[RFC PATCH v3 1/2] Implement --first-parent for git rev-list --bisect

[RFC PATCH v3 1/2] Implement --first-parent for git rev-list --bisect

[Tiago Botelho]

This will enable users to implement bisecting on first parents
which can be useful for when the commits from a feature branch
that we want to merge are not always tested.

Signed-off-by: Tiago Botelho <tiagonbotelho@hotmail.com>
---
 bisect.c           | 53 +++++++++++++++++++++++++++++++----------------------
 bisect.h           |  3 ++-
 builtin/rev-list.c |  3 +++
 revision.c         |  3 ---
 4 files changed, 36 insertions(+), 26 deletions(-)

diff --git a/bisect.c b/bisect.c
index 4eafc8262..f43713574 100644
--- a/bisect.c
+++ b/bisect.c
@@ -34,7 +34,7 @@ static const char *term_good;
  * We care just barely enough to avoid recursing for
  * non-merge entries.
  */
-static int count_distance(struct commit_list *entry)
+static int count_distance(struct commit_list *entry, unsigned bisect_flags)
 {
 	int nr = 0;
 
@@ -49,10 +49,10 @@ static int count_distance(struct commit_list *entry)
 		commit->object.flags |= COUNTED;
 		p = commit->parents;
 		entry = p;
-		if (p) {
+		if (p && !(bisect_flags & BISECT_FIRST_PARENT)) {
 			p = p->next;
 			while (p) {
-				nr += count_distance(p);
+				nr += count_distance(p, bisect_flags);
 				p = p->next;
 			}
 		}
@@ -82,15 +82,16 @@ static inline void weight_set(struct commit_list *elem, int weight)
 	*((int*)(elem->item->util)) = weight;
 }
 
-static int count_interesting_parents(struct commit *commit)
+static int count_interesting_parents(struct commit *commit, unsigned bisect_flags)
 {
 	struct commit_list *p;
 	int count;
 
 	for (count = 0, p = commit->parents; p; p = p->next) {
-		if (p->item->object.flags & UNINTERESTING)
-			continue;
-		count++;
+		if (!(p->item->object.flags & UNINTERESTING))
+		    count++;
+		if (bisect_flags & BISECT_FIRST_PARENT)
+			break;
 	}
 	return count;
 }
@@ -117,10 +118,10 @@ static inline int halfway(struct commit_list *p, int nr)
 }
 
 #if !DEBUG_BISECT
-#define show_list(a,b,c,d) do { ; } while (0)
+#define show_list(a,b,c,d,e) do { ; } while (0)
 #else
 static void show_list(const char *debug, int counted, int nr,
-		      struct commit_list *list)
+		      struct commit_list *list, unsigned bisect_flags)
 {
 	struct commit_list *p;
 
@@ -146,10 +147,14 @@ static void show_list(const char *debug, int counted, int nr,
 		else
 			fprintf(stderr, "---");
 		fprintf(stderr, " %.*s", 8, oid_to_hex(&commit->object.oid));
-		for (pp = commit->parents; pp; pp = pp->next)
+		for (pp = commit->parents; pp; pp = pp->next) {
 			fprintf(stderr, " %.*s", 8,
 				oid_to_hex(&pp->item->object.oid));
 
+			if (bisect_flags & BISECT_FIRST_PARENT)
+				break;
+		}
+
 		subject_len = find_commit_subject(buf, &subject_start);
 		if (subject_len)
 			fprintf(stderr, " %.*s", subject_len, subject_start);
@@ -267,13 +272,13 @@ static struct commit_list *do_find_bisection(struct commit_list *list,
 		unsigned flags = commit->object.flags;
 
 		p->item->util = &weights[n++];
-		switch (count_interesting_parents(commit)) {
+		switch (count_interesting_parents(commit, bisect_flags)) {
 		case 0:
 			if (!(flags & TREESAME)) {
 				weight_set(p, 1);
 				counted++;
 				show_list("bisection 2 count one",
-					  counted, nr, list);
+					  counted, nr, list, bisect_flags);
 			}
 			/*
 			 * otherwise, it is known not to reach any
@@ -289,7 +294,7 @@ static struct commit_list *do_find_bisection(struct commit_list *list,
 		}
 	}
 
-	show_list("bisection 2 initialize", counted, nr, list);
+	show_list("bisection 2 initialize", counted, nr, list, bisect_flags);
 
