[WIP RFC PATCH 5/7] clone: use dir-iterator to avoid explicit dir traversal

["Ævar Arnfjörð Bjarmason" <avarab@gmail.com>]

From: Matheus Tavares <matheus.bernardino@usp.br>

Replace usage of opendir/readdir/closedir API to traverse directories
recursively, at copy_or_link_directory function, by the dir-iterator
API. This simplifies the code and avoid recursive calls to
copy_or_link_directory.

[Ævar: This should be bug-compatible with the existing "clone"
behavior. The whole bit here with "iter->relative_path[0] == '.'" is a
dirty hack. We don't copy dot-dirs, and then later on just blindly
ignore ENOENT errors as we descend into them. That case really wants
to be a is_dotdir_or_file_within() test instead]

Now, copy_or_link_directory will call die() in case of an error on
openddir, readdir or lstat, inside dir_iterator_advance. That means it
will abort in case of an error trying to fetch any iteration entry.

Signed-off-by: Matheus Tavares <matheus.bernardino@usp.br>
Signed-off-by: Ævar Arnfjörð Bjarmason <avarab@gmail.com>
---
 builtin/clone.c | 55 +++++++++++++++++++++++++++++--------------------
 1 file changed, 33 insertions(+), 22 deletions(-)

diff --git a/builtin/clone.c b/builtin/clone.c
index 862d2ea69c..c32e9022b3 100644
--- a/builtin/clone.c
+++ b/builtin/clone.c
@@ -23,6 +23,8 @@
 #include "transport.h"
 #include "strbuf.h"
 #include "dir.h"
+#include "dir-iterator.h"
+#include "iterator.h"
 #include "sigchain.h"
 #include "branch.h"
 #include "remote.h"
@@ -411,42 +413,47 @@ static void mkdir_if_missing(const char *pathname, mode_t mode)
 }
 
 static void copy_or_link_directory(struct strbuf *src, struct strbuf *dest,
-				   const char *src_repo, int src_baselen)
+				   const char *src_repo)
 {
-	struct dirent *de;
-	struct stat buf;
 	int src_len, dest_len;
-	DIR *dir;
-
-	dir = opendir(src->buf);
-	if (!dir)
-		die_errno(_("failed to open '%s'"), src->buf);
+	struct dir_iterator *iter;
+	int iter_status;
+	struct stat st;
 
 	mkdir_if_missing(dest->buf, 0777);
 
+	iter = dir_iterator_begin(src->buf, 1);
+
 	strbuf_addch(src, '/');
 	src_len = src->len;
 	strbuf_addch(dest, '/');
 	dest_len = dest->len;
 
-	while ((de = readdir(dir)) != NULL) {
+	while ((iter_status = dir_iterator_advance(iter)) == ITER_OK) {
 		strbuf_setlen(src, src_len);
-		strbuf_addstr(src, de->d_name);
+		strbuf_addstr(src, iter->relative_path);
 		strbuf_setlen(dest, dest_len);
-		strbuf_addstr(dest, de->d_name);
-		if (stat(src->buf, &buf)) {
+		strbuf_addstr(dest, iter->relative_path);
+
+		/*
+		 * dir_iterator_advance already calls lstat to populate iter->st
+		 * but, unlike stat, lstat does not checks for permissions on
+		 * the given path.
+		 */
+		if (stat(src->buf, &st)) {
 			warning (_("failed to stat %s\n"), src->buf);
 			continue;
 		}
-		if (S_ISDIR(buf.st_mode)) {
-			if (de->d_name[0] != '.')
-				copy_or_link_directory(src, dest,
-						       src_repo, src_baselen);
+
+		if (S_ISDIR(iter->st.st_mode)) {
+			if (iter->relative_path[0] == '.')
+				continue;
+			mkdir_if_missing(dest->buf, 0777);
 			continue;
 		}
 
 		/* Files that cannot be copied bit-for-bit... */
-		if (!strcmp(src->buf + src_baselen, "/info/alternates")) {
+		if (!strcmp(iter->relative_path, "info/alternates")) {
 			copy_alternates(src, dest, src_repo);
 			continue;
 		}
@@ -456,14 +463,18 @@ static void copy_or_link_directory(struct strbuf *src, struct strbuf *dest,
 		if (!option_no_hardlinks) {
 			if (!link(src->buf, dest->buf))
 				continue;
-			if (option_local > 0)
-				die_errno(_("failed to create link '%s'"), dest->buf);
+			if (option_local > 0 && errno != ENOENT)
+				warning_errno(_("failed to create link '%s'"), dest->buf);
 			option_no_hardlinks = 1;
 		}
-		if (copy_file_with_time(dest->buf, src->buf, 0666))
+		if (copy_file_with_time(dest->buf, src->buf, 0666) && errno != ENOENT)
 			die_errno(_("failed to copy file to '%s'"), dest->buf);
 	}
-	closedir(dir);
+
+	if (iter_status != ITER_DONE) {
+		strbuf_setlen(src, src_len);
+		die(_("failed to iterate over '%s'"), src->buf);
+	}
 }
 
 static void clone_local(const char *src_repo, const char *dest_repo)
@@ -481,7 +492,7 @@ static void clone_local(const char *src_repo, const char *dest_repo)
 		get_common_dir(&dest, dest_repo);
 		strbuf_addstr(&src, "/objects");
 		strbuf_addstr(&dest, "/objects");
-		copy_or_link_directory(&src, &dest, src_repo, src.len);
+		copy_or_link_directory(&src, &dest, src_repo);
 		strbuf_release(&src);
 		strbuf_release(&dest);
 	}
-- 
2.21.0.rc2.1.g2d5e20a900.dirty