Make spoolandsort a pushable iterator behavior

An earlier change to `git_diff_from_iterators` introduced a
memory leak where the allocated spoolandsort iterator was not
returned to the caller and thus not freed.

One proposal changes all iterator APIs to use git_iterator** so
we can reallocate the iterator at will, but that seems unexpected.
This commit makes it so that an iterator can be changed in place.
The callbacks are isolated in a separate structure and a pointer
to that structure can be reassigned by the spoolandsort extension.

This means that spoolandsort doesn't create a new iterator; it
just allocates a new block of callbacks (along with space for its
own extra data) and swaps that into the iterator.

Additionally, since spoolandsort is only needed to switch the
case sensitivity of an iterator, this simplifies the API to only
take the ignore_case boolean and to be a no-op if the iterator
already matches the requested case sensitivity.

4 files changed, 148 insertions, 127 deletions

diff --git a/src/checkout.c b/src/checkout.c
index 972366fbb..66eb698ab 100644
--- a/src/checkout.c
+++ b/src/checkout.c
@@ -452,9 +452,7 @@ static int checkout_get_actions(
 		goto fail;
 
 	if ((diff->opts.flags & GIT_DIFF_DELTAS_ARE_ICASE) != 0 &&
-		!hiter->ignore_case &&
-		(error = git_iterator_spoolandsort(
-			&hiter, hiter, diff->entrycomp, true)) < 0)
+		(error = git_iterator_spoolandsort_push(hiter, true)) < 0)
 		goto fail;
 
 	if ((error = git_iterator_current(hiter, &he)) < 0)
diff --git a/src/diff.c b/src/diff.c
index 9c0b45f8e..83e73cd03 100644
--- a/src/diff.c
+++ b/src/diff.c
@@ -589,18 +589,13 @@ int git_diff__from_iterators(
 		goto fail;
 
 	if (diff->opts.flags & GIT_DIFF_DELTAS_ARE_ICASE) {
-		/* If one of the iterators doesn't have ignore_case set,
-		 * then that's unfortunate because we'll have to spool
-		 * its data, sort it icase, and then use that for our
-		 * merge join to the other iterator that is icase sorted */
-		if (!old_iter->ignore_case &&
-			git_iterator_spoolandsort(
-				&old_iter, old_iter, diff->entrycomp, true) < 0)
-			goto fail;
-
-		if (!new_iter->ignore_case &&
-			git_iterator_spoolandsort(
-				&new_iter, new_iter, diff->entrycomp, true) < 0)
+		/* If either iterator does not have ignore_case set, then we will
+		 * spool its data, sort it icase, and use that for the merge join
+		 * with the other iterator which was icase sorted.  This call is
+		 * a no-op on an iterator that already matches "ignore_case".
+		 */
+		if (git_iterator_spoolandsort_push(old_iter, true) < 0 ||
+			git_iterator_spoolandsort_push(new_iter, true) < 0)
 			goto fail;
 	}
 
diff --git a/src/iterator.c b/src/iterator.c
index 706106703..28fccce0e 100644
--- a/src/iterator.c
+++ b/src/iterator.c
@@ -12,19 +12,24 @@
 #include "git2/submodule.h"
 #include <ctype.h>
 
