Merge branch 'jc/post-simplify' into tr/filter-branch

* jc/post-simplify:
  Topo-sort before --simplify-merges
  revision traversal: show full history with merge simplification
  revision.c: whitespace fix

4 files changed, 253 insertions, 23 deletions

diff --git a/Documentation/rev-list-options.txt b/Documentation/rev-list-options.txt
index 1d857559ef..67ff0eab9f 100644
--- a/Documentation/rev-list-options.txt
+++ b/Documentation/rev-list-options.txt
@@ -193,12 +193,18 @@ endif::git-rev-list[]
 
 --full-history::
 
-	Show also parts of history irrelevant to current state of a given
-	path. This turns off history simplification, which removed merges
+	Show also parts of history irrelevant to current state of given
+	paths. This turns off history simplification, which removed merges
 	which didn't change anything at all at some child. It will still actually
 	simplify away merges that didn't change anything at all into either
 	child.
 
+--simplify-merges::
+
+	Simplify away commits that did not change the given paths, similar
+	to `--full-history`, and further remove merges none of whose
+	parent history changes the given paths.
+
 --no-merges::
 
 	Do not print commits with more than one parent.
diff --git a/revision.c b/revision.c
index e75079a6e1..0aaa4c10b9 100644
--- a/revision.c
+++ b/revision.c
@@ -489,7 +489,7 @@ static int add_parents_to_list(struct rev_info *revs, struct commit *commit,
 			p->object.flags |= SEEN;
 			insert_by_date_cached(p, list, cached_base, cache_ptr);
 		}
-		if(revs->first_parent_only)
+		if (revs->first_parent_only)
 			break;
 	}
 	return 0;
@@ -1045,6 +1045,11 @@ static int handle_revision_opt(struct rev_info *revs, int argc, const char **arg
 	} else if (!strcmp(arg, "--topo-order")) {
 		revs->lifo = 1;
 		revs->topo_order = 1;
+	} else if (!strcmp(arg, "--simplify-merges")) {
+		revs->simplify_merges = 1;
+		revs->rewrite_parents = 1;
+		revs->simplify_history = 0;
+		revs->limited = 1;
 	} else if (!strcmp(arg, "--date-order")) {
 		revs->lifo = 0;
 		revs->topo_order = 1;
@@ -1378,6 +1383,149 @@ static void add_child(struct rev_info *revs, struct commit *parent, struct commi
 	l->next = add_decoration(&revs->children, &parent->object, l);
 }
 
