merge(third_party/git): Merge squashed git subtree at v2.23.0

Merge commit '1b593e1ea4' as 'third_party/git'

third_party/git/t/t5311-pack-bitmaps-shallow.sh

@@ -0,0 +1,39 @@
+#!/bin/sh
+
+test_description='check bitmap operation with shallow repositories'
+. ./test-lib.sh
+
+# We want to create a situation where the shallow, grafted
+# view of reachability does not match reality in a way that
+# might cause us to send insufficient objects.
+#
+# We do this with a history that repeats a state, like:
+#
+#      A    --   B    --   C
+#    file=1    file=2    file=1
+#
+# and then create a shallow clone to the second commit, B.
+# In a non-shallow clone, that would mean we already have
+# the tree for A. But in a shallow one, we've grafted away
+# A, and fetching A to B requires that the other side send
+# us the tree for file=1.
+test_expect_success 'setup shallow repo' '
+	echo 1 >file &&
+	git add file &&
+	git commit -m orig &&
+	echo 2 >file &&
+	git commit -a -m update &&
+	git clone --no-local --bare --depth=1 . shallow.git &&
+	echo 1 >file &&
+	git commit -a -m repeat
+'
+
+test_expect_success 'turn on bitmaps in the parent' '
+	git repack -adb
+'
+
+test_expect_success 'shallow fetch from bitmapped repo' '
+	(cd shallow.git && git fetch)
+'
+
+test_done