+#define ITERATOR_SET_CB(P,NAME_LC) do { \
+	(P)->cb.current = NAME_LC ## _iterator__current; \
+	(P)->cb.at_end  = NAME_LC ## _iterator__at_end; \
+	(P)->cb.advance = NAME_LC ## _iterator__advance; \
+	(P)->cb.seek    = NAME_LC ## _iterator__seek; \
+	(P)->cb.reset   = NAME_LC ## _iterator__reset; \
+	(P)->cb.free    = NAME_LC ## _iterator__free; \
+	} while (0)
+
 #define ITERATOR_BASE_INIT(P,NAME_LC,NAME_UC) do { \
 	(P) = git__calloc(1, sizeof(NAME_LC ## _iterator)); \
 	GITERR_CHECK_ALLOC(P); \
 	(P)->base.type    = GIT_ITERATOR_ ## NAME_UC; \
+	(P)->base.cb    = &(P)->cb; \
+	ITERATOR_SET_CB(P,NAME_LC); \
 	(P)->base.start   = start ? git__strdup(start) : NULL; \
 	(P)->base.end     = end ? git__strdup(end) : NULL; \
 	(P)->base.ignore_case = false; \
-	(P)->base.current = NAME_LC ## _iterator__current; \
-	(P)->base.at_end  = NAME_LC ## _iterator__at_end; \
-	(P)->base.advance = NAME_LC ## _iterator__advance; \
-	(P)->base.seek    = NAME_LC ## _iterator__seek; \
-	(P)->base.reset   = NAME_LC ## _iterator__reset; \
-	(P)->base.free    = NAME_LC ## _iterator__free; \
 	if ((start && !(P)->base.start) || (end && !(P)->base.end)) \
 		return -1; \
 	} while (0)
@@ -81,20 +86,26 @@ static void empty_iterator__free(git_iterator *iter)
 	GIT_UNUSED(iter);
 }
 
+typedef struct {
+	git_iterator base;
+	git_iterator_callbacks cb;
+} empty_iterator;
+
 int git_iterator_for_nothing(git_iterator **iter)
 {
-	git_iterator *i = git__calloc(1, sizeof(git_iterator));
+	empty_iterator *i = git__calloc(1, sizeof(empty_iterator));
 	GITERR_CHECK_ALLOC(i);
 
-	i->type    = GIT_ITERATOR_EMPTY;
-	i->current = empty_iterator__no_item;
-	i->at_end  = empty_iterator__at_end;
-	i->advance = empty_iterator__no_item;
-	i->seek    = empty_iterator__seek;
-	i->reset   = empty_iterator__reset;
-	i->free    = empty_iterator__free;
+	i->base.type  = GIT_ITERATOR_EMPTY;
+	i->base.cb    = &i->cb;
+	i->cb.current = empty_iterator__no_item;
+	i->cb.at_end  = empty_iterator__at_end;
+	i->cb.advance = empty_iterator__no_item;
+	i->cb.seek    = empty_iterator__seek;
+	i->cb.reset   = empty_iterator__reset;
+	i->cb.free    = empty_iterator__free;
 
-	*iter = i;
+	*iter = (git_iterator *)i;
 
 	return 0;
 }
@@ -110,6 +121,7 @@ struct tree_iterator_frame {
 
 typedef struct {
 	git_iterator base;
+	git_iterator_callbacks cb;
 	tree_iterator_frame *stack, *tail;
 	git_index_entry entry;
 	git_buf path;
@@ -365,9 +377,9 @@ int git_iterator_for_tree_range(
 
 typedef struct {
 	git_iterator base;
+	git_iterator_callbacks cb;
 	git_index *index;
 	size_t current;
-	bool free_index;
 } index_iterator;
 
 static int index_iterator__current(
@@ -447,8 +459,7 @@ static int index_iterator__reset(
 static void index_iterator__free(git_iterator *self)
 {
 	index_iterator *ii = (index_iterator *)self;
-	if (ii->free_index)
-		git_index_free(ii->index);
+	git_index_free(ii->index);
 	ii->index = NULL;
 }
 
@@ -462,9 +473,10 @@ int git_iterator_for_index_range(
 
 	ITERATOR_BASE_INIT(ii, index, INDEX);
 
-	ii->index = index;
 	ii->base.repo = git_index_owner(index);
-	ii->base.ignore_case = ii->index->ignore_case;
+	ii->base.ignore_case = index->ignore_case;
+	ii->index = index;
+	GIT_REFCOUNT_INC(index);
 
 	index_iterator__reset((git_iterator *)ii, NULL, NULL);
 
@@ -482,13 +494,10 @@ int git_iterator_for_repo_index_range(
 	int error;
 	git_index *index;
 
-	if ((error = git_repository_index(&index, repo)) < 0)
+	if ((error = git_repository_index__weakptr(&index, repo)) < 0)
 		return error;
 
