thodg/libgit2

diff --git a/src/attr.c b/src/attr.c
index a021726..df139e0 100644
--- a/src/attr.c
+++ b/src/attr.c
@@ -29,6 +29,7 @@ git_attr_t git_attr_value(const char *attr)
 
 static int collect_attr_files(
 	git_repository *repo,
+	git_attr_session *attr_session,
 	uint32_t flags,
 	const char *path,
 	git_vector *files);
@@ -57,7 +58,7 @@ int git_attr_get(
 	if (git_attr_path__init(&path, pathname, git_repository_workdir(repo)) < 0)
 		return -1;
 
-	if ((error = collect_attr_files(repo, flags, pathname, &files)) < 0)
+	if ((error = collect_attr_files(repo, NULL, flags, pathname, &files)) < 0)
 		goto cleanup;
 
 	memset(&attr, 0, sizeof(attr));
@@ -90,9 +91,10 @@ typedef struct {
 	git_attr_assignment *found;
 } attr_get_many_info;
 
-int git_attr_get_many(
+int git_attr_get_many_with_session(
 	const char **values,
 	git_repository *repo,
+	git_attr_session *attr_session,
 	uint32_t flags,
 	const char *pathname,
 	size_t num_attr,
@@ -115,7 +117,7 @@ int git_attr_get_many(
 	if (git_attr_path__init(&path, pathname, git_repository_workdir(repo)) < 0)
 		return -1;
 
-	if ((error = collect_attr_files(repo, flags, pathname, &files)) < 0)
+	if ((error = collect_attr_files(repo, attr_session, flags, pathname, &files)) < 0)
 		goto cleanup;
 
 	info = git__calloc(num_attr, sizeof(attr_get_many_info));
@@ -161,6 +163,17 @@ cleanup:
 	return error;
 }
 
+int git_attr_get_many(
+	const char **values,
+	git_repository *repo,
+	uint32_t flags,
+	const char *pathname,
+	size_t num_attr,
+	const char **names)
+{
+	return git_attr_get_many_with_session(
+		values, repo, NULL, flags, pathname, num_attr, names);
+}
 
 int git_attr_foreach(
 	git_repository *repo,
@@ -183,7 +196,7 @@ int git_attr_foreach(
 	if (git_attr_path__init(&path, pathname, git_repository_workdir(repo)) < 0)
 		return -1;
 
-	if ((error = collect_attr_files(repo, flags, pathname, &files)) < 0 ||
+	if ((error = collect_attr_files(repo, NULL, flags, pathname, &files)) < 0 ||
 		(error = git_strmap_alloc(&seen)) < 0)
 		goto cleanup;
 
@@ -219,6 +232,7 @@ cleanup:
 
 static int preload_attr_file(
 	git_repository *repo,
+	git_attr_session *attr_session,
 	git_attr_file_source source,
 	const char *base,
 	const char *file)
@@ -229,19 +243,22 @@ static int preload_attr_file(
 	if (!file)
 		return 0;
 	if (!(error = git_attr_cache__get(
-			&preload, repo, source, base, file, git_attr_file__parse_buffer)))
+			&preload, repo, attr_session, source, base, file, git_attr_file__parse_buffer)))
 		git_attr_file__free(preload);
 
 	return error;
 }
 
-static int attr_setup(git_repository *repo)
+static int attr_setup(git_repository *repo, git_attr_session *attr_session)
 {
 	int error = 0;
 	const char *workdir = git_repository_workdir(repo);
 	git_index *idx = NULL;
 	git_buf sys = GIT_BUF_INIT;
 
+	if (attr_session && attr_session->setup)
+		return 0;
+
 	if ((error = git_attr_cache__init(repo)) < 0)
 		return error;
 
