375   Some boolean values packed as bits of a single byte.

   375   A single `flags` byte that packs some boolean values as bits.

   384     MODE_IS_SYMLINK = 1 << 7

   384     MODE_IS_SYMLINK = 1 << 6

   385 

   385 

   386 

   386   The meaning of each bit is described below.

   387   Other bits are unset. The meaning of these bits are:

   387   Other bits are unset.

   388 

   388 

   389   `WDIR_TRACKED`

   389 * Offset 31:

   390       Set if the working directory contains a tracked file at this node’s path.

   390   A `size` field described below, as a 32-bit integer.

   391       This is typically set and unset by `hg add` and `hg rm`.

   391   Unlike in dirstate-v1, negative values are not used.

   392 

   392 

   393   `P1_TRACKED`

   393 * Offset 35:

   394       set if the working directory’s first parent changeset

   394   The seconds component of an `mtime` field described below,

   395       (whose node identifier is found in tree metadata)

   395   as a 32-bit integer.

   396       contains a tracked file at this node’s path.

   396   Unlike in dirstate-v1, negative values are not used.

   397       This is a cache to reduce manifest lookups.

   397 

   398 

   398 * Offset 39:

   399   `P2_INFO`

   399   The nanoseconds component of an `mtime` field described below,

   400       Set if the file has been involved in some merge operation.

   400   as a 32-bit integer.

   401       Either because it was actually merged,

   402       or because the version in the second parent p2 version was ahead,

   403       or because some rename moved it there.

   404       In either case `hg status` will want it displayed as modified.

   405 

   406   Files that would be mentioned at all in the `dirstate-v1` file format

   407   have a node with at least one of the above three bits set in `dirstate-v2`.

   408   Let’s call these files "tracked anywhere",

   409   and "untracked" the nodes with all three of these bits unset.

   410   Untracked nodes are typically for directories:

   411   they hold child nodes and form the tree structure.

   412   Additional untracked nodes may also exist.

   413   Although implementations should strive to clean up nodes

   414   that are entirely unused, other untracked nodes may also exist.

   415   For example, a future version of Mercurial might in some cases

   416   add nodes for untracked files or/and ignored files in the working directory

   417   in order to optimize `hg status`

   418   by enabling it to skip `readdir` in more cases.

   419 

   420   When a node is for a file tracked anywhere:

   421   - If `HAS_MODE_AND_SIZE` is set, the file is expected

   422     to be a symbolic link or a normal file based on `MODE_IS_SYMLINK`.

   423   - If `HAS_MODE_AND_SIZE` is set, the file’s owner is expected

   424     to have execute permission or not based on `MODE_EXEC_PERM`.

   425   - If `HAS_MODE_AND_SIZE` is unset,

   426     the expected type of file and permission are unknown.

   427   The rest of the node data is three fields:

   428 

   429   * Offset 31:

   430     4 unused bytes, set to zero

   431 

   432   * Offset 35:

   433     If `HAS_MODE_AND_SIZE` is unset, four zero bytes.

   434     Otherwise, a 32-bit integer for expected size of the file

   435     truncated to its 31 least-significant bits.

   436     Unlike in dirstate-v1, negative values are not used.

   437 

   438   * Offset 39:

   439     If `HAS_MTIME` is unset, four zero bytes.

   440     Otherwise, a 32-bit integer for expected modified time of the file

   441     (as in `stat_result.st_mtime`),

   442     truncated to its 31 least-significant bits.

   443     Unlike in dirstate-v1, negative values are not used.

   444 

   445   If an untracked node `HAS_MTIME` *unset*, this space is unused:

   446 

   447   * Offset 31:

   448     12 unused bytes, set to zero

   449 

   450   If an untracked node `HAS_MTIME` *set*,

   451   what follows is the modification time of a directory

   452   represented similarly to the C `timespec` struct:

   453 

   454   * Offset 31:

   455     4 unused bytes, set to zero

   456 

   457   * Offset 35:

   458     The number of seconds elapsed since the Unix epoch,

   459     truncated to its lower 31 bits,

   460     as a 32-bit integer.

   461 

   462   * Offset 39:

   463     The sub-second number of nanoseconds elapsed since the Unix epoch,

   464     as 32-