git notes merge: Manual conflict resolution, part 1/2

Conflicts (that are to be resolved manually) are written into a special-
purpose working tree, located at .git/NOTES_MERGE_WORKTREE. Within this
directory, conflicting notes entries are stored (with conflict markers
produced by ll_merge()) using the SHA1 of the annotated object. The
.git/NOTES_MERGE_WORKTREE directory will only contain the _conflicting_
note entries. The non-conflicting note entries (aka. the partial merge
result) are stored in 'local_tree', and the SHA1 of the resulting commit
is written to 'result_sha1'. The return value from notes_merge() is -1.

The user is told to edit the files within the .git/NOTES_MERGE_WORKTREE
directory in order to resolve the conflicts.

The patch also contains documentation and testcases for the correct setup
of .git/NOTES_MERGE_WORKTREE.

The next part will recombine the partial notes merge result with the
resolved conflicts in .git/NOTES_MERGE_WORKTREE to produce the complete
merge result.

This patch has been improved by the following contributions:
- Jonathan Nieder: Use trace_printf(...) instead of OUTPUT(o, 5, ...)

Thanks-to: Jonathan Nieder <jrnieder@gmail.com>
Signed-off-by: Johan Herland <johan@herland.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

Documentation/git-notes.txt

@@ -92,7 +92,9 @@ merge::
 +
 If conflicts arise and a strategy for automatically resolving
 conflicting notes (see the -s/--strategy option) is not given,
-the merge fails (TODO).
+the "manual" resolver is used. This resolver checks out the
+conflicting notes in a special worktree (`.git/NOTES_MERGE_WORKTREE`),
+and instructs the user to manually resolve the conflicts there.
 
 remove::
 	Remove the notes for a given object (defaults to HEAD).
@@ -191,8 +193,10 @@ object, in which case the history of the notes can be read with
 NOTES MERGE STRATEGIES
 ----------------------
 
-The default notes merge strategy is "manual", which is not yet
-implemented (TODO).
+The default notes merge strategy is "manual", which checks out
+conflicting notes in a special work tree for resolving notes conflicts
+(`.git/NOTES_MERGE_WORKTREE`), and instructs the user to resolve the
+conflicts in that work tree.
 
 "ours" automatically resolves conflicting notes in favor of the local
 version (i.e. the current notes ref).

builtin/notes.c

@@ -820,14 +820,14 @@ static int merge(int argc, const char **argv, const char *prefix)
 		/* Update default notes ref with new commit */
 		update_ref(msg.buf, default_notes_ref(), result_sha1, NULL,
 			   0, DIE_ON_ERR);
-	else
-		/* TODO: */
-		die("'git notes merge' cannot yet handle conflicts!");
+	else /* Merge has unresolved conflicts */
+		printf("Automatic notes merge failed. Fix conflicts in %s.\n",
+		       git_path(NOTES_MERGE_WORKTREE));
 
 	free_notes(t);
 	strbuf_release(&remote_ref);
 	strbuf_release(&msg);
-	return 0;
+	return result < 0; /* return non-zero on conflicts */
 }
 
 static int remove_cmd(int argc, const char **argv, const char *prefix)

notes-merge.c

@@ -3,6 +3,9 @@
 #include "refs.h"
 #include "diff.h"
 #include "diffcore.h"
+#include "xdiff-interface.h"
+#include "ll-merge.h"
+#include "dir.h"
 #include "notes.h"
 #include "notes-merge.h"
 
@@ -263,16 +266,169 @@ static void diff_tree_local(struct notes_merge_options *o,
 	diff_tree_release_paths(&opt);
 }
 
