[PATCH 0/4] Blame in reverse

[PATCH 0/4] Blame in reverse

[Junio C Hamano]

This is still rough, but I think it would be a good foundation to build
interesting archaeology tools on.

Usual "git blame" starts from the latest revision and finds where each
line came from (i.e. who came up with that brilliant idea, or more often
who introduced that bug).  This new mode starts from an old revision, and
annotates in reverse --- up to which point each line survived, before it
got replaced with something else.  A line that began its life in one file
can be removed from the original file but migrate to another, and we will
find its final resting place when you use the usual -C -C option.

 [1/4] "log" and friends: --children option
 [2/4] builtin-blame.c: move prepare_final() into a separate function.
 [3/4]  builtin-blame.c: allow more than 16 parents
 [4/4] git-blame --reverse

 builtin-blame.c |  206 +++++++++++++++++++++++++++++++++++++++----------------
 log-tree.c      |   20 ++++++
 revision.c      |   28 ++++++++
 revision.h      |    1 +
 4 files changed, 196 insertions(+), 59 deletions(-)

[PATCH 1/4] "log" and friends: --children option

[Junio C Hamano]

This adds a new --children option to the revision machinery.  In addition
to the list of parents, child commits of each commit are computed and
shown in the output from "git log" and friends.

Note that this does _not_ show all children of a commit.  It only shows
children on the commit ancestry you made the revision machinery traverse.
For example, "git log --children master..next" will not show side branches
forked from any commits shown in the range that have not been merged to
"next" (i.e. what are queued in 'pu' but not yet merged to 'next').

This patch was primarily done for adding the infrastructure to allow users
of revision machinery to find out children of commits; please consider the
current output not much more than debugging aid.  If you want to use it
from "git log" and friends, the output format needs a bit more serious
thought.

Signed-off-by: Junio C Hamano <gitster@pobox.com>
---
 log-tree.c |   20 ++++++++++++++++++++
 revision.c |   28 ++++++++++++++++++++++++++++
 revision.h |    1 +
 3 files changed, 49 insertions(+), 0 deletions(-)

diff --git a/log-tree.c b/log-tree.c
index 5b29639..75851d1 100644
--- a/log-tree.c
+++ b/log-tree.c
@@ -32,6 +32,24 @@ void show_decorations(struct commit *commit)
 	putchar(')');
 }
 
+static void show_children(struct rev_info *revs, struct commit *commit, int abbrev)
+{
+	struct commit_list *p;
+
+	if (!revs->children.name)
+		return;
+	p = lookup_decoration(&revs->children, &commit->object);
+	if (!p)
+		return;
+	printf("child");
+	while (p) {
+		struct commit *child = p->item;
+		printf(" %s", diff_unique_abbrev(child->object.sha1, abbrev));
+		p = p->next;
+	}
+	putchar(revs->diffopt.line_termination);
+}
+
 /*
  * Search for "^[-A-Za-z]+: [^@]+@" pattern. It usually matches
  * Signed-off-by: and Acked-by: lines.
@@ -236,6 +254,7 @@ void show_log(struct rev_info *opt, const char *sep)
 			show_parents(commit, abbrev_commit);
 		show_decorations(commit);
 		putchar(opt->diffopt.line_termination);
+		show_children(opt, commit, abbrev_commit);
 		return;
 	}
 
@@ -297,6 +316,7 @@ void show_log(struct rev_info *opt, const char *sep)
 				return;
 			}
 		}
+		show_children(opt, commit, abbrev_commit);
 	}
 
 	if (!commit->buffer)
diff --git a/revision.c b/revision.c
index 196fedc..e5138b7 100644
--- a/revision.c
+++ b/revision.c
@@ -9,6 +9,7 @@
 #include "grep.h"
 #include "reflog-walk.h"
 #include "patch-ids.h"
+#include "decorate.h"
 
 volatile show_early_output_fn_t show_early_output;
 
