From 62f7aae477bc542dce0bb6f8b59438442a77d154 Mon Sep 17 00:00:00 2001
From: Derrick Stolee <stolee@gmail.com>
Date: Thu, 29 Aug 2024 12:27:28 -0400
Subject: [PATCH 1/7] path-walk: introduce an object walk by path

In anticipation of a few planned applications, introduce the most basic form
of a path-walk API. It currently assumes that there are no UNINTERESTING
objects, and does not include any complicated filters. It calls a function
pointer on groups of tree and blob objects as grouped by path. This only
includes objects the first time they are discovered, so an object that
appears at multiple paths will not be included in two batches.

These batches are collected in 'struct type_and_oid_list' objects, which
store an object type and an oid_array of objects.

The data structures are documented in 'struct path_walk_context', but in
summary the most important are:

  * 'paths_to_lists' is a strmap that connects a path to a
    type_and_oid_list for that path. To avoid conflicts in path names,
    we make sure that tree paths end in "/" (except the root path with
    is an empty string) and blob paths do not end in "/".

  * 'path_stack' is a string list that is added to in an append-only
    way. This stores the stack of our depth-first search on the heap
    instead of using recursion.

  * 'path_stack_pushed' is a strmap that stores path names that were
    already added to 'path_stack', to avoid repeating paths in the
    stack. Mostly, this saves us from quadratic lookups from doing
    unsorted checks into the string_list.

The coupling of 'path_stack' and 'path_stack_pushed' is protected by the
push_to_stack() method. Call this instead of inserting into these
structures directly.

The walk_objects_by_path() method initializes these structures and
starts walking commits from the given rev_info struct. The commits are
used to find the list of root trees which populate the start of our
depth-first search.

The core of our depth-first search is in a while loop that continues
while we have not indicated an early exit and our 'path_stack' still has
entries in it. The loop body pops a path off of the stack and "visits"
the path via the walk_path() method.

The walk_path() method gets the list of OIDs from the 'path_to_lists'
strmap and executes the callback method on that list with the given path
and type. If the OIDs correspond to tree objects, then iterate over all
trees in the list and run add_children() to add the child objects to
their own lists, adding new entries to the stack if necessary.

In testing, this depth-first search approach was the one that used the
least memory while iterating over the object lists. There is still a
chance that repositories with too-wide path patterns could cause memory
pressure issues. Limiting the stack size could be done in the future by
limiting how many objects are being considered in-progress, or by
visiting blob paths earlier than trees.

There are many future adaptations that could be made, but they are left for
future updates when consumers are ready to take advantage of those features.

Signed-off-by: Derrick Stolee <stolee@gmail.com>
---
 Documentation/technical/api-path-walk.txt |  45 ++++
 Makefile                                  |   1 +
 path-walk.c                               | 279 ++++++++++++++++++++++
 path-walk.h                               |  47 ++++
 4 files changed, 372 insertions(+)
 create mode 100644 Documentation/technical/api-path-walk.txt
 create mode 100644 path-walk.c
 create mode 100644 path-walk.h

diff --git a/Documentation/technical/api-path-walk.txt b/Documentation/technical/api-path-walk.txt
new file mode 100644
index 00000000000000..c550c77ca30754
--- /dev/null
+++ b/Documentation/technical/api-path-walk.txt
@@ -0,0 +1,45 @@
+Path-Walk API
+=============
+
+The path-walk API is used to walk reachable objects, but to visit objects
+in batches based on a common path they appear in, or by type.
+
+For example, all reachable commits are visited in a group. All tags are
+visited in a group. Then, all root trees are visited. At some point, all
+blobs reachable via a path `my/dir/to/A` are visited. When there are
+multiple paths possible to reach the same object, then only one of those
+paths is used to visit the object.
+
+Basics
+------
+
+To use the path-walk API, include `path-walk.h` and call
+`walk_objects_by_path()` with a customized `path_walk_info` struct. The
+struct is used to set all of the options for how the walk should proceed.
+Let's dig into the different options and their use.
+
+`path_fn` and `path_fn_data`::
+	The most important option is the `path_fn` option, which is a
+	function pointer to the callback that can execute logic on the
+	object IDs for objects grouped by type and path. This function
+	also receives a `data` value that corresponds to the
+	`path_fn_data` member, for providing custom data structures to
+	this callback function.
+
+`revs`::
+	To configure the exact details of the reachable set of objects,
+	use the `revs` member and initialize it using the revision
+	machinery in `revision.h`. Initialize `revs` using calls such as
+	`setup_revisions()` or `parse_revision_opt()`. Do not call
+	`prepare_revision_walk()`, as that will be called within
+	`walk_objects_by_path()`.
++
+It is also important that you do not specify the `--objects` flag for the
+`revs` struct. The revision walk should only be used to walk commits, and
+the objects will be walked in a separate way based on those starting
+commits.
+
+Examples
+--------
+
+See example usages in future changes.
diff --git a/Makefile b/Makefile
index 7344a7f7257af6..d0d8d6888e3c47 100644
--- a/Makefile
+++ b/Makefile
@@ -1094,6 +1094,7 @@ LIB_OBJS += parse-options.o
 LIB_OBJS += patch-delta.o
 LIB_OBJS += patch-ids.o
 LIB_OBJS += path.o
+LIB_OBJS += path-walk.o
 LIB_OBJS += pathspec.o
 LIB_OBJS += pkt-line.o
 LIB_OBJS += preload-index.o
diff --git a/path-walk.c b/path-walk.c
new file mode 100644
index 00000000000000..021840ab41b56a
--- /dev/null
+++ b/path-walk.c
@@ -0,0 +1,279 @@
+/*
+ * path-walk.c: implementation for path-based walks of the object graph.
+ */
+#include "git-compat-util.h"
+#include "path-walk.h"
+#include "blob.h"
+#include "commit.h"
+#include "dir.h"
+#include "hashmap.h"
+#include "hex.h"
+#include "object.h"
+#include "oid-array.h"
+#include "revision.h"
+#include "string-list.h"
+#include "strmap.h"
+#include "trace2.h"
+#include "tree.h"
+#include "tree-walk.h"
+
+struct type_and_oid_list {
+	enum object_type type;
+	struct oid_array oids;
+};
+
+#define TYPE_AND_OID_LIST_INIT { \
+	.type = OBJ_NONE, 	 \
+	.oids = OID_ARRAY_INIT	 \
+}
+
+struct path_walk_context {
+	/**
+	 * Repeats of data in 'struct path_walk_info' for
+	 * access with fewer characters.
+	 */
+	struct repository *repo;
+	struct rev_info *revs;
+	struct path_walk_info *info;
+
+	/**
+	 * Map a path to a 'struct type_and_oid_list'
+	 * containing the objects discovered at that
+	 * path.
+	 */
+	struct strmap paths_to_lists;
+
+	/**
+	 * Store the current list of paths in a stack, to
+	 * facilitate depth-first-search without recursion.
+	 *
+	 * Use path_stack_pushed to indicate whether a path
+	 * was previously added to path_stack.
+	 */
+	struct string_list path_stack;
+	struct strset path_stack_pushed;
+};
+
+static void push_to_stack(struct path_walk_context *ctx,
+			  const char *path)
+{
+	if (strset_contains(&ctx->path_stack_pushed, path))
+		return;
+
+	strset_add(&ctx->path_stack_pushed, path);
+	string_list_append(&ctx->path_stack, path);
+}
+
+static int add_tree_entries(struct path_walk_context *ctx,
+			    const char *base_path,
+			    struct object_id *oid)
+{
+	struct tree_desc desc;
+	struct name_entry entry;
+	struct strbuf path = STRBUF_INIT;
+	size_t base_len;
+	struct tree *tree = lookup_tree(ctx->repo, oid);
+
+	if (!tree) {
+		error(_("failed to walk children of tree %s: not found"),
+		      oid_to_hex(oid));
+		return -1;
+	} else if (parse_tree_gently(tree, 1)) {
+		error("bad tree object %s", oid_to_hex(oid));
+		return -1;
+	}
+
+	strbuf_addstr(&path, base_path);
+	base_len = path.len;
+
+	parse_tree(tree);
+	init_tree_desc(&desc, &tree->object.oid, tree->buffer, tree->size);
+	while (tree_entry(&desc, &entry)) {
+		struct type_and_oid_list *list;
+		struct object *o;
+		/* Not actually true, but we will ignore submodules later. */
+		enum object_type type = S_ISDIR(entry.mode) ? OBJ_TREE : OBJ_BLOB;
+
+		/* Skip submodules. */
+		if (S_ISGITLINK(entry.mode))
+			continue;
+
+		if (type == OBJ_TREE) {
+			struct tree *child = lookup_tree(ctx->repo, &entry.oid);
+			o = child ? &child->object : NULL;
+		} else if (type == OBJ_BLOB) {
+			struct blob *child = lookup_blob(ctx->repo, &entry.oid);
+			o = child ? &child->object : NULL;
+		} else {
+			BUG("invalid type for tree entry: %d", type);
+		}
+
+		if (!o) {
+			error(_("failed to find object %s"),
+			      oid_to_hex(&o->oid));
+			return -1;
+		}
+
+		/* Skip this object if already seen. */
+		if (o->flags & SEEN)
+			continue;
+		o->flags |= SEEN;
+
+		strbuf_setlen(&path, base_len);
+		strbuf_add(&path, entry.path, entry.pathlen);
+
+		/*
+		 * Trees will end with "/" for concatenation and distinction
+		 * from blobs at the same path.
+		 */
+		if (type == OBJ_TREE)
+			strbuf_addch(&path, '/');
+
+		if (!(list = strmap_get(&ctx->paths_to_lists, path.buf))) {
+			CALLOC_ARRAY(list, 1);
+			list->type = type;
+			strmap_put(&ctx->paths_to_lists, path.buf, list);
+		}
+		push_to_stack(ctx, path.buf);
+		oid_array_append(&list->oids, &entry.oid);
+	}
+
+	free_tree_buffer(tree);
+	strbuf_release(&path);
+	return 0;
+}
+
+/*
+ * For each path in paths_to_explore, walk the trees another level
+ * and add any found blobs to the batch (but only if they exist and
+ * haven't been added yet).
+ */
+static int walk_path(struct path_walk_context *ctx,
+		     const char *path)
+{
+	struct type_and_oid_list *list;
+	int ret = 0;
+
+	list = strmap_get(&ctx->paths_to_lists, path);
+
+	if (!list->oids.nr)
+		return 0;
+
+	/* Evaluate function pointer on this data. */
+	ret = ctx->info->path_fn(path, &list->oids, list->type,
+				 ctx->info->path_fn_data);
+
+	/* Expand data for children. */
+	if (list->type == OBJ_TREE) {
+		for (size_t i = 0; i < list->oids.nr; i++) {
+			ret |= add_tree_entries(ctx,
+					    path,
+					    &list->oids.oid[i]);
+		}
+	}
+
+	oid_array_clear(&list->oids);
+	strmap_remove(&ctx->paths_to_lists, path, 1);
+	return ret;
+}
+
+static void clear_paths_to_lists(struct strmap *map)
+{
+	struct hashmap_iter iter;
+	struct strmap_entry *e;
+
+	hashmap_for_each_entry(&map->map, &iter, e, ent) {
+		struct type_and_oid_list *list = e->value;
+		oid_array_clear(&list->oids);
+	}
+	strmap_clear(map, 1);
+	strmap_init(map);
+}
+
+/**
+ * Given the configuration of 'info', walk the commits based on 'info->revs' and
+ * call 'info->path_fn' on each discovered path.
+ *
+ * Returns nonzero on an error.
+ */
+int walk_objects_by_path(struct path_walk_info *info)
+{
+	const char *root_path = "";
+	int ret = 0;
+	size_t commits_nr = 0, paths_nr = 0;
+	struct commit *c;
+	struct type_and_oid_list *root_tree_list;
+	struct path_walk_context ctx = {
+		.repo = info->revs->repo,
+		.revs = info->revs,
+		.info = info,
+		.path_stack = STRING_LIST_INIT_DUP,
+		.path_stack_pushed = STRSET_INIT,
+		.paths_to_lists = STRMAP_INIT
+	};
+
+	trace2_region_enter("path-walk", "commit-walk", info->revs->repo);
+
+	/* Insert a single list for the root tree into the paths. */
+	CALLOC_ARRAY(root_tree_list, 1);
+	root_tree_list->type = OBJ_TREE;
+	strmap_put(&ctx.paths_to_lists, root_path, root_tree_list);
+	push_to_stack(&ctx, root_path);
+
+	if (prepare_revision_walk(info->revs))
+		die(_("failed to setup revision walk"));
+
+	while ((c = get_revision(info->revs))) {
+		struct object_id *oid = get_commit_tree_oid(c);
+		struct tree *t;
+		commits_nr++;
+
+		oid = get_commit_tree_oid(c);
+		t = lookup_tree(info->revs->repo, oid);
+
+		if (!t) {
+			error("could not find tree %s", oid_to_hex(oid));
+			return -1;
+		}
+
+		if (t->object.flags & SEEN)
+			continue;
+		t->object.flags |= SEEN;
+		oid_array_append(&root_tree_list->oids, oid);
+	}
+
+	trace2_data_intmax("path-walk", ctx.repo, "commits", commits_nr);
+	trace2_region_leave("path-walk", "commit-walk", info->revs->repo);
+
+	trace2_region_enter("path-walk", "path-walk", info->revs->repo);
+	while (!ret && ctx.path_stack.nr) {
+		char *path = ctx.path_stack.items[ctx.path_stack.nr - 1].string;
+		ctx.path_stack.nr--;
+		paths_nr++;
+
+		ret = walk_path(&ctx, path);
+
+		free(path);
+	}
+	trace2_data_intmax("path-walk", ctx.repo, "paths", paths_nr);
+	trace2_region_leave("path-walk", "path-walk", info->revs->repo);
+
+	clear_paths_to_lists(&ctx.paths_to_lists);
+	strset_clear(&ctx.path_stack_pushed);
+	string_list_clear(&ctx.path_stack, 0);
+	return ret;
+}
+
+void path_walk_info_init(struct path_walk_info *info)
+{
+	struct path_walk_info empty = PATH_WALK_INFO_INIT;
+	memcpy(info, &empty, sizeof(empty));
+}
+
+void path_walk_info_clear(struct path_walk_info *info UNUSED)
+{
+	/*
+	 * This destructor is empty for now, as info->revs
+	 * is not owned by 'struct path_walk_info'.
+	 */
+}
diff --git a/path-walk.h b/path-walk.h
new file mode 100644
index 00000000000000..7cb3538cd8f4af
--- /dev/null
+++ b/path-walk.h
@@ -0,0 +1,47 @@
+/*
+ * path-walk.h : Methods and structures for walking the object graph in batches
+ * by the paths that can reach those objects.
+ */
+#include "object.h" /* Required for 'enum object_type'. */
+
+struct rev_info;
+struct oid_array;
+
+/**
+ * The type of a function pointer for the method that is called on a list of
+ * objects reachable at a given path.
+ */
+typedef int (*path_fn)(const char *path,
+		       struct oid_array *oids,
+		       enum object_type type,
+		       void *data);
+
+struct path_walk_info {
+	/**
+	 * revs provides the definitions for the commit walk, including
+	 * which commits are UNINTERESTING or not. This structure is
+	 * expected to be owned by the caller.
+	 */
+	struct rev_info *revs;
+
+	/**
+	 * The caller wishes to execute custom logic on objects reachable at a
+	 * given path. Every reachable object will be visited exactly once, and
+	 * the first path to see an object wins. This may not be a stable choice.
+	 */
+	path_fn path_fn;
+	void *path_fn_data;
+};
+
+#define PATH_WALK_INFO_INIT { 0 }
+
+void path_walk_info_init(struct path_walk_info *info);
+void path_walk_info_clear(struct path_walk_info *info);
+
+/**
+ * Given the configuration of 'info', walk the commits based on 'info->revs' and
+ * call 'info->path_fn' on each discovered path.
+ *
+ * Returns nonzero on an error.
+ */
+int walk_objects_by_path(struct path_walk_info *info);