 	/*
 	 * If you have only one parent in the resulting set
@@ -310,7 +315,7 @@ static struct commit_list *do_find_bisection(struct commit_list *list,
 			continue;
 		if (weight(p) != -2)
 			continue;
-		weight_set(p, count_distance(p));
+		weight_set(p, count_distance(p, bisect_flags));
 		clear_distance(list);
 
 		/* Does it happen to be at exactly half-way? */
@@ -319,7 +324,7 @@ static struct commit_list *do_find_bisection(struct commit_list *list,
 		counted++;
 	}
 
-	show_list("bisection 2 count_distance", counted, nr, list);
+	show_list("bisection 2 count_distance", counted, nr, list, bisect_flags);
 
 	while (counted < nr) {
 		for (p = list; p; p = p->next) {
@@ -329,9 +334,10 @@ static struct commit_list *do_find_bisection(struct commit_list *list,
 			if (0 <= weight(p))
 				continue;
 			for (q = p->item->parents; q; q = q->next) {
-				if (q->item->object.flags & UNINTERESTING)
-					continue;
-				if (0 <= weight(q))
+				if (!(q->item->object.flags & UNINTERESTING))
+					if (0 <= weight(q))
+						break;
+				if (bisect_flags & BISECT_FIRST_PARENT)
 					break;
 			}
 			if (!q)
@@ -346,7 +352,7 @@ static struct commit_list *do_find_bisection(struct commit_list *list,
 				weight_set(p, weight(q)+1);
 				counted++;
 				show_list("bisection 2 count one",
-					  counted, nr, list);
+					  counted, nr, list, bisect_flags);
 			}
 			else
 				weight_set(p, weight(q));
@@ -357,7 +363,7 @@ static struct commit_list *do_find_bisection(struct commit_list *list,
 		}
 	}
 
-	show_list("bisection 2 counted all", counted, nr, list);
+	show_list("bisection 2 counted all", counted, nr, list, bisect_flags);
 
 	if (!find_all)
 		return best_bisection(list, nr);
@@ -372,7 +378,7 @@ void find_bisection(struct commit_list **commit_list, int *reaches,
 	struct commit_list *list, *p, *best, *next, *last;
 	int *weights;
 
-	show_list("bisection 2 entry", 0, 0, *commit_list);
+	show_list("bisection 2 entry", 0, 0, *commit_list, bisect_flags);
 
 	/*
 	 * Count the number of total and tree-changing items on the
@@ -395,7 +401,7 @@ void find_bisection(struct commit_list **commit_list, int *reaches,
 		on_list++;
 	}
 	list = last;
-	show_list("bisection 2 sorted", 0, nr, list);
+	show_list("bisection 2 sorted", 0, nr, list, bisect_flags);
 
 	*all = nr;
 	weights = xcalloc(on_list, sizeof(*weights));
@@ -962,6 +968,9 @@ int bisect_next_all(const char *prefix, int no_checkout)
 	if (skipped_revs.nr)
 		bisect_flags |= BISECT_FIND_ALL;
 
+	if (revs.first_parent_only)
+		bisect_flags |= BISECT_FIRST_PARENT;
+
 	find_bisection(&revs.commits, &reaches, &all, bisect_flags);
 	revs.commits = managed_skipped(revs.commits, &tried);
 
diff --git a/bisect.h b/bisect.h
index 1d40a33ad..5b7358fc9 100644
--- a/bisect.h
+++ b/bisect.h
@@ -1,7 +1,8 @@
 #ifndef BISECT_H
 #define BISECT_H
 
-#define BISECT_FIND_ALL		(1u<<0)
+#define BISECT_FIND_ALL		  (1u<<0)
+#define BISECT_FIRST_PARENT (1u<<1)
 
 /*
  * Find bisection. If something is found, `reaches` will be the number of
diff --git a/builtin/rev-list.c b/builtin/rev-list.c
index 8752f5bbe..66439e1b3 100644
--- a/builtin/rev-list.c
+++ b/builtin/rev-list.c
@@ -538,6 +538,9 @@ int cmd_rev_list(int argc, const char **argv, const char *prefix)
 	if (bisect_list) {
 		int reaches, all;
 
+		if (revs.first_parent_only)
+			bisect_flags |= BISECT_FIRST_PARENT;
+
 		find_bisection(&revs.commits, &reaches, &all, bisect_flags);
 
 		if (bisect_show_vars)
diff --git a/revision.c b/revision.c
index 4e0e193e5..b9d063805 100644
--- a/revision.c
+++ b/revision.c
@@ -2474,9 +2474,6 @@ int setup_revisions(int argc, const char **argv, struct rev_info *revs, struct s
 	if (!revs->reflog_info && revs->grep_filter.use_reflog_filter)
 		die("cannot use --grep-reflog without --walk-reflogs");
 
