git notes merge: Initial implementation handling trivial merges only

This initial implementation of 'git notes merge' only handles the trivial
merge cases (i.e. where the merge is either a no-op, or a fast-forward).

The patch includes testcases for these trivial merge cases.

Future patches will extend the functionality of 'git notes merge'.

This patch has been improved by the following contributions:
- Stephen Boyd: Simplify argc logic
- Stephen Boyd: Use test_commit
- Ævar Arnfjörð Bjarmason: Don't use C99 comments.
- Jonathan Nieder: Add constants for common verbosity values
- Jonathan Nieder: Use trace_printf(...) instead of OUTPUT(o, 5, ...)
- Jonathan Nieder: Remove extraneous show() function
- Jonathan Nieder: Clarify handling of empty/missing notes ref in notes_merge()
- Junio C Hamano: fixup minor style issues

Thanks-to: Stephen Boyd <[email protected]>
Thanks-to: Ævar Arnfjörð Bjarmason <[email protected]>
Thanks-to: Jonathan Nieder <[email protected]>
Thanks-to: Junio C Hamano <[email protected]>
Signed-off-by: Johan Herland <[email protected]>
Signed-off-by: Junio C Hamano <[email protected]>

Makefile

@@ -503,6 +503,7 @@ LIB_H += mailmap.h
 LIB_H += merge-recursive.h
 LIB_H += notes.h
 LIB_H += notes-cache.h
+LIB_H += notes-merge.h
 LIB_H += object.h
 LIB_H += pack.h
 LIB_H += pack-refs.h
@@ -593,6 +594,7 @@ LIB_OBJS += merge-recursive.o
 LIB_OBJS += name-hash.o
 LIB_OBJS += notes.o
 LIB_OBJS += notes-cache.o
+LIB_OBJS += notes-merge.o
 LIB_OBJS += object.o
 LIB_OBJS += pack-check.o
 LIB_OBJS += pack-refs.o

builtin/notes.c

@@ -17,6 +17,7 @@
 #include "run-command.h"
 #include "parse-options.h"
 #include "string-list.h"
+#include "notes-merge.h"
 
 static const char * const git_notes_usage[] = {
 	"git notes [--ref <notes_ref>] [list [<object>]]",
@@ -25,6 +26,7 @@ static const char * const git_notes_usage[] = {
 	"git notes [--ref <notes_ref>] append [-m <msg> | -F <file> | (-c | -C) <object>] [<object>]",
 	"git notes [--ref <notes_ref>] edit [<object>]",
 	"git notes [--ref <notes_ref>] show [<object>]",
+	"git notes [--ref <notes_ref>] merge [-v | -q] <notes_ref>",
 	"git notes [--ref <notes_ref>] remove [<object>]",
 	"git notes [--ref <notes_ref>] prune [-n | -v]",
 	NULL
@@ -61,6 +63,11 @@ static const char * const git_notes_show_usage[] = {
 	NULL
 };
 
+static const char * const git_notes_merge_usage[] = {
+	"git notes merge [<options>] <notes_ref>",
+	NULL
+};
+
 static const char * const git_notes_remove_usage[] = {
 	"git notes remove [<object>]",
 	NULL
@@ -772,6 +779,51 @@ static int show(int argc, const char **argv, const char *prefix)
 	return retval;
 }
 
+static int merge(int argc, const char **argv, const char *prefix)
+{
+	struct strbuf remote_ref = STRBUF_INIT, msg = STRBUF_INIT;
+	unsigned char result_sha1[20];
+	struct notes_merge_options o;
+	int verbosity = 0, result;
+	struct option options[] = {
+		OPT__VERBOSITY(&verbosity),
+		OPT_END()
+	};
+
+	argc = parse_options(argc, argv, prefix, options,
+			     git_notes_merge_usage, 0);
+
+	if (argc != 1) {
+		error("Must specify a notes ref to merge");
+		usage_with_options(git_notes_merge_usage, options);
+	}
+
+	init_notes_merge_options(&o);
+	o.verbosity = verbosity + NOTES_MERGE_VERBOSITY_DEFAULT;
+
+	o.local_ref = default_notes_ref();
+	strbuf_addstr(&remote_ref, argv[0]);
+	expand_notes_ref(&remote_ref);
+	o.remote_ref = remote_ref.buf;
+
+	result = notes_merge(&o, result_sha1);
+
+	strbuf_addf(&msg, "notes: Merged notes from %s into %s",
+		    remote_ref.buf, default_notes_ref());
+	if (result == 0) { /* Merge resulted (trivially) in result_sha1 */
+		/* 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 non-trivial merges!");
+	}
+
+	strbuf_release(&remote_ref);
+	strbuf_release(&msg);
+	return 0;
+}
+
 static int remove_cmd(int argc, const char **argv, const char *prefix)
 {
 	struct option options[] = {
@@ -865,6 +917,8 @@ int cmd_notes(int argc, const char **argv, const char *prefix)
 		result = append_edit(argc, argv, prefix);
 	else if (!strcmp(argv[0], "show"))
 		result = show(argc, argv, prefix);
+	else if (!strcmp(argv[0], "merge"))
+		result = merge(argc, argv, prefix);
 	else if (!strcmp(argv[0], "remove"))
 		result = remove_cmd(argc, argv, prefix);
 	else if (!strcmp(argv[0], "prune"))