From 8ad2a5e79a25975394e5863f7a35293f1e2e5a44 Mon Sep 17 00:00:00 2001
From: Derrick Stolee <stolee@gmail.com>
Date: Mon, 28 Oct 2024 21:23:27 -0400
Subject: [PATCH 2/7] test-lib-functions: add test_cmp_sorted

This test helper will be helpful to reduce repeated logic in
t6601-path-walk.sh, but may be helpful elsewhere, too.

Signed-off-by: Derrick Stolee <stolee@gmail.com>
---
 t/test-lib-functions.sh | 10 ++++++++++
 1 file changed, 10 insertions(+)

diff --git a/t/test-lib-functions.sh b/t/test-lib-functions.sh
index fde9bf54fc35fc..16b70aebd60749 100644
--- a/t/test-lib-functions.sh
+++ b/t/test-lib-functions.sh
@@ -1267,6 +1267,16 @@ test_cmp () {
 	eval "$GIT_TEST_CMP" '"$@"'
 }
 
+# test_cmp_sorted runs test_cmp on sorted versions of the two
+# input files. Uses "$1.sorted" and "$2.sorted" as temp files.
+
+test_cmp_sorted () {
+	sort <"$1" >"$1.sorted" &&
+	sort <"$2" >"$2.sorted" &&
+	test_cmp "$1.sorted" "$2.sorted" &&
+	rm "$1.sorted" "$2.sorted"
+}
+
 # Check that the given config key has the expected value.
 #
 #    test_cmp_config [-C <dir>] <expected-value>

From 2bc0538bce9ae2f502cd88aedf3b82c66e87c467 Mon Sep 17 00:00:00 2001
From: Derrick Stolee <stolee@gmail.com>
Date: Wed, 18 Sep 2024 10:03:03 -0400
Subject: [PATCH 3/7] t6601: add helper for testing path-walk API

Add some tests based on the current behavior, doing interesting checks
for different sets of branches, ranges, and the --boundary option. This
sets a baseline for the behavior and we can extend it as new options are
introduced.

Store and output a 'batch_nr' value so we can demonstrate that the paths are
grouped together in a batch and not following some other ordering. This
allows us to test the depth-first behavior of the path-walk API. However, we
purposefully do not test the order of the objects in the batch, so the
output is compared to the expected output through a sort.

It is important to mention that the behavior of the API will change soon as
we start to handle UNINTERESTING objects differently, but these tests will
demonstrate the change in behavior.

Signed-off-by: Derrick Stolee <stolee@gmail.com>
---
 Documentation/technical/api-path-walk.txt |   3 +-
 Makefile                                  |   1 +
 t/helper/test-path-walk.c                 |  84 +++++++++++++++
 t/helper/test-tool.c                      |   1 +
 t/helper/test-tool.h                      |   1 +
 t/t6601-path-walk.sh                      | 120 ++++++++++++++++++++++
 6 files changed, 209 insertions(+), 1 deletion(-)
 create mode 100644 t/helper/test-path-walk.c
 create mode 100755 t/t6601-path-walk.sh

diff --git a/Documentation/technical/api-path-walk.txt b/Documentation/technical/api-path-walk.txt
index c550c77ca30754..662162ec70b38b 100644
--- a/Documentation/technical/api-path-walk.txt
+++ b/Documentation/technical/api-path-walk.txt
@@ -42,4 +42,5 @@ commits.
 Examples
 --------
 
-See example usages in future changes.
+See example usages in:
+	`t/helper/test-path-walk.c`
diff --git a/Makefile b/Makefile
index d0d8d6888e3c47..50413d964920e7 100644
--- a/Makefile
+++ b/Makefile
@@ -818,6 +818,7 @@ TEST_BUILTINS_OBJS += test-parse-options.o
 TEST_BUILTINS_OBJS += test-parse-pathspec-file.o
 TEST_BUILTINS_OBJS += test-partial-clone.o
 TEST_BUILTINS_OBJS += test-path-utils.o
+TEST_BUILTINS_OBJS += test-path-walk.o
 TEST_BUILTINS_OBJS += test-pcre2-config.o
 TEST_BUILTINS_OBJS += test-pkt-line.o
 TEST_BUILTINS_OBJS += test-proc-receive.o
diff --git a/t/helper/test-path-walk.c b/t/helper/test-path-walk.c
new file mode 100644
index 00000000000000..def7c81ac4fac2
--- /dev/null
+++ b/t/helper/test-path-walk.c
@@ -0,0 +1,84 @@
+#define USE_THE_REPOSITORY_VARIABLE
+
+#include "test-tool.h"
+#include "environment.h"
+#include "hex.h"
+#include "object-name.h"
+#include "object.h"
+#include "pretty.h"
+#include "revision.h"
+#include "setup.h"
+#include "parse-options.h"
+#include "path-walk.h"
+#include "oid-array.h"
+
+static const char * const path_walk_usage[] = {
+	N_("test-tool path-walk <options> -- <revision-options>"),
+	NULL
+};
+
+struct path_walk_test_data {
+	uintmax_t batch_nr;
+	uintmax_t tree_nr;
+	uintmax_t blob_nr;
+};
+
+static int emit_block(const char *path, struct oid_array *oids,
+		      enum object_type type, void *data)
+{
+	struct path_walk_test_data *tdata = data;
+	const char *typestr;
+
+	if (type == OBJ_TREE)
+		tdata->tree_nr += oids->nr;
+	else if (type == OBJ_BLOB)
+		tdata->blob_nr += oids->nr;
+	else
+		BUG("we do not understand this type");
+
+	typestr = type_name(type);
+
+	for (size_t i = 0; i < oids->nr; i++)
+		printf("%"PRIuMAX":%s:%s:%s\n",
+		       tdata->batch_nr, typestr, path,
+		       oid_to_hex(&oids->oid[i]));
+
+	tdata->batch_nr++;
+	return 0;
+}
+
+int cmd__path_walk(int argc, const char **argv)
+{
+	int res;
+	struct rev_info revs = REV_INFO_INIT;
+	struct path_walk_info info = PATH_WALK_INFO_INIT;
+	struct path_walk_test_data data = { 0 };
+	struct option options[] = {
+		OPT_END(),
+	};
+
+	setup_git_directory();
+	revs.repo = the_repository;
+
+	argc = parse_options(argc, argv, NULL,
+			     options, path_walk_usage,
+			     PARSE_OPT_KEEP_UNKNOWN_OPT | PARSE_OPT_KEEP_ARGV0);
+
+	if (argc > 1)
+		setup_revisions(argc, argv, &revs, NULL);
+	else
+		usage(path_walk_usage[0]);
+
+	info.revs = &revs;
+	info.path_fn = emit_block;
+	info.path_fn_data = &data;
+
+	res = walk_objects_by_path(&info);
+
+	printf("trees:%" PRIuMAX "\n"
+	       "blobs:%" PRIuMAX "\n",
+	       data.tree_nr, data.blob_nr);
+
+	release_revisions(&revs);
+	return res;
+}
diff --git a/t/helper/test-tool.c b/t/helper/test-tool.c
index 1ebb69a5dc4c17..43676e7b93a43f 100644
--- a/t/helper/test-tool.c
+++ b/t/helper/test-tool.c
@@ -52,6 +52,7 @@ static struct test_cmd cmds[] = {
 	{ "parse-subcommand", cmd__parse_subcommand },
 	{ "partial-clone", cmd__partial_clone },
 	{ "path-utils", cmd__path_utils },
+	{ "path-walk", cmd__path_walk },
 	{ "pcre2-config", cmd__pcre2_config },
 	{ "pkt-line", cmd__pkt_line },
 	{ "proc-receive", cmd__proc_receive },
diff --git a/t/helper/test-tool.h b/t/helper/test-tool.h
index 21802ac27da37f..9cfc5da6e57b00 100644
--- a/t/helper/test-tool.h
+++ b/t/helper/test-tool.h
@@ -45,6 +45,7 @@ int cmd__parse_pathspec_file(int argc, const char** argv);
 int cmd__parse_subcommand(int argc, const char **argv);
 int cmd__partial_clone(int argc, const char **argv);
 int cmd__path_utils(int argc, const char **argv);
+int cmd__path_walk(int argc, const char **argv);
 int cmd__pcre2_config(int argc, const char **argv);
 int cmd__pkt_line(int argc, const char **argv);
 int cmd__proc_receive(int argc, const char **argv);
diff --git a/t/t6601-path-walk.sh b/t/t6601-path-walk.sh
new file mode 100755
index 00000000000000..4e052c093095ab
--- /dev/null
+++ b/t/t6601-path-walk.sh
@@ -0,0 +1,120 @@
+#!/bin/sh
+
+TEST_PASSES_SANITIZE_LEAK=true
+
+test_description='direct path-walk API tests'
+
+. ./test-lib.sh
+
+test_expect_success 'setup test repository' '
+	git checkout -b base &&
+
+	mkdir left &&
+	mkdir right &&
+	echo a >a &&
+	echo b >left/b &&
+	echo c >right/c &&
+	git add . &&
+	git commit -m "first" &&
+
+	echo d >right/d &&
+	git add right &&
+	git commit -m "second" &&
+
+	echo bb >left/b &&
+	git commit -a -m "third" &&
+
+	git checkout -b topic HEAD~1 &&
+	echo cc >right/c &&
+	git commit -a -m "topic"
+'
+
+test_expect_success 'all' '
+	test-tool path-walk -- --all >out &&
+
+	cat >expect <<-EOF &&
+	0:tree::$(git rev-parse topic^{tree})
+	0:tree::$(git rev-parse base^{tree})
+	0:tree::$(git rev-parse base~1^{tree})
+	0:tree::$(git rev-parse base~2^{tree})
+	1:tree:right/:$(git rev-parse topic:right)
+	1:tree:right/:$(git rev-parse base~1:right)
+	1:tree:right/:$(git rev-parse base~2:right)
+	2:blob:right/d:$(git rev-parse base~1:right/d)
+	3:blob:right/c:$(git rev-parse base~2:right/c)
+	3:blob:right/c:$(git rev-parse topic:right/c)
+	4:tree:left/:$(git rev-parse base:left)
+	4:tree:left/:$(git rev-parse base~2:left)
+	5:blob:left/b:$(git rev-parse base~2:left/b)
+	5:blob:left/b:$(git rev-parse base:left/b)
+	6:blob:a:$(git rev-parse base~2:a)
+	blobs:6
+	trees:9
+	EOF
+
+	test_cmp_sorted expect out
+'
+
+test_expect_success 'topic only' '
+	test-tool path-walk -- topic >out &&
+
+	cat >expect <<-EOF &&
+	0:tree::$(git rev-parse topic^{tree})
+	0:tree::$(git rev-parse base~1^{tree})
+	0:tree::$(git rev-parse base~2^{tree})
+	1:tree:right/:$(git rev-parse topic:right)
+	1:tree:right/:$(git rev-parse base~1:right)
+	1:tree:right/:$(git rev-parse base~2:right)
+	2:blob:right/d:$(git rev-parse base~1:right/d)
+	3:blob:right/c:$(git rev-parse base~2:right/c)
+	3:blob:right/c:$(git rev-parse topic:right/c)
+	4:tree:left/:$(git rev-parse base~2:left)
+	5:blob:left/b:$(git rev-parse base~2:left/b)
+	6:blob:a:$(git rev-parse base~2:a)
+	blobs:5
+	trees:7
+	EOF
+
+	test_cmp_sorted expect out
+'
+
+test_expect_success 'topic, not base' '
+	test-tool path-walk -- topic --not base >out &&
+
+	cat >expect <<-EOF &&
+	0:tree::$(git rev-parse topic^{tree})
+	1:tree:right/:$(git rev-parse topic:right)
+	2:blob:right/d:$(git rev-parse topic:right/d)
+	3:blob:right/c:$(git rev-parse topic:right/c)
+	4:tree:left/:$(git rev-parse topic:left)
+	5:blob:left/b:$(git rev-parse topic:left/b)
+	6:blob:a:$(git rev-parse topic:a)
+	blobs:4
+	trees:3
+	EOF
+
+	test_cmp_sorted expect out
+'
+
+test_expect_success 'topic, not base, boundary' '
+	test-tool path-walk -- --boundary topic --not base >out &&
+
+	cat >expect <<-EOF &&
+	0:tree::$(git rev-parse topic^{tree})
+	0:tree::$(git rev-parse base~1^{tree})
+	1:tree:right/:$(git rev-parse topic:right)
+	1:tree:right/:$(git rev-parse base~1:right)
+	2:blob:right/d:$(git rev-parse base~1:right/d)
+	3:blob:right/c:$(git rev-parse base~1:right/c)
+	3:blob:right/c:$(git rev-parse topic:right/c)
+	4:tree:left/:$(git rev-parse base~1:left)
+	5:blob:left/b:$(git rev-parse base~1:left/b)
+	6:blob:a:$(git rev-parse base~1:a)
+	blobs:5
+	trees:5
+	EOF
+
+	test_cmp_sorted expect out
+'
+
+test_done

