WIP: add a test for push --path-walk not reusing deltas

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>

t/t5590-push-path-walk.sh

@@ -0,0 +1,59 @@
+#!/bin/sh
+
+test_description='verify that push respects `pack.usePathWalk`'
+
+TEST_PASSES_SANITIZE_LEAK=true
+. ./test-lib.sh
+. "$TEST_DIRECTORY"/lib-pack.sh
+
+test_expect_success 'setup bare repository and clone' '
+	git init --bare -b main bare.git &&
+	git --git-dir bare.git commit-tree -m initial $EMPTY_TREE >head_oid &&
+	git --git-dir bare.git update-ref refs/heads/main $(cat head_oid) &&
+	git clone --bare bare.git clone.git
+'
+test_expect_success 'avoid reusing deltified objects' '
+	x="0123456789abcdef" &&
+	printf "$x$x$x$x$x$x$x$x" >x128 &&
+	printf "$x$x$x$x$x$x$x$x$x$x$x$x$x$x$x$x" >x256 &&
+	oid128=$(git hash-object x128) &&
+	oid256=$(git hash-object x256) &&
+
+	pack=clone.git/objects/pack/pack-tmp.pack &&
+	pack_header 2 >$pack &&
+
+	# add x256 as a non-deltified object, using uncompressed zlib for simplicity
+	# 0x30 = OBJ_BLOB << 4, 0x80 = size larger than 15, 0x0 = lower 4 bits of size, 0x10 = bits 5-9 of size (size = 256)
+	printf "\xb0\x10" >>$pack &&
+	# Uncompressed zlib stream always starts with 0x78 0x01 0x01, followed
+	# by two bytes encoding the size, little endian, then two bytes with
+	# the bitwise-complement of that size, then the payload, and then the
+	# Adler32 checksum. For some reason, the checksum is in big-endian format.
+	printf "\x78\x01\x01\0\x01\xff\xfe" >>$pack &&
+	cat x256 >>$pack &&
+	# Manually-computed Adler32 checksum: 0xd7ae4621
+	printf "\xd7\xae\x46\x21" >>$pack &&
+
+	# add x128 as a very badly deltified object
+	# 0x60 = OBJ_OFS_DELTA << 4, 0x80 = total size larger than 15, 0x4 = lower 4 bits of size, 0x03 = bits 5-9 of size (size = 128 * 3 + 2 + 2)
+	printf "\xe4\x18" >>$pack &&
+	# 0x010d = size (i.e. the relative negative offset) of the previous object (x256, used as base object)
+	# encoded as 0x80 | ((0x010d >> 7) - 1), 0x010d & 0x7f
+	printf "\x81\x0d" >>$pack &&
+	# Uncompressed zlib stream, as before, size = 2 + 2 + 128 * 3 (i.e. 0x184)
+	printf "\x78\x01\x01\x84\x01\x7b\xfe" >>$pack &&
+	# base object size = 0x0100 (encoded as 0x80 | (0x0100 & 0x7f), 0x0100 >> 7
+	printf "\x80\x02" >>$pack &&
+	# object size = 0x80 (encoded as 0x80 | (0x80 & 0x7f), 0x80 >> 7
+	printf "\x80\x01" >>$pack &&
+	# enourmously badly-deltified object: copy every single byte individually
+	# 0x80 = copy, 0x01 = use 1 byte to encode the offset (0), 0x10 = use 1 byte to encode the size (1, i.e. 0x01)
+	printf "$(printf "\\\\x91\\\\x%02x\\\\x01" $(test_seq 0 127))" >>$pack &&
+	# Manually-computed Adler32 checksum: 0x99c369c4
+	printf "\x99\xc3\x69\xc4" >>$pack &&
+
+	pack_trailer $pack &&
+	git index-pack -v $pack
+'
+
+test_done