Re: [PATCH] test: make SYMLINKS prerequisite more robust

["Ævar Arnfjörð Bjarmason" <avarab@gmail.com>]

On Wed, Feb 08 2023, Junio C Hamano wrote:

> I see many failures around SYMLINKS prerequisite in Windows tests.
> There are too many to point at, but the pattern seems to be the
> same.  Here is one example:
>
>   https://github.com/git/git/actions/runs/4127147009/jobs/7130175639#step:5:502
>
> where "ln -s x y && test -h y" succeeds and declares SYMLINKS
> lazy prerequisite is satisfied, but then it fails to run
>
> 	"ln -s unrelated DS && git update-index --add DS"
>
> with:
>
> 	error: readlink("DS"): Function not implemented
>
> I wonder if something like this is in order?

I don't have much to contribute on that front, but this is really
missing some "why", this worked before, why is it failing now? Do we
have any idea.

We use "windows-latest", at first I suspected that this was the
2019->2022 migration, which seems to be happening around now:
https://github.blog/changelog/2022-01-11-github-actions-jobs-running-on-windows-latest-are-now-running-on-windows-server-2022/

But looking at a previous successful run on master:
https://github.com/git/git/actions/runs/4089369223/jobs/7052074004

V.s. this current failure:
https://github.com/git/git/actions/runs/4127146869/jobs/7130173444

Shows that both run 2022, and seem to be running the same software,
except that in "set up job" this is different, it was:

	Download action repository
	'git-for-windows/setup-git-for-windows-sdk@v1'
	(SHA:cbe017cd7ae39629bf4e34fce8b1ccd211fec009)

Now:

	Download action repository
	'git-for-windows/setup-git-for-windows-sdk@v1'
	(SHA:848609620edfa4c2fc64838b85fbe19e534236ee)

I have no idea if that's related though...

> diff --git a/t/helper/test-readlink.c b/t/helper/test-readlink.c
> new file mode 100644
> index 0000000000..c300dc8a1a
> --- /dev/null
> +++ b/t/helper/test-readlink.c
> @@ -0,0 +1,19 @@
> +#include "test-tool.h"
> +#include "strbuf.h"
> +
> +static const char *usage_msg = "test-tool readlink file";
> +
> +int cmd__readlink(int ac, const char **av)
> +{
> +	struct strbuf buf;

You're leaving the strbuf uninitialized here, use STRBUF_INIT...

> +	int ret;
> +
> +	if (ac != 2 || !av[1])
> +		usage(usage_msg);
> +
> +	ret = strbuf_readlink(&buf, av[1], 0);

...it's used here, and there's no implicit strbuf_init() on
strbuf_readlink(). The first thing it does is inspect sb->alloc.

> +	if (!ret)
> +		printf("%s\n", buf.buf);

Nit: puts(buf.buf);

All in all a simple helper, but isn't this redundant to "test_readlink"?

That requires perl, and once we have this we could just replace it, but
then let's do that here, no?

> diff --git a/t/test-lib.sh b/t/test-lib.sh
> index 01e88781dd..c8094f643b 100644
> --- a/t/test-lib.sh
> +++ b/t/test-lib.sh
> @@ -1773,7 +1773,8 @@ test_lazy_prereq PIPE '
>  
>  test_lazy_prereq SYMLINKS '
>  	# test whether the filesystem supports symbolic links
> -	ln -s x y && test -h y
> +	ln -s x y && test -h y && test-tool readlink y >/dev/null &&
> +	test "$(test-tool readlink y)" = x

Why get the exit code, and then proceed to hide the exit code with the
test "$()" pattern, we can just (untested):

	echo x >expect &&
	test-tool readlink y >actual &&
	test_cmp expect actual

If you're trying to avoid leaving litter or cleaning up that's not
needed anymore with these lazy prereqs for a while now (they get their
throw-away temporary directory).