From db5c86112300130d9f1a62f67800fc5bc824b268 Mon Sep 17 00:00:00 2001
From: Derrick Stolee <derrickstolee@github.com>
Date: Sun, 1 Sep 2024 14:25:33 -0400
Subject: [PATCH 4/7] path-walk: allow consumer to specify object types

We add the ability to filter the object types in the path-walk API so
the callback function is called fewer times.

This adds the ability to ask for the commits in a list, as well. We
re-use the empty string for this set of objects because these are passed
directly to the callback function instead of being part of the
'path_stack'.

Future changes will add the ability to visit annotated tags.

Signed-off-by: Derrick Stolee <stolee@gmail.com>
---
 Documentation/technical/api-path-walk.txt |   9 ++
 path-walk.c                               |  33 ++++-
 path-walk.h                               |  14 +-
 t/helper/test-path-walk.c                 |  15 ++-
 t/t6601-path-walk.sh                      | 149 +++++++++++++++-------
 5 files changed, 170 insertions(+), 50 deletions(-)

diff --git a/Documentation/technical/api-path-walk.txt b/Documentation/technical/api-path-walk.txt
index 662162ec70b38b..dce553b6114e1c 100644
--- a/Documentation/technical/api-path-walk.txt
+++ b/Documentation/technical/api-path-walk.txt
@@ -39,6 +39,15 @@ It is also important that you do not specify the `--objects` flag for the
 the objects will be walked in a separate way based on those starting
 commits.
 
+`commits`, `blobs`, `trees`::
+	By default, these members are enabled and signal that the path-walk
+	API should call the `path_fn` on objects of these types. Specialized
+	applications could disable some options to make it simpler to walk
+	the objects or to have fewer calls to `path_fn`.
++
+While it is possible to walk only commits in this way, consumers would be
+better off using the revision walk API instead.
+
 Examples
 --------
 
diff --git a/path-walk.c b/path-walk.c
index 021840ab41b56a..05ca7b2442a813 100644
--- a/path-walk.c
+++ b/path-walk.c
@@ -98,6 +98,10 @@ static int add_tree_entries(struct path_walk_context *ctx,
 		if (S_ISGITLINK(entry.mode))
 			continue;
 
+		/* If the caller doesn't want blobs, then don't bother. */
+		if (!ctx->info->blobs && type == OBJ_BLOB)
+			continue;
+
 		if (type == OBJ_TREE) {
 			struct tree *child = lookup_tree(ctx->repo, &entry.oid);
 			o = child ? &child->object : NULL;
@@ -159,9 +163,11 @@ static int walk_path(struct path_walk_context *ctx,
 	if (!list->oids.nr)
 		return 0;
 
-	/* Evaluate function pointer on this data. */
-	ret = ctx->info->path_fn(path, &list->oids, list->type,
-				 ctx->info->path_fn_data);
+	/* Evaluate function pointer on this data, if requested. */
+	if ((list->type == OBJ_TREE && ctx->info->trees) ||
+	    (list->type == OBJ_BLOB && ctx->info->blobs))
+		ret = ctx->info->path_fn(path, &list->oids, list->type,
+					ctx->info->path_fn_data);
 
 	/* Expand data for children. */
 	if (list->type == OBJ_TREE) {
@@ -203,6 +209,7 @@ int walk_objects_by_path(struct path_walk_info *info)
 	size_t commits_nr = 0, paths_nr = 0;
 	struct commit *c;
 	struct type_and_oid_list *root_tree_list;
+	struct type_and_oid_list *commit_list;
 	struct path_walk_context ctx = {
 		.repo = info->revs->repo,
 		.revs = info->revs,
@@ -214,6 +221,9 @@ int walk_objects_by_path(struct path_walk_info *info)
 
 	trace2_region_enter("path-walk", "commit-walk", info->revs->repo);
 
+	CALLOC_ARRAY(commit_list, 1);
+	commit_list->type = OBJ_COMMIT;
+
 	/* Insert a single list for the root tree into the paths. */
 	CALLOC_ARRAY(root_tree_list, 1);
 	root_tree_list->type = OBJ_TREE;
@@ -224,10 +234,18 @@ int walk_objects_by_path(struct path_walk_info *info)
 		die(_("failed to setup revision walk"));
 
 	while ((c = get_revision(info->revs))) {
-		struct object_id *oid = get_commit_tree_oid(c);
+		struct object_id *oid;
 		struct tree *t;
 		commits_nr++;
 
+		if (info->commits)
+			oid_array_append(&commit_list->oids,
+					 &c->object.oid);
+
+		/* If we only care about commits, then skip trees. */
+		if (!info->trees && !info->blobs)
+			continue;
+
 		oid = get_commit_tree_oid(c);
 		t = lookup_tree(info->revs->repo, oid);
 
@@ -245,6 +263,13 @@ int walk_objects_by_path(struct path_walk_info *info)
 	trace2_data_intmax("path-walk", ctx.repo, "commits", commits_nr);
 	trace2_region_leave("path-walk", "commit-walk", info->revs->repo);
 
+	/* Track all commits. */
+	if (info->commits && commit_list->oids.nr)
+		ret = info->path_fn("", &commit_list->oids, OBJ_COMMIT,
+				    info->path_fn_data);
+	oid_array_clear(&commit_list->oids);
+	free(commit_list);
+
 	trace2_region_enter("path-walk", "path-walk", info->revs->repo);
 	while (!ret && ctx.path_stack.nr) {
 		char *path = ctx.path_stack.items[ctx.path_stack.nr - 1].string;
diff --git a/path-walk.h b/path-walk.h
index 7cb3538cd8f4af..2cafc71e153c19 100644
--- a/path-walk.h
+++ b/path-walk.h
@@ -31,9 +31,21 @@ struct path_walk_info {
 	 */
 	path_fn path_fn;
 	void *path_fn_data;
+
+	/**
+	 * Initialize which object types the path_fn should be called on. This
+	 * could also limit the walk to skip blobs if not set.
+	 */
+	int commits;
+	int trees;
+	int blobs;
 };
 
-#define PATH_WALK_INFO_INIT { 0 }
+#define PATH_WALK_INFO_INIT {   \
+	.blobs = 1,		\
+	.trees = 1,		\
+	.commits = 1,		\
+}
 
 void path_walk_info_init(struct path_walk_info *info);
 void path_walk_info_clear(struct path_walk_info *info);
diff --git a/t/helper/test-path-walk.c b/t/helper/test-path-walk.c
index def7c81ac4fac2..a57a05a6391fcb 100644
--- a/t/helper/test-path-walk.c
+++ b/t/helper/test-path-walk.c
@@ -19,6 +19,8 @@ static const char * const path_walk_usage[] = {
 
 struct path_walk_test_data {
 	uintmax_t batch_nr;
+
+	uintmax_t commit_nr;
 	uintmax_t tree_nr;
 	uintmax_t blob_nr;
 };
@@ -33,6 +35,8 @@ static int emit_block(const char *path, struct oid_array *oids,
 		tdata->tree_nr += oids->nr;
 	else if (type == OBJ_BLOB)
 		tdata->blob_nr += oids->nr;
+	else if (type == OBJ_COMMIT)
+		tdata->commit_nr += oids->nr;
 	else
 		BUG("we do not understand this type");
 
@@ -54,6 +58,12 @@ int cmd__path_walk(int argc, const char **argv)
 	struct path_walk_info info = PATH_WALK_INFO_INIT;
 	struct path_walk_test_data data = { 0 };
 	struct option options[] = {
+		OPT_BOOL(0, "blobs", &info.blobs,
+			 N_("toggle inclusion of blob objects")),
+		OPT_BOOL(0, "commits", &info.commits,
+			 N_("toggle inclusion of commit objects")),
+		OPT_BOOL(0, "trees", &info.trees,
+			 N_("toggle inclusion of tree objects")),
 		OPT_END(),
 	};
 
@@ -75,9 +85,10 @@ int cmd__path_walk(int argc, const char **argv)
 
 	res = walk_objects_by_path(&info);
 
-	printf("trees:%" PRIuMAX "\n"
+	printf("commits:%" PRIuMAX "\n"
+	       "trees:%" PRIuMAX "\n"
 	       "blobs:%" PRIuMAX "\n",
-	       data.tree_nr, data.blob_nr);
+	       data.commit_nr, data.tree_nr, data.blob_nr);
 
 	release_revisions(&revs);
 	return res;
diff --git a/t/t6601-path-walk.sh b/t/t6601-path-walk.sh
index 4e052c093095ab..4a4939a1b02bb1 100755
--- a/t/t6601-path-walk.sh
+++ b/t/t6601-path-walk.sh
@@ -33,22 +33,27 @@ test_expect_success 'all' '
 	test-tool path-walk -- --all >out &&
 
 	cat >expect <<-EOF &&
-	0:tree::$(git rev-parse topic^{tree})
-	0:tree::$(git rev-parse base^{tree})
-	0:tree::$(git rev-parse base~1^{tree})
-	0:tree::$(git rev-parse base~2^{tree})
-	1:tree:right/:$(git rev-parse topic:right)
-	1:tree:right/:$(git rev-parse base~1:right)
-	1:tree:right/:$(git rev-parse base~2:right)
-	2:blob:right/d:$(git rev-parse base~1:right/d)
-	3:blob:right/c:$(git rev-parse base~2:right/c)
-	3:blob:right/c:$(git rev-parse topic:right/c)
-	4:tree:left/:$(git rev-parse base:left)
-	4:tree:left/:$(git rev-parse base~2:left)
-	5:blob:left/b:$(git rev-parse base~2:left/b)
-	5:blob:left/b:$(git rev-parse base:left/b)
-	6:blob:a:$(git rev-parse base~2:a)
+	0:commit::$(git rev-parse topic)
+	0:commit::$(git rev-parse base)
+	0:commit::$(git rev-parse base~1)
+	0:commit::$(git rev-parse base~2)
+	1:tree::$(git rev-parse topic^{tree})
+	1:tree::$(git rev-parse base^{tree})
+	1:tree::$(git rev-parse base~1^{tree})
+	1:tree::$(git rev-parse base~2^{tree})
+	2:tree:right/:$(git rev-parse topic:right)
+	2:tree:right/:$(git rev-parse base~1:right)
+	2:tree:right/:$(git rev-parse base~2:right)
+	3:blob:right/d:$(git rev-parse base~1:right/d)
+	4:blob:right/c:$(git rev-parse base~2:right/c)
+	4:blob:right/c:$(git rev-parse topic:right/c)
+	5:tree:left/:$(git rev-parse base:left)
+	5:tree:left/:$(git rev-parse base~2:left)
+	6:blob:left/b:$(git rev-parse base~2:left/b)
+	6:blob:left/b:$(git rev-parse base:left/b)
+	7:blob:a:$(git rev-parse base~2:a)
 	blobs:6
+	commits:4
 	trees:9
 	EOF
 