@@ -1309,6 +1310,11 @@ int setup_revisions(int argc, const char **argv, struct rev_info *revs, const ch
 				revs->no_walk = 0;
 				continue;
 			}
+			if (!strcmp(arg, "--children")) {
+				revs->children.name = "children";
+				revs->limited = 1;
+				continue;
+			}
 
 			opts = diff_opt_parse(&revs->diffopt, argv+i, argc-i);
 			if (opts > 0) {
@@ -1398,6 +1404,26 @@ int setup_revisions(int argc, const char **argv, struct rev_info *revs, const ch
 	return left;
 }
 
+static void add_child(struct rev_info *revs, struct commit *parent, struct commit *child)
+{
+	struct commit_list *l = xcalloc(1, sizeof(*l));
+
+	l->item = child;
+	l->next = add_decoration(&revs->children, &parent->object, l);
+}
+
+static void set_children(struct rev_info *revs)
+{
+	struct commit_list *l;
+	for (l = revs->commits; l; l = l->next) {
+		struct commit *commit = l->item;
+		struct commit_list *p;
+
+		for (p = commit->parents; p; p = p->next)
+			add_child(revs, p->item, commit);
+	}
+}
+
 int prepare_revision_walk(struct rev_info *revs)
 {
 	int nr = revs->pending.nr;
@@ -1426,6 +1452,8 @@ int prepare_revision_walk(struct rev_info *revs)
 			return -1;
 	if (revs->topo_order)
 		sort_in_topological_order(&revs->commits, revs->lifo);
+	if (revs->children.name)
+		set_children(revs);
 	return 0;
 }
 
diff --git a/revision.h b/revision.h
index c8b3b94..966116c 100644
--- a/revision.h
+++ b/revision.h
@@ -98,6 +98,7 @@ struct rev_info {
 	struct diff_options pruning;
 
 	struct reflog_walk_info *reflog_info;
+	struct decoration children;
 };
 
 #define REV_TREE_SAME		0
-- 
1.5.5.rc3.139.g8b2cf

Re: [PATCH 1/4] "log" and friends: --children option

[Johannes Schindelin]

Hi,

On Thu, 3 Apr 2008, Junio C Hamano wrote:

> @@ -1398,6 +1404,26 @@ int setup_revisions(int argc, const char **argv, struct rev_info *revs, const ch
>  	return left;
>  }
>  
> +static void add_child(struct rev_info *revs, struct commit *parent, struct commit *child)
> +{
> +	struct commit_list *l = xcalloc(1, sizeof(*l));
> +
> +	l->item = child;
> +	l->next = add_decoration(&revs->children, &parent->object, l);
> +}
> +
> +static void set_children(struct rev_info *revs)

I'd call this add_children().

Other than that, nicely done!  I did not think it was possible with as few 
changes.

Ciao,
Dscho

[PATCH 2/4] builtin-blame.c: move prepare_final() into a separate function.

[Junio C Hamano]

After parsing the command line, we had a rather long loop to compute the
commit object to start annotating from.  Move the logic to a separate
function, so that later patches become easier to read.

It also makes fill_origin_blob() function to return void; the check on its
return value by its callers is always done on !file->ptr, and nobody looks
at the return value from the function (which is the same as file->ptr).

Signed-off-by: Junio C Hamano <gitster@pobox.com>
---
 builtin-blame.c |   56 ++++++++++++++++++++++++++++++++----------------------
 1 files changed, 33 insertions(+), 23 deletions(-)

diff --git a/builtin-blame.c b/builtin-blame.c
index bfd562d..996f535 100644
--- a/builtin-blame.c
+++ b/builtin-blame.c
@@ -91,7 +91,7 @@ struct origin {
  * Given an origin, prepare mmfile_t structure to be used by the
  * diff machinery
  */
-static char *fill_origin_blob(struct origin *o, mmfile_t *file)
+static void fill_origin_blob(struct origin *o, mmfile_t *file)
 {
 	if (!o->file.ptr) {
 		enum object_type type;
@@ -106,7 +106,6 @@ static char *fill_origin_blob(struct origin *o, mmfile_t *file)
 	}
 	else
 		*file = o->file;
-	return file->ptr;
 }
 