+static void check_notes_merge_worktree(struct notes_merge_options *o)
+{
+	if (!o->has_worktree) {
+		/*
+		 * Must establish NOTES_MERGE_WORKTREE.
+		 * Abort if NOTES_MERGE_WORKTREE already exists
+		 */
+		if (file_exists(git_path(NOTES_MERGE_WORKTREE))) {
+			if (advice_resolve_conflict)
+				die("You have not concluded your previous "
+				    "notes merge (%s exists).\nPlease, use "
+				    "'git notes merge --commit' or 'git notes "
+				    "merge --reset' to commit/abort the "
+				    "previous merge before you start a new "
+				    "notes merge.", git_path("NOTES_MERGE_*"));
+			else
+				die("You have not concluded your notes merge "
+				    "(%s exists).", git_path("NOTES_MERGE_*"));
+		}
+
+		if (safe_create_leading_directories(git_path(
+				NOTES_MERGE_WORKTREE "/.test")))
+			die_errno("unable to create directory %s",
+				  git_path(NOTES_MERGE_WORKTREE));
+		o->has_worktree = 1;
+	} else if (!file_exists(git_path(NOTES_MERGE_WORKTREE)))
+		/* NOTES_MERGE_WORKTREE should already be established */
+		die("missing '%s'. This should not happen",
+		    git_path(NOTES_MERGE_WORKTREE));
+}
+
+static void write_buf_to_worktree(const unsigned char *obj,
+				  const char *buf, unsigned long size)
+{
+	int fd;
+	char *path = git_path(NOTES_MERGE_WORKTREE "/%s", sha1_to_hex(obj));
+	if (safe_create_leading_directories(path))
+		die_errno("unable to create directory for '%s'", path);
+	if (file_exists(path))
+		die("found existing file at '%s'", path);
+
+	fd = open(path, O_WRONLY | O_TRUNC | O_CREAT, 0666);
+	if (fd < 0)
+		die_errno("failed to open '%s'", path);
+
+	while (size > 0) {
+		long ret = write_in_full(fd, buf, size);
+		if (ret < 0) {
+			/* Ignore epipe */
+			if (errno == EPIPE)
+				break;
+			die_errno("notes-merge");
+		} else if (!ret) {
+			die("notes-merge: disk full?");
+		}
+		size -= ret;
+		buf += ret;
+	}
+
+	close(fd);
+}
+
+static void write_note_to_worktree(const unsigned char *obj,
+				   const unsigned char *note)
+{
+	enum object_type type;
+	unsigned long size;
+	void *buf = read_sha1_file(note, &type, &size);
+
+	if (!buf)
+		die("cannot read note %s for object %s",
+		    sha1_to_hex(note), sha1_to_hex(obj));
+	if (type != OBJ_BLOB)
+		die("blob expected in note %s for object %s",
+		    sha1_to_hex(note), sha1_to_hex(obj));
+	write_buf_to_worktree(obj, buf, size);
+	free(buf);
+}
+
+static int ll_merge_in_worktree(struct notes_merge_options *o,
+				struct notes_merge_pair *p)
+{
+	mmbuffer_t result_buf;
+	mmfile_t base, local, remote;
+	int status;
+
+	read_mmblob(&base, p->base);
+	read_mmblob(&local, p->local);
+	read_mmblob(&remote, p->remote);
+
+	status = ll_merge(&result_buf, sha1_to_hex(p->obj), &base, NULL,
+			  &local, o->local_ref, &remote, o->remote_ref, 0);
+
+	free(base.ptr);
+	free(local.ptr);
+	free(remote.ptr);
+
+	if ((status < 0) || !result_buf.ptr)
+		die("Failed to execute internal merge");
+
+	write_buf_to_worktree(p->obj, result_buf.ptr, result_buf.size);
+	free(result_buf.ptr);
+
+	return status;
+}
+
+static int merge_one_change_manual(struct notes_merge_options *o,
+				   struct notes_merge_pair *p,
+				   struct notes_tree *t)
+{
+	const char *lref = o->local_ref ? o->local_ref : "local version";
+	const char *rref = o->remote_ref ? o->remote_ref : "remote version";
+
+	trace_printf("\t\t\tmerge_one_change_manual(obj = %.7s, base = %.7s, "
+	       "local = %.7s, remote = %.7s)\n",
+	       sha1_to_hex(p->obj), sha1_to_hex(p->base),
+	       sha1_to_hex(p->local), sha1_to_hex(p->remote));
+
+	OUTPUT(o, 2, "Auto-merging notes for %s", sha1_to_hex(p->obj));
+	check_notes_merge_worktree(o);
+	if (is_null_sha1(p->local)) {
+		/* D/F conflict, checkout p->remote */
+		assert(!is_null_sha1(p->remote));
+		OUTPUT(o, 1, "CONFLICT (delete/modify): Notes for object %s "
+		       "deleted in %s and modified in %s. Version from %s "
+		       "left in tree.", sha1_to_hex(p->obj), lref, rref, rref);
+		write_note_to_worktree(p->obj, p->remote);
+	} else if (is_null_sha1(p->remote)) {
+		/* D/F conflict, checkout p->local */
+		assert(!is_null_sha1(p->local));
+		OUTPUT(o, 1, "CONFLICT (delete/modify): Notes for object %s "
+		       "deleted in %s and modified in %s. Version from %s "
+		       "left in tree.", sha1_to_hex(p->obj), rref, lref, lref);
+		write_note_to_worktree(p->obj, p->local);
+	} else {
+		/* "regular" conflict, checkout result of ll_merge() */
+		const char *reason = "content";
+		if (is_null_sha1(p->base))
+			reason = "add/add";
+		assert(!is_null_sha1(p->local));
+		assert(!is_null_sha1(p->remote));
+		OUTPUT(o, 1, "CONFLICT (%s): Merge conflict in notes for "
+		       "object %s", reason, sha1_to_hex(p->obj));
+		ll_merge_in_worktree(o, p);
+	}
+
+	trace_printf("\t\t\tremoving from partial merge result\n");
+	remove_note(t, p->obj);
+
+	return 1;
+}
+
 static int merge_one_change(struct notes_merge_options *o,
 			    struct notes_merge_pair *p, struct notes_tree *t)
 {
 	/*
-	 * Return 0 if change was resolved (and added to notes_tree),
-	 * 1 if conflict
+	 * Return 0 if change is successfully resolved (stored in notes_tree).
+	 * Return 1 is change results in a conflict (NOT stored in notes_tree,
+	 * but instead written to NOTES_MERGE_WORKTREE with conflict markers).
 	 */
 	switch (o->strategy) {
 	case NOTES_MERGE_RESOLVE_MANUAL:
-		return 1;
+		return merge_one_change_manual(o, p, t);
 	case NOTES_MERGE_RESOLVE_OURS:
 		OUTPUT(o, 2, "Using local notes for %s", sha1_to_hex(p->obj));
 		/* nothing to do */
@@ -479,8 +635,8 @@ int notes_merge(struct notes_merge_options *o,
 	result = merge_from_diffs(o, base_tree_sha1, local->tree->object.sha1,
 				  remote->tree->object.sha1, local_tree);
 