@@ -251,7 +268,7 @@ static int attr_setup(git_repository *repo)
 
 	if (!(error = git_sysdir_find_system_file(&sys, GIT_ATTR_FILE_SYSTEM))) {
 		error = preload_attr_file(
-			repo, GIT_ATTR_FILE__FROM_FILE, NULL, sys.ptr);
+			repo, attr_session, GIT_ATTR_FILE__FROM_FILE, NULL, sys.ptr);
 		git_buf_free(&sys);
 	}
 	if (error < 0) {
@@ -263,25 +280,28 @@ static int attr_setup(git_repository *repo)
 	}
 
 	if ((error = preload_attr_file(
-			repo, GIT_ATTR_FILE__FROM_FILE,
+			repo, attr_session, GIT_ATTR_FILE__FROM_FILE,
 			NULL, git_repository_attr_cache(repo)->cfg_attr_file)) < 0)
 		return error;
 
 	if ((error = preload_attr_file(
-			repo, GIT_ATTR_FILE__FROM_FILE,
+			repo, attr_session, GIT_ATTR_FILE__FROM_FILE,
 			git_repository_path(repo), GIT_ATTR_FILE_INREPO)) < 0)
 		return error;
 
 	if (workdir != NULL &&
 		(error = preload_attr_file(
-			repo, GIT_ATTR_FILE__FROM_FILE, workdir, GIT_ATTR_FILE)) < 0)
+			repo, attr_session, GIT_ATTR_FILE__FROM_FILE, workdir, GIT_ATTR_FILE)) < 0)
 		return error;
 
 	if ((error = git_repository_index__weakptr(&idx, repo)) < 0 ||
 		(error = preload_attr_file(
-			repo, GIT_ATTR_FILE__FROM_INDEX, NULL, GIT_ATTR_FILE)) < 0)
+			repo, attr_session, GIT_ATTR_FILE__FROM_INDEX, NULL, GIT_ATTR_FILE)) < 0)
 		return error;
 
+	if (attr_session)
+		attr_session->setup = 1;
+
 	return error;
 }
 
@@ -321,6 +341,7 @@ int git_attr_add_macro(
 
 typedef struct {
 	git_repository *repo;
+	git_attr_session *attr_session;
 	uint32_t flags;
 	const char *workdir;
 	git_index *index;
@@ -356,6 +377,7 @@ static int attr_decide_sources(
 
 static int push_attr_file(
 	git_repository *repo,
+	git_attr_session *attr_session,
 	git_vector *list,
 	git_attr_file_source source,
 	const char *base,
@@ -364,8 +386,9 @@ static int push_attr_file(
 	int error = 0;
 	git_attr_file *file = NULL;
 
-	error = git_attr_cache__get(
-		&file, repo, source, base, filename, git_attr_file__parse_buffer);
+	error = git_attr_cache__get(&file, repo, attr_session,
+		source, base, filename, git_attr_file__parse_buffer);
+
 	if (error < 0)
 		return error;
 
@@ -387,8 +410,8 @@ static int push_one_attr(void *ref, const char *path)
 		info->flags, info->workdir != NULL, info->index != NULL, src);
 
 	for (i = 0; !error && i < n_src; ++i)
-		error = push_attr_file(
-			info->repo, info->files, src[i], path, GIT_ATTR_FILE);
+		error = push_attr_file(info->repo, info->attr_session,
+			info->files, src[i], path, GIT_ATTR_FILE);
 
 	return error;
 }
@@ -407,6 +430,7 @@ static void release_attr_files(git_vector *files)
 
 static int collect_attr_files(
 	git_repository *repo,
+	git_attr_session *attr_session,
 	uint32_t flags,
 	const char *path,
 	git_vector *files)
@@ -416,7 +440,7 @@ static int collect_attr_files(
 	const char *workdir = git_repository_workdir(repo);
 	attr_walk_up_info info = { NULL };
 
-	if ((error = attr_setup(repo)) < 0)
+	if ((error = attr_setup(repo, attr_session)) < 0)
 		return error;
 
 	/* Resolve path in a non-bare repo */
@@ -435,12 +459,13 @@ static int collect_attr_files(
 	 */
 
 	error = push_attr_file(
-		repo, files, GIT_ATTR_FILE__FROM_FILE,
+		repo, attr_session, files, GIT_ATTR_FILE__FROM_FILE,
 		git_repository_path(repo), GIT_ATTR_FILE_INREPO);
 	if (error < 0)
 		goto cleanup;
 
