Merge branch 'no-ahead-behind-v5'

Especially in huge code bases with fast-moving `master`, it can be
prohibitively expensive to calculate whether an upstream branch of
a local branch is ahead, behind or diverged.

This topic branch introduces a set of flags to avoid that computation
when we're not even interested in it to begin with.

This merge commit takes the feature early, therefore it is marked
experimental.

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>

Documentation/git-status.txt

@@ -137,6 +137,12 @@ ignored, then the directory is not shown, but all contents are shown.
 	update it afterwards if any changes were detected. Defaults to
 	`--lock-index`.
 
+--ahead-behind::
+--no-ahead-behind::
+	EXPERIMENTAL, Display or do not display detailed ahead/behind
+	counts for the branch relative to its upstream branch.  Defaults
+	to true.
+
 <pathspec>...::
 	See the 'pathspec' entry in linkgit:gitglossary[7].
 

builtin/checkout.c

@@ -607,7 +607,7 @@ static void report_tracking(struct branch_info *new)
 	struct strbuf sb = STRBUF_INIT;
 	struct branch *branch = branch_get(new->name);
 
-	if (!format_tracking_info(branch, &sb))
+	if (!format_tracking_info(branch, &sb, AHEAD_BEHIND_FULL))
 		return;
 	fputs(sb.buf, stdout);
 	strbuf_release(&sb);

builtin/commit.c

@@ -1150,6 +1150,9 @@ static void finalize_deferred_config(struct wt_status *s)
 		s->show_branch = status_deferred_config.show_branch;
 	if (s->show_branch < 0)
 		s->show_branch = 0;
+
+	if (s->ahead_behind_flags == AHEAD_BEHIND_UNSPECIFIED)
+		s->ahead_behind_flags = AHEAD_BEHIND_FULL;
 }
 
 static int parse_and_validate_options(int argc, const char *argv[],
@@ -1366,6 +1369,8 @@ int cmd_status(int argc, const char **argv, const char *prefix)
 			 N_("show branch information")),
 		OPT_BOOL(0, "show-stash", &s.show_stash,
 			 N_("show stash information")),
+		OPT_BOOL(0, "ahead-behind", &s.ahead_behind_flags,
+			 N_("compute full ahead/behind values (EXPERIMENTAL)")),
 		{ OPTION_CALLBACK, 0, "porcelain", &status_format,
 		  N_("version"), N_("machine-readable output"),
 		  PARSE_OPT_OPTARG, opt_parse_porcelain },
@@ -1669,6 +1674,8 @@ int cmd_commit(int argc, const char **argv, const char *prefix)
 		OPT_SET_INT(0, "short", &status_format, N_("show status concisely"),
 			    STATUS_FORMAT_SHORT),
 		OPT_BOOL(0, "branch", &s.show_branch, N_("show branch information")),
+		OPT_BOOL(0, "ahead-behind", &s.ahead_behind_flags,
+			 N_("compute full ahead/behind values (EXPERIMENTAL)")),
 		OPT_SET_INT(0, "porcelain", &status_format,
 			    N_("machine-readable output"), STATUS_FORMAT_PORCELAIN),
 		OPT_SET_INT(0, "long", &status_format,

ref-filter.c

@@ -1249,8 +1249,8 @@ static void fill_remote_ref_details(struct used_atom *atom, const char *refname,
 	if (atom->u.remote_ref.option == RR_REF)
 		*s = show_ref(&atom->u.remote_ref.refname, refname);
 	else if (atom->u.remote_ref.option == RR_TRACK) {
-		if (stat_tracking_info(branch, &num_ours,
-				       &num_theirs, NULL)) {
+		if (stat_tracking_info(branch, &num_ours, &num_theirs,
+				       NULL, AHEAD_BEHIND_FULL) < 0) {
 			*s = xstrdup(msgs.gone);
 		} else if (!num_ours && !num_theirs)
 			*s = "";
@@ -1267,8 +1267,8 @@ static void fill_remote_ref_details(struct used_atom *atom, const char *refname,
 			free((void *)to_free);
 		}
 	} else if (atom->u.remote_ref.option == RR_TRACKSHORT) {
-		if (stat_tracking_info(branch, &num_ours,
-				       &num_theirs, NULL))
+		if (stat_tracking_info(branch, &num_ours, &num_theirs,
+				       NULL, AHEAD_BEHIND_FULL) < 0)
 			return;
 
 		if (!num_ours && !num_theirs)

remote.c

@@ -2007,16 +2007,23 @@ int ref_newer(const struct object_id *new_oid, const struct object_id *old_oid)
 }
 