 /*
@@ -2006,6 +2005,10 @@ static int git_blame_config(const char *var, const char *value)
 	return git_default_config(var, value);
 }
 
+/*
+ * Prepare a dummy commit that represents the work tree (or staged) item.
+ * Note that annotating work tree item never works in the reverse.
+ */
 static struct commit *fake_working_tree_commit(const char *path, const char *contents_from)
 {
 	struct commit *commit;
@@ -2122,6 +2125,33 @@ static struct commit *fake_working_tree_commit(const char *path, const char *con
 	return commit;
 }
 
+static const char *prepare_final(struct scoreboard *sb, struct rev_info *revs)
+{
+	int i;
+	const char *final_commit_name = NULL;
+
+	/*
+	 * There must be one and only one positive commit in the
+	 * revs->pending array.
+	 */
+	for (i = 0; i < revs->pending.nr; i++) {
+		struct object *obj = revs->pending.objects[i].item;
+		if (obj->flags & UNINTERESTING)
+			continue;
+		while (obj->type == OBJ_TAG)
+			obj = deref_tag(obj, NULL, 0);
+		if (obj->type != OBJ_COMMIT)
+			die("Non commit %s?", revs->pending.objects[i].name);
+		if (sb->final)
+			die("More than one commit to dig from %s and %s?",
+			    revs->pending.objects[i].name,
+			    final_commit_name);
+		sb->final = (struct commit *) obj;
+		final_commit_name = revs->pending.objects[i].name;
+	}
+	return final_commit_name;
+}
+
 int cmd_blame(int argc, const char **argv, const char *prefix)
 {
 	struct rev_info revs;
@@ -2327,27 +2357,7 @@ int cmd_blame(int argc, const char **argv, const char *prefix)
 	setup_revisions(unk, argv, &revs, NULL);
 	memset(&sb, 0, sizeof(sb));
 
-	/*
-	 * There must be one and only one positive commit in the
-	 * revs->pending array.
-	 */
-	for (i = 0; i < revs.pending.nr; i++) {
-		struct object *obj = revs.pending.objects[i].item;
-		if (obj->flags & UNINTERESTING)
-			continue;
-		while (obj->type == OBJ_TAG)
-			obj = deref_tag(obj, NULL, 0);
-		if (obj->type != OBJ_COMMIT)
-			die("Non commit %s?",
-			    revs.pending.objects[i].name);
-		if (sb.final)
-			die("More than one commit to dig from %s and %s?",
-			    revs.pending.objects[i].name,
-			    final_commit_name);
-		sb.final = (struct commit *) obj;
-		final_commit_name = revs.pending.objects[i].name;
-	}
-
+	final_commit_name = prepare_final(&sb, &revs);
 	if (!sb.final) {
 		/*
 		 * "--not A B -- path" without anything positive;
-- 
1.5.5.rc3.139.g8b2cf

[PATCH 3/4] builtin-blame.c: allow more than 16 parents

[Junio C Hamano]

This removes the hardcoded 16 parents limit from git-blame by allowing the
parent array to be allocated dynamically.

As the ultimate objective is not about computing blame across dodecapus,
but about annotating the history upside down, it also renames "parent" in
the code to "scapegoat".  The name of the game used to be "pass blame to
your parents", but now it is "find a scapegoat to pass blame on".

