3 files changed, 86 insertions, 15 deletions
diff --git a/contrib/subtree/git-subtree.sh b/contrib/subtree/git-subtree.sh
index b90ca0036f..2c67989fe8 100755
--- a/contrib/subtree/git-subtree.sh
+++ b/contrib/subtree/git-subtree.sh
@@ -371,20 +371,45 @@ try_remove_previous () {
 	fi
 }
 
-# Usage: process_subtree_split_trailer SPLIT_HASH MAIN_HASH
+# Usage: process_subtree_split_trailer SPLIT_HASH MAIN_HASH [REPOSITORY]
 process_subtree_split_trailer () {
-	assert test $# = 2
+	assert test $# = 2 -o $# = 3
 	b="$1"
 	sq="$2"
-	sub="$(git rev-parse --verify --quiet "$b^{commit}")" ||
-	die "fatal: could not rev-parse split hash $b from commit $sq"
+	repository=""
+	if test "$#" = 3
+	then
+		repository="$3"
+	fi
+	fail_msg="fatal: could not rev-parse split hash $b from commit $sq"
+	if ! sub="$(git rev-parse --verify --quiet "$b^{commit}")"
+	then
+		# if 'repository' was given, try to fetch the 'git-subtree-split' hash
+		# before 'rev-parse'-ing it again, as it might be a tag that we do not have locally
+		if test -n "${repository}"
+		then
+			git fetch "$repository" "$b"
+			sub="$(git rev-parse --verify --quiet "$b^{commit}")" ||
+				die "$fail_msg"
+		else
+			hint1=$(printf "hint: hash might be a tag, try fetching it from the subtree repository:")
+			hint2=$(printf "hint:    git fetch <subtree-repository> $b")
+			fail_msg=$(printf "$fail_msg\n$hint1\n$hint2")
+			die "$fail_msg"
+		fi
+	fi
 }
 
-# Usage: find_latest_squash DIR
+# Usage: find_latest_squash DIR [REPOSITORY]
 find_latest_squash () {
-	assert test $# = 1
+	assert test $# = 1 -o $# = 2
 	dir="$1"
-	debug "Looking for latest squash ($dir)..."
+	repository=""
+	if test "$#" = 2
+	then
+		repository="$2"
+	fi
+	debug "Looking for latest squash (dir=$dir, repository=$repository)..."
 	local indent=$(($indent + 1))
 
 	sq=
@@ -404,7 +429,7 @@ find_latest_squash () {
 			main="$b"
 			;;
 		git-subtree-split:)
-			process_subtree_split_trailer "$b" "$sq"
+			process_subtree_split_trailer "$b" "$sq" "$repository"
 			;;
 		END)
 			if test -n "$sub"
@@ -969,17 +994,22 @@ cmd_split () {
 	exit 0
 }
 
-# Usage: cmd_merge REV
+# Usage: cmd_merge REV [REPOSITORY]
 cmd_merge () {
-	test $# -eq 1 ||
-		die "fatal: you must provide exactly one revision.  Got: '$*'"
+	test $# -eq 1 -o $# -eq 2 ||
+		die "fatal: you must provide exactly one revision, and optionally a repository. Got: '$*'"
 	rev=$(git rev-parse -q --verify "$1^{commit}") ||
 		die "fatal: '$1' does not refer to a commit"
+	repository=""
+	if test "$#" = 2
+	then
+		repository="$2"
+	fi
 	ensure_clean
 
 	if test -n "$arg_addmerge_squash"
 	then
-		first_split="$(find_latest_squash "$dir")" || exit $?
+		first_split="$(find_latest_squash "$dir" "$repository")" || exit $?
 		if test -z "$first_split"
 		then
 			die "fatal: can't squash-merge: '$dir' was never added."
@@ -1017,7 +1047,7 @@ cmd_pull () {
 	ensure_clean
 	ensure_valid_ref_format "$ref"
 	git fetch "$repository" "$ref" || exit $?
-	cmd_merge FETCH_HEAD
+	cmd_merge FETCH_HEAD "$repository"
 }
 
 # Usage: cmd_push REPOSITORY [+][LOCALREV:]REMOTEREF
diff --git a/contrib/subtree/git-subtree.txt b/contrib/subtree/git-subtree.txt
index 9cddfa2654..0e7524d786 100644
--- a/contrib/subtree/git-subtree.txt
+++ b/contrib/subtree/git-subtree.txt
@@ -11,7 +11,7 @@ SYNOPSIS
 [verse]
 'git subtree' [<options>] -P <prefix> add <local-commit>
 'git subtree' [<options>] -P <prefix> add <repository> <remote-ref>
-'git subtree' [<options>] -P <prefix> merge <local-commit>
+'git subtree' [<options>] -P <prefix> merge <local-commit> [<repository>]
 'git subtree' [<options>] -P <prefix> split [<local-commit>]
 
 [verse]
@@ -76,7 +76,7 @@ add <repository> <remote-ref>::
 	only a single commit from the subproject, rather than its
 	entire history.
 
