Re: [PATCH] t5582: remove spurious 'cd "$D"' line

["SZEDER Gábor" <szeder.dev@gmail.com>]

On Wed, Aug 25, 2021 at 09:12:37AM -0700, Junio C Hamano wrote:
> Jeff King <peff@peff.net> writes:
> 
> > Hmm. I think that one is different, in that the "cd" is not redundant,
> > but wrong. But it turns out not to matter to the test. ;)
> 
> Funny. 
> 
> We are lucky because 'cd ""' stays in the same repository as the
> current one and not to a random place,

Actually, the results of 'cd ""' are unspecified, though most shells
do as you said.  Do we want something like this?

  ---  >8  ---

Subject: [PATCH] test-lib: catch 'cd "$dir"' with unset variable

We just had to fix two test cases [1] that invoked 'cd "$dir"' while
the given variable was accidentally unset.  While POSIX states that if
'cd's directory parameter "is an empty string, the results are
unspecified" [2], most shells treat this as a no-op [3], i.e. they
neither change directory nor return error, that's why both of those
tests happened to succeed on common shells, and thus these issues
remained hidden for a while.

Catch 'cd ""' by adding a thin wrapper function overriding the
shell's 'cd' command to verify the non-emptiness of its parameters and
call BUG if necessary.

[1] bd72824c60 (t5582: remove spurious 'cd "$D"' line, 2021-08-23)
    c21b2511c2 (t5323: drop mentions of "master", 2021-08-24)
[2] https://pubs.opengroup.org/onlinepubs/9699919799/utilities/cd.html
[3] 'ksh' and 'ksh93' are the only shells I found that error out on
    'cd ""' with "cd: bad directory" (though these shells are unable
    to run significant portion of our test sute anyway).

Signed-off-by: SZEDER Gábor <szeder.dev@gmail.com>
---
 t/test-lib.sh | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/t/test-lib.sh b/t/test-lib.sh
index abcfbed6d6..06b75d8430 100644
--- a/t/test-lib.sh
+++ b/t/test-lib.sh
@@ -1436,6 +1436,14 @@ EMPTY_TREE=$(test_oid empty_tree)
 EMPTY_BLOB=$(test_oid empty_blob)
 _z40=$ZERO_OID
 
+cd () {
+	if test -z "$@"
+	then
+		BUG "cd invoked with empty parameter"
+	fi
+	command cd "$@"
+}
+
 # Provide an implementation of the 'yes' utility; the upper bound
 # limit is there to help Windows that cannot stop this loop from
 # wasting cycles when the downstream stops reading, so do not be
-- 
2.33.0.358.g803110d36e