Signed-off-by: Junio C Hamano <gitster@pobox.com>
---
 builtin-blame.c |   93 ++++++++++++++++++++++++++++++++++++-------------------
 1 files changed, 61 insertions(+), 32 deletions(-)

diff --git a/builtin-blame.c b/builtin-blame.c
index 996f535..fbc441f 100644
--- a/builtin-blame.c
+++ b/builtin-blame.c
@@ -1191,18 +1191,45 @@ static void pass_whole_blame(struct scoreboard *sb,
 	}
 }
 
-#define MAXPARENT 16
+/*
+ * We pass blame from the current commit to its parents.  We keep saying
+ * "parent" (and "porigin"), but what we mean is to find scapegoat to
+ * exonerate ourselves.
+ */
+static struct commit_list *first_scapegoat(struct commit *commit)
+{
+	return commit->parents;
+}
+
+static int num_scapegoats(struct commit *commit)
+{
+	int cnt;
+	struct commit_list *l = first_scapegoat(commit);
+	for (cnt = 0; l; l = l->next)
+		cnt++;
+	return cnt;
+}
+
+#define MAXSG 16
 
 static void pass_blame(struct scoreboard *sb, struct origin *origin, int opt)
 {
-	int i, pass;
+	int i, pass, num_sg;
 	struct commit *commit = origin->commit;
-	struct commit_list *parent;
-	struct origin *parent_origin[MAXPARENT], *porigin;
-
-	memset(parent_origin, 0, sizeof(parent_origin));
+	struct commit_list *sg;
+	struct origin *sg_buf[MAXSG];
+	struct origin *porigin, **sg_origin = sg_buf;
+
+	num_sg = num_scapegoats(commit);
+	if (!num_sg)
+		goto finish;
+	else if (num_sg < ARRAY_SIZE(sg_buf))
+		memset(sg_buf, 0, sizeof(sg_buf));
+	else
+		sg_origin = xcalloc(num_sg, sizeof(*sg_origin));
 
-	/* The first pass looks for unrenamed path to optimize for
+	/*
+	 * The first pass looks for unrenamed path to optimize for
 	 * common cases, then we look for renames in the second pass.
 	 */
 	for (pass = 0; pass < 2; pass++) {
@@ -1210,13 +1237,13 @@ static void pass_blame(struct scoreboard *sb, struct origin *origin, int opt)
 				       struct commit *, struct origin *);
 		find = pass ? find_rename : find_origin;
 
-		for (i = 0, parent = commit->parents;
-		     i < MAXPARENT && parent;
-		     parent = parent->next, i++) {
-			struct commit *p = parent->item;
+		for (i = 0, sg = first_scapegoat(commit);
+		     i < num_sg && sg;
+		     sg = sg->next, i++) {
+			struct commit *p = sg->item;
 			int j, same;
 
-			if (parent_origin[i])
+			if (sg_origin[i])
 				continue;
 			if (parse_commit(p))
 				continue;
@@ -1229,24 +1256,24 @@ static void pass_blame(struct scoreboard *sb, struct origin *origin, int opt)
 				goto finish;
 			}
 			for (j = same = 0; j < i; j++)
-				if (parent_origin[j] &&
-				    !hashcmp(parent_origin[j]->blob_sha1,
+				if (sg_origin[j] &&
+				    !hashcmp(sg_origin[j]->blob_sha1,
 					     porigin->blob_sha1)) {
 					same = 1;
 					break;
 				}
 			if (!same)
-				parent_origin[i] = porigin;
+				sg_origin[i] = porigin;
 			else
 				origin_decref(porigin);
 		}
 	}
 