+static int remove_duplicate_parents(struct commit *commit)
+{
+	struct commit_list **pp, *p;
+	int surviving_parents;
+
+	/* Examine existing parents while marking ones we have seen... */
+	pp = &commit->parents;
+	while ((p = *pp) != NULL) {
+		struct commit *parent = p->item;
+		if (parent->object.flags & TMP_MARK) {
+			*pp = p->next;
+			continue;
+		}
+		parent->object.flags |= TMP_MARK;
+		pp = &p->next;
+	}
+	/* count them while clearing the temporary mark */
+	surviving_parents = 0;
+	for (p = commit->parents; p; p = p->next) {
+		p->item->object.flags &= ~TMP_MARK;
+		surviving_parents++;
+	}
+	return surviving_parents;
+}
+
+static struct commit_list **simplify_one(struct commit *commit, struct commit_list **tail)
+{
+	struct commit_list *p;
+	int cnt;
+
+	/*
+	 * We store which commit each one simplifies to in its util field.
+	 * Have we handled this one?
+	 */
+	if (commit->util)
+		return tail;
+
+	/*
+	 * An UNINTERESTING commit simplifies to itself, so does a
+	 * root commit.  We do not rewrite parents of such commit
+	 * anyway.
+	 */
+	if ((commit->object.flags & UNINTERESTING) || !commit->parents) {
+		commit->util = commit;
+		return tail;
+	}
+
+	/*
+	 * Do we know what commit all of our parents should be rewritten to?
+	 * Otherwise we are not ready to rewrite this one yet.
+	 */
+	for (cnt = 0, p = commit->parents; p; p = p->next) {
+		if (!p->item->util) {
+			tail = &commit_list_insert(p->item, tail)->next;
+			cnt++;
+		}
+	}
+	if (cnt)
+		return tail;
+
+	/*
+	 * Rewrite our list of parents.
+	 */
+	for (p = commit->parents; p; p = p->next)
+		p->item = p->item->util;
+	cnt = remove_duplicate_parents(commit);
+
+	/*
+	 * It is possible that we are a merge and one side branch
+	 * does not have any commit that touches the given paths;
+	 * in such a case, the immediate parents will be rewritten
+	 * to different commits.
+	 *
+	 *      o----X		X: the commit we are looking at;
+	 *     /    /		o: a commit that touches the paths;
+	 * ---o----'
+	 *
+	 * Further reduce the parents by removing redundant parents.
+	 */
+	if (1 < cnt) {
+		struct commit_list *h = reduce_heads(commit->parents);
+		cnt = commit_list_count(h);
+		free_commit_list(commit->parents);
+		commit->parents = h;
+	}
+
+	/*
+	 * A commit simplifies to itself if it is a root, if it is
+	 * UNINTERESTING, if it touches the given paths, or if it is a
+	 * merge and its parents simplifies to more than one commits
+	 * (the first two cases are already handled at the beginning of
+	 * this function).
+	 *
+	 * Otherwise, it simplifies to what its sole parent simplifies to.
+	 */
+	if (!cnt ||
+	    (commit->object.flags & UNINTERESTING) ||
+	    !(commit->object.flags & TREESAME) ||
+	    (1 < cnt))
+		commit->util = commit;
+	else
+		commit->util = commit->parents->item->util;
+	return tail;
+}
+
+static void simplify_merges(struct rev_info *revs)
+{
+	struct commit_list *list;
+	struct commit_list *yet_to_do, **tail;
+
+	sort_in_topological_order(&revs->commits, revs->lifo);
+
+	/* feed the list reversed */
+	yet_to_do = NULL;
+	for (list = revs->commits; list; list = list->next)
+		commit_list_insert(list->item, &yet_to_do);
+	while (yet_to_do) {
+		list = yet_to_do;
+		yet_to_do = NULL;
+		tail = &yet_to_do;
+		while (list) {
+			struct commit *commit = list->item;
+			struct commit_list *next = list->next;
+			free(list);
+			list = next;
+			tail = simplify_one(commit, tail);
+		}
+	}
+
+	/* clean up the result, removing the simplified ones */
+	list = revs->commits;
+	revs->commits = NULL;
+	tail = &revs->commits;
+	while (list) {
+		struct commit *commit = list->item;
+		struct commit_list *next = list->next;
+		free(list);
+		list = next;
+		if (commit->util == commit)
+			tail = &commit_list_insert(commit, tail)->next;
+	}
+}
+
 static void set_children(struct rev_info *revs)
 {
 	struct commit_list *l;
@@ -1418,6 +1566,8 @@ int prepare_revision_walk(struct rev_info *revs)
 			return -1;
 	if (revs->topo_order)
 		sort_in_topological_order(&revs->commits, revs->lifo);
+	if (revs->simplify_merges)
+		simplify_merges(revs);
 	if (revs->children.name)
 		set_children(revs);
 	return 0;
@@ -1450,26 +1600,6 @@ static enum rewrite_result rewrite_one(struct rev_info *revs, struct commit **pp
 	}
 }
 