-	if (revs->first_parent_only && revs->bisect)
-		die(_("--first-parent is incompatible with --bisect"));
-
 	if (revs->expand_tabs_in_log < 0)
 		revs->expand_tabs_in_log = revs->expand_tabs_in_log_default;
 
-- 
2.16.3

Re: [RFC PATCH v3 1/2] Implement --first-parent for git rev-list --bisect

[Junio C Hamano]

Tiago Botelho <tiagonbotelho@gmail.com> writes:

> -static int count_interesting_parents(struct commit *commit)
> +static int count_interesting_parents(struct commit *commit, unsigned bisect_flags)
>  {
>  	struct commit_list *p;
>  	int count;
>  
>  	for (count = 0, p = commit->parents; p; p = p->next) {
> -		if (p->item->object.flags & UNINTERESTING)
> -			continue;
> -		count++;
> +		if (!(p->item->object.flags & UNINTERESTING))
> +		    count++;
> +		if (bisect_flags & BISECT_FIRST_PARENT)
> +			break;
>  	}
>  	return count;
>  }

Since this change makes the function never return anything more than 1,...

> @@ -310,7 +315,7 @@ static struct commit_list *do_find_bisection(struct commit_list *list,
>  			continue;
>  		if (weight(p) != -2)
>  			continue;
> -		weight_set(p, count_distance(p));
> +		weight_set(p, count_distance(p, bisect_flags));
>  		clear_distance(list);

... this code will not be reached when in the first-parent mode,
where we count the weight for merge commits the hard way.

Am I reading the code correctly?  Not pointing out a problem; just
double checking how the code works.

> @@ -329,9 +334,10 @@ static struct commit_list *do_find_bisection(struct commit_list *list,
>  			if (0 <= weight(p))
>  				continue;
>  			for (q = p->item->parents; q; q = q->next) {
> -				if (q->item->object.flags & UNINTERESTING)
> -					continue;
> -				if (0 <= weight(q))
> +				if (!(q->item->object.flags & UNINTERESTING))
> +					if (0 <= weight(q))
> +						break;
> +				if (bisect_flags & BISECT_FIRST_PARENT)
>  					break;
>  			}
>  			if (!q)
>  				continue;

This loop propagates the known weight of an ancestor through a
single strand of pearls.

When this loop is entered, any commit that has non-negative weight
has only one parent of interest, as we counted weight for all merges
the hard way and also weight for root and boundary commits, in the
previous loop.  The original goes through p's parents and see if an
interesting parent has non-negative weight (i.e. weight is known for
that parent), at which point break out of the loop, with q that is
non-NULL.  Immediately after the loop, q != NULL means we can now
compute weight for p based on q's weight.

I think this patch breaks the logic.  When we are looking at a
commit 'p' whose weight is not known yet, we grab its first parent
in 'q'.  Imagine that it is not an UNINTERESTING commit (i.e. a
commit whose weight matters when deciding the bisection) whose
weight is not yet known.  With the updated code under the
first-parent mode, we break out of the loop, 'q' pointing at the
commit whose weight is not yet known.  The computation done by the
code that immediately follows the above part is now broken, as it
will call weight(q) to get -1 and propagate it to p (or add 1 and
set 0 to p), no?

Perhaps something along this line may be closer to what we want:

	if (0 <= weight(p))
		continue; /* already known */
	for (q = p->item->parents; q; q = q->next) {
        	if ((bisect_flags & BISECT_FIRST_PARENT)) {
			if (weight(q) < 0)
				q = NULL;
			break;
		}
		if (q->item->object.flags & UNINTERESTING)
			continue;
		if (0 <= weight(q))
			break;
	}
	if (!q)
		continue; /* parent's weight not yet usable */

That is, under the first-parent mode, we would pay attention only to
the first parent of 'p' and break out of this loop without even
looking at q->next.  If the weight of that parent is not known yet,
we mark that fact by clearing q to NULL and break out of the loop.
If the weight is known, we do not clear q, so we compute weight of p
based on weight(q).

I am not offhand certain what should happen when p's first parent is
uninteresting.  The updated count_interesting_parents() would have
returned 0 for p in such a case, so at this point of the code where
p's weight is unknown, its first parent can never be UNINTERESTING,
I would think.