-	info.repo  = repo;
+	info.repo = repo;
+	info.attr_session = attr_session;
 	info.flags = flags;
 	info.workdir = workdir;
 	if (git_repository_index__weakptr(&info.index, repo) < 0)
@@ -457,7 +482,7 @@ static int collect_attr_files(
 
 	if (git_repository_attr_cache(repo)->cfg_attr_file != NULL) {
 		error = push_attr_file(
-			repo, files, GIT_ATTR_FILE__FROM_FILE,
+			repo, attr_session, files, GIT_ATTR_FILE__FROM_FILE,
 			NULL, git_repository_attr_cache(repo)->cfg_attr_file);
 		if (error < 0)
 			goto cleanup;
@@ -467,7 +492,8 @@ static int collect_attr_files(
 		error = git_sysdir_find_system_file(&dir, GIT_ATTR_FILE_SYSTEM);
 		if (!error)
 			error = push_attr_file(
-				repo, files, GIT_ATTR_FILE__FROM_FILE, NULL, dir.ptr);
+				repo, attr_session, files, GIT_ATTR_FILE__FROM_FILE,
+				NULL, dir.ptr);
 		else if (error == GIT_ENOTFOUND) {
 			giterr_clear();
 			error = 0;
diff --git a/src/attr_file.c b/src/attr_file.c
index 5b008b0..9896df4 100644
--- a/src/attr_file.c
+++ b/src/attr_file.c
@@ -96,6 +96,7 @@ static int attr_file_oid_from_index(
 int git_attr_file__load(
 	git_attr_file **out,
 	git_repository *repo,
+	git_attr_session *attr_session,
 	git_attr_file_entry *entry,
 	git_attr_file_source source,
 	git_attr_file_parser parser)
@@ -105,6 +106,7 @@ int git_attr_file__load(
 	git_buf content = GIT_BUF_INIT;
 	git_attr_file *file;
 	struct stat st;
+	bool nonexistent = false;
 
 	*out = NULL;
 
@@ -127,22 +129,16 @@ int git_attr_file__load(
 	case GIT_ATTR_FILE__FROM_FILE: {
 		int fd;
 
-		if (p_stat(entry->fullpath, &st) < 0)
-			return git_path_set_error(errno, entry->fullpath, "stat");
-		if (S_ISDIR(st.st_mode))
-			return GIT_ENOTFOUND;
-
-		/* For open or read errors, return ENOTFOUND to skip item */
+		/* For open or read errors, pretend that we got ENOTFOUND. */
 		/* TODO: issue warning when warning API is available */
 
-		if ((fd = git_futils_open_ro(entry->fullpath)) < 0)
-			return GIT_ENOTFOUND;
-
-		error = git_futils_readbuffer_fd(&content, fd, (size_t)st.st_size);
-		p_close(fd);
-
-		if (error < 0)
-			return GIT_ENOTFOUND;
+		if (p_stat(entry->fullpath, &st) < 0 ||
+			S_ISDIR(st.st_mode) ||
+			(fd = git_futils_open_ro(entry->fullpath)) < 0 ||
+			(error = git_futils_readbuffer_fd(&content, fd, (size_t)st.st_size)) < 0)
+			nonexistent = true;
+		else
+			p_close(fd);
 
 		break;
 	}
@@ -154,13 +150,21 @@ int git_attr_file__load(
 	if ((error = git_attr_file__new(&file, entry, source)) < 0)
 		goto cleanup;
 
+	/* store the key of the attr_reader; don't bother with cache
+	 * invalidation during the same attr reader session.
+	 */
+	if (attr_session)
+		file->session_key = attr_session->key;
+
 	if (parser && (error = parser(repo, file, git_buf_cstr(&content))) < 0) {
 		git_attr_file__free(file);
 		goto cleanup;
 	}
 
-	/* write cache breaker */
-	if (source == GIT_ATTR_FILE__FROM_INDEX)
+	/* write cache breakers */
+	if (nonexistent)
+		file->nonexistent = 1;
+	else if (source == GIT_ATTR_FILE__FROM_INDEX)
 		git_oid_cpy(&file->cache_data.oid, git_blob_id(blob));
 	else if (source == GIT_ATTR_FILE__FROM_FILE)
 		git_futils_filestamp_set_from_stat(&file->cache_data.stamp, &st);
@@ -175,11 +179,22 @@ cleanup:
 	return error;
 }
 
-int git_attr_file__out_of_date(git_repository *repo, git_attr_file *file)
+int git_attr_file__out_of_date(
+	git_repository *repo,
+	git_attr_session *attr_session,
+	git_attr_file *file)
 {
 	if (!file)
 		return 1;
 