-static void remove_duplicate_parents(struct commit *commit)
-{
-	struct commit_list **pp, *p;
-
-	/* Examine existing parents while marking ones we have seen... */
-	pp = &commit->parents;
-	while ((p = *pp) != NULL) {
-		struct commit *parent = p->item;
-		if (parent->object.flags & TMP_MARK) {
-			*pp = p->next;
-			continue;
-		}
-		parent->object.flags |= TMP_MARK;
-		pp = &p->next;
-	}
-	/* ... and clear the temporary mark */
-	for (p = commit->parents; p; p = p->next)
-		p->item->object.flags &= ~TMP_MARK;
-}
-
 static int rewrite_parents(struct rev_info *revs, struct commit *commit)
 {
 	struct commit_list **pp = &commit->parents;
diff --git a/revision.h b/revision.h
index f64e8ce7ff..dfa06b5210 100644
--- a/revision.h
+++ b/revision.h
@@ -41,6 +41,7 @@ struct rev_info {
 			simplify_history:1,
 			lifo:1,
 			topo_order:1,
+			simplify_merges:1,
 			tag_objects:1,
 			tree_objects:1,
 			blob_objects:1,
diff --git a/t/t6012-rev-list-simplify.sh b/t/t6012-rev-list-simplify.sh
new file mode 100755
index 0000000000..510bb9679f
--- /dev/null
+++ b/t/t6012-rev-list-simplify.sh
@@ -0,0 +1,93 @@
+#!/bin/sh
+
+test_description='merge simplification'
+
+. ./test-lib.sh
+
+note () {
+	git tag "$1"
+}
+
+_x40='[0-9a-f][0-9a-f][0-9a-f][0-9a-f][0-9a-f]'
+_x40="$_x40$_x40$_x40$_x40$_x40$_x40$_x40$_x40"
+
+unnote () {
+	git name-rev --tags --stdin | sed -e "s|$_x40 (tags/\([^)]*\)) |\1 |g"
+}
+
+test_expect_success setup '
+	echo "Hi there" >file &&
+	git add file &&
+	test_tick && git commit -m "Initial file" &&
+	note A &&
+
+	git branch other-branch &&
+
+	echo "Hello" >file &&
+	git add file &&
+	test_tick && git commit -m "Modified file" &&
+	note B &&
+
+	git checkout other-branch &&
+
+	echo "Hello" >file &&
+	git add file &&
+	test_tick && git commit -m "Modified the file identically" &&
+	note C &&
+
+	echo "This is a stupid example" >another-file &&
+	git add another-file &&
+	test_tick && git commit -m "Add another file" &&
+	note D &&
+
+	test_tick && git merge -m "merge" master &&
+	note E &&
+
+	echo "Yet another" >elif &&
+	git add elif &&
+	test_tick && git commit -m "Irrelevant change" &&
+	note F &&
+
+	git checkout master &&
+	echo "Yet another" >elif &&
+	git add elif &&
+	test_tick && git commit -m "Another irrelevant change" &&
+	note G &&
+
+	test_tick && git merge -m "merge" other-branch &&
+	note H &&
+
+	echo "Final change" >file &&
+	test_tick && git commit -a -m "Final change" &&
+	note I
+'
+
+FMT='tformat:%P 	%H | %s'
+
+check_result () {
+	for c in $1
+	do
+		echo "$c"
+	done >expect &&
+	shift &&
+	param="$*" &&
+	test_expect_success "log $param" '
+		git log --pretty="$FMT" --parents $param |
+		unnote >actual &&
+		sed -e "s/^.*	\([^ ]*\) .*/\1/" >check <actual &&
+		test_cmp expect check || {
+			cat actual
+			false
+		}
+	'
+}
+
+check_result 'I H G F E D C B A' --full-history
+check_result 'I H E C B A' --full-history -- file
+check_result 'I H E C B A' --full-history --topo-order -- file
+check_result 'I H E C B A' --full-history --date-order -- file
+check_result 'I E C B A' --simplify-merges -- file
+check_result 'I B A' -- file
+check_result 'I B A' --topo-order -- file
+
+test_done