-	if (!(error = git_iterator_for_index_range(iter, index, start, end)))
-		((index_iterator *)(*iter))->free_index = true;
-
-	return error;
+	return git_iterator_for_index_range(iter, index, start, end);
 }
 
 typedef struct workdir_iterator_frame workdir_iterator_frame;
@@ -500,6 +509,7 @@ struct workdir_iterator_frame {
 
 typedef struct {
 	git_iterator base;
+	git_iterator_callbacks cb;
 	workdir_iterator_frame *stack;
 	int (*entrycmp)(const void *pfx, const void *item);
 	git_ignores ignores;
@@ -830,46 +840,43 @@ int git_iterator_for_workdir_range(
 }
 
 typedef struct {
-	git_iterator base;
-	git_iterator *wrapped;
+	/* replacement callbacks */
+	git_iterator_callbacks cb;
+	/* original iterator values */
+	git_iterator_callbacks *orig;
+	git_iterator_type_t orig_type;
+	/* spoolandsort data */
 	git_vector entries;
-	git_vector_cmp comparer;
 	git_pool entry_pool;
 	git_pool string_pool;
-	unsigned int position;
-} spoolandsort_iterator;
+	size_t position;
+} spoolandsort_callbacks;
 
 static int spoolandsort_iterator__current(
 	git_iterator *self, const git_index_entry **entry)
 {
-	spoolandsort_iterator *si = (spoolandsort_iterator *)self;
+	spoolandsort_callbacks *scb = (spoolandsort_callbacks *)self->cb;
 
-	if (si->position < si->entries.length)
-		*entry = (const git_index_entry *)git_vector_get(
-			&si->entries, si->position);
-	else
-		*entry = NULL;
+	*entry = (const git_index_entry *)
+		git_vector_get(&scb->entries, scb->position);
 
 	return 0;
 }
 
 static int spoolandsort_iterator__at_end(git_iterator *self)
 {
-	spoolandsort_iterator *si = (spoolandsort_iterator *)self;
+	spoolandsort_callbacks *scb = (spoolandsort_callbacks *)self->cb;
 
-	return 0 == si->entries.length || si->entries.length - 1 <= si->position;
+	return 0 == scb->entries.length || scb->entries.length - 1 <= scb->position;
 }
 
 static int spoolandsort_iterator__advance(
 	git_iterator *self, const git_index_entry **entry)
 {
-	spoolandsort_iterator *si = (spoolandsort_iterator *)self;
+	spoolandsort_callbacks *scb = (spoolandsort_callbacks *)self->cb;
 
-	if (si->position < si->entries.length)
-		*entry = (const git_index_entry *)git_vector_get(
-			&si->entries, ++si->position);
-	else
-		*entry = NULL;
+	*entry = (const git_index_entry *)
+		git_vector_get(&scb->entries, ++scb->position);
 
 	return 0;
 }
@@ -885,77 +892,100 @@ static int spoolandsort_iterator__seek(git_iterator *self, const char *prefix)
 static int spoolandsort_iterator__reset(
 	git_iterator *self, const char *start, const char *end)
 {
-	spoolandsort_iterator *si = (spoolandsort_iterator *)self;
+	spoolandsort_callbacks *scb = (spoolandsort_callbacks *)self->cb;
 
 	GIT_UNUSED(start); GIT_UNUSED(end);
 
-	si->position = 0;
+	scb->position = 0;
 
 	return 0;
 }
 
-static void spoolandsort_iterator__free(git_iterator *self)
+static void spoolandsort_iterator__free_callbacks(spoolandsort_callbacks *scb)
 {
-	spoolandsort_iterator *si = (spoolandsort_iterator *)self;
+	git_pool_clear(&scb->string_pool);
+	git_pool_clear(&scb->entry_pool);
+	git_vector_free(&scb->entries);
+	git__free(scb);
+}
 