+	/* we are never out of date if we just created this data in the same
+	 * attr_session; otherwise, nonexistent files must be invalidated
+	 */
+	if (attr_session && attr_session->key == file->session_key)
+		return 0;
+	else if (file->nonexistent)
+		return 1;
+
 	switch (file->source) {
 	case GIT_ATTR_FILE__IN_MEMORY:
 		return 0;
@@ -831,3 +846,11 @@ void git_attr_rule__free(git_attr_rule *rule)
 	git__free(rule);
 }
 
+int git_attr_session__init(git_attr_session *session, git_repository *repo)
+{
+	assert(repo);
+
+	session->key = git_atomic_inc(&repo->attr_session_key);
+
+	return 0;
+}
diff --git a/src/attr_file.h b/src/attr_file.h
index 93de84d..b8e3725 100644
--- a/src/attr_file.h
+++ b/src/attr_file.h
@@ -38,11 +38,11 @@
 	 GIT_ATTR_FNMATCH_ALLOWMACRO | GIT_ATTR_FNMATCH_NOLEADINGDIR)
 
 typedef enum {
-	GIT_ATTR_FILE__IN_MEMORY  = 0,
-	GIT_ATTR_FILE__FROM_FILE  = 1,
-	GIT_ATTR_FILE__FROM_INDEX = 2,
+	GIT_ATTR_FILE__IN_MEMORY   = 0,
+	GIT_ATTR_FILE__FROM_FILE   = 1,
+	GIT_ATTR_FILE__FROM_INDEX  = 2,
 
-	GIT_ATTR_FILE_NUM_SOURCES = 3
+	GIT_ATTR_FILE_NUM_SOURCES  = 3
 } git_attr_file_source;
 
 extern const char *git_attr__true;
@@ -84,6 +84,8 @@ typedef struct {
 	git_attr_file_source source;
 	git_vector rules;			/* vector of <rule*> or <fnmatch*> */
 	git_pool pool;
+	unsigned int nonexistent:1;
+	int session_key;
 	union {
 		git_oid oid;
 		git_futils_filestamp stamp;
@@ -96,11 +98,6 @@ struct git_attr_file_entry {
 	char fullpath[GIT_FLEX_ARRAY];
 };
 
-typedef int (*git_attr_file_parser)(
-	git_repository *repo,
-	git_attr_file *file,
-	const char *data);
-
 typedef struct {
 	git_buf  full;
 	char    *path;
@@ -108,6 +105,32 @@ typedef struct {
 	int      is_dir;
 } git_attr_path;
 
+/* A git_attr_session can provide an "instance" of reading, to prevent cache
+ * invalidation during a single operation instance (like checkout).
+ */
+
+typedef struct {
+	int key;
+	unsigned int setup;
+} git_attr_session;
+
+extern int git_attr_session__init(git_attr_session *attr_session, git_repository *repo);
+extern void git_attr_session__free(git_attr_session *session);
+
+extern int git_attr_get_many_with_session(
+	const char **values_out,
+	git_repository *repo,
+	git_attr_session *attr_session,
+	uint32_t flags,
+	const char *path,
+	size_t num_attr,
+	const char **names);
+
+typedef int (*git_attr_file_parser)(
+	git_repository *repo,
+	git_attr_file *file,
+	const char *data);
+
 /*
  * git_attr_file API
  */
@@ -122,6 +145,7 @@ void git_attr_file__free(git_attr_file *file);
 int git_attr_file__load(
 	git_attr_file **out,
 	git_repository *repo,
+	git_attr_session *attr_session,
 	git_attr_file_entry *ce,
 	git_attr_file_source source,
 	git_attr_file_parser parser);
@@ -130,7 +154,7 @@ int git_attr_file__load_standalone(
 	git_attr_file **out, const char *path);
 
 int git_attr_file__out_of_date(
-	git_repository *repo, git_attr_file *file);
+	git_repository *repo, git_attr_session *session, git_attr_file *file);
 
 int git_attr_file__parse_buffer(
 	git_repository *repo, git_attr_file *attrs, const char *data);
diff --git a/src/attrcache.c b/src/attrcache.c
index b4579bf..f75edad 100644
--- a/src/attrcache.c
+++ b/src/attrcache.c
@@ -196,6 +196,7 @@ cleanup:
 int git_attr_cache__get(
 	git_attr_file **out,
 	git_repository *repo,
+	git_attr_session *attr_session,
 	git_attr_file_source source,
 	const char *base,
 	const char *filename,
@@ -211,8 +212,8 @@ int git_attr_cache__get(
 		return error;
 
