[v4,06/10] diff-lib: define diff_get_merge_base()

Commit Message

Denton Liu Sept. 20, 2020, 11:22 a.m. UTC

In a future commit, we will be using this function to implement
--merge-base functionality in various diff commands.

Signed-off-by: Denton Liu <[e-mail]>
---
 diff-lib.c | 45 +++++++++++++++++++++++++++++++++++++++++++++
 diff.h     |  2 ++
 2 files changed, 47 insertions(+)

Patch

diff --git a/diff-lib.c b/diff-lib.c
index d5b2c8af56..fa64e64bbe 100644
--- a/diff-lib.c
+++ b/diff-lib.c
@@ -13,6 +13,7 @@ 
 #include "submodule.h"
 #include "dir.h"
 #include "fsmonitor.h"
+#include "commit-reach.h"
 
 /*
  * diff-files
@@ -518,6 +519,50 @@  static int diff_cache(struct rev_info *revs,
 	return unpack_trees(1, &t, &opts);
 }
 
+void diff_get_merge_base(const struct rev_info *revs, struct object_id *mb)
+{
+	int i;
+	struct commit *mb_child[2] = {0};
+	struct commit_list *merge_bases;
+
+	for (i = 0; i < revs->pending.nr; i++) {
+		struct object *obj = revs->pending.objects[i].item;
+		if (obj->flags)
+			die(_("--merge-base does not work with ranges"));
+		if (obj->type != OBJ_COMMIT)
+			die(_("--merge-base only works with commits"));
+	}
+
+	/*
+	 * This check must go after the for loop above because A...B
+	 * ranges produce three pending commits, resulting in a
+	 * misleading error message.
+	 */
+	if (revs->pending.nr < 1 || revs->pending.nr > 2)
+		BUG("unexpected revs->pending.nr: %d", revs->pending.nr);
+
+	for (i = 0; i < revs->pending.nr; i++)
+		mb_child[i] = lookup_commit_reference(the_repository, &revs->pending.objects[i].item->oid);
+	if (revs->pending.nr == 1) {
+		struct object_id oid;
+
+		if (get_oid("HEAD", &oid))
+			die(_("unable to get HEAD"));
+
+		mb_child[1] = lookup_commit_reference(the_repository, &oid);
+	}
+
+	merge_bases = repo_get_merge_bases(the_repository, mb_child[0], mb_child[1]);
+	if (!merge_bases)
+		die(_("no merge base found"));
+	if (merge_bases->next)
+		die(_("multiple merge bases found"));
+
+	oidcpy(mb, &merge_bases->item->object.oid);
+
+	free_commit_list(merge_bases);
+}
+
 int run_diff_index(struct rev_info *revs, unsigned int option)
 {
 	struct object_array_entry *ent;
diff --git a/diff.h b/diff.h
index aea0d5b96b..fedfeab7a2 100644
--- a/diff.h
+++ b/diff.h
@@ -580,6 +580,8 @@  void diff_warn_rename_limit(const char *varname, int needed, int degraded_cc);
  */
 const char *diff_aligned_abbrev(const struct object_id *sha1, int);
 
+void diff_get_merge_base(const struct rev_info *revs, struct object_id *mb);
+
 /* do not report anything on removed paths */
 #define DIFF_SILENT_ON_REMOVED 01
 /* report racily-clean paths as modified */