Subject: Re: [PATCH v3 07/14] remote.c: introduce branch_get_upstream helper

From: Jeff King <[email-masked]>
Date: Thu, 21 May 2015 14:35:00 -0400

On Thu, May 21, 2015 at 02:14:29PM -0400, Jeff King wrote:

> There is a related cleanup I resisted, which is that several call-sites
> will call stat_tracking_info, then later look directly at
> branch->merge[0]->dst without a check for NULL (fill_tracking_info is
> such a site).
> 
> This works because stat_tracking_info's return value tells us that we
> did indeed find an upstream to compare with. But it feels a little leaky
> to me. One solution is for stat_tracking_info to pass out the name of
> thte upstream, making the caller side something like:

So just for fun, here is what a whole patch, with the refactoring of the
return value, would look like.

diff --git a/builtin/branch.c b/builtin/branch.c
index cc55ff2..8ecabd1 100644
--- a/builtin/branch.c
+++ b/builtin/branch.c
@@ -425,25 +425,19 @@ static void fill_tracking_info(struct strbuf *stat, const char *branch_name,
 	int ours, theirs;
 	char *ref = NULL;
 	struct branch *branch = branch_get(branch_name);
+	const char *upstream;
 	struct strbuf fancy = STRBUF_INIT;
 	int upstream_is_gone = 0;
 	int added_decoration = 1;
 
-	switch (stat_tracking_info(branch, &ours, &theirs)) {
-	case 0:
-		/* no base */
-		return;
-	case -1:
-		/* with "gone" base */
+	if (stat_tracking_info(branch, &ours, &theirs, &upstream) < 0) {
+		if (!upstream)
+			return;
 		upstream_is_gone = 1;
-		break;
-	default:
-		/* with base */
-		break;
 	}
 
 	if (show_upstream_ref) {
-		ref = shorten_unambiguous_ref(branch->merge[0]->dst, 0);
+		ref = shorten_unambiguous_ref(upstream, 0);
 		if (want_color(branch_use_color))
 			strbuf_addf(&fancy, "%s%s%s",
 					branch_get_color(BRANCH_COLOR_UPSTREAM),
diff --git a/builtin/for-each-ref.c b/builtin/for-each-ref.c
index 6847400..05dd23d 100644
--- a/builtin/for-each-ref.c
+++ b/builtin/for-each-ref.c
@@ -730,7 +730,7 @@ static void populate_value(struct refinfo *ref)
 				char buf[40];
 
 				if (stat_tracking_info(branch, &num_ours,
-						       &num_theirs) != 1)
+						       &num_theirs, NULL))
 					continue;
 
 				if (!num_ours && !num_theirs)
@@ -753,7 +753,7 @@ static void populate_value(struct refinfo *ref)
 				assert(branch);
 
 				if (stat_tracking_info(branch, &num_ours,
-							&num_theirs) != 1)
+							&num_theirs, NULL))
 					continue;
 
 				if (!num_ours && !num_theirs)
diff --git a/remote.c b/remote.c
index be45a39..6765051 100644
--- a/remote.c
+++ b/remote.c
@@ -2016,12 +2016,15 @@ int ref_newer(const unsigned char *new_sha1, const unsigned char *old_sha1)
 
 /*
  * Compare a branch with its upstream, and save their differences (number
- * of commits) in *num_ours and *num_theirs.
+ * 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.
  *
- * Return 0 if branch has no upstream (no base), -1 if upstream is missing
- * (with "gone" base), otherwise 1 (with base).
+ * 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.
  */
-int stat_tracking_info(struct branch *branch, int *num_ours, int *num_theirs)
+int stat_tracking_info(struct branch *branch, int *num_ours, int *num_theirs,
+		       const char **upstream_name)
 {
 	unsigned char sha1[20];
 	struct commit *ours, *theirs;
@@ -2032,8 +2035,10 @@ int stat_tracking_info(struct branch *branch, int *num_ours, int *num_theirs)
 
 	/* Cannot stat unless we are marked to build on top of somebody else. */
 	base = branch_get_upstream(branch, NULL);
+	if (upstream_name)
+		*upstream_name = base;
 	if (!base)
-		return 0;
+		return -1;
 
 	/* Cannot stat if what we used to build on no longer exists */
 	if (read_ref(base, sha1))
@@ -2051,7 +2056,7 @@ int stat_tracking_info(struct branch *branch, int *num_ours, int *num_theirs)
 	/* are we the same? */
 	if (theirs == ours) {
 		*num_theirs = *num_ours = 0;
-		return 1;
+		return 0;
 	}
 
 	/* Run "rev-list --left-right ours...theirs" internally... */
@@ -2087,7 +2092,7 @@ int stat_tracking_info(struct branch *branch, int *num_ours, int *num_theirs)
 	/* clear object flags smudged by the above traversal */
 	clear_commit_marks(ours, ALL_REV_FLAGS);
 	clear_commit_marks(theirs, ALL_REV_FLAGS);
-	return 1;
+	return 0;
 }
 
 /*
@@ -2096,23 +2101,17 @@ int stat_tracking_info(struct branch *branch, int *num_ours, int *num_theirs)
 int format_tracking_info(struct branch *branch, struct strbuf *sb)
 {
 	int ours, theirs;
+	const char *full_base;
 	char *base;
 	int upstream_is_gone = 0;
 
-	switch (stat_tracking_info(branch, &ours, &theirs)) {
-	case 0:
-		/* no base */
-		return 0;
-	case -1:
-		/* with "gone" base */
+	if (stat_tracking_info(branch, &ours, &theirs, &full_base) < 0) {
+		if (!full_base)
+			return 0;
 		upstream_is_gone = 1;
-		break;
-	default:
-		/* with base */
-		break;
 	}
 
-	base = shorten_unambiguous_ref(branch->merge[0]->dst, 0);
+	base = shorten_unambiguous_ref(full_base, 0);
 	if (upstream_is_gone) {
 		strbuf_addf(sb,
 			_("Your branch is based on '%s', but the upstream is gone.\n"),
diff --git a/remote.h b/remote.h
index 3326f2b..312b7ca 100644
--- a/remote.h
+++ b/remote.h
@@ -249,7 +249,8 @@ enum match_refs_flags {
 };
 
 /* Reporting of tracking info */
-int stat_tracking_info(struct branch *branch, int *num_ours, int *num_theirs);
+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);
 
 struct ref *get_local_heads(void);
diff --git a/wt-status.c b/wt-status.c
index 38cb165..7c8ae57 100644
--- a/wt-status.c
+++ b/wt-status.c
@@ -1532,21 +1532,15 @@ static void wt_shortstatus_print_tracking(struct wt_status *s)
 
 	color_fprintf(s->fp, branch_color_local, "%s", branch_name);
 
-	switch (stat_tracking_info(branch, &num_ours, &num_theirs)) {
-	case 0:
-		/* no base */
-		fputc(s->null_termination ? '\0' : '\n', s->fp);
-		return;
-	case -1:
-		/* with "gone" base */
+	if (stat_tracking_info(branch, &num_ours, &num_theirs, &base) < 0) {
+		if (!base) {
+			fputc(s->null_termination ? '\0' : '\n', s->fp);
+			return;
+		}
+
 		upstream_is_gone = 1;
-		break;
-	default:
-		/* with base */
-		break;
 	}
 
-	base = branch->merge[0]->dst;
 	base = shorten_unambiguous_ref(base, 0);
 	color_fprintf(s->fp, header_color, "...");
 	color_fprintf(s->fp, branch_color_remote, "%s", base);