merge-ort: copy and adapt merge_submodule() from merge-recursive.c

Take merge_submodule() from merge-recursive.c and make slight
adjustments, predominantly around deferring output using path_msg()
instead of using merge-recursive's output() and show() functions.
There's also a fix for recursive cases (when call_depth > 0) and a
slight change to argument order for find_first_merges().

find_first_merges() and format_commit() are left unimplemented for
now, but will be added by subsequent commits.

Signed-off-by: Elijah Newren <newren@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

Author: newren

merge-ort.c

@@ -26,6 +26,7 @@
 #include "ll-merge.h"
 #include "object-store.h"
 #include "strmap.h"
+#include "submodule.h"
 #include "tree.h"
 #include "unpack-trees.h"
 #include "xdiff-interface.h"
@@ -323,6 +324,13 @@ static int err(struct merge_options *opt, const char *err, ...)
 	return -1;
 }
 
+static void format_commit(struct strbuf *sb,
+			  int indent,
+			  struct commit *commit)
+{
+	die("Not yet implemented.");
+}
+
 __attribute__((format (printf, 4, 5)))
 static void path_msg(struct merge_options *opt,
 		     const char *path,
@@ -632,14 +640,130 @@ static int collect_merge_info(struct merge_options *opt,
 
 /*** Function Grouping: functions related to threeway content merges ***/
 
+static int find_first_merges(struct repository *repo,
+			     const char *path,
+			     struct commit *a,
+			     struct commit *b,
+			     struct object_array *result)
+{
+	die("Not yet implemented.");
+}
+
 static int merge_submodule(struct merge_options *opt,
 			   const char *path,
 			   const struct object_id *o,
 			   const struct object_id *a,
 			   const struct object_id *b,
 			   struct object_id *result)
 {
-	die("Not yet implemented.");
+	struct commit *commit_o, *commit_a, *commit_b;
+	int parent_count;
+	struct object_array merges;
+	struct strbuf sb = STRBUF_INIT;
+
+	int i;
+	int search = !opt->priv->call_depth;
+
+	/* store fallback answer in result in case we fail */
+	oidcpy(result, opt->priv->call_depth ? o : a);
+
+	/* we can not handle deletion conflicts */
+	if (is_null_oid(o))
+		return 0;
+	if (is_null_oid(a))
+		return 0;
+	if (is_null_oid(b))
+		return 0;
+
+	if (add_submodule_odb(path)) {
+		path_msg(opt, path, 0,
+			 _("Failed to merge submodule %s (not checked out)"),
+			 path);
+		return 0;
+	}
+
+	if (!(commit_o = lookup_commit_reference(opt->repo, o)) ||
+	    !(commit_a = lookup_commit_reference(opt->repo, a)) ||
+	    !(commit_b = lookup_commit_reference(opt->repo, b))) {
+		path_msg(opt, path, 0,
+			 _("Failed to merge submodule %s (commits not present)"),
+			 path);
+		return 0;
+	}
+
+	/* check whether both changes are forward */
+	if (!in_merge_bases(commit_o, commit_a) ||
+	    !in_merge_bases(commit_o, commit_b)) {
+		path_msg(opt, path, 0,
+			 _("Failed to merge submodule %s "
+			   "(commits don't follow merge-base)"),
+			 path);
+		return 0;
+	}
+
+	/* Case #1: a is contained in b or vice versa */
+	if (in_merge_bases(commit_a, commit_b)) {
+		oidcpy(result, b);
+		path_msg(opt, path, 1,
+			 _("Note: Fast-forwarding submodule %s to %s"),
+			 path, oid_to_hex(b));
+		return 1;
+	}
+	if (in_merge_bases(commit_b, commit_a)) {
+		oidcpy(result, a);
+		path_msg(opt, path, 1,
+			 _("Note: Fast-forwarding submodule %s to %s"),
+			 path, oid_to_hex(a));
+		return 1;
+	}
+
+	/*
+	 * Case #2: There are one or more merges that contain a and b in
+	 * the submodule. If there is only one, then present it as a
+	 * suggestion to the user, but leave it marked unmerged so the
+	 * user needs to confirm the resolution.
+	 */
+
+	/* Skip the search if makes no sense to the calling context.  */
+	if (!search)
+		return 0;
+
+	/* find commit which merges them */
+	parent_count = find_first_merges(opt->repo, path, commit_a, commit_b,
+					 &merges);
+	switch (parent_count) {
+	case 0:
+		path_msg(opt, path, 0, _("Failed to merge submodule %s"), path);
+		break;
+
+	case 1:
+		format_commit(&sb, 4,
+			      (struct commit *)merges.objects[0].item);
+		path_msg(opt, path, 0,
+			 _("Failed to merge submodule %s, but a possible merge "
+			   "resolution exists:\n%s\n"),
+			 path, sb.buf);
+		path_msg(opt, path, 1,
+			 _("If this is correct simply add it to the index "
+			   "for example\n"
+			   "by using:\n\n"
+			   "  git update-index --cacheinfo 160000 %s \"%s\"\n\n"
+			   "which will accept this suggestion.\n"),
+			 oid_to_hex(&merges.objects[0].item->oid), path);
+		strbuf_release(&sb);
+		break;
+	default:
+		for (i = 0; i < merges.nr; i++)
+			format_commit(&sb, 4,
+				      (struct commit *)merges.objects[i].item);
+		path_msg(opt, path, 0,
+			 _("Failed to merge submodule %s, but multiple "
+			   "possible merges exist:\n%s"), path, sb.buf);
+		strbuf_release(&sb);
+	}
+
+	object_array_clear(&merges);
+	return 0;
 }
 
 static int merge_3way(struct merge_options *opt,