 	num_commits++;
-	for (i = 0, parent = commit->parents;
-	     i < MAXPARENT && parent;
-	     parent = parent->next, i++) {
-		struct origin *porigin = parent_origin[i];
+	for (i = 0, sg = first_scapegoat(commit);
+	     i < num_sg && sg;
+	     sg = sg->next, i++) {
+		struct origin *porigin = sg_origin[i];
 		if (!porigin)
 			continue;
 		if (pass_blame_to_parent(sb, origin, porigin))
@@ -1257,10 +1284,10 @@ static void pass_blame(struct scoreboard *sb, struct origin *origin, int opt)
 	 * Optionally find moves in parents' files.
 	 */
 	if (opt & PICKAXE_BLAME_MOVE)
-		for (i = 0, parent = commit->parents;
-		     i < MAXPARENT && parent;
-		     parent = parent->next, i++) {
-			struct origin *porigin = parent_origin[i];
+		for (i = 0, sg = first_scapegoat(commit);
+		     i < num_sg && sg;
+		     sg = sg->next, i++) {
+			struct origin *porigin = sg_origin[i];
 			if (!porigin)
 				continue;
 			if (find_move_in_parent(sb, origin, porigin))
@@ -1271,23 +1298,25 @@ static void pass_blame(struct scoreboard *sb, struct origin *origin, int opt)
 	 * Optionally find copies from parents' files.
 	 */
 	if (opt & PICKAXE_BLAME_COPY)
-		for (i = 0, parent = commit->parents;
-		     i < MAXPARENT && parent;
-		     parent = parent->next, i++) {
-			struct origin *porigin = parent_origin[i];
-			if (find_copy_in_parent(sb, origin, parent->item,
+		for (i = 0, sg = first_scapegoat(commit);
+		     i < num_sg && sg;
+		     sg = sg->next, i++) {
+			struct origin *porigin = sg_origin[i];
+			if (find_copy_in_parent(sb, origin, sg->item,
 						porigin, opt))
 				goto finish;
 		}
 
  finish:
-	for (i = 0; i < MAXPARENT; i++) {
-		if (parent_origin[i]) {
-			drop_origin_blob(parent_origin[i]);
-			origin_decref(parent_origin[i]);
+	for (i = 0; i < num_sg; i++) {
+		if (sg_origin[i]) {
+			drop_origin_blob(sg_origin[i]);
+			origin_decref(sg_origin[i]);
 		}
 	}
 	drop_origin_blob(origin);
+	if (sg_buf != sg_origin)
+		free(sg_origin);
 }
 
 /*
-- 
1.5.5.rc3.139.g8b2cf

[PATCH 4/4] git-blame --reverse

[Junio C Hamano]

This new option allows "git blame" to read an old version of the file, and
find up to which commit each line survived (i.e. their children rewrote
the line and removed the original from the contents).

The previous revision machinery update to decorate each commit with its
children was leading to this change.  When the --reverse option is given,
we read the old version and pass blame to the children of the current
suspect, instead of the usual order of starting from the latest and
passing blame to parents (hence, the earlier "scapegoat" rename).

The standard yardstick of "blame" in git.git history is still the file
"rev-list.c", which was refactored heavily during its existence.  For
example, output from:

  $ git blame -C -C -w --reverse 9de48752..master -- rev-list.c

begins like this:

6c41b801 builtin-rev-list.c (JC Hamano   2008-04-02  1) #include "cache...
6c41b801 builtin-rev-list.c (JC Hamano   2008-04-02  2) #include "commi...
6c41b801 builtin-rev-list.c (JC Hamano   2008-04-02  3) #include "tree....
6c41b801 builtin-rev-list.c (JC Hamano   2008-04-02  4) #include "blob....
213523f4 rev-list.c         (JC Hamano   2006-03-01  5) #include "epoch...
6c41b801 builtin-rev-list.c (JC Hamano   2008-04-02  6)
ab57c8dd rev-list.c         (JC Hamano   2006-02-24  7) #define SEEN
ab57c8dd rev-list.c         (JC Hamano   2006-02-24  8) #define INTERES...
213523f4 rev-list.c         (JC Hamano   2006-03-01  9) #define COUNTED...
7e21c29b rev-list.c         (LTorvalds   2005-07-06 10) #define SHOWN  ...
6c41b801 builtin-rev-list.c (JC Hamano   2008-04-02 11)
6c41b801 builtin-rev-list.c (JC Hamano   2008-04-02 12) static const ch...
b1349229 rev-list.c         (LTorvalds   2005-07-26 13)    "usage: git-...