@@ -59,19 +64,23 @@ test_expect_success 'topic only' '
 	test-tool path-walk -- topic >out &&
 
 	cat >expect <<-EOF &&
-	0:tree::$(git rev-parse topic^{tree})
-	0:tree::$(git rev-parse base~1^{tree})
-	0:tree::$(git rev-parse base~2^{tree})
-	1:tree:right/:$(git rev-parse topic:right)
-	1:tree:right/:$(git rev-parse base~1:right)
-	1:tree:right/:$(git rev-parse base~2:right)
-	2:blob:right/d:$(git rev-parse base~1:right/d)
-	3:blob:right/c:$(git rev-parse base~2:right/c)
-	3:blob:right/c:$(git rev-parse topic:right/c)
-	4:tree:left/:$(git rev-parse base~2:left)
-	5:blob:left/b:$(git rev-parse base~2:left/b)
-	6:blob:a:$(git rev-parse base~2:a)
+	0:commit::$(git rev-parse topic)
+	0:commit::$(git rev-parse base~1)
+	0:commit::$(git rev-parse base~2)
+	1:tree::$(git rev-parse topic^{tree})
+	1:tree::$(git rev-parse base~1^{tree})
+	1:tree::$(git rev-parse base~2^{tree})
+	2:tree:right/:$(git rev-parse topic:right)
+	2:tree:right/:$(git rev-parse base~1:right)
+	2:tree:right/:$(git rev-parse base~2:right)
+	3:blob:right/d:$(git rev-parse base~1:right/d)
+	4:blob:right/c:$(git rev-parse base~2:right/c)
+	4:blob:right/c:$(git rev-parse topic:right/c)
+	5:tree:left/:$(git rev-parse base~2:left)
+	6:blob:left/b:$(git rev-parse base~2:left/b)
+	7:blob:a:$(git rev-parse base~2:a)
 	blobs:5
+	commits:3
 	trees:7
 	EOF
 
@@ -82,15 +91,66 @@ test_expect_success 'topic, not base' '
 	test-tool path-walk -- topic --not base >out &&
 
 	cat >expect <<-EOF &&
+	0:commit::$(git rev-parse topic)
+	1:tree::$(git rev-parse topic^{tree})
+	2:tree:right/:$(git rev-parse topic:right)
+	3:blob:right/d:$(git rev-parse topic:right/d)
+	4:blob:right/c:$(git rev-parse topic:right/c)
+	5:tree:left/:$(git rev-parse topic:left)
+	6:blob:left/b:$(git rev-parse topic:left/b)
+	7:blob:a:$(git rev-parse topic:a)
+	blobs:4
+	commits:1
+	trees:3
+	EOF
+
+	test_cmp_sorted expect out
+'
+
+test_expect_success 'topic, not base, only blobs' '
+	test-tool path-walk --no-trees --no-commits \
+		-- topic --not base >out &&
+
+	cat >expect <<-EOF &&
+	commits:0
+	trees:0
+	0:blob:right/d:$(git rev-parse topic:right/d)
+	1:blob:right/c:$(git rev-parse topic:right/c)
+	2:blob:left/b:$(git rev-parse topic:left/b)
+	3:blob:a:$(git rev-parse topic:a)
+	blobs:4
+	EOF
+
+	test_cmp_sorted expect out
+'
+
+# No, this doesn't make a lot of sense for the path-walk API,
+# but it is possible to do.
+test_expect_success 'topic, not base, only commits' '
+	test-tool path-walk --no-blobs --no-trees \
+		-- topic --not base >out &&
+
+	cat >expect <<-EOF &&
+	0:commit::$(git rev-parse topic)
+	commits:1
+	trees:0
+	blobs:0
+	EOF
+
+	test_cmp_sorted expect out
+'
+
+test_expect_success 'topic, not base, only trees' '
+	test-tool path-walk --no-blobs --no-commits \
+		-- topic --not base >out &&
+
+	cat >expect <<-EOF &&
+	commits:0
 	0:tree::$(git rev-parse topic^{tree})
 	1:tree:right/:$(git rev-parse topic:right)
-	2:blob:right/d:$(git rev-parse topic:right/d)
-	3:blob:right/c:$(git rev-parse topic:right/c)
-	4:tree:left/:$(git rev-parse topic:left)
-	5:blob:left/b:$(git rev-parse topic:left/b)
-	6:blob:a:$(git rev-parse topic:a)
-	blobs:4
+	2:tree:left/:$(git rev-parse topic:left)
 	trees:3
+	blobs:0
 	EOF
 
 	test_cmp_sorted expect out
@@ -100,17 +160,20 @@ test_expect_success 'topic, not base, boundary' '
 	test-tool path-walk -- --boundary topic --not base >out &&
 
 	cat >expect <<-EOF &&
-	0:tree::$(git rev-parse topic^{tree})
-	0:tree::$(git rev-parse base~1^{tree})
-	1:tree:right/:$(git rev-parse topic:right)
-	1:tree:right/:$(git rev-parse base~1:right)
-	2:blob:right/d:$(git rev-parse base~1:right/d)
-	3:blob:right/c:$(git rev-parse base~1:right/c)
-	3:blob:right/c:$(git rev-parse topic:right/c)
-	4:tree:left/:$(git rev-parse base~1:left)
-	5:blob:left/b:$(git rev-parse base~1:left/b)
-	6:blob:a:$(git rev-parse base~1:a)
+	0:commit::$(git rev-parse topic)
+	0:commit::$(git rev-parse base~1)
+	1:tree::$(git rev-parse topic^{tree})
+	1:tree::$(git rev-parse base~1^{tree})
+	2:tree:right/:$(git rev-parse topic:right)
+	2:tree:right/:$(git rev-parse base~1:right)
+	3:blob:right/d:$(git rev-parse base~1:right/d)
+	4:blob:right/c:$(git rev-parse base~1:right/c)
+	4:blob:right/c:$(git rev-parse topic:right/c)
+	5:tree:left/:$(git rev-parse base~1:left)
+	6:blob:left/b:$(git rev-parse base~1:left/b)
+	7:blob:a:$(git rev-parse base~1:a)
 	blobs:5
+	commits:2
 	trees:5
 	EOF
 

From 6df56f465d7bdb2c2d360752f6530e29b4d3dc3c Mon Sep 17 00:00:00 2001
From: Derrick Stolee <stolee@gmail.com>
Date: Mon, 9 Sep 2024 12:31:21 -0400
Subject: [PATCH 5/7] path-walk: visit tags and cached objects

The rev_info that is specified for a path-walk traversal may specify
visiting tag refs (both lightweight and annotated) and also may specify
indexed objects (blobs and trees). Update the path-walk API to walk
these objects as well.

When walking tags, we need to peel the annotated objects until reaching
a non-tag object. If we reach a commit, then we can add it to the
pending objects to make sure we visit in the commit walk portion. If we
reach a tree, then we will assume that it is a root tree. If we reach a
blob, then we have no good path name and so add it to a new list of
"tagged blobs".

When the rev_info includes the "--indexed-objects" flag, then the
pending set includes blobs and trees found in the cache entries and
cache-tree. The cache entries are usually blobs, though they could be
trees in the case of a sparse index. The cache-tree stores
previously-hashed tree objects but these are cleared out when staging
objects below those paths. We add tests that demonstrate this.

The indexed objects come with a non-NULL 'path' value in the pending
item. This allows us to prepopulate the 'path_to_lists' strmap with
lists for these paths.

The tricky thing about this walk is that we will want to combine the
indexed objects walk with the commit walk, especially in the future case
of walking objects during a command like 'git repack'.

Whenever possible, we want the objects from the index to be grouped with
similar objects in history. We don't want to miss any paths that appear
only in the index and not in the commit history.

Thus, we need to be careful to let the path stack be populated initially
with only the root tree path (and possibly tags and tagged blobs) and go
through the normal depth-first search. Afterwards, if there are other
paths that are remaining in the paths_to_lists strmap, we should then
iterate through the stack and visit those objects recursively.

Signed-off-by: Derrick Stolee <stolee@gmail.com>
---
 Documentation/technical/api-path-walk.txt |   2 +-
 path-walk.c                               | 184 ++++++++++++++++++++-
 path-walk.h                               |   2 +
 t/helper/test-path-walk.c                 |  15 +-
 t/t6601-path-walk.sh                      | 186 +++++++++++++++++++---
 5 files changed, 362 insertions(+), 27 deletions(-)

diff --git a/Documentation/technical/api-path-walk.txt b/Documentation/technical/api-path-walk.txt
index dce553b6114e1c..6022c381b7c3f0 100644
--- a/Documentation/technical/api-path-walk.txt
+++ b/Documentation/technical/api-path-walk.txt
@@ -39,7 +39,7 @@ It is also important that you do not specify the `--objects` flag for the
 the objects will be walked in a separate way based on those starting
 commits.
 
-`commits`, `blobs`, `trees`::
+`commits`, `blobs`, `trees`, `tags`::
 	By default, these members are enabled and signal that the path-walk
 	API should call the `path_fn` on objects of these types. Specialized
 	applications could disable some options to make it simpler to walk
diff --git a/path-walk.c b/path-walk.c
index 05ca7b2442a813..f34dbf61de0a0f 100644
--- a/path-walk.c
+++ b/path-walk.c
@@ -13,10 +13,13 @@
 #include "revision.h"
 #include "string-list.h"
 #include "strmap.h"
+#include "tag.h"
 #include "trace2.h"
 #include "tree.h"
 #include "tree-walk.h"
 
+static const char *root_path = "";
+
 struct type_and_oid_list {
 	enum object_type type;
 	struct oid_array oids;
@@ -160,12 +163,16 @@ static int walk_path(struct path_walk_context *ctx,
 
 	list = strmap_get(&ctx->paths_to_lists, path);
 
+	if (!list)
+		BUG("provided path '%s' that had no associated list", path);
+
 	if (!list->oids.nr)
 		return 0;
 
 	/* Evaluate function pointer on this data, if requested. */
 	if ((list->type == OBJ_TREE && ctx->info->trees) ||
-	    (list->type == OBJ_BLOB && ctx->info->blobs))
+	    (list->type == OBJ_BLOB && ctx->info->blobs) ||
+	    (list->type == OBJ_TAG && ctx->info->tags))
 		ret = ctx->info->path_fn(path, &list->oids, list->type,
 					ctx->info->path_fn_data);
 
@@ -196,6 +203,139 @@ static void clear_paths_to_lists(struct strmap *map)
 	strmap_init(map);
 }
 
+static int setup_pending_objects(struct path_walk_info *info,
+				 struct path_walk_context *ctx)
+{
+	struct type_and_oid_list *tags = NULL;
+	struct type_and_oid_list *tagged_blobs = NULL;
+	struct type_and_oid_list *root_tree_list = NULL;
+
+	if (info->tags)
+		CALLOC_ARRAY(tags, 1);
+	if (info->blobs)
+		CALLOC_ARRAY(tagged_blobs, 1);
+	if (info->trees)
+		root_tree_list = strmap_get(&ctx->paths_to_lists, root_path);
+
+	/*
+	 * Pending objects include:
+	 * * Commits at branch tips.
+	 * * Annotated tags at tag tips.
+	 * * Any kind of object at lightweight tag tips.
+	 * * Trees and blobs in the index (with an associated path).
+	 */
+	for (size_t i = 0; i < info->revs->pending.nr; i++) {
+		struct object_array_entry *pending = info->revs->pending.objects + i;
+		struct object *obj = pending->item;
+
+		/* Commits will be picked up by revision walk. */
+		if (obj->type == OBJ_COMMIT)
+			continue;
+
+		/* Navigate annotated tag object chains. */
+		while (obj->type == OBJ_TAG) {
+			struct tag *tag = lookup_tag(info->revs->repo, &obj->oid);
+			if (!tag) {
+				error(_("failed to find tag %s"),
+				      oid_to_hex(&obj->oid));
+				return -1;
+			}
+			if (tag->object.flags & SEEN)
+				break;
+			tag->object.flags |= SEEN;
+
+			if (tags)
+				oid_array_append(&tags->oids, &obj->oid);
+			obj = tag->tagged;
+		}
+
+		if (obj->type == OBJ_TAG)
+			continue;
+
+		/* We are now at a non-tag object. */
+		if (obj->flags & SEEN)
+			continue;
+		obj->flags |= SEEN;
+
+		switch (obj->type) {
+		case OBJ_TREE:
+			if (!info->trees)
+				continue;
+			if (pending->path) {
+				struct type_and_oid_list *list;
+				char *path = *pending->path ? xstrfmt("%s/", pending->path)
+							    : xstrdup("");
+				if (!(list = strmap_get(&ctx->paths_to_lists, path))) {
+					CALLOC_ARRAY(list, 1);
+					list->type = OBJ_TREE;
+					strmap_put(&ctx->paths_to_lists, path, list);
+				}
+				oid_array_append(&list->oids, &obj->oid);
+				free(path);
+			} else {
+				/* assume a root tree, such as a lightweight tag. */
+				oid_array_append(&root_tree_list->oids, &obj->oid);
+			}
+			break;
+
+		case OBJ_BLOB:
+			if (!info->blobs)
+				continue;
+			if (pending->path) {
+				struct type_and_oid_list *list;
+				char *path = pending->path;
+				if (!(list = strmap_get(&ctx->paths_to_lists, path))) {
+					CALLOC_ARRAY(list, 1);
+					list->type = OBJ_BLOB;
+					strmap_put(&ctx->paths_to_lists, path, list);
+				}
+				oid_array_append(&list->oids, &obj->oid);
+			} else {
+				/* assume a root tree, such as a lightweight tag. */
+				oid_array_append(&tagged_blobs->oids, &obj->oid);
+			}
+			break;
+
+		case OBJ_COMMIT:
+			/* Make sure it is in the object walk */
+			if (obj != pending->item)
+				add_pending_object(info->revs, obj, "");
+			break;
+
+		default:
+			BUG("should not see any other type here");
+		}
+	}
+
+	/*
+	 * Add tag objects and tagged blobs if they exist.
+	 */
+	if (tagged_blobs) {
+		if (tagged_blobs->oids.nr) {
+			const char *tagged_blob_path = "/tagged-blobs";
+			tagged_blobs->type = OBJ_BLOB;
+			push_to_stack(ctx, tagged_blob_path);
+			strmap_put(&ctx->paths_to_lists, tagged_blob_path, tagged_blobs);
+		} else {
+			oid_array_clear(&tagged_blobs->oids);
+			free(tagged_blobs);
+		}
+	}
+	if (tags) {
+		if (tags->oids.nr) {
+			const char *tag_path = "/tags";
+			tags->type = OBJ_TAG;
+			push_to_stack(ctx, tag_path);
+			strmap_put(&ctx->paths_to_lists, tag_path, tags);
+		} else {
+			oid_array_clear(&tags->oids);
+			free(tags);
+		}
+	}
+
+	return 0;
+}
+
 /**
  * Given the configuration of 'info', walk the commits based on 'info->revs' and
  * call 'info->path_fn' on each discovered path.
@@ -204,8 +344,7 @@ static void clear_paths_to_lists(struct strmap *map)
  */
 int walk_objects_by_path(struct path_walk_info *info)
 {
-	const char *root_path = "";
-	int ret = 0;
+	int ret;
 	size_t commits_nr = 0, paths_nr = 0;
 	struct commit *c;
 	struct type_and_oid_list *root_tree_list;
@@ -224,15 +363,34 @@ int walk_objects_by_path(struct path_walk_info *info)
 	CALLOC_ARRAY(commit_list, 1);
 	commit_list->type = OBJ_COMMIT;
 