 	/* load file if we don't have one or if existing one is out of date */
-	if (!file || (error = git_attr_file__out_of_date(repo, file)) > 0)
-		error = git_attr_file__load(&updated, repo, entry, source, parser);
+	if (!file || (error = git_attr_file__out_of_date(repo, attr_session, file)) > 0)
+		error = git_attr_file__load(&updated, repo, attr_session, entry, source, parser);
 
 	/* if we loaded the file, insert into and/or update cache */
 	if (updated) {
diff --git a/src/attrcache.h b/src/attrcache.h
index be0a22f..44e1ffd 100644
--- a/src/attrcache.h
+++ b/src/attrcache.h
@@ -31,6 +31,7 @@ extern int git_attr_cache__do_init(git_repository *repo);
 extern int git_attr_cache__get(
 	git_attr_file **file,
 	git_repository *repo,
+	git_attr_session *attr_session,
 	git_attr_file_source source,
 	const char *base,
 	const char *filename,
diff --git a/src/checkout.c b/src/checkout.c
index 52a076d..04493a3 100644
--- a/src/checkout.c
+++ b/src/checkout.c
@@ -28,6 +28,7 @@
 #include "buf_text.h"
 #include "merge_file.h"
 #include "path.h"
+#include "attr.h"
 
 /* See docs/checkout-internals.md for more information */
 
@@ -69,6 +70,7 @@ typedef struct {
 	size_t completed_steps;
 	git_checkout_perfdata perfdata;
 	git_buf last_mkdir;
+	git_attr_session attr_session;
 } checkout_data;
 
 typedef struct {
@@ -1425,8 +1427,8 @@ static int blob_content_to_file(
 		hint_path = path;
 
 	if (!data->opts.disable_filters)
-		error = git_filter_list_load(
-			&fl, git_blob_owner(blob), blob, hint_path,
+		error = git_filter_list__load_with_attr_session(
+			&fl, data->repo, &data->attr_session, blob, hint_path,
 			GIT_FILTER_TO_WORKTREE, GIT_FILTER_OPT_DEFAULT);
 
 	if (!error)
@@ -2008,7 +2010,8 @@ static int checkout_write_merge(
 		in_data.ptr = (char *)result.ptr;
 		in_data.size = result.len;
 
-		if ((error = git_filter_list_load(&fl, data->repo, NULL, git_buf_cstr(&path_workdir),
+		if ((error = git_filter_list__load_with_attr_session(
+				&fl, data->repo, &data->attr_session, NULL, git_buf_cstr(&path_workdir),
 				GIT_FILTER_TO_WORKTREE, GIT_FILTER_OPT_DEFAULT)) < 0 ||
 			(error = git_filter_list_apply_to_data(&out_data, fl, &in_data)) < 0)
 			goto done;
@@ -2218,6 +2221,8 @@ static void checkout_data_clear(checkout_data *data)
 
 	git_index_free(data->index);
 	data->index = NULL;
+
+	git_attr_session__free(&data->attr_session);
 }
 
 static int checkout_data_init(
@@ -2360,6 +2365,8 @@ static int checkout_data_init(
 
 	data->workdir_len = git_buf_len(&data->path);
 
+	git_attr_session__init(&data->attr_session, data->repo);
+
 cleanup:
 	if (error < 0)
 		checkout_data_clear(data);
diff --git a/src/filter.c b/src/filter.c
index b5a8bdd..22eaf51 100644
--- a/src/filter.c
+++ b/src/filter.c
@@ -394,15 +394,19 @@ static int filter_list_new(
 }
 
 static int filter_list_check_attributes(
-	const char ***out, git_filter_def *fdef, const git_filter_source *src)
+	const char ***out,
+	git_repository *repo,
+	git_attr_session *attr_session,
+	git_filter_def *fdef,
+	const git_filter_source *src)
 {
 	int error;
 	size_t i;
 	const char **strs = git__calloc(fdef->nattrs, sizeof(const char *));
 	GITERR_CHECK_ALLOC(strs);
 
