
then remove it so that the link may occur." seems ever so much more
useful than GNU ln -F "allow root to try to hardlink directories, note
that it will probably fail due to filesystem semantics".

But, this is especially not portable so this is not a suitable
replacement for -T either, even though -T is essentially just "FreeBSD's
-F flag, but raises an error instead".

ln -nf covers the other case where the destination is neither a file
(-f) nor a directory (-fT or -F), but a symlink to a directory (-fT
works here too). The -n option is implemented on a variety of ln
programs, including GNU, busybox, FreeBSD, OpenBSD, NetBSD, macOS, etc.

-- 
Eli Schwartz
Bug Wrangler and Trusted User

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