 /*
- * Compare a branch with its upstream, and save their differences (number
- * of commits) in *num_ours and *num_theirs. The name of the upstream branch
- * (or NULL if no upstream is defined) is returned via *upstream_name, if it
- * is not itself NULL.
+ * Lookup the upstream branch for the given branch and if present, optionally
+ * compute the commit ahead/behind values for the pair.
+ *
+ * If abf is AHEAD_BEHIND_FULL, compute the full ahead/behind and return the
+ * counts in *num_ours and *num_theirs.  If abf is AHEAD_BEHIND_QUICK, skip
+ * the (potentially expensive) a/b computation (*num_ours and *num_theirs are
+ * set to zero).
+ *
+ * The name of the upstream branch (or NULL if no upstream is defined) is
+ * returned via *upstream_name, if it is not itself NULL.
  *
  * Returns -1 if num_ours and num_theirs could not be filled in (e.g., no
- * upstream defined, or ref does not exist), 0 otherwise.
+ * upstream defined, or ref does not exist).  Returns 0 if the commits are
+ * identical.  Returns 1 if commits are different.
  */
 int stat_tracking_info(struct branch *branch, int *num_ours, int *num_theirs,
-		       const char **upstream_name)
+		       const char **upstream_name, enum ahead_behind_flags abf)
 {
 	struct object_id oid;
 	struct commit *ours, *theirs;
@@ -2044,11 +2051,15 @@ int stat_tracking_info(struct branch *branch, int *num_ours, int *num_theirs,
 	if (!ours)
 		return -1;
 
+	*num_theirs = *num_ours = 0;
+
 	/* are we the same? */
-	if (theirs == ours) {
-		*num_theirs = *num_ours = 0;
+	if (theirs == ours)
 		return 0;
-	}
+	if (abf == AHEAD_BEHIND_QUICK)
+		return 1;
+	if (abf != AHEAD_BEHIND_FULL)
+		BUG("stat_tracking_info: invalid abf '%d'", abf);
 
 	/* Run "rev-list --left-right ours...theirs" internally... */
 	argv_array_push(&argv, ""); /* ignored */
@@ -2064,8 +2075,6 @@ int stat_tracking_info(struct branch *branch, int *num_ours, int *num_theirs,
 		die("revision walk setup failed");
 
 	/* ... and count the commits on each side. */
-	*num_ours = 0;
-	*num_theirs = 0;
 	while (1) {
 		struct commit *c = get_revision(&revs);
 		if (!c)
@@ -2081,20 +2090,22 @@ int stat_tracking_info(struct branch *branch, int *num_ours, int *num_theirs,
 	clear_commit_marks(theirs, ALL_REV_FLAGS);
 
 	argv_array_clear(&argv);
-	return 0;
+	return 1;
 }
 
 /*
  * Return true when there is anything to report, otherwise false.
  */
-int format_tracking_info(struct branch *branch, struct strbuf *sb)
+int format_tracking_info(struct branch *branch, struct strbuf *sb,
+			 enum ahead_behind_flags abf)
 {
-	int ours, theirs;
+	int ours, theirs, sti;
 	const char *full_base;
 	char *base;
 	int upstream_is_gone = 0;
 
-	if (stat_tracking_info(branch, &ours, &theirs, &full_base) < 0) {
+	sti = stat_tracking_info(branch, &ours, &theirs, &full_base, abf);
+	if (sti < 0) {
 		if (!full_base)
 			return 0;
 		upstream_is_gone = 1;
@@ -2108,10 +2119,17 @@ int format_tracking_info(struct branch *branch, struct strbuf *sb)
 		if (advice_status_hints)
 			strbuf_addstr(sb,
 				_("  (use \"git branch --unset-upstream\" to fixup)\n"));
-	} else if (!ours && !theirs) {
+	} else if (!sti) {
 		strbuf_addf(sb,
 			_("Your branch is up to date with '%s'.\n"),
 			base);
+	} else if (abf == AHEAD_BEHIND_QUICK) {
+		strbuf_addf(sb,
+			    _("Your branch and '%s' refer to different commits.\n"),
+			    base);
+		if (advice_status_hints)
+			strbuf_addf(sb, _("  (use \"%s\" for details)\n"),
+				    "git status --ahead-behind");
 	} else if (!theirs) {
 		strbuf_addf(sb,
 			Q_("Your branch is ahead of '%s' by %d commit.\n",

remote.h

@@ -257,10 +257,18 @@ enum match_refs_flags {
 	MATCH_REFS_FOLLOW_TAGS	= (1 << 3)
 };
 
