t5351: avoid using `test_cmp` for binary data

The `test_cmp` function is meant to provide nicer output than `cmp` when
expected and actual output of Git commands disagree. The implicit
assumption is that the output is line-based and human readable.

However, aaf81223f48 (unpack-objects: use stream_loose_object() to
unpack large objects, 2022-06-11) introduced a call that compares the
contents of pack files, which are distinctly not line-based nor human
readable.

This causes problems because on Windows, we hand off to the Bash
function `mingw_test_cmp` that compares the lines while ignoring line
ending differences. And this Bash function spends an insane amount of
cycles trying to read in that binary pack file, so that it is almost
indistinguishable from an infinite loop.

For example, t5351 took 1486 seconds in the CI run at
https://github.com/git/git/runs/7398490747?check_suite_focus=true#step:5:171,
to complete. And yes, that is almost half an hour.

Since Git's tests already use `cmp` consistently when comparing pack
files, let's change this instance to use `cmp` instead of `test_cmp`,
too, and fix that performance problem.

Now t5351 takes all of 22 seconds.

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

diff --git a/t/t5351-unpack-large-objects.sh b/t/t5351-unpack-large-objects.sh
index dd7ebc4007280d2539bac8e3105042c645d08dbc..e936f91c3ba628556e02a2f95b753289308ea6fe 100755 (executable)
--- a/t/t5351-unpack-large-objects.sh
+++ b/t/t5351-unpack-large-objects.sh
@@ -93,7 +93,7 @@ test_expect_success 'do not unpack existing large objects' '
 
        # The destination came up with the exact same pack...
        DEST_PACK=$(echo dest.git/objects/pack/pack-*.pack) &&
-       test_cmp pack-$PACK.pack $DEST_PACK &&
+       cmp pack-$PACK.pack $DEST_PACK &&
 
        # ...and wrote no loose objects
        test_stdout_line_count = 0 find dest.git/objects -type f ! -name "pack-*"