-	if (result > 0) { /* successful non-trivial merge */
-		/* Commit result */
+	if (result != 0) { /* non-trivial merge (with or without conflicts) */
+		/* Commit (partial) result */
 		struct commit_list *parents = NULL;
 		commit_list_insert(remote, &parents); /* LIFO order */
 		commit_list_insert(local, &parents);

notes-merge.h

@@ -1,6 +1,8 @@
 #ifndef NOTES_MERGE_H
 #define NOTES_MERGE_H
 
+#define NOTES_MERGE_WORKTREE "NOTES_MERGE_WORKTREE"
+
 enum notes_merge_verbosity {
 	NOTES_MERGE_VERBOSITY_DEFAULT = 2,
 	NOTES_MERGE_VERBOSITY_MAX = 5
@@ -17,6 +19,7 @@ struct notes_merge_options {
 		NOTES_MERGE_RESOLVE_THEIRS,
 		NOTES_MERGE_RESOLVE_UNION
 	} strategy;
+	unsigned has_worktree:1;
 };
 
 void init_notes_merge_options(struct notes_merge_options *o);
@@ -51,7 +54,13 @@ void create_notes_commit(struct notes_tree *t, struct commit_list *parents,
  * 2. The merge successfully completes, producing a merge commit. local_tree
  *    contains the updated notes tree, the SHA1 of the resulting commit is
  *    written into 'result_sha1', and 1 is returned.
- * 3. The merge fails. result_sha1 is set to null_sha1, and -1 is returned.
+ * 3. The merge results in conflicts. This is similar to #2 in that the
+ *    partial merge result (i.e. merge result minus the unmerged entries)
+ *    are stored in 'local_tree', and the SHA1 or the resulting commit
+ *    (to be amended when the conflicts have been resolved) is written into
+ *    'result_sha1'. The unmerged entries are written into the
+ *    .git/NOTES_MERGE_WORKTREE directory with conflict markers.
+ *    -1 is returned.
  *
  * Both o->local_ref and o->remote_ref must be given (non-NULL), but either ref
  * (although not both) may refer to a non-existing notes ref, in which case