dirstate-v2: Swap the order of size and mtime on disk

This makes the dirstate-v2 file format match dirstate-v1 for the order of
`mode`, `size`, and `mtime`. This order does not matter as long as these
components are handled through named fields/attributes in code, but in a few
places we still have tuples so having the same order everywhere might help
avoid a bug that might not be obvious since those components have the same type.

Differential Revision: https://phab.mercurial-scm.org/D11620

mercurial/helptext/internals/dirstate-v2.txt

@@ -424,15 +424,15 b' Node components are:'
     Only the `S_IXUSR` bit (owner has execute permission) is considered.
 
   * Offset 35:
-    If `HAS_MTIME` is unset, four zero bytes.
-    Otherwise, a 32-bit integer for expected modified time of the file
-    (as in `stat_result.st_mtime`),
+    If `HAS_MODE_AND_SIZE` is unset, four zero bytes.
+    Otherwise, a 32-bit integer for expected size of the file
     truncated to its 31 least-significant bits.
     Unlike in dirstate-v1, negative values are not used.
 
   * Offset 39:
-    If `HAS_MODE_AND_SIZE` is unset, four zero bytes.
-    Otherwise, a 32-bit integer for expected size of the file
+    If `HAS_MTIME` is unset, four zero bytes.
+    Otherwise, a 32-bit integer for expected modified time of the file
+    (as in `stat_result.st_mtime`),
     truncated to its 31 least-significant bits.
     Unlike in dirstate-v1, negative values are not used.
 

rust/hg-core/src/dirstate_tree/on_disk.rs

@@ -114,8 +114,8 b' bitflags! {'
 #[repr(C)]
 struct Entry {
     mode: I32Be,
+    size: I32Be,
     mtime: I32Be,
-    size: I32Be,
 }
 
 /// Duration since the Unix epoch