Re: [PATCH 3/5] tests: explicitly skip `chmod` calls on Windows

From: Johannes Schindelin <johannes.schindelin@gmx.de>
Date: Aug 22, 2022, 10:19 UTC
Message-ID: <p79ppo86-022r-7sss-41q1-39n499n3266s@tzk.qr>
In-Reply-To: <220811.86wnbfowbg.gmgdl@evledraar.gmail.com>

Hi Ævar,

On Thu, 11 Aug 2022, Ævar Arnfjörð Bjarmason wrote:

Show 40 quoted lines

> On Wed, Aug 10 2022, Johannes Schindelin via GitGitGadget wrote:
>
> > From: Johannes Schindelin <johannes.schindelin@gmx.de>
> > [...]
> > However, this quirk is only in effect as long as `chmod` is run inside
> > the pseudo Unix root directory structure or within the home directory.
> > When run outside, such invocations fail like this:
> >
> > 	chmod: changing permissions of '<file>': Invalid argument
>
> ..ok, but...
>
> > diff --git a/t/test-lib-functions.sh b/t/test-lib-functions.sh
> > index 6da7273f1d5..7c63b22acab 100644
> > --- a/t/test-lib-functions.sh
> > +++ b/t/test-lib-functions.sh
> > @@ -492,7 +492,10 @@ test_commit_bulk () {
> >  # of a file in the working directory and add it to the index.
> >
> >  test_chmod () {
> > -	chmod "$@" &&
> > +	if test_have_prereq !MINGW
> > +	then
> > +		chmod "$@"
> > +	fi &&
> >  	git update-index --add "--chmod=$@"
> >  }
> >
> > @@ -548,7 +551,10 @@ write_script () {
> >  		echo "#!${2-"$SHELL_PATH"}" &&
> >  		cat
> >  	} >"$1" &&
> > -	chmod +x "$1"
> > +	if test_have_prereq !MINGW
> > +	then
> > +		chmod +x "$1"
> > +	fi
>
> ... you get +x semantics by default, so we didn't need that "chmod +x"
> in the first place?

No. We do not get that `chmod +x` semantics by default. Those `chmod +x` statements are treated as (expensive) no-ops by default. This is what I meant when I said this in the commit message (that is missing from the quoted text above):

	[...] it pretends that it succeeded, when in reality it did not
	do a thing [...]

I do not know how to say this more clearly.

> The rest of "test_chmod" seems to *happen to* pass +x or -x, but we
> don't care about that, regardless of the "pseudo Unix root directory"?

The rest of "test_chmod" is even quoted above, so we do not need to leave anybody guessing as to what it does:

	git update-index --add "--chmod=$@"

This asks Git to update the index with the executable bit explicitly turned on or off, regardless of the information that is available on disk.

And yes, Git does what we expect it to do here.

> What if we get a "test_chmod -o <file>", won't this silently do the
> wrong thing?

But we don't?

The code under discussion is Git's test suite, after all, not something that every Git user is expected to use in more ways than the core Git developers can imagine.

So even a cursory `git grep test_chmod upstream/seen` could have shown that there is no such user, and if this was supposed to be a "But what if we do that at some stage in the future?" feedback, said feedback could be construed as to intentionally use up valuable contributor time.

Show 26 quoted lines

> If so isn't something in this direction (untested) a more targeted &
> obvious fix?:
>
> diff --git a/t/test-lib.sh b/t/test-lib.sh
> index 10258def7be..1c3b6692388 100644
> --- a/t/test-lib.sh
> +++ b/t/test-lib.sh
> @@ -1690,6 +1690,16 @@ case $uname_s in
>  	find () {
>  		/usr/bin/find "$@"
>  	}
> +	chmod () {
> +		case "$1" in
> +		+x|-x)
> +			return;
> +			;;
> +		*)
> +			;;
> +		esac &&
> +		/usr/bin/chmod "$@"
> +	}
>  	# git sees Windows-style pwd
>  	pwd () {
>  		builtin pwd -W
>
>

In that form, I will reject this suggestion as over-engineered and convoluted. Why is the `*)` clause empty? Why is there an early return guarding a single statement? Why is the `/usr/bin/chmod` call not in the `*)` clause to begin with? Why does this code take pains to handle cases other than `-x` and `+x` when we do not have any callers, and even in the experimental patches, there are no such users in sight? I would like to encourage you to address such issues during review before even sending the mail in the future.

Having said that, there is a nugget in this feedback that I find valuable. Instead of wasting the run time (even on non-Windows platforms!) to determine whether the `MINGW` prereq is set in order to skip the `chmod` call or not, we can make `chmod` a no-op explicitly in that `case $uname_s` block.

I will make it so.

Ciao, Johannes