+	if (info->tags)
+		info->revs->tag_objects = 1;
+
 	/* Insert a single list for the root tree into the paths. */
 	CALLOC_ARRAY(root_tree_list, 1);
 	root_tree_list->type = OBJ_TREE;
 	strmap_put(&ctx.paths_to_lists, root_path, root_tree_list);
 	push_to_stack(&ctx, root_path);
 
+	/*
+	 * Set these values before preparing the walk to catch
+	 * lightweight tags pointing to non-commits and indexed objects.
+	 */
+	info->revs->blob_objects = info->blobs;
+	info->revs->tree_objects = info->trees;
+
 	if (prepare_revision_walk(info->revs))
 		die(_("failed to setup revision walk"));
 
+	info->revs->blob_objects = info->revs->tree_objects = 0;
+
+	trace2_region_enter("path-walk", "pending-walk", info->revs->repo);
+	ret = setup_pending_objects(info, &ctx);
+	trace2_region_leave("path-walk", "pending-walk", info->revs->repo);
+
+	if (ret)
+		return ret;
+
 	while ((c = get_revision(info->revs))) {
 		struct object_id *oid;
 		struct tree *t;
@@ -280,6 +438,26 @@ int walk_objects_by_path(struct path_walk_info *info)
 
 		free(path);
 	}
+
+	/* Are there paths remaining? Likely they are from indexed objects. */
+	if (!strmap_empty(&ctx.paths_to_lists)) {
+		struct hashmap_iter iter;
+		struct strmap_entry *entry;
+
+		strmap_for_each_entry(&ctx.paths_to_lists, &iter, entry)
+			push_to_stack(&ctx, entry->key);
+
+		while (!ret && ctx.path_stack.nr) {
+			char *path = ctx.path_stack.items[ctx.path_stack.nr - 1].string;
+			ctx.path_stack.nr--;
+			paths_nr++;
+
+			ret = walk_path(&ctx, path);
+
+			free(path);
+		}
+	}
+
 	trace2_data_intmax("path-walk", ctx.repo, "paths", paths_nr);
 	trace2_region_leave("path-walk", "path-walk", info->revs->repo);
 
diff --git a/path-walk.h b/path-walk.h
index 2cafc71e153c19..3679fa7a859f67 100644
--- a/path-walk.h
+++ b/path-walk.h
@@ -39,12 +39,14 @@ struct path_walk_info {
 	int commits;
 	int trees;
 	int blobs;
+	int tags;
 };
 
 #define PATH_WALK_INFO_INIT {   \
 	.blobs = 1,		\
 	.trees = 1,		\
 	.commits = 1,		\
+	.tags = 1,		\
 }
 
 void path_walk_info_init(struct path_walk_info *info);
diff --git a/t/helper/test-path-walk.c b/t/helper/test-path-walk.c
index a57a05a6391fcb..56289859e69f8d 100644
--- a/t/helper/test-path-walk.c
+++ b/t/helper/test-path-walk.c
@@ -23,6 +23,7 @@ struct path_walk_test_data {
 	uintmax_t commit_nr;
 	uintmax_t tree_nr;
 	uintmax_t blob_nr;
+	uintmax_t tag_nr;
 };
 
 static int emit_block(const char *path, struct oid_array *oids,
@@ -37,11 +38,18 @@ static int emit_block(const char *path, struct oid_array *oids,
 		tdata->blob_nr += oids->nr;
 	else if (type == OBJ_COMMIT)
 		tdata->commit_nr += oids->nr;
+	else if (type == OBJ_TAG)
+		tdata->tag_nr += oids->nr;
 	else
 		BUG("we do not understand this type");
 
 	typestr = type_name(type);
 
+	/* This should never be output during tests. */
+	if (!oids->nr)
+		printf("%"PRIuMAX":%s:%s:EMPTY\n",
+		       tdata->batch_nr, typestr, path);
+
 	for (size_t i = 0; i < oids->nr; i++)
 		printf("%"PRIuMAX":%s:%s:%s\n",
 		       tdata->batch_nr, typestr, path,
@@ -62,6 +70,8 @@ int cmd__path_walk(int argc, const char **argv)
 			 N_("toggle inclusion of blob objects")),
 		OPT_BOOL(0, "commits", &info.commits,
 			 N_("toggle inclusion of commit objects")),
+		OPT_BOOL(0, "tags", &info.tags,
+			 N_("toggle inclusion of tag objects")),
 		OPT_BOOL(0, "trees", &info.trees,
 			 N_("toggle inclusion of tree objects")),
 		OPT_END(),
@@ -87,8 +97,9 @@ int cmd__path_walk(int argc, const char **argv)
 
 	printf("commits:%" PRIuMAX "\n"
 	       "trees:%" PRIuMAX "\n"
-	       "blobs:%" PRIuMAX "\n",
-	       data.commit_nr, data.tree_nr, data.blob_nr);
+	       "blobs:%" PRIuMAX "\n"
+	       "tags:%" PRIuMAX "\n",
+	       data.commit_nr, data.tree_nr, data.blob_nr, data.tag_nr);
 
 	release_revisions(&revs);
 	return res;
diff --git a/t/t6601-path-walk.sh b/t/t6601-path-walk.sh
index 4a4939a1b02bb1..1f3d2e0cb76a76 100755
--- a/t/t6601-path-walk.sh
+++ b/t/t6601-path-walk.sh
@@ -9,29 +9,142 @@ test_description='direct path-walk API tests'
 test_expect_success 'setup test repository' '
 	git checkout -b base &&
 
+	# Make some objects that will only be reachable
+	# via non-commit tags.
+	mkdir child &&
+	echo file >child/file &&
+	git add child &&
+	git commit -m "will abandon" &&
+	git tag -a -m "tree" tree-tag HEAD^{tree} &&
+	echo file2 >file2 &&
+	git add file2 &&
+	git commit --amend -m "will abandon" &&
+	git tag tree-tag2 HEAD^{tree} &&
+
+	echo blob >file &&
+	blob_oid=$(git hash-object -t blob -w --stdin <file) &&
+	git tag -a -m "blob" blob-tag "$blob_oid" &&
+	echo blob2 >file2 &&
+	blob2_oid=$(git hash-object -t blob -w --stdin <file2) &&
+	git tag blob-tag2 "$blob2_oid" &&
+
+	rm -fr child file file2 &&
+
 	mkdir left &&
 	mkdir right &&
 	echo a >a &&
 	echo b >left/b &&
 	echo c >right/c &&
 	git add . &&
-	git commit -m "first" &&
+	git commit --amend -m "first" &&
+	git tag -m "first" first HEAD &&
 
 	echo d >right/d &&
 	git add right &&
 	git commit -m "second" &&
+	git tag -a -m "second (under)" second.1 HEAD &&
+	git tag -a -m "second (top)" second.2 second.1 &&
 
+	# Set up file/dir collision in history.
+	rm a &&
+	mkdir a &&
+	echo a >a/a &&
 	echo bb >left/b &&
-	git commit -a -m "third" &&
+	git add a left &&
+	git commit -m "third" &&
+	git tag -a -m "third" third &&
 
 	git checkout -b topic HEAD~1 &&
 	echo cc >right/c &&
-	git commit -a -m "topic"
+	git commit -a -m "topic" &&
+	git tag -a -m "fourth" fourth
 '
 
 test_expect_success 'all' '
 	test-tool path-walk -- --all >out &&
 
+	cat >expect <<-EOF &&
+	0:commit::$(git rev-parse topic)
+	0:commit::$(git rev-parse base)
+	0:commit::$(git rev-parse base~1)
+	0:commit::$(git rev-parse base~2)
+	1:tag:/tags:$(git rev-parse refs/tags/first)
+	1:tag:/tags:$(git rev-parse refs/tags/second.1)
+	1:tag:/tags:$(git rev-parse refs/tags/second.2)
+	1:tag:/tags:$(git rev-parse refs/tags/third)
+	1:tag:/tags:$(git rev-parse refs/tags/fourth)
+	1:tag:/tags:$(git rev-parse refs/tags/tree-tag)
+	1:tag:/tags:$(git rev-parse refs/tags/blob-tag)
+	2:blob:/tagged-blobs:$(git rev-parse refs/tags/blob-tag^{})
+	2:blob:/tagged-blobs:$(git rev-parse refs/tags/blob-tag2^{})
+	3:tree::$(git rev-parse topic^{tree})
+	3:tree::$(git rev-parse base^{tree})
+	3:tree::$(git rev-parse base~1^{tree})
+	3:tree::$(git rev-parse base~2^{tree})
+	3:tree::$(git rev-parse refs/tags/tree-tag^{})
+	3:tree::$(git rev-parse refs/tags/tree-tag2^{})
+	4:blob:a:$(git rev-parse base~2:a)
+	5:tree:right/:$(git rev-parse topic:right)
+	5:tree:right/:$(git rev-parse base~1:right)
+	5:tree:right/:$(git rev-parse base~2:right)
+	6:blob:right/d:$(git rev-parse base~1:right/d)
+	7:blob:right/c:$(git rev-parse base~2:right/c)
+	7:blob:right/c:$(git rev-parse topic:right/c)
+	8:tree:left/:$(git rev-parse base:left)
+	8:tree:left/:$(git rev-parse base~2:left)
+	9:blob:left/b:$(git rev-parse base~2:left/b)
+	9:blob:left/b:$(git rev-parse base:left/b)
+	10:tree:a/:$(git rev-parse base:a)
+	11:blob:file2:$(git rev-parse refs/tags/tree-tag2^{}:file2)
+	12:tree:child/:$(git rev-parse refs/tags/tree-tag:child)
+	13:blob:child/file:$(git rev-parse refs/tags/tree-tag:child/file)
+	blobs:10
+	commits:4
+	tags:7
+	trees:13
+	EOF
+
+	test_cmp_sorted expect out
+'
+
+test_expect_success 'indexed objects' '
+	test_when_finished git reset --hard &&
+
+	# stage change into index, adding a blob but
+	# also invalidating the cache-tree for the root
+	# and the "left" directory.
+	echo bogus >left/c &&
+	git add left &&
+
+	test-tool path-walk -- --indexed-objects >out &&
+
+	cat >expect <<-EOF &&
+	0:blob:a:$(git rev-parse HEAD:a)
+	1:blob:left/b:$(git rev-parse HEAD:left/b)
+	2:blob:left/c:$(git rev-parse :left/c)
+	3:blob:right/c:$(git rev-parse HEAD:right/c)
+	4:blob:right/d:$(git rev-parse HEAD:right/d)
+	5:tree:right/:$(git rev-parse topic:right)
+	blobs:5
+	commits:0
+	tags:0
+	trees:1
+	EOF
+
+	test_cmp_sorted expect out
+'
+
+test_expect_success 'branches and indexed objects mix well' '
+	test_when_finished git reset --hard &&
+
+	# stage change into index, adding a blob but
+	# also invalidating the cache-tree for the root
+	# and the "right" directory.
+	echo fake >right/d &&
+	git add right &&
+
+	test-tool path-walk -- --indexed-objects --branches >out &&
+
 	cat >expect <<-EOF &&
 	0:commit::$(git rev-parse topic)
 	0:commit::$(git rev-parse base)
@@ -41,20 +154,23 @@ test_expect_success 'all' '
 	1:tree::$(git rev-parse base^{tree})
 	1:tree::$(git rev-parse base~1^{tree})
 	1:tree::$(git rev-parse base~2^{tree})
-	2:tree:right/:$(git rev-parse topic:right)
-	2:tree:right/:$(git rev-parse base~1:right)
-	2:tree:right/:$(git rev-parse base~2:right)
-	3:blob:right/d:$(git rev-parse base~1:right/d)
-	4:blob:right/c:$(git rev-parse base~2:right/c)
-	4:blob:right/c:$(git rev-parse topic:right/c)
-	5:tree:left/:$(git rev-parse base:left)
-	5:tree:left/:$(git rev-parse base~2:left)
-	6:blob:left/b:$(git rev-parse base~2:left/b)
-	6:blob:left/b:$(git rev-parse base:left/b)
-	7:blob:a:$(git rev-parse base~2:a)
-	blobs:6
+	2:blob:a:$(git rev-parse base~2:a)
+	3:tree:right/:$(git rev-parse topic:right)
+	3:tree:right/:$(git rev-parse base~1:right)
+	3:tree:right/:$(git rev-parse base~2:right)
+	4:blob:right/d:$(git rev-parse base~1:right/d)
+	4:blob:right/d:$(git rev-parse :right/d)
+	5:blob:right/c:$(git rev-parse base~2:right/c)
+	5:blob:right/c:$(git rev-parse topic:right/c)
+	6:tree:left/:$(git rev-parse base:left)
+	6:tree:left/:$(git rev-parse base~2:left)
+	7:blob:left/b:$(git rev-parse base:left/b)
+	7:blob:left/b:$(git rev-parse base~2:left/b)
+	8:tree:a/:$(git rev-parse refs/tags/third:a)
+	blobs:7
 	commits:4
-	trees:9
+	tags:0
+	trees:10
 	EOF
 
