Fixed name ordering when names only differ in length

Wild this hasn't been caught until now.

Because the exact ordering of the comparison in lfs_bd_cmp is a bit
ambiguous, lfs_dir_find_match returned the wrong result when filenames
were equal, and only differed in length.

For example:

  - cmp("a", "aa") should be LFS_CMP_LT
  - cmp("aaa", "aa") should be LFS_CMP_GT

We're quite lucky that none of the littlefs internals currently depend
on the sorted order, otherwise we'd probably be stuck with this weird
ordering for backwards compatibility reasons...

Fixed, and added some test cases over directory ordering to prevent
regression in the future.

Found by andriyndev

lfs.c

diff --git a/lfs.c b/lfs.c
index a152687..49897cc 100644
--- a/lfs.c
+++ b/lfs.c
@@ -1430,8 +1430,8 @@
     }
 
     // only equal if our size is still the same
-    if (name->size != lfs_tag_size(tag)) {
-        return (name->size < lfs_tag_size(tag)) ? LFS_CMP_LT : LFS_CMP_GT;
+    if (lfs_tag_size(tag) != name->size) {
+        return (lfs_tag_size(tag) < name->size) ? LFS_CMP_LT : LFS_CMP_GT;
     }
 
     // found a match!

tests/test_dirs.toml

diff --git a/tests/test_dirs.toml b/tests/test_dirs.toml
index 4262a1a..06363d5 100644
--- a/tests/test_dirs.toml
+++ b/tests/test_dirs.toml
@@ -717,6 +717,105 @@
     lfs_unmount(&lfs) => 0;
 '''
 
+# littlefs should keep directories in lexicographic order
+[cases.test_dirs_ordering]
+# ORDER=0 => inorder
+# ORDER=1 => reversed
+# ORDER=2 => random
+defines.ORDER = [0, 1, 2]
+code = '''
+    lfs_t lfs;
+    lfs_format(&lfs, cfg) => 0;
+    lfs_mount(&lfs, cfg) => 0;
+    if (ORDER == 0) {
+        lfs_mkdir(&lfs, "a") => 0;
+        lfs_mkdir(&lfs, "b") => 0;
+        lfs_mkdir(&lfs, "c") => 0;
+    } else if (ORDER == 1) {
+        lfs_mkdir(&lfs, "c") => 0;
+        lfs_mkdir(&lfs, "b") => 0;
+        lfs_mkdir(&lfs, "a") => 0;
+    } else if (ORDER == 2) {
+        // "random"
+        lfs_mkdir(&lfs, "a") => 0;
+        lfs_mkdir(&lfs, "c") => 0;
+        lfs_mkdir(&lfs, "b") => 0;
+    }
+
+    // check the order
+    lfs_dir_t dir;
+    lfs_dir_open(&lfs, &dir, "/") => 0;
+    struct lfs_info info;
+    lfs_dir_read(&lfs, &dir, &info) => 1;
+    assert(info.type == LFS_TYPE_DIR);
+    assert(strcmp(info.name, ".") == 0);
+    lfs_dir_read(&lfs, &dir, &info) => 1;
+    assert(info.type == LFS_TYPE_DIR);
+    assert(strcmp(info.name, "..") == 0);
+    lfs_dir_read(&lfs, &dir, &info) => 1;
+    assert(info.type == LFS_TYPE_DIR);
+    assert(strcmp(info.name, "a") == 0);
+    lfs_dir_read(&lfs, &dir, &info) => 1;
+    assert(info.type == LFS_TYPE_DIR);
+    assert(strcmp(info.name, "b") == 0);
+    lfs_dir_read(&lfs, &dir, &info) => 1;
+    assert(info.type == LFS_TYPE_DIR);
+    assert(strcmp(info.name, "c") == 0);
+    lfs_dir_read(&lfs, &dir, &info) => 0;
+    lfs_dir_close(&lfs, &dir) => 0;
+
+    lfs_unmount(&lfs) => 0;
+'''
+
+[cases.test_dirs_ordering_length]
+# ORDER=0 => inorder
+# ORDER=1 => reversed
+# ORDER=2 => random
+defines.ORDER = [0, 1, 2]
+code = '''
+    lfs_t lfs;
+    lfs_format(&lfs, cfg) => 0;
+    lfs_mount(&lfs, cfg) => 0;
+    if (ORDER == 0) {
+        lfs_mkdir(&lfs, "a") => 0;
+        lfs_mkdir(&lfs, "aa") => 0;
+        lfs_mkdir(&lfs, "aaa") => 0;
+    } else if (ORDER == 1) {
+        lfs_mkdir(&lfs, "aaa") => 0;
+        lfs_mkdir(&lfs, "aa") => 0;
+        lfs_mkdir(&lfs, "a") => 0;
+    } else if (ORDER == 2) {
+        // "random"
+        lfs_mkdir(&lfs, "a") => 0;
+        lfs_mkdir(&lfs, "aaa") => 0;
+        lfs_mkdir(&lfs, "aa") => 0;
+    }
+
+    // check the order
+    lfs_dir_t dir;
+    lfs_dir_open(&lfs, &dir, "/") => 0;
+    struct lfs_info info;
+    lfs_dir_read(&lfs, &dir, &info) => 1;
+    assert(info.type == LFS_TYPE_DIR);
+    assert(strcmp(info.name, ".") == 0);
+    lfs_dir_read(&lfs, &dir, &info) => 1;
+    assert(info.type == LFS_TYPE_DIR);
+    assert(strcmp(info.name, "..") == 0);
+    lfs_dir_read(&lfs, &dir, &info) => 1;
+    assert(info.type == LFS_TYPE_DIR);
+    assert(strcmp(info.name, "a") == 0);
+    lfs_dir_read(&lfs, &dir, &info) => 1;
+    assert(info.type == LFS_TYPE_DIR);
+    assert(strcmp(info.name, "aa") == 0);
+    lfs_dir_read(&lfs, &dir, &info) => 1;
+    assert(info.type == LFS_TYPE_DIR);
+    assert(strcmp(info.name, "aaa") == 0);
+    lfs_dir_read(&lfs, &dir, &info) => 0;
+    lfs_dir_close(&lfs, &dir) => 0;
+
+    lfs_unmount(&lfs) => 0;
+'''
+
 [cases.test_dirs_other_errors]
 code = '''
     lfs_t lfs;