notes-merge.c

@@ -0,0 +1,120 @@
+#include "cache.h"
+#include "commit.h"
+#include "refs.h"
+#include "notes-merge.h"
+
+void init_notes_merge_options(struct notes_merge_options *o)
+{
+	memset(o, 0, sizeof(struct notes_merge_options));
+	o->verbosity = NOTES_MERGE_VERBOSITY_DEFAULT;
+}
+
+#define OUTPUT(o, v, ...) \
+	do { \
+		if ((o)->verbosity >= (v)) { \
+			printf(__VA_ARGS__); \
+			puts(""); \
+		} \
+	} while (0)
+
+int notes_merge(struct notes_merge_options *o,
+		unsigned char *result_sha1)
+{
+	unsigned char local_sha1[20], remote_sha1[20];
+	struct commit *local, *remote;
+	struct commit_list *bases = NULL;
+	const unsigned char *base_sha1;
+	int result = 0;
+
+	assert(o->local_ref && o->remote_ref);
+	hashclr(result_sha1);
+
+	trace_printf("notes_merge(o->local_ref = %s, o->remote_ref = %s)\n",
+	       o->local_ref, o->remote_ref);
+
+	/* Dereference o->local_ref into local_sha1 */
+	if (!resolve_ref(o->local_ref, local_sha1, 0, NULL))
+		die("Failed to resolve local notes ref '%s'", o->local_ref);
+	else if (!check_ref_format(o->local_ref) && is_null_sha1(local_sha1))
+		local = NULL; /* local_sha1 == null_sha1 indicates unborn ref */
+	else if (!(local = lookup_commit_reference(local_sha1)))
+		die("Could not parse local commit %s (%s)",
+		    sha1_to_hex(local_sha1), o->local_ref);
+	trace_printf("\tlocal commit: %.7s\n", sha1_to_hex(local_sha1));
+
+	/* Dereference o->remote_ref into remote_sha1 */
+	if (get_sha1(o->remote_ref, remote_sha1)) {
+		/*
+		 * Failed to get remote_sha1. If o->remote_ref looks like an
+		 * unborn ref, perform the merge using an empty notes tree.
+		 */
+		if (!check_ref_format(o->remote_ref)) {
+			hashclr(remote_sha1);
+			remote = NULL;
+		} else {
+			die("Failed to resolve remote notes ref '%s'",
+			    o->remote_ref);
+		}
+	} else if (!(remote = lookup_commit_reference(remote_sha1))) {
+		die("Could not parse remote commit %s (%s)",
+		    sha1_to_hex(remote_sha1), o->remote_ref);
+	}
+	trace_printf("\tremote commit: %.7s\n", sha1_to_hex(remote_sha1));
+
+	if (!local && !remote)
+		die("Cannot merge empty notes ref (%s) into empty notes ref "
+		    "(%s)", o->remote_ref, o->local_ref);
+	if (!local) {
+		/* result == remote commit */
+		hashcpy(result_sha1, remote_sha1);
+		goto found_result;
+	}
+	if (!remote) {
+		/* result == local commit */
+		hashcpy(result_sha1, local_sha1);
+		goto found_result;
+	}
+	assert(local && remote);
+
+	/* Find merge bases */
+	bases = get_merge_bases(local, remote, 1);
+	if (!bases) {
+		base_sha1 = null_sha1;
+		OUTPUT(o, 4, "No merge base found; doing history-less merge");
+	} else if (!bases->next) {
+		base_sha1 = bases->item->object.sha1;
+		OUTPUT(o, 4, "One merge base found (%.7s)",
+		       sha1_to_hex(base_sha1));
+	} else {
+		/* TODO: How to handle multiple merge-bases? */
+		base_sha1 = bases->item->object.sha1;
+		OUTPUT(o, 3, "Multiple merge bases found. Using the first "
+		       "(%.7s)", sha1_to_hex(base_sha1));
+	}
+
+	OUTPUT(o, 4, "Merging remote commit %.7s into local commit %.7s with "
+	       "merge-base %.7s", sha1_to_hex(remote->object.sha1),
+	       sha1_to_hex(local->object.sha1), sha1_to_hex(base_sha1));
+
+	if (!hashcmp(remote->object.sha1, base_sha1)) {
+		/* Already merged; result == local commit */
+		OUTPUT(o, 2, "Already up-to-date!");
+		hashcpy(result_sha1, local->object.sha1);
+		goto found_result;
+	}
+	if (!hashcmp(local->object.sha1, base_sha1)) {
+		/* Fast-forward; result == remote commit */
+		OUTPUT(o, 2, "Fast-forward");
+		hashcpy(result_sha1, remote->object.sha1);
+		goto found_result;
+	}
+
+	/* TODO: */
+	result = error("notes_merge() cannot yet handle real merges.");
+
+found_result:
+	free_commit_list(bases);
+	trace_printf("notes_merge(): result = %i, result_sha1 = %.7s\n",
+	       result, sha1_to_hex(result_sha1));
+	return result;
+}

notes-merge.h

@@ -0,0 +1,36 @@
+#ifndef NOTES_MERGE_H
+#define NOTES_MERGE_H
+
+enum notes_merge_verbosity {
+	NOTES_MERGE_VERBOSITY_DEFAULT = 2,
+	NOTES_MERGE_VERBOSITY_MAX = 5
+};
+
+struct notes_merge_options {
+	const char *local_ref;
+	const char *remote_ref;
+	int verbosity;
+};
+
+void init_notes_merge_options(struct notes_merge_options *o);
+
+/*
+ * Merge notes from o->remote_ref into o->local_ref
+ *
+ * The commits given by the two refs are merged, producing one of the following
+ * outcomes:
+ *
+ * 1. The merge trivially results in an existing commit (e.g. fast-forward or
+ *    already-up-to-date). The SHA1 of the result is written into 'result_sha1'
+ *    and 0 is returned.
+ * 2. The merge fails. result_sha1 is set to null_sha1, and non-zero 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
+ * that notes ref is interpreted as an empty notes tree, and the merge
+ * trivially results in what the other ref points to.
+ */
+int notes_merge(struct notes_merge_options *o,
+		unsigned char *result_sha1);
+
+#endif