-	git_pool_clear(&si->string_pool);
-	git_pool_clear(&si->entry_pool);
-	git_vector_free(&si->entries);
-	git_iterator_free(si->wrapped);
+void git_iterator_spoolandsort_pop(git_iterator *self)
+{
+	spoolandsort_callbacks *scb = (spoolandsort_callbacks *)self->cb;
+
+	if (self->type != GIT_ITERATOR_SPOOLANDSORT)
+		return;
+
+	self->cb   = scb->orig;
+	self->type = scb->orig_type;
+	self->ignore_case = !self->ignore_case;
+
+	spoolandsort_iterator__free_callbacks(scb);
 }
 
-int git_iterator_spoolandsort_range(
-	git_iterator **iter,
-	git_iterator *towrap,
-	git_vector_cmp comparer,
-	bool ignore_case,
-	const char *start,
-	const char *end)
+static void spoolandsort_iterator__free(git_iterator *self)
+{
+	git_iterator_spoolandsort_pop(self);
+	self->cb->free(self);
+}
+
+int git_iterator_spoolandsort_push(git_iterator *iter, bool ignore_case)
 {
-	spoolandsort_iterator *si;
 	const git_index_entry *item;
+	spoolandsort_callbacks *scb;
+	int (*entrycomp)(const void *a, const void *b);
 
-	assert(iter && towrap && comparer);
+	if (iter->ignore_case == ignore_case)
+		return 0;
 
-	ITERATOR_BASE_INIT(si, spoolandsort, SPOOLANDSORT);
-	si->base.ignore_case = ignore_case;
-	si->wrapped = towrap;
-	si->comparer = comparer;
-	si->position = 0;
+	scb = git__calloc(1, sizeof(spoolandsort_callbacks));
+	GITERR_CHECK_ALLOC(scb);
 
-	if (git_vector_init(&si->entries, 16, si->comparer) < 0 ||
-		git_iterator_current(towrap, &item) < 0 ||
-		git_pool_init(&si->entry_pool, sizeof(git_index_entry), 0) ||
-		git_pool_init(&si->string_pool, 1, 0))
-	{
-		git__free(si);
-		return -1;
-	}
+	ITERATOR_SET_CB(scb,spoolandsort);
+
+	scb->orig      = iter->cb;
+	scb->orig_type = iter->type;
+	scb->position  = 0;
+
+	entrycomp = ignore_case ? git_index_entry__cmp_icase : git_index_entry__cmp;
+
+	if (git_vector_init(&scb->entries, 16, entrycomp) < 0 ||
+		git_pool_init(&scb->entry_pool, sizeof(git_index_entry), 0) < 0 ||
+		git_pool_init(&scb->string_pool, 1, 0) < 0 ||
+		git_iterator_current(iter, &item) < 0)
+		goto fail;
+
+	while (item) {
+		git_index_entry *clone = git_pool_malloc(&scb->entry_pool, 1);
+		if (!clone)
+			goto fail;
 
-	while (item)
-	{
-		git_index_entry *clone = git_pool_malloc(&si->entry_pool, 1);
 		memcpy(clone, item, sizeof(git_index_entry));
 
-		if (item->path)
-		{
-			clone->path = git_pool_strdup(&si->string_pool, item->path);
+		if (item->path) {
+			clone->path = git_pool_strdup(&scb->string_pool, item->path);
+			if (!clone->path)
+				goto fail;
 		}
 
-		git_vector_insert(&si->entries, clone);
+		if (git_vector_insert(&scb->entries, clone) < 0)
+			goto fail;
 
-		if (git_iterator_advance(towrap, &item) < 0)
-		{
-			git__free(si);
-			return -1;
-		}
+		if (git_iterator_advance(iter, &item) < 0)
+			goto fail;
 	}
 
-	git_vector_sort(&si->entries);
+	git_vector_sort(&scb->entries);
 