+/* Flags for --ahead-behind option. */
+enum ahead_behind_flags {
+	AHEAD_BEHIND_UNSPECIFIED = -1,
+	AHEAD_BEHIND_QUICK       =  0,  /* just eq/neq reporting */
+	AHEAD_BEHIND_FULL        =  1,  /* traditional a/b reporting */
+};
+
 /* Reporting of tracking info */
 int stat_tracking_info(struct branch *branch, int *num_ours, int *num_theirs,
-		       const char **upstream_name);
-int format_tracking_info(struct branch *branch, struct strbuf *sb);
+		       const char **upstream_name, enum ahead_behind_flags abf);
+int format_tracking_info(struct branch *branch, struct strbuf *sb,
+			 enum ahead_behind_flags abf);
 
 struct ref *get_local_heads(void);
 /*

t/t6040-tracking-info.sh

@@ -146,6 +146,48 @@ test_expect_success 'status -s -b (diverged from upstream)' '
 	test_i18ncmp expect actual
 '
 
+cat >expect <<\EOF
+## b1...origin/master [different]
+EOF
+
+test_expect_success 'status -s -b --no-ahead-behind (diverged from upstream)' '
+	(
+		cd test &&
+		git checkout b1 >/dev/null &&
+		git status -s -b --no-ahead-behind | head -1
+	) >actual &&
+	test_i18ncmp expect actual
+'
+
+cat >expect <<\EOF
+On branch b1
+Your branch and 'origin/master' have diverged,
+and have 1 and 1 different commits each, respectively.
+EOF
+
+test_expect_success 'status --long --branch' '
+	(
+		cd test &&
+		git checkout b1 >/dev/null &&
+		git status --long -b | head -3
+	) >actual &&
+	test_i18ncmp expect actual
+'
+
+cat >expect <<\EOF
+On branch b1
+Your branch and 'origin/master' refer to different commits.
+EOF
+
+test_expect_success 'status --long --branch --no-ahead-behind' '
+	(
+		cd test &&
+		git checkout b1 >/dev/null &&
+		git status --long -b --no-ahead-behind | head -2
+	) >actual &&
+	test_i18ncmp expect actual
+'
+
 cat >expect <<\EOF
 ## b5...brokenbase [gone]
 EOF

t/t7064-wtstatus-pv2.sh

@@ -390,6 +390,68 @@ test_expect_success 'verify upstream fields in branch header' '
 	)
 '
 
+test_expect_success 'verify --[no-]ahead-behind with V2 format' '
+	git checkout master &&
+	test_when_finished "rm -rf sub_repo" &&
+	git clone . sub_repo &&
+	(
+		## Confirm local master tracks remote master.
+		cd sub_repo &&
+		HUF=$(git rev-parse HEAD) &&
+
+		# Confirm --no-ahead-behind reports traditional branch.ab with 0/0 for equal branches.
+		cat >expect <<-EOF &&
+		# branch.oid $HUF
+		# branch.head master
+		# branch.upstream origin/master
+		# branch.ab +0 -0
+		EOF
+
+		git status --no-ahead-behind --porcelain=v2 --branch --untracked-files=all >actual &&
+		test_cmp expect actual &&
+
+		# Confirm --ahead-behind reports traditional branch.ab with 0/0.
+		cat >expect <<-EOF &&
+		# branch.oid $HUF
+		# branch.head master
+		# branch.upstream origin/master
+		# branch.ab +0 -0
+		EOF
+
+		git status --ahead-behind --porcelain=v2 --branch --untracked-files=all >actual &&
+		test_cmp expect actual &&
+
+		## Test non-equal ahead/behind.
+		echo xyz >file_xyz &&
+		git add file_xyz &&
+		git commit -m xyz &&
+
+		HUF=$(git rev-parse HEAD) &&
+
+		# Confirm --no-ahead-behind reports branch.ab with ?/? for non-equal branches.
+		cat >expect <<-EOF &&
+		# branch.oid $HUF
+		# branch.head master
+		# branch.upstream origin/master
+		# branch.ab +? -?
+		EOF
+
+		git status --no-ahead-behind --porcelain=v2 --branch --untracked-files=all >actual &&
+		test_cmp expect actual &&
+
+		# Confirm --ahead-behind reports traditional branch.ab with 1/0.
+		cat >expect <<-EOF &&
+		# branch.oid $HUF
+		# branch.head master
+		# branch.upstream origin/master
+		# branch.ab +1 -0
+		EOF
+
+		git status --ahead-behind --porcelain=v2 --branch --untracked-files=all >actual &&
+		test_cmp expect actual
+	)
+'
+
 test_expect_success 'create and add submodule, submodule appears clean (A. S...)' '
 	git checkout master &&
 	git clone . sub_repo &&