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

[Eli Schwartz]

On 4/17/21 10:14 PM, Eli Schwartz wrote:
> 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.

And I've implemented this all in the patch I just sent.

-- 
Eli Schwartz
Bug Wrangler and Trusted User

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