-merge <local-commit>::
+merge <local-commit> [<repository>]::
 	Merge recent changes up to <local-commit> into the <prefix>
 	subtree.  As with normal 'git merge', this doesn't
 	remove your own local changes; it just merges those
@@ -88,6 +88,11 @@ If you use '--squash', the merge direction doesn't always have to be
 forward; you can use this command to go back in time from v2.5 to v2.4,
 for example.  If your merge introduces a conflict, you can resolve it in
 the usual ways.
++
+When using '--squash', and the previous merge with '--squash' merged an
+annotated tag of the subtree repository, that tag needs to be available locally.
+If <repository> is given, a missing tag will automatically be fetched from that
+repository.
 
 split [<local-commit>]::
 	Extract a new, synthetic project history from the
diff --git a/contrib/subtree/t/t7900-subtree.sh b/contrib/subtree/t/t7900-subtree.sh
index 249743ab9a..d0671676c7 100755
--- a/contrib/subtree/t/t7900-subtree.sh
+++ b/contrib/subtree/t/t7900-subtree.sh
@@ -43,6 +43,30 @@ last_commit_subject () {
 	git log --pretty=format:%s -1
 }
 
+# Upon 'git subtree add|merge --squash' of an annotated tag,
+# pre-2.32.0 versions of 'git subtree' would write the hash of the tag
+# (sub1 below), instead of the commit (sub1^{commit}) in the
+# "git-subtree-split" trailer.
+# We immitate this behaviour below using a replace ref.
+# This function creates 3 repositories:
+# - $1
+# - $1-sub (added as subtree "sub" in $1)
+# - $1-clone (clone of $1)
+test_create_pre2_32_repo () {
+	subtree_test_create_repo "$1" &&
+	subtree_test_create_repo "$1-sub" &&
+	test_commit -C "$1" main1 &&
+	test_commit -C "$1-sub" --annotate sub1 &&
+	git -C "$1" subtree add --prefix="sub" --squash "../$1-sub" sub1 &&
+	tag=$(git -C "$1" rev-parse FETCH_HEAD) &&
+	commit=$(git -C "$1" rev-parse FETCH_HEAD^{commit}) &&
+	git -C "$1" log -1 --format=%B HEAD^2 >msg &&
+	test_commit -C "$1-sub" --annotate sub2 &&
+	git clone --no-local "$1" "$1-clone" &&
+	new_commit=$(cat msg | sed -e "s/$commit/$tag/" | git -C "$1-clone" commit-tree HEAD^2^{tree}) &&
+	git -C "$1-clone" replace HEAD^2 $new_commit
+}
+
 test_expect_success 'shows short help text for -h' '
 	test_expect_code 129 git subtree -h >out 2>err &&
 	test_must_be_empty err &&
@@ -264,6 +288,13 @@ test_expect_success 'merge new subproj history into subdir/ with a slash appende
 	)
 '
 
+test_expect_success 'merge with --squash after annotated tag was added/merged with --squash pre-v2.32.0 ' '
+	test_create_pre2_32_repo "$test_count" &&
+	git -C "$test_count-clone" fetch "../$test_count-sub" sub2  &&
+	test_must_fail git -C "$test_count-clone" subtree merge --prefix="sub" --squash FETCH_HEAD &&
+	git -C "$test_count-clone" subtree merge --prefix="sub" --squash FETCH_HEAD  "../$test_count-sub"
+'
+
 #
 # Tests for 'git subtree split'
 #
@@ -630,6 +661,11 @@ test_expect_success 'pull rejects flags for split' '
 	)
 '
 
+test_expect_success 'pull with --squash after annotated tag was added/merged with --squash pre-v2.32.0 ' '
+	test_create_pre2_32_repo "$test_count" &&
+	git -C "$test_count-clone" subtree -d pull --prefix="sub" --squash "../$test_count-sub" sub2
+'
+
 #
 # Tests for 'git subtree push'
 #