This sample output reveals that the original first four lines survived up
to now but were moved to builtin-rev-list.c and inclusion of "epoch.h" was
removed after 213523f4, and the line was last seen in rev-list.c.

To be useful, this mode probably needs some more tweaking so that the
commit that removed the line (i.e. the children of the commits listed in
the above sample output) is shown instead, but then there is a little
matter of which child of a fork point to show.

For now, you can find the diff that rewrote the fifth line above by doing:

    $ git log --children 213523f4^..

to find its child, which is 1025fe5 (Merge branch 'lt/rev-list' into next,
2006-03-01), and then look at that child with:

    $ git show 1025fe5

Yes, it is a bit awkward, but it is a good start.

Signed-off-by: Junio C Hamano <gitster@pobox.com>
---
 builtin-blame.c |   81 ++++++++++++++++++++++++++++++++++++++++++++-----------
 1 files changed, 65 insertions(+), 16 deletions(-)

diff --git a/builtin-blame.c b/builtin-blame.c
index fbc441f..5c7546d 100644
--- a/builtin-blame.c
+++ b/builtin-blame.c
@@ -43,6 +43,7 @@ static int max_orig_digits;
 static int max_digits;
 static int max_score_digits;
 static int show_root;
+static int reverse;
 static int blank_boundary;
 static int incremental;
 static int cmd_is_annotate;
@@ -177,7 +178,7 @@ struct blame_entry {
 struct scoreboard {
 	/* the final commit (i.e. where we started digging from) */
 	struct commit *final;
-
+	struct rev_info *revs;
 	const char *path;
 
 	/*
@@ -1196,15 +1197,17 @@ static void pass_whole_blame(struct scoreboard *sb,
  * "parent" (and "porigin"), but what we mean is to find scapegoat to
  * exonerate ourselves.
  */
-static struct commit_list *first_scapegoat(struct commit *commit)
+static struct commit_list *first_scapegoat(struct rev_info *revs, struct commit *commit)
 {
-	return commit->parents;
+	if (!reverse)
+		return commit->parents;
+	return lookup_decoration(&revs->children, &commit->object);
 }
 
-static int num_scapegoats(struct commit *commit)
+static int num_scapegoats(struct rev_info *revs, struct commit *commit)
 {
 	int cnt;
-	struct commit_list *l = first_scapegoat(commit);
+	struct commit_list *l = first_scapegoat(revs, commit);
 	for (cnt = 0; l; l = l->next)
 		cnt++;
 	return cnt;
@@ -1214,13 +1217,14 @@ static int num_scapegoats(struct commit *commit)
 
 static void pass_blame(struct scoreboard *sb, struct origin *origin, int opt)
 {
+	struct rev_info *revs = sb->revs;
 	int i, pass, num_sg;
 	struct commit *commit = origin->commit;
 	struct commit_list *sg;
 	struct origin *sg_buf[MAXSG];
 	struct origin *porigin, **sg_origin = sg_buf;
 
-	num_sg = num_scapegoats(commit);
+	num_sg = num_scapegoats(revs, commit);
 	if (!num_sg)
 		goto finish;
 	else if (num_sg < ARRAY_SIZE(sg_buf))
@@ -1237,7 +1241,7 @@ static void pass_blame(struct scoreboard *sb, struct origin *origin, int opt)
 				       struct commit *, struct origin *);
 		find = pass ? find_rename : find_origin;
 