 	test_cmp_sorted expect out
@@ -81,6 +197,7 @@ test_expect_success 'topic only' '
 	7:blob:a:$(git rev-parse base~2:a)
 	blobs:5
 	commits:3
+	tags:0
 	trees:7
 	EOF
 
@@ -101,6 +218,7 @@ test_expect_success 'topic, not base' '
 	7:blob:a:$(git rev-parse topic:a)
 	blobs:4
 	commits:1
+	tags:0
 	trees:3
 	EOF
 
@@ -112,13 +230,14 @@ test_expect_success 'topic, not base, only blobs' '
 		-- topic --not base >out &&
 
 	cat >expect <<-EOF &&
-	commits:0
-	trees:0
 	0:blob:right/d:$(git rev-parse topic:right/d)
 	1:blob:right/c:$(git rev-parse topic:right/c)
 	2:blob:left/b:$(git rev-parse topic:left/b)
 	3:blob:a:$(git rev-parse topic:a)
 	blobs:4
+	commits:0
+	tags:0
+	trees:0
 	EOF
 
 	test_cmp_sorted expect out
@@ -133,8 +252,9 @@ test_expect_success 'topic, not base, only commits' '
 	cat >expect <<-EOF &&
 	0:commit::$(git rev-parse topic)
 	commits:1
-	trees:0
 	blobs:0
+	tags:0
+	trees:0
 	EOF
 
 	test_cmp_sorted expect out
@@ -145,12 +265,13 @@ test_expect_success 'topic, not base, only trees' '
 		-- topic --not base >out &&
 
 	cat >expect <<-EOF &&
-	commits:0
 	0:tree::$(git rev-parse topic^{tree})
 	1:tree:right/:$(git rev-parse topic:right)
 	2:tree:left/:$(git rev-parse topic:left)
-	trees:3
+	commits:0
 	blobs:0
+	tags:0
+	trees:3
 	EOF
 
 	test_cmp_sorted expect out
@@ -174,10 +295,33 @@ test_expect_success 'topic, not base, boundary' '
 	7:blob:a:$(git rev-parse base~1:a)
 	blobs:5
 	commits:2
+	tags:0
 	trees:5
 	EOF
 
 	test_cmp_sorted expect out
 '
 
+test_expect_success 'trees are reported exactly once' '
+	test_when_finished "rm -rf unique-trees" &&
+	test_create_repo unique-trees &&
+	(
+		cd unique-trees &&
+		mkdir initial &&
+		test_commit initial/file &&
+
+		git switch -c move-to-top &&
+		git mv initial/file.t ./ &&
+		test_tick &&
+		git commit -m moved &&
+
+		git update-ref refs/heads/other HEAD
+	) &&
+
+	test-tool -C unique-trees path-walk -- --all >out &&
+	tree=$(git -C unique-trees rev-parse HEAD:) &&
+	grep "$tree" out >out-filtered &&
+	test_line_count = 1 out-filtered
+'
+
 test_done

From f2ffc32a3033549420fb9e3a902cce1cc739440e Mon Sep 17 00:00:00 2001
From: Derrick Stolee <stolee@gmail.com>
Date: Tue, 3 Sep 2024 21:55:47 -0400
Subject: [PATCH 6/7] path-walk: mark trees and blobs as UNINTERESTING

When the input rev_info has UNINTERESTING starting points, we want to be
sure that the UNINTERESTING flag is passed appropriately through the
objects. To match how this is done in places such as 'git pack-objects', we
use the mark_edges_uninteresting() method.

This method has an option for using the "sparse" walk, which is similar in
spirit to the path-walk API's walk. To be sure to keep it independent, add a
new 'prune_all_uninteresting' option to the path_walk_info struct.

To check how the UNINTERSTING flag is spread through our objects, extend the
'test-tool path-walk' command to output whether or not an object has that
flag. This changes our tests significantly, including the removal of some
objects that were previously visited due to the incomplete implementation.

Signed-off-by: Derrick Stolee <stolee@gmail.com>
---
 Documentation/technical/api-path-walk.txt |  8 +++
 path-walk.c                               | 74 +++++++++++++++++++++
 path-walk.h                               |  8 +++
 t/helper/test-path-walk.c                 | 12 +++-
 t/t6601-path-walk.sh                      | 79 +++++++++++++++++------
 5 files changed, 159 insertions(+), 22 deletions(-)

diff --git a/Documentation/technical/api-path-walk.txt b/Documentation/technical/api-path-walk.txt
index 6022c381b7c3f0..7075d0d5ab50fd 100644
--- a/Documentation/technical/api-path-walk.txt
+++ b/Documentation/technical/api-path-walk.txt
@@ -48,6 +48,14 @@ commits.
 While it is possible to walk only commits in this way, consumers would be
 better off using the revision walk API instead.
 
+`prune_all_uninteresting`::
+	By default, all reachable paths are emitted by the path-walk API.
+	This option allows consumers to declare that they are not
+	interested in paths where all included objects are marked with the
+	`UNINTERESTING` flag. This requires using the `boundary` option in
+	the revision walk so that the walk emits commits marked with the
+	`UNINTERESTING` flag.
+
 Examples
 --------
 
diff --git a/path-walk.c b/path-walk.c
index f34dbf61de0a0f..4013569e9e4cbe 100644
--- a/path-walk.c
+++ b/path-walk.c
@@ -8,6 +8,7 @@
 #include "dir.h"
 #include "hashmap.h"
 #include "hex.h"
+#include "list-objects.h"
 #include "object.h"
 #include "oid-array.h"
 #include "revision.h"
@@ -23,6 +24,7 @@ static const char *root_path = "";
 struct type_and_oid_list {
 	enum object_type type;
 	struct oid_array oids;
+	int maybe_interesting;
 };
 
 #define TYPE_AND_OID_LIST_INIT { \
@@ -142,6 +144,10 @@ static int add_tree_entries(struct path_walk_context *ctx,
 			strmap_put(&ctx->paths_to_lists, path.buf, list);
 		}
 		push_to_stack(ctx, path.buf);
+
+		if (!(o->flags & UNINTERESTING))
+			list->maybe_interesting = 1;
+
 		oid_array_append(&list->oids, &entry.oid);
 	}
 
@@ -169,6 +175,43 @@ static int walk_path(struct path_walk_context *ctx,
 	if (!list->oids.nr)
 		return 0;
 
+	if (ctx->info->prune_all_uninteresting) {
+		/*
+		 * This is true if all objects were UNINTERESTING
+		 * when added to the list.
+		 */
+		if (!list->maybe_interesting)
+			return 0;
+
+		/*
+		 * But it's still possible that the objects were set
+		 * as UNINTERESTING after being added. Do a quick check.
+		 */
+		list->maybe_interesting = 0;
+		for (size_t i = 0;
+		     !list->maybe_interesting && i < list->oids.nr;
+		     i++) {
+			if (list->type == OBJ_TREE) {
+				struct tree *t = lookup_tree(ctx->repo,
+							     &list->oids.oid[i]);
+				if (t && !(t->object.flags & UNINTERESTING))
+					list->maybe_interesting = 1;
+			} else if (list->type == OBJ_BLOB) {
+				struct blob *b = lookup_blob(ctx->repo,
+							     &list->oids.oid[i]);
+				if (b && !(b->object.flags & UNINTERESTING))
+					list->maybe_interesting = 1;
+			} else {
+				/* Tags are always interesting if visited. */
+				list->maybe_interesting = 1;
+			}
+		}
+
+		/* We have confirmed that all objects are UNINTERESTING. */
+		if (!list->maybe_interesting)
+			return 0;
+	}
+
 	/* Evaluate function pointer on this data, if requested. */
 	if ((list->type == OBJ_TREE && ctx->info->trees) ||
 	    (list->type == OBJ_BLOB && ctx->info->blobs) ||
@@ -203,6 +246,26 @@ static void clear_paths_to_lists(struct strmap *map)
 	strmap_init(map);
 }
 
+static struct repository *edge_repo;
+static struct type_and_oid_list *edge_tree_list;
+
+static void show_edge(struct commit *commit)
+{
+	struct tree *t = repo_get_commit_tree(edge_repo, commit);
+
+	if (!t)
+		return;
+
+	if (commit->object.flags & UNINTERESTING)
+		t->object.flags |= UNINTERESTING;
+
+	if (t->object.flags & SEEN)
+		return;
+	t->object.flags |= SEEN;
+
+	oid_array_append(&edge_tree_list->oids, &t->object.oid);
+}
+
 static int setup_pending_objects(struct path_walk_info *info,
 				 struct path_walk_context *ctx)
 {
@@ -314,6 +377,7 @@ static int setup_pending_objects(struct path_walk_info *info,
 		if (tagged_blobs->oids.nr) {
 			const char *tagged_blob_path = "/tagged-blobs";
 			tagged_blobs->type = OBJ_BLOB;
+			tagged_blobs->maybe_interesting = 1;
 			push_to_stack(ctx, tagged_blob_path);
 			strmap_put(&ctx->paths_to_lists, tagged_blob_path, tagged_blobs);
 		} else {
@@ -325,6 +389,7 @@ static int setup_pending_objects(struct path_walk_info *info,
 		if (tags->oids.nr) {
 			const char *tag_path = "/tags";
 			tags->type = OBJ_TAG;
+			tags->maybe_interesting = 1;
 			push_to_stack(ctx, tag_path);
 			strmap_put(&ctx->paths_to_lists, tag_path, tags);
 		} else {
@@ -369,6 +434,7 @@ int walk_objects_by_path(struct path_walk_info *info)
 	/* Insert a single list for the root tree into the paths. */
 	CALLOC_ARRAY(root_tree_list, 1);
 	root_tree_list->type = OBJ_TREE;
+	root_tree_list->maybe_interesting = 1;
 	strmap_put(&ctx.paths_to_lists, root_path, root_tree_list);
 	push_to_stack(&ctx, root_path);
 
@@ -382,6 +448,14 @@ int walk_objects_by_path(struct path_walk_info *info)
 	if (prepare_revision_walk(info->revs))
 		die(_("failed to setup revision walk"));
 
+	/* Walk trees to mark them as UNINTERESTING. */
+	edge_repo = info->revs->repo;
+	edge_tree_list = root_tree_list;
+	mark_edges_uninteresting(info->revs, show_edge,
+				 info->prune_all_uninteresting);
+	edge_repo = NULL;
+	edge_tree_list = NULL;
+
 	info->revs->blob_objects = info->revs->tree_objects = 0;
 
 	trace2_region_enter("path-walk", "pending-walk", info->revs->repo);
diff --git a/path-walk.h b/path-walk.h
index 3679fa7a859f67..414d6db23c23b6 100644
--- a/path-walk.h
+++ b/path-walk.h
@@ -40,6 +40,14 @@ struct path_walk_info {
 	int trees;
 	int blobs;
 	int tags;
+
+	/**
+	 * When 'prune_all_uninteresting' is set and a path has all objects
+	 * marked as UNINTERESTING, then the path-walk will not visit those
+	 * objects. It will not call path_fn on those objects and will not
+	 * walk the children of such trees.
+	 */
+	int prune_all_uninteresting;
 };
 
