Merge branch 'dl/diff-merge-base'

"git diff A...B" learned "git diff --merge-base A B", which is a
longer short-hand to say the same thing.

* dl/diff-merge-base:
  contrib/completion: complete `git diff --merge-base`
  builtin/diff-tree: learn --merge-base
  builtin/diff-index: learn --merge-base
  t4068: add --merge-base tests
  diff-lib: define diff_get_merge_base()
  diff-lib: accept option flags in run_diff_index()
  contrib/completion: extract common diff/difftool options
  git-diff.txt: backtick quote command text
  git-diff-index.txt: make --cached description a proper sentence
  t4068: remove unnecessary >tmp

1 files changed, 16 insertions, 1 deletions

diff --git a/builtin/diff-tree.c b/builtin/diff-tree.c
index 802363d..9fc95e9 100644
--- a/builtin/diff-tree.c
+++ b/builtin/diff-tree.c
@@ -111,6 +111,7 @@ int cmd_diff_tree(int argc, const char **argv, const char *prefix)
 	struct setup_revision_opt s_r_opt;
 	struct userformat_want w;
 	int read_stdin = 0;
+	int merge_base = 0;
 
 	if (argc == 2 && !strcmp(argv[1], "-h"))
 		usage(diff_tree_usage);
@@ -143,9 +144,18 @@ int cmd_diff_tree(int argc, const char **argv, const char *prefix)
 			read_stdin = 1;
 			continue;
 		}
+		if (!strcmp(arg, "--merge-base")) {
+			merge_base = 1;
+			continue;
+		}
 		usage(diff_tree_usage);
 	}
 
+	if (read_stdin && merge_base)
+		die(_("--stdin and --merge-base are mutually exclusive"));
+	if (merge_base && opt->pending.nr != 2)
+		die(_("--merge-base only works with two commits"));
+
 	/*
 	 * NOTE!  We expect "a..b" to expand to "^a b" but it is
 	 * perfectly valid for revision range parser to yield "b ^a",
@@ -165,7 +175,12 @@ int cmd_diff_tree(int argc, const char **argv, const char *prefix)
 	case 2:
 		tree1 = opt->pending.objects[0].item;
 		tree2 = opt->pending.objects[1].item;
-		if (tree2->flags & UNINTERESTING) {
+		if (merge_base) {
+			struct object_id oid;
+
+			diff_get_merge_base(opt, &oid);
+			tree1 = lookup_object(the_repository, &oid);
+		} else if (tree2->flags & UNINTERESTING) {
 			SWAP(tree2, tree1);
 		}
 		diff_tree_oid(&tree1->oid, &tree2->oid, "", &opt->diffopt);