apply: fall back on three-way merge

Grab the preimage blob the patch claims to be based on out of the object
store, apply the patch, and then call three-way-merge function.  This step
still does not plug the actual three-way merge logic yet, but we are
getting there.

Signed-off-by: Junio C Hamano <gitster@pobox.com>

diff --git a/builtin/apply.c b/builtin/apply.c
index 51b695bac8f16691bed381ede764b3faaec6fddb..5a7201fc86db9462c901481f8cb2b394604977b5 100644 (file)
--- a/builtin/apply.c
+++ b/builtin/apply.c
@@ -3140,10 +3140,54 @@ static int load_preimage(struct image *image,
        return 0;
 }
 
+static int three_way_merge(struct image *image,
+                          char *path,
+                          const unsigned char *base,
+                          const unsigned char *ours,
+                          const unsigned char *theirs)
+{
+       return -1; /* for now */
+}
+
 static int try_threeway(struct image *image, struct patch *patch,
                        struct stat *st, struct cache_entry *ce)
 {
-       return -1; /* for now */
+       unsigned char pre_sha1[20], post_sha1[20], our_sha1[20];
+       struct strbuf buf = STRBUF_INIT;
+       size_t len;
+       char *img;
+       struct image tmp_image;
+
+       /* No point falling back to 3-way merge in these cases */
+       if (patch->is_new || patch->is_delete ||
+           S_ISGITLINK(patch->old_mode) || S_ISGITLINK(patch->new_mode))
+               return -1;
+
+       /* Preimage the patch was prepared for */
+       if (get_sha1(patch->old_sha1_prefix, pre_sha1) ||
+           read_blob_object(&buf, pre_sha1, patch->old_mode))
+               return error("repository lacks the necessary blob to fall back on 3-way merge.");
+       img = strbuf_detach(&buf, &len);
+       prepare_image(&tmp_image, img, len, 1);
+       /* Apply the patch to get the post image */
+       if (apply_fragments(&tmp_image, patch) < 0) {
+               clear_image(&tmp_image);
+               return -1;
+       }
+       /* post_sha1[] is theirs */
+       write_sha1_file(tmp_image.buf, tmp_image.len, blob_type, post_sha1);
+       clear_image(&tmp_image);
+
+       /* our_sha1[] is ours */
+       if (load_preimage(&tmp_image, patch, st, ce))
+               return error("cannot read the current contents of '%s'",
+                            patch->old_name);
+       write_sha1_file(tmp_image.buf, tmp_image.len, blob_type, our_sha1);
+       clear_image(&tmp_image);
+
+       /* in-core three-way merge between post and our using pre as base */
+       return three_way_merge(image,
+                              patch->new_name, pre_sha1, our_sha1, post_sha1);
 }
 
 static int apply_data(struct patch *patch, struct stat *st, struct cache_entry *ce)