 #define PATH_WALK_INFO_INIT {   \
diff --git a/t/helper/test-path-walk.c b/t/helper/test-path-walk.c
index 56289859e69f8d..7f2d409c5bca63 100644
--- a/t/helper/test-path-walk.c
+++ b/t/helper/test-path-walk.c
@@ -50,10 +50,14 @@ static int emit_block(const char *path, struct oid_array *oids,
 		printf("%"PRIuMAX":%s:%s:EMPTY\n",
 		       tdata->batch_nr, typestr, path);
 
-	for (size_t i = 0; i < oids->nr; i++)
-		printf("%"PRIuMAX":%s:%s:%s\n",
+	for (size_t i = 0; i < oids->nr; i++) {
+		struct object *o = lookup_unknown_object(the_repository,
+							 &oids->oid[i]);
+		printf("%"PRIuMAX":%s:%s:%s%s\n",
 		       tdata->batch_nr, typestr, path,
-		       oid_to_hex(&oids->oid[i]));
+		       oid_to_hex(&oids->oid[i]),
+		       o->flags & UNINTERESTING ? ":UNINTERESTING" : "");
+	}
 
 	tdata->batch_nr++;
 	return 0;
@@ -74,6 +78,8 @@ int cmd__path_walk(int argc, const char **argv)
 			 N_("toggle inclusion of tag objects")),
 		OPT_BOOL(0, "trees", &info.trees,
 			 N_("toggle inclusion of tree objects")),
+		OPT_BOOL(0, "prune", &info.prune_all_uninteresting,
+			 N_("toggle pruning of uninteresting paths")),
 		OPT_END(),
 	};
 
diff --git a/t/t6601-path-walk.sh b/t/t6601-path-walk.sh
index 1f3d2e0cb76a76..a317cdf289e278 100755
--- a/t/t6601-path-walk.sh
+++ b/t/t6601-path-walk.sh
@@ -211,11 +211,11 @@ test_expect_success 'topic, not base' '
 	0:commit::$(git rev-parse topic)
 	1:tree::$(git rev-parse topic^{tree})
 	2:tree:right/:$(git rev-parse topic:right)
-	3:blob:right/d:$(git rev-parse topic:right/d)
+	3:blob:right/d:$(git rev-parse topic:right/d):UNINTERESTING
 	4:blob:right/c:$(git rev-parse topic:right/c)
-	5:tree:left/:$(git rev-parse topic:left)
-	6:blob:left/b:$(git rev-parse topic:left/b)
-	7:blob:a:$(git rev-parse topic:a)
+	5:tree:left/:$(git rev-parse topic:left):UNINTERESTING
+	6:blob:left/b:$(git rev-parse topic:left/b):UNINTERESTING
+	7:blob:a:$(git rev-parse topic:a):UNINTERESTING
 	blobs:4
 	commits:1
 	tags:0
@@ -225,15 +225,38 @@ test_expect_success 'topic, not base' '
 	test_cmp_sorted expect out
 '
 
+test_expect_success 'fourth, blob-tag2, not base' '
+	test-tool path-walk -- fourth blob-tag2 --not base >out &&
+
+	cat >expect <<-EOF &&
+	0:commit::$(git rev-parse topic)
+	1:tag:/tags:$(git rev-parse fourth)
+	2:blob:/tagged-blobs:$(git rev-parse refs/tags/blob-tag2^{})
+	3:tree::$(git rev-parse topic^{tree})
+	4:tree:right/:$(git rev-parse topic:right)
+	5:blob:right/d:$(git rev-parse base~1:right/d):UNINTERESTING
+	6:blob:right/c:$(git rev-parse topic:right/c)
+	7:tree:left/:$(git rev-parse base~1:left):UNINTERESTING
+	8:blob:left/b:$(git rev-parse base~1:left/b):UNINTERESTING
+	9:blob:a:$(git rev-parse base~1:a):UNINTERESTING
+	blobs:5
+	commits:1
+	tags:1
+	trees:3
+	EOF
+
+	test_cmp_sorted expect out
+'
+
 test_expect_success 'topic, not base, only blobs' '
 	test-tool path-walk --no-trees --no-commits \
 		-- topic --not base >out &&
 
 	cat >expect <<-EOF &&
-	0:blob:right/d:$(git rev-parse topic:right/d)
+	0:blob:right/d:$(git rev-parse topic:right/d):UNINTERESTING
 	1:blob:right/c:$(git rev-parse topic:right/c)
-	2:blob:left/b:$(git rev-parse topic:left/b)
-	3:blob:a:$(git rev-parse topic:a)
+	2:blob:left/b:$(git rev-parse topic:left/b):UNINTERESTING
+	3:blob:a:$(git rev-parse topic:a):UNINTERESTING
 	blobs:4
 	commits:0
 	tags:0
@@ -267,7 +290,7 @@ test_expect_success 'topic, not base, only trees' '
 	cat >expect <<-EOF &&
 	0:tree::$(git rev-parse topic^{tree})
 	1:tree:right/:$(git rev-parse topic:right)
-	2:tree:left/:$(git rev-parse topic:left)
+	2:tree:left/:$(git rev-parse topic:left):UNINTERESTING
 	commits:0
 	blobs:0
 	tags:0
@@ -282,17 +305,17 @@ test_expect_success 'topic, not base, boundary' '
 
 	cat >expect <<-EOF &&
 	0:commit::$(git rev-parse topic)
-	0:commit::$(git rev-parse base~1)
+	0:commit::$(git rev-parse base~1):UNINTERESTING
 	1:tree::$(git rev-parse topic^{tree})
-	1:tree::$(git rev-parse base~1^{tree})
+	1:tree::$(git rev-parse base~1^{tree}):UNINTERESTING
 	2:tree:right/:$(git rev-parse topic:right)
-	2:tree:right/:$(git rev-parse base~1:right)
-	3:blob:right/d:$(git rev-parse base~1:right/d)
-	4:blob:right/c:$(git rev-parse base~1:right/c)
+	2:tree:right/:$(git rev-parse base~1:right):UNINTERESTING
+	3:blob:right/d:$(git rev-parse base~1:right/d):UNINTERESTING
+	4:blob:right/c:$(git rev-parse base~1:right/c):UNINTERESTING
 	4:blob:right/c:$(git rev-parse topic:right/c)
-	5:tree:left/:$(git rev-parse base~1:left)
-	6:blob:left/b:$(git rev-parse base~1:left/b)
-	7:blob:a:$(git rev-parse base~1:a)
+	5:tree:left/:$(git rev-parse base~1:left):UNINTERESTING
+	6:blob:left/b:$(git rev-parse base~1:left/b):UNINTERESTING
+	7:blob:a:$(git rev-parse base~1:a):UNINTERESTING
 	blobs:5
 	commits:2
 	tags:0
@@ -302,6 +325,27 @@ test_expect_success 'topic, not base, boundary' '
 	test_cmp_sorted expect out
 '
 
+test_expect_success 'topic, not base, boundary with pruning' '
+	test-tool path-walk --prune -- --boundary topic --not base >out &&
+
+	cat >expect <<-EOF &&
+	0:commit::$(git rev-parse topic)
+	0:commit::$(git rev-parse base~1):UNINTERESTING
+	1:tree::$(git rev-parse topic^{tree})
+	1:tree::$(git rev-parse base~1^{tree}):UNINTERESTING
+	2:tree:right/:$(git rev-parse topic:right)
+	2:tree:right/:$(git rev-parse base~1:right):UNINTERESTING
+	3:blob:right/c:$(git rev-parse base~1:right/c):UNINTERESTING
+	3:blob:right/c:$(git rev-parse topic:right/c)
+	blobs:2
+	commits:2
+	tags:0
+	trees:4
+	EOF
+
+	test_cmp_sorted expect out
+'
+
 test_expect_success 'trees are reported exactly once' '
 	test_when_finished "rm -rf unique-trees" &&
 	test_create_repo unique-trees &&
@@ -309,15 +353,12 @@ test_expect_success 'trees are reported exactly once' '
 		cd unique-trees &&
 		mkdir initial &&
 		test_commit initial/file &&
-
 		git switch -c move-to-top &&
 		git mv initial/file.t ./ &&
 		test_tick &&
 		git commit -m moved &&
-
 		git update-ref refs/heads/other HEAD
 	) &&
-
 	test-tool -C unique-trees path-walk -- --all >out &&
 	tree=$(git -C unique-trees rev-parse HEAD:) &&
 	grep "$tree" out >out-filtered &&

From ef543429ed9cb92e209900e7c7fc4f8e0698a306 Mon Sep 17 00:00:00 2001
From: Derrick Stolee <stolee@gmail.com>
Date: Tue, 3 Dec 2024 16:33:46 -0500
Subject: [PATCH 7/7] path-walk: reorder object visits

The path-walk API currently uses a stack-based approach to recursing
through the list of paths within the repository. This guarantees that
after a tree path is explored, all paths contained within that tree path
will be explored before continuing to explore siblings of that tree
path.

The initial motivation of this depth-first approach was to minimize
memory pressure while exploring the repository. A breadth-first approach
would have too many "active" paths being stored in the paths_to_lists
map.

We can take this approach one step further by making sure that blob
paths are visited before tree paths. This allows the API to free the
memory for these blob objects before continuing to perform the
depth-first search. This modifies the order in which we visit siblings,
but does not change the fact that we are performing depth-first search.

To achieve this goal, use a priority queue with a custom sorting method.
The sort needs to handle tags, blobs, and trees (commits are handled
slightly differently). When objects share a type, we can sort by path
name. This will keep children of the latest path to leave the stack be
preferred over the rest of the paths in the stack, since they agree in
prefix up to and including a directory separator. When the types are
different, we can prefer tags over other types and blobs over trees.

This causes significant adjustments to t6601-path-walk.sh to rearrange
the order of the visited paths.

Signed-off-by: Derrick Stolee <stolee@gmail.com>
---
 path-walk.c          |  60 ++++++++++++++++-----
 t/t6601-path-walk.sh | 124 +++++++++++++++++++++----------------------
 2 files changed, 110 insertions(+), 74 deletions(-)

diff --git a/path-walk.c b/path-walk.c
index 4013569e9e4cbe..136ec08fb0ed72 100644
--- a/path-walk.c
+++ b/path-walk.c
@@ -11,6 +11,7 @@
 #include "list-objects.h"
 #include "object.h"
 #include "oid-array.h"
+#include "prio-queue.h"
 #include "revision.h"
 #include "string-list.h"
 #include "strmap.h"
@@ -49,16 +50,50 @@ struct path_walk_context {
 	struct strmap paths_to_lists;
 
 	/**
-	 * Store the current list of paths in a stack, to
-	 * facilitate depth-first-search without recursion.
+	 * Store the current list of paths in a priority queue,
+	 * using object type as a sorting mechanism, mostly to
+	 * make sure blobs are popped off the stack first. No
+	 * other sort is made, so within each object type it acts
+	 * like a stack and performs a DFS within the trees.
 	 *
 	 * Use path_stack_pushed to indicate whether a path
 	 * was previously added to path_stack.
 	 */
-	struct string_list path_stack;
+	struct prio_queue path_stack;
 	struct strset path_stack_pushed;
 };
 
+static int compare_by_type(const void *one, const void *two, void *cb_data)
+{
+	struct type_and_oid_list *list1, *list2;
+	const char *str1 = one;
+	const char *str2 = two;
+	struct path_walk_context *ctx = cb_data;
+
+	list1 = strmap_get(&ctx->paths_to_lists, str1);
+	list2 = strmap_get(&ctx->paths_to_lists, str2);
+
+	/*
+	 * If object types are equal, then use path comparison.
+	 */
+	if (!list1 || !list2 || list1->type == list2->type)
+		return strcmp(str1, str2);
+
+	/* Prefer tags to be popped off first. */
+	if (list1->type == OBJ_TAG)
+		return -1;
+	if (list2->type == OBJ_TAG)
+		return 1;
+
+	/* Prefer blobs to be popped off second. */
+	if (list1->type == OBJ_BLOB)
+		return -1;
+	if (list2->type == OBJ_BLOB)
+		return 1;
+
+	return 0;
+}
+
 static void push_to_stack(struct path_walk_context *ctx,
 			  const char *path)
 {
@@ -66,7 +101,7 @@ static void push_to_stack(struct path_walk_context *ctx,
 		return;
 
 	strset_add(&ctx->path_stack_pushed, path);
-	string_list_append(&ctx->path_stack, path);
+	prio_queue_put(&ctx->path_stack, xstrdup(path));
 }
 
 static int add_tree_entries(struct path_walk_context *ctx,
@@ -378,8 +413,8 @@ static int setup_pending_objects(struct path_walk_info *info,
 			const char *tagged_blob_path = "/tagged-blobs";
 			tagged_blobs->type = OBJ_BLOB;
 			tagged_blobs->maybe_interesting = 1;
-			push_to_stack(ctx, tagged_blob_path);
 			strmap_put(&ctx->paths_to_lists, tagged_blob_path, tagged_blobs);
+			push_to_stack(ctx, tagged_blob_path);
 		} else {
 			oid_array_clear(&tagged_blobs->oids);
 			free(tagged_blobs);
@@ -390,8 +425,8 @@ static int setup_pending_objects(struct path_walk_info *info,
 			const char *tag_path = "/tags";
 			tags->type = OBJ_TAG;
 			tags->maybe_interesting = 1;
-			push_to_stack(ctx, tag_path);
 			strmap_put(&ctx->paths_to_lists, tag_path, tags);
+			push_to_stack(ctx, tag_path);
 		} else {
 			oid_array_clear(&tags->oids);
 			free(tags);
@@ -418,7 +453,10 @@ int walk_objects_by_path(struct path_walk_info *info)
 		.repo = info->revs->repo,
 		.revs = info->revs,
 		.info = info,
-		.path_stack = STRING_LIST_INIT_DUP,
+		.path_stack = {
+			.compare = compare_by_type,
+			.cb_data = &ctx
+		},
 		.path_stack_pushed = STRSET_INIT,
 		.paths_to_lists = STRMAP_INIT
 	};
@@ -504,8 +542,7 @@ int walk_objects_by_path(struct path_walk_info *info)
 