-	*iter = (git_iterator *)si;
+	iter->cb   = (git_iterator_callbacks *)scb;
+	iter->type = GIT_ITERATOR_SPOOLANDSORT;
+	iter->ignore_case = !iter->ignore_case;
 
 	return 0;
+
+fail:
+	spoolandsort_iterator__free_callbacks(scb);
+	return -1;
 }
 
 int git_iterator_current_tree_entry(
diff --git a/src/iterator.h b/src/iterator.h
index 9fe684412..8bcb6fb0c 100644
--- a/src/iterator.h
+++ b/src/iterator.h
@@ -26,19 +26,22 @@ typedef enum {
 	GIT_ITERATOR_SPOOLANDSORT = 4
 } git_iterator_type_t;
 
-struct git_iterator {
-	git_iterator_type_t type;
-	git_repository *repo;
-	char *start;
-	char *end;
-	bool ignore_case;
-
+typedef struct {
 	int (*current)(git_iterator *, const git_index_entry **);
 	int (*at_end)(git_iterator *);
 	int (*advance)(git_iterator *, const git_index_entry **);
 	int (*seek)(git_iterator *, const char *prefix);
 	int (*reset)(git_iterator *, const char *start, const char *end);
 	void (*free)(git_iterator *);
+} git_iterator_callbacks;
+
+struct git_iterator {
+	git_iterator_type_t type;
+	git_iterator_callbacks *cb;
+	git_repository *repo;
+	char *start;
+	char *end;
+	bool ignore_case;
 };
 
 extern int git_iterator_for_nothing(git_iterator **iter);
@@ -82,18 +85,13 @@ GIT_INLINE(int) git_iterator_for_workdir(
 	return git_iterator_for_workdir_range(iter, repo, NULL, NULL);
 }
 
-extern int git_iterator_spoolandsort_range(
-	git_iterator **iter, git_iterator *towrap,
-	git_vector_cmp comparer, bool ignore_case,
-	const char *start, const char *end);
+/* Spool all iterator values, resort with alternative ignore_case value
+ * and replace callbacks with spoolandsort alternates.
+ */
+extern int git_iterator_spoolandsort_push(git_iterator *iter, bool ignore_case);
 
-GIT_INLINE(int) git_iterator_spoolandsort(
-	git_iterator **iter, git_iterator *towrap,
-	git_vector_cmp comparer, bool ignore_case)
-{
-	return git_iterator_spoolandsort_range(
-		iter, towrap, comparer, ignore_case, NULL, NULL);
-}
+/* Restore original callbacks - not required in most circumstances */
+extern void git_iterator_spoolandsort_pop(git_iterator *iter);
 
 /* Entry is not guaranteed to be fully populated.  For a tree iterator,
  * we will only populate the mode, oid and path, for example.  For a workdir
@@ -106,30 +104,30 @@ GIT_INLINE(int) git_iterator_spoolandsort(
 GIT_INLINE(int) git_iterator_current(
 	git_iterator *iter, const git_index_entry **entry)
 {
-	return iter->current(iter, entry);
+	return iter->cb->current(iter, entry);
 }
 
 GIT_INLINE(int) git_iterator_at_end(git_iterator *iter)
 {
-	return iter->at_end(iter);
+	return iter->cb->at_end(iter);
 }
 
 GIT_INLINE(int) git_iterator_advance(
 	git_iterator *iter, const git_index_entry **entry)
 {
-	return iter->advance(iter, entry);
+	return iter->cb->advance(iter, entry);
 }
 
 GIT_INLINE(int) git_iterator_seek(
 	git_iterator *iter, const char *prefix)
 {
-	return iter->seek(iter, prefix);
+	return iter->cb->seek(iter, prefix);
 }
 
 GIT_INLINE(int) git_iterator_reset(
 	git_iterator *iter, const char *start, const char *end)
 {
-	return iter->reset(iter, start, end);
+	return iter->cb->reset(iter, start, end);
 }
 
 GIT_INLINE(void) git_iterator_free(git_iterator *iter)
@@ -137,7 +135,7 @@ GIT_INLINE(void) git_iterator_free(git_iterator *iter)
 	if (iter == NULL)
 		return;
 
-	iter->free(iter);
+	iter->cb->free(iter);
 
 	git__free(iter->start);
 	git__free(iter->end);