-		for (i = 0, sg = first_scapegoat(commit);
+		for (i = 0, sg = first_scapegoat(revs, commit);
 		     i < num_sg && sg;
 		     sg = sg->next, i++) {
 			struct commit *p = sg->item;
@@ -1270,7 +1274,7 @@ static void pass_blame(struct scoreboard *sb, struct origin *origin, int opt)
 	}
 
 	num_commits++;
-	for (i = 0, sg = first_scapegoat(commit);
+	for (i = 0, sg = first_scapegoat(revs, commit);
 	     i < num_sg && sg;
 	     sg = sg->next, i++) {
 		struct origin *porigin = sg_origin[i];
@@ -1284,7 +1288,7 @@ static void pass_blame(struct scoreboard *sb, struct origin *origin, int opt)
 	 * Optionally find moves in parents' files.
 	 */
 	if (opt & PICKAXE_BLAME_MOVE)
-		for (i = 0, sg = first_scapegoat(commit);
+		for (i = 0, sg = first_scapegoat(revs, commit);
 		     i < num_sg && sg;
 		     sg = sg->next, i++) {
 			struct origin *porigin = sg_origin[i];
@@ -1298,7 +1302,7 @@ static void pass_blame(struct scoreboard *sb, struct origin *origin, int opt)
 	 * Optionally find copies from parents' files.
 	 */
 	if (opt & PICKAXE_BLAME_COPY)
-		for (i = 0, sg = first_scapegoat(commit);
+		for (i = 0, sg = first_scapegoat(revs, commit);
 		     i < num_sg && sg;
 		     sg = sg->next, i++) {
 			struct origin *porigin = sg_origin[i];
@@ -1515,8 +1519,10 @@ static void found_guilty_entry(struct blame_entry *ent)
  * is still unknown, pick one blame_entry, and allow its current
  * suspect to pass blames to its parents.
  */
-static void assign_blame(struct scoreboard *sb, struct rev_info *revs, int opt)
+static void assign_blame(struct scoreboard *sb, int opt)
 {
+	struct rev_info *revs = sb->revs;
+
 	while (1) {
 		struct blame_entry *ent;
 		struct commit *commit;
@@ -1537,8 +1543,9 @@ static void assign_blame(struct scoreboard *sb, struct rev_info *revs, int opt)
 		commit = suspect->commit;
 		if (!commit->object.parsed)
 			parse_commit(commit);
-		if (!(commit->object.flags & UNINTERESTING) &&
-		    !(revs->max_age != -1 && commit->date < revs->max_age))
+		if (reverse ||
+		    (!(commit->object.flags & UNINTERESTING) &&
+		     !(revs->max_age != -1 && commit->date < revs->max_age)))
 			pass_blame(sb, suspect, opt);
 		else {
 			commit->object.flags |= UNINTERESTING;
@@ -2154,10 +2161,11 @@ static struct commit *fake_working_tree_commit(const char *path, const char *con
 	return commit;
 }
 
-static const char *prepare_final(struct scoreboard *sb, struct rev_info *revs)
+static const char *prepare_final(struct scoreboard *sb)
 {
 	int i;
 	const char *final_commit_name = NULL;
+	struct rev_info *revs = sb->revs;
 
 	/*
 	 * There must be one and only one positive commit in the
@@ -2181,6 +2189,36 @@ static const char *prepare_final(struct scoreboard *sb, struct rev_info *revs)
 	return final_commit_name;
 }
 
