[PATCH v2 09/14] commit-graph: teach git-commit-graph --delete-expired

[Derrick Stolee <stolee@gmail.com>]

Teach git-commit-graph to delete the graph previously referenced by 'graph_head'
when writing a new graph file and updating 'graph_head'. This prevents
data creep by storing a list of useless graphs. Be careful to not delete
the graph if the file did not change.

Signed-off-by: Derrick Stolee <dstolee@microsoft.com>
---
 Documentation/git-commit-graph.txt |  8 +++--
 builtin/commit-graph.c             | 16 ++++++++-
 t/t5318-commit-graph.sh            | 66 +++++++++++++++++++++++++++++++++++++-
 3 files changed, 86 insertions(+), 4 deletions(-)

diff --git a/Documentation/git-commit-graph.txt b/Documentation/git-commit-graph.txt
index 33d6567f11..7b376e9212 100644
--- a/Documentation/git-commit-graph.txt
+++ b/Documentation/git-commit-graph.txt
@@ -39,6 +39,10 @@ OPTIONS
 	When used with --write, update the graph-head file to point to
 	the written graph file.
 
+--delete-expired::
+	When used with --write and --update-head, delete the graph file
+	previously referenced by graph-head.
+
 EXAMPLES
 --------
 
@@ -55,10 +59,10 @@ $ git commit-graph --write
 ------------------------------------------------
 
 * Write a graph file for the packed commits in your local .git folder,
-* and update graph-head.
+* update graph-head, and delete the old graph-<oid>.graph file.
 +
 ------------------------------------------------
-$ git commit-graph --write --update-head
+$ git commit-graph --write --update-head --delete-expired
 ------------------------------------------------
 
 * Read basic information from a graph file.
diff --git a/builtin/commit-graph.c b/builtin/commit-graph.c
index 4970dec133..766f09e6fc 100644
--- a/builtin/commit-graph.c
+++ b/builtin/commit-graph.c
@@ -12,7 +12,7 @@ static char const * const builtin_commit_graph_usage[] = {
 	N_("git commit-graph [--pack-dir <packdir>]"),
 	N_("git commit-graph --clear [--pack-dir <packdir>]"),
 	N_("git commit-graph --read [--graph-hash=<hash>]"),
-	N_("git commit-graph --write [--pack-dir <packdir>] [--update-head]"),
+	N_("git commit-graph --write [--pack-dir <packdir>] [--update-head] [--delete-expired]"),
 	NULL
 };
 
@@ -23,6 +23,7 @@ static struct opts_commit_graph {
 	const char *graph_hash;
 	int write;
 	int update_head;
+	int delete_expired;
 	int has_existing;
 	struct object_id old_graph_hash;
 } opts;
@@ -121,6 +122,17 @@ static int graph_write(void)
 	if (graph_hash)
 		printf("%s\n", oid_to_hex(graph_hash));
 
+
+	if (opts.delete_expired && opts.update_head && opts.has_existing &&
+	    oidcmp(graph_hash, &opts.old_graph_hash)) {
+		char *old_path = get_commit_graph_filename_hash(opts.pack_dir,
+								&opts.old_graph_hash);
+		if (remove_path(old_path))
+			die("failed to remove path %s", old_path);
+
+		free(old_path);
+	}
+
 	free(graph_hash);
 	return 0;
 }
@@ -139,6 +151,8 @@ int cmd_commit_graph(int argc, const char **argv, const char *prefix)
 			N_("write commit graph file")),
 		OPT_BOOL('u', "update-head", &opts.update_head,
 			N_("update graph-head to written graph file")),
+		OPT_BOOL('d', "delete-expired", &opts.delete_expired,
+			N_("delete expired head graph file")),
 		{ OPTION_STRING, 'H', "graph-hash", &opts.graph_hash,
 			N_("hash"),
 			N_("A hash for a specific graph file in the pack-dir."),
diff --git a/t/t5318-commit-graph.sh b/t/t5318-commit-graph.sh
index 6e3b62b754..b56a6d4217 100755
--- a/t/t5318-commit-graph.sh
+++ b/t/t5318-commit-graph.sh
@@ -101,9 +101,73 @@ test_expect_success 'write graph with merges' \
      _graph_read_expect "18" "${packdir}" &&
      cmp expect output'
 
+test_expect_success 'Add more commits' \
+    'for i in $(test_seq 16 20)
+     do
+        echo $i >$i.txt &&
+        git add $i.txt &&
+        git commit -m "commit $i" &&
+        git branch commits/$i
+     done &&
+     git repack'
+
+# Current graph structure:
+#
+#      20
+#       |
+#      19
+#       |
+#      18
+#       |
+#      17
+#       |
+#      16
+#       |
+#      M3
+#     / |\_____
+#    / 10      15
+#   /   |      |
+#  /    9 M2   14
+# |     |/  \  |
+# |     8 M1 | 13
+# |     |/ | \_|
+# 5     7  |   12
+# |     |   \__|
+# 4     6      11
+# |____/______/
+# 3
+# |
+# 2
+# |
+# 1
+
+test_expect_success 'write graph with merges' \
+    'graph3=$(git commit-graph --write --update-head --delete-expired) &&
+     test_path_is_file ${packdir}/graph-${graph3}.graph &&
+     test_path_is_missing ${packdir}/graph-${graph2}.graph &&
+     test_path_is_file ${packdir}/graph-${graph1}.graph &&
+     test_path_is_file ${packdir}/graph-head &&
+     echo ${graph3} >expect &&
+     cmp -n 40 expect ${packdir}/graph-head &&
+     git commit-graph --read --graph-hash=${graph3} >output &&
+     _graph_read_expect "23" "${packdir}" &&
+     cmp expect output'
+
+test_expect_success 'write graph with nothing new' \
+    'graph4=$(git commit-graph --write --update-head --delete-expired) &&
+     test_path_is_file ${packdir}/graph-${graph4}.graph &&
+     test_path_is_file ${packdir}/graph-${graph1}.graph &&
+     test_path_is_file ${packdir}/graph-head &&
+     echo ${graph4} >expect &&
+     cmp -n 40 expect ${packdir}/graph-head &&
+     git commit-graph --read --graph-hash=${graph4} >output &&
+     _graph_read_expect "23" "${packdir}" &&
+     cmp expect output'
+
 test_expect_success 'clear graph' \
     'git commit-graph --clear &&
      test_path_is_missing ${packdir}/graph-${graph2}.graph &&
+     test_path_is_file ${packdir}/graph-${graph1}.graph &&
      test_path_is_missing ${packdir}/graph-head'
 
 test_expect_success 'setup bare repo' \
@@ -121,7 +185,7 @@ test_expect_success 'write graph in bare repo' \
      echo ${graphbare} >expect &&
      cmp -n 40 expect ${baredir}/graph-head &&
      git commit-graph --read --graph-hash=${graphbare} >output &&
-     _graph_read_expect "18" "${baredir}" &&
+     _graph_read_expect "23" "${baredir}" &&
      cmp expect output'
 
 test_done
-- 
2.16.0.15.g9c3cf44.dirty