Merge branch 'en/merge-recursive'

* en/merge-recursive:
  merge-recursive: tweak magic band-aid
  merge-recursive: When we detect we can skip an update, actually skip it
  t6022: New test checking for unnecessary updates of files in D/F conflicts
  t6022: New test checking for unnecessary updates of renamed+modified files

merge-recursive.c

@@ -344,10 +344,11 @@ static void make_room_for_directories_of_df_conflicts(struct merge_options *o,
 	 * make room for the corresponding directory.  Such paths will
 	 * later be processed in process_df_entry() at the end.  If
 	 * the corresponding directory ends up being removed by the
-	 * merge, then the file will be reinstated at that time;
+	 * merge, then the file will be reinstated at that time
-	 * otherwise, if the file is not supposed to be removed by the
+	 * (albeit with a different timestamp!); otherwise, if the
-	 * merge, the contents of the file will be placed in another
+	 * file is not supposed to be removed by the merge, the
-	 * unique filename.
+	 * contents of the file will be placed in another unique
+	 * filename.
 	 *
 	 * NOTE: This function relies on the fact that entries for a
 	 * D/F conflict will appear adjacent in the index, with the
@@ -358,6 +359,13 @@ static void make_room_for_directories_of_df_conflicts(struct merge_options *o,
 	int last_len = 0;
 	int i;
 
+	/*
+	 * Do not do any of this crazyness during the recursive; we don't
+	 * even write anything to the working tree!
+	 */
+	if (o->call_depth)
+		return;
+
 	for (i = 0; i < entries->nr; i++) {
 		const char *path = entries->items[i].string;
 		int len = strlen(path);
@@ -1260,9 +1268,13 @@ static int merge_content(struct merge_options *o,
 	}
 
 	if (mfi.clean && !df_conflict_remains &&
-	    sha_eq(mfi.sha, a_sha) && mfi.mode == a.mode)
+	    sha_eq(mfi.sha, a_sha) && mfi.mode == a.mode &&
+	    !o->call_depth && !lstat(path, &st)) {
 		output(o, 3, "Skipped %s (merged same as existing)", path);
-	else
+		add_cacheinfo(mfi.mode, mfi.sha, path,
+			      0 /*stage*/, 1 /*refresh*/, 0 /*options*/);
+		return mfi.clean;
+	} else
 		output(o, 2, "Auto-merging %s", path);
 
 	if (!mfi.clean) {

t/t6022-merge-rename.sh

@@ -609,4 +609,67 @@ test_expect_success 'check handling of differently renamed file with D/F conflic
 	! test -f original
 '
 
+test_expect_success 'setup avoid unnecessary update, normal rename' '
+	git reset --hard &&
+	git checkout --orphan avoid-unnecessary-update-1 &&
+	git rm -rf . &&
+	git clean -fdqx &&
+
+	printf "1\n2\n3\n4\n5\n6\n7\n8\n9\n10\n" >original &&
+	git add -A &&
+	git commit -m "Common commmit" &&
+
+	git mv original rename &&
+	echo 11 >>rename &&
+	git add -u &&
+	git commit -m "Renamed and modified" &&
+
+	git checkout -b merge-branch-1 HEAD~1 &&
+	echo "random content" >random-file &&
+	git add -A &&
+	git commit -m "Random, unrelated changes"
+'
+
+test_expect_success 'avoid unnecessary update, normal rename' '
+	git checkout -q avoid-unnecessary-update-1^0 &&
+	test-chmtime =1000000000 rename &&
+	test-chmtime -v +0 rename >expect &&
+	git merge merge-branch-1 &&
+	test-chmtime -v +0 rename >actual &&
+	test_cmp expect actual # "rename" should have stayed intact
+'
+
+test_expect_success 'setup to test avoiding unnecessary update, with D/F conflict' '
+	git reset --hard &&
+	git checkout --orphan avoid-unnecessary-update-2 &&
+	git rm -rf . &&
+	git clean -fdqx &&
+
+	mkdir df &&
+	printf "1\n2\n3\n4\n5\n6\n7\n8\n9\n10\n" >df/file &&
+	git add -A &&
+	git commit -m "Common commmit" &&
+
+	git mv df/file temp &&
+	rm -rf df &&
+	git mv temp df &&
+	echo 11 >>df &&
+	git add -u &&
+	git commit -m "Renamed and modified" &&
+
+	git checkout -b merge-branch-2 HEAD~1 &&
+	>unrelated-change &&
+	git add unrelated-change &&
+	git commit -m "Only unrelated changes"
+'
+
+test_expect_failure 'avoid unnecessary update, with D/F conflict' '
+	git checkout -q avoid-unnecessary-update-2^0 &&
+	test-chmtime =1000000000 df &&
+	test-chmtime -v +0 df >expect &&
+	git merge merge-branch-2 &&
+	test-chmtime -v +0 df >actual &&
+	test_cmp expect actual # "df" should have stayed intact
+'
+
 test_done