 	trace2_region_enter("path-walk", "path-walk", info->revs->repo);
 	while (!ret && ctx.path_stack.nr) {
-		char *path = ctx.path_stack.items[ctx.path_stack.nr - 1].string;
-		ctx.path_stack.nr--;
+		char *path = prio_queue_get(&ctx.path_stack);
 		paths_nr++;
 
 		ret = walk_path(&ctx, path);
@@ -522,8 +559,7 @@ int walk_objects_by_path(struct path_walk_info *info)
 			push_to_stack(&ctx, entry->key);
 
 		while (!ret && ctx.path_stack.nr) {
-			char *path = ctx.path_stack.items[ctx.path_stack.nr - 1].string;
-			ctx.path_stack.nr--;
+			char *path = prio_queue_get(&ctx.path_stack);
 			paths_nr++;
 
 			ret = walk_path(&ctx, path);
@@ -537,7 +573,7 @@ int walk_objects_by_path(struct path_walk_info *info)
 
 	clear_paths_to_lists(&ctx.paths_to_lists);
 	strset_clear(&ctx.path_stack_pushed);
-	string_list_clear(&ctx.path_stack, 0);
+	clear_prio_queue(&ctx.path_stack);
 	return ret;
 }
 
diff --git a/t/t6601-path-walk.sh b/t/t6601-path-walk.sh
index a317cdf289e278..5f04acb8a2f79a 100755
--- a/t/t6601-path-walk.sh
+++ b/t/t6601-path-walk.sh
@@ -84,20 +84,20 @@ test_expect_success 'all' '
 	3:tree::$(git rev-parse refs/tags/tree-tag^{})
 	3:tree::$(git rev-parse refs/tags/tree-tag2^{})
 	4:blob:a:$(git rev-parse base~2:a)
-	5:tree:right/:$(git rev-parse topic:right)
-	5:tree:right/:$(git rev-parse base~1:right)
-	5:tree:right/:$(git rev-parse base~2:right)
-	6:blob:right/d:$(git rev-parse base~1:right/d)
-	7:blob:right/c:$(git rev-parse base~2:right/c)
-	7:blob:right/c:$(git rev-parse topic:right/c)
-	8:tree:left/:$(git rev-parse base:left)
-	8:tree:left/:$(git rev-parse base~2:left)
-	9:blob:left/b:$(git rev-parse base~2:left/b)
-	9:blob:left/b:$(git rev-parse base:left/b)
-	10:tree:a/:$(git rev-parse base:a)
-	11:blob:file2:$(git rev-parse refs/tags/tree-tag2^{}:file2)
-	12:tree:child/:$(git rev-parse refs/tags/tree-tag:child)
-	13:blob:child/file:$(git rev-parse refs/tags/tree-tag:child/file)
+	5:blob:file2:$(git rev-parse refs/tags/tree-tag2^{}:file2)
+	6:tree:a/:$(git rev-parse base:a)
+	7:tree:child/:$(git rev-parse refs/tags/tree-tag:child)
+	8:blob:child/file:$(git rev-parse refs/tags/tree-tag:child/file)
+	9:tree:left/:$(git rev-parse base:left)
+	9:tree:left/:$(git rev-parse base~2:left)
+	10:blob:left/b:$(git rev-parse base~2:left/b)
+	10:blob:left/b:$(git rev-parse base:left/b)
+	11:tree:right/:$(git rev-parse topic:right)
+	11:tree:right/:$(git rev-parse base~1:right)
+	11:tree:right/:$(git rev-parse base~2:right)
+	12:blob:right/c:$(git rev-parse base~2:right/c)
+	12:blob:right/c:$(git rev-parse topic:right/c)
+	13:blob:right/d:$(git rev-parse base~1:right/d)
 	blobs:10
 	commits:4
 	tags:7
@@ -154,19 +154,19 @@ test_expect_success 'branches and indexed objects mix well' '
 	1:tree::$(git rev-parse base^{tree})
 	1:tree::$(git rev-parse base~1^{tree})
 	1:tree::$(git rev-parse base~2^{tree})
-	2:blob:a:$(git rev-parse base~2:a)
-	3:tree:right/:$(git rev-parse topic:right)
-	3:tree:right/:$(git rev-parse base~1:right)
-	3:tree:right/:$(git rev-parse base~2:right)
-	4:blob:right/d:$(git rev-parse base~1:right/d)
-	4:blob:right/d:$(git rev-parse :right/d)
-	5:blob:right/c:$(git rev-parse base~2:right/c)
-	5:blob:right/c:$(git rev-parse topic:right/c)
-	6:tree:left/:$(git rev-parse base:left)
-	6:tree:left/:$(git rev-parse base~2:left)
-	7:blob:left/b:$(git rev-parse base:left/b)
-	7:blob:left/b:$(git rev-parse base~2:left/b)
-	8:tree:a/:$(git rev-parse refs/tags/third:a)
+	2:tree:a/:$(git rev-parse refs/tags/third:a)
+	3:tree:left/:$(git rev-parse base:left)
+	3:tree:left/:$(git rev-parse base~2:left)
+	4:blob:left/b:$(git rev-parse base:left/b)
+	4:blob:left/b:$(git rev-parse base~2:left/b)
+	5:tree:right/:$(git rev-parse topic:right)
+	5:tree:right/:$(git rev-parse base~1:right)
+	5:tree:right/:$(git rev-parse base~2:right)
+	6:blob:right/c:$(git rev-parse base~2:right/c)
+	6:blob:right/c:$(git rev-parse topic:right/c)
+	7:blob:right/d:$(git rev-parse base~1:right/d)
+	7:blob:right/d:$(git rev-parse :right/d)
+	8:blob:a:$(git rev-parse base~2:a)
 	blobs:7
 	commits:4
 	tags:0
@@ -186,15 +186,15 @@ test_expect_success 'topic only' '
 	1:tree::$(git rev-parse topic^{tree})
 	1:tree::$(git rev-parse base~1^{tree})
 	1:tree::$(git rev-parse base~2^{tree})
-	2:tree:right/:$(git rev-parse topic:right)
-	2:tree:right/:$(git rev-parse base~1:right)
-	2:tree:right/:$(git rev-parse base~2:right)
-	3:blob:right/d:$(git rev-parse base~1:right/d)
-	4:blob:right/c:$(git rev-parse base~2:right/c)
-	4:blob:right/c:$(git rev-parse topic:right/c)
-	5:tree:left/:$(git rev-parse base~2:left)
-	6:blob:left/b:$(git rev-parse base~2:left/b)
-	7:blob:a:$(git rev-parse base~2:a)
+	2:blob:a:$(git rev-parse base~2:a)
+	3:tree:left/:$(git rev-parse base~2:left)
+	4:blob:left/b:$(git rev-parse base~2:left/b)
+	5:tree:right/:$(git rev-parse topic:right)
+	5:tree:right/:$(git rev-parse base~1:right)
+	5:tree:right/:$(git rev-parse base~2:right)
+	6:blob:right/c:$(git rev-parse base~2:right/c)
+	6:blob:right/c:$(git rev-parse topic:right/c)
+	7:blob:right/d:$(git rev-parse base~1:right/d)
 	blobs:5
 	commits:3
 	tags:0
@@ -210,12 +210,12 @@ test_expect_success 'topic, not base' '
 	cat >expect <<-EOF &&
 	0:commit::$(git rev-parse topic)
 	1:tree::$(git rev-parse topic^{tree})
-	2:tree:right/:$(git rev-parse topic:right)
-	3:blob:right/d:$(git rev-parse topic:right/d):UNINTERESTING
-	4:blob:right/c:$(git rev-parse topic:right/c)
-	5:tree:left/:$(git rev-parse topic:left):UNINTERESTING
-	6:blob:left/b:$(git rev-parse topic:left/b):UNINTERESTING
-	7:blob:a:$(git rev-parse topic:a):UNINTERESTING
+	2:blob:a:$(git rev-parse topic:a):UNINTERESTING
+	3:tree:left/:$(git rev-parse topic:left):UNINTERESTING
+	4:blob:left/b:$(git rev-parse topic:left/b):UNINTERESTING
+	5:tree:right/:$(git rev-parse topic:right)
+	6:blob:right/c:$(git rev-parse topic:right/c)
+	7:blob:right/d:$(git rev-parse topic:right/d):UNINTERESTING
 	blobs:4
 	commits:1
 	tags:0
@@ -233,12 +233,12 @@ test_expect_success 'fourth, blob-tag2, not base' '
 	1:tag:/tags:$(git rev-parse fourth)
 	2:blob:/tagged-blobs:$(git rev-parse refs/tags/blob-tag2^{})
 	3:tree::$(git rev-parse topic^{tree})
-	4:tree:right/:$(git rev-parse topic:right)
-	5:blob:right/d:$(git rev-parse base~1:right/d):UNINTERESTING
-	6:blob:right/c:$(git rev-parse topic:right/c)
-	7:tree:left/:$(git rev-parse base~1:left):UNINTERESTING
-	8:blob:left/b:$(git rev-parse base~1:left/b):UNINTERESTING
-	9:blob:a:$(git rev-parse base~1:a):UNINTERESTING
+	4:blob:a:$(git rev-parse base~1:a):UNINTERESTING
+	5:tree:left/:$(git rev-parse base~1:left):UNINTERESTING
+	6:blob:left/b:$(git rev-parse base~1:left/b):UNINTERESTING
+	7:tree:right/:$(git rev-parse topic:right)
+	8:blob:right/c:$(git rev-parse topic:right/c)
+	9:blob:right/d:$(git rev-parse base~1:right/d):UNINTERESTING
 	blobs:5
 	commits:1
 	tags:1
@@ -253,10 +253,10 @@ test_expect_success 'topic, not base, only blobs' '
 		-- topic --not base >out &&
 
 	cat >expect <<-EOF &&
-	0:blob:right/d:$(git rev-parse topic:right/d):UNINTERESTING
-	1:blob:right/c:$(git rev-parse topic:right/c)
-	2:blob:left/b:$(git rev-parse topic:left/b):UNINTERESTING
-	3:blob:a:$(git rev-parse topic:a):UNINTERESTING
+	0:blob:a:$(git rev-parse topic:a):UNINTERESTING
+	1:blob:left/b:$(git rev-parse topic:left/b):UNINTERESTING
+	2:blob:right/c:$(git rev-parse topic:right/c)
+	3:blob:right/d:$(git rev-parse topic:right/d):UNINTERESTING
 	blobs:4
 	commits:0
 	tags:0
@@ -289,8 +289,8 @@ test_expect_success 'topic, not base, only trees' '
 
 	cat >expect <<-EOF &&
 	0:tree::$(git rev-parse topic^{tree})
-	1:tree:right/:$(git rev-parse topic:right)
-	2:tree:left/:$(git rev-parse topic:left):UNINTERESTING
+	1:tree:left/:$(git rev-parse topic:left):UNINTERESTING
+	2:tree:right/:$(git rev-parse topic:right)
 	commits:0
 	blobs:0
 	tags:0
@@ -308,14 +308,14 @@ test_expect_success 'topic, not base, boundary' '
 	0:commit::$(git rev-parse base~1):UNINTERESTING
 	1:tree::$(git rev-parse topic^{tree})
 	1:tree::$(git rev-parse base~1^{tree}):UNINTERESTING
-	2:tree:right/:$(git rev-parse topic:right)
-	2:tree:right/:$(git rev-parse base~1:right):UNINTERESTING
-	3:blob:right/d:$(git rev-parse base~1:right/d):UNINTERESTING
-	4:blob:right/c:$(git rev-parse base~1:right/c):UNINTERESTING
-	4:blob:right/c:$(git rev-parse topic:right/c)
-	5:tree:left/:$(git rev-parse base~1:left):UNINTERESTING
-	6:blob:left/b:$(git rev-parse base~1:left/b):UNINTERESTING
-	7:blob:a:$(git rev-parse base~1:a):UNINTERESTING
+	2:blob:a:$(git rev-parse base~1:a):UNINTERESTING
+	3:tree:left/:$(git rev-parse base~1:left):UNINTERESTING
+	4:blob:left/b:$(git rev-parse base~1:left/b):UNINTERESTING
+	5:tree:right/:$(git rev-parse topic:right)
+	5:tree:right/:$(git rev-parse base~1:right):UNINTERESTING
+	6:blob:right/c:$(git rev-parse base~1:right/c):UNINTERESTING
+	6:blob:right/c:$(git rev-parse topic:right/c)
+	7:blob:right/d:$(git rev-parse base~1:right/d):UNINTERESTING
 	blobs:5
 	commits:2
 	tags:0