-	error = git_attr_get_many(
-		strs, src->repo, 0, src->path, fdef->nattrs, fdef->attrs);
+	error = git_attr_get_many_with_session(
+		strs, repo, attr_session, 0, src->path, fdef->nattrs, fdef->attrs);
 
 	/* if no values were found but no matches are needed, it's okay! */
 	if (error == GIT_ENOTFOUND && !fdef->nmatches) {
@@ -448,9 +452,10 @@ int git_filter_list_new(
 	return filter_list_new(out, &src);
 }
 
-int git_filter_list_load(
+int git_filter_list__load_with_attr_session(
 	git_filter_list **filters,
 	git_repository *repo,
+	git_attr_session *attr_session,
 	git_blob *blob, /* can be NULL */
 	const char *path,
 	git_filter_mode_t mode,
@@ -481,7 +486,9 @@ int git_filter_list_load(
 			continue;
 
 		if (fdef->nattrs > 0) {
-			error = filter_list_check_attributes(&values, fdef, &src);
+			error = filter_list_check_attributes(
+				&values, repo, attr_session, fdef, &src);
+
 			if (error == GIT_ENOTFOUND) {
 				error = 0;
 				continue;
@@ -523,6 +530,18 @@ int git_filter_list_load(
 	return error;
 }
 
+int git_filter_list_load(
+	git_filter_list **filters,
+	git_repository *repo,
+	git_blob *blob, /* can be NULL */
+	const char *path,
+	git_filter_mode_t mode,
+	uint32_t options)
+{
+	return git_filter_list__load_with_attr_session(
+		filters, repo, NULL, blob, path, mode, options);
+}
+
 void git_filter_list_free(git_filter_list *fl)
 {
 	uint32_t i;
diff --git a/src/filter.h b/src/filter.h
index 5a36610..390ffeb 100644
--- a/src/filter.h
+++ b/src/filter.h
@@ -8,6 +8,7 @@
 #define INCLUDE_filter_h__
 
 #include "common.h"
+#include "attr_file.h"
 #include "git2/filter.h"
 
 /* Amount of file to examine for NUL byte when checking binary-ness */
@@ -25,6 +26,15 @@ typedef enum {
 
 extern void git_filter_free(git_filter *filter);
 
+extern int git_filter_list__load_with_attr_session(
+	git_filter_list **filters,
+	git_repository *repo,
+	git_attr_session *attr_session,
+	git_blob *blob, /* can be NULL */
+	const char *path,
+	git_filter_mode_t mode,
+	uint32_t options);
+
 /*
  * Available filters
  */
diff --git a/src/ignore.c b/src/ignore.c
index 6e00f7d..dd299f0 100644
--- a/src/ignore.c
+++ b/src/ignore.c
@@ -161,7 +161,7 @@ static int push_ignore_file(
 	git_attr_file *file = NULL;
 
 	error = git_attr_cache__get(
-		&file, ignores->repo, GIT_ATTR_FILE__FROM_FILE,
+		&file, ignores->repo, NULL, GIT_ATTR_FILE__FROM_FILE,
 		base, filename, parse_ignore_file);
 	if (error < 0)
 		return error;
@@ -189,7 +189,7 @@ static int get_internal_ignores(git_attr_file **out, git_repository *repo)
 		return error;
 
 	error = git_attr_cache__get(
-		out, repo, GIT_ATTR_FILE__IN_MEMORY, NULL, GIT_IGNORE_INTERNAL, NULL);
+		out, repo, NULL, GIT_ATTR_FILE__IN_MEMORY, NULL, GIT_IGNORE_INTERNAL, NULL);
 
 	/* if internal rules list is empty, insert default rules */
 	if (!error && !(*out)->rules.length)
diff --git a/src/repository.h b/src/repository.h
index 6da8c28..dffa9a8 100644
--- a/src/repository.h
+++ b/src/repository.h
@@ -133,6 +133,8 @@ struct git_repository {
 		has_8dot3_default:1;
 	unsigned int lru_counter;
 
+	git_atomic attr_session_key;
+
 	git_cvar_value cvar_cache[GIT_CVAR_CACHE_MAX];
 };