+static const char *prepare_initial(struct scoreboard *sb)
+{
+	int i;
+	const char *final_commit_name = NULL;
+	struct rev_info *revs = sb->revs;
+
+	/*
+	 * There must be one and only one negative commit, and it must be
+	 * the boundary.
+	 */
+	for (i = 0; i < revs->pending.nr; i++) {
+		struct object *obj = revs->pending.objects[i].item;
+		if (!(obj->flags & UNINTERESTING))
+			continue;
+		while (obj->type == OBJ_TAG)
+			obj = deref_tag(obj, NULL, 0);
+		if (obj->type != OBJ_COMMIT)
+			die("Non commit %s?", revs->pending.objects[i].name);
+		if (sb->final)
+			die("More than one commit to dig down to %s and %s?",
+			    revs->pending.objects[i].name,
+			    final_commit_name);
+		sb->final = (struct commit *) obj;
+		final_commit_name = revs->pending.objects[i].name;
+	}
+	if (!final_commit_name)
+		die("No commit to dig down to?");
+	return final_commit_name;
+}
+
 int cmd_blame(int argc, const char **argv, const char *prefix)
 {
 	struct rev_info revs;
@@ -2213,6 +2251,10 @@ int cmd_blame(int argc, const char **argv, const char *prefix)
 			blank_boundary = 1;
 		else if (!strcmp("--root", arg))
 			show_root = 1;
+		else if (!strcmp("--reverse", arg)) {
+			argv[unk++] = "--children";
+			reverse = 1;
+		}
 		else if (!strcmp(arg, "--show-stats"))
 			show_stats = 1;
 		else if (!strcmp("-c", arg))
@@ -2386,7 +2428,14 @@ int cmd_blame(int argc, const char **argv, const char *prefix)
 	setup_revisions(unk, argv, &revs, NULL);
 	memset(&sb, 0, sizeof(sb));
 
-	final_commit_name = prepare_final(&sb, &revs);
+	sb.revs = &revs;
+	if (!reverse)
+		final_commit_name = prepare_final(&sb);
+	else if (contents_from)
+		die("--contents and --children do not blend well.");
+	else
+		final_commit_name = prepare_initial(&sb);
+
 	if (!sb.final) {
 		/*
 		 * "--not A B -- path" without anything positive;
@@ -2464,7 +2513,7 @@ int cmd_blame(int argc, const char **argv, const char *prefix)
 	if (!incremental)
 		setup_pager();
 
-	assign_blame(&sb, &revs, opt);
+	assign_blame(&sb, opt);
 
 	if (incremental)
 		return 0;
-- 
1.5.5.rc3.139.g8b2cf

Re: [PATCH 0/4] Blame in reverse

[Johannes Sixt]

Junio C Hamano schrieb:
> Usual "git blame" starts from the latest revision and finds where each
> line came from (i.e. who came up with that brilliant idea, or more often
> who introduced that bug).  This new mode starts from an old revision, and
> annotates in reverse --- up to which point each line survived, before it
> got replaced with something else. 

Nice!! Is the result somehow different from

	$ git rev-list --reverse HEAD > /tmp/blame.revs
	$ git blame -S /tmp/blame.revs foo.c

?

-- Hannes

Re: [PATCH 0/4] Blame in reverse

[Junio C Hamano]

Johannes Sixt <j.sixt@viscovery.net> writes:

> Junio C Hamano schrieb:
>> Usual "git blame" starts from the latest revision and finds where each
>> line came from (i.e. who came up with that brilliant idea, or more often
>> who introduced that bug).  This new mode starts from an old revision, and
>> annotates in reverse --- up to which point each line survived, before it
>> got replaced with something else. 
>
> Nice!! Is the result somehow different from
>
> 	$ git rev-list --reverse HEAD > /tmp/blame.revs
> 	$ git blame -S /tmp/blame.revs foo.c

Doesn't -S read from a graft-like file, where each line shows a commit and
then its parents?

Come to think of it, I probably should have done:

	git rev-list --children

which is a mirror image of "git rev-list --parents".  Unlike the
additional "child" header in the output of the log-tree family, that would
not have any controversial format or UI design issues.  Also the resulting
output from such command can then be fed via -S to blame.

However, as I mentioned in the message of [4/4], I think showing the
commit that "introduced" the line is not useful when blame runs in
reverse; blame needs to have a switch to tell it which commit to show
(either "the guilty party" or "the ones the guilty party tried to pass
blame on") anyway, so even though feeding an upside-down topology to the
command via its "-S" can try to mimic what it does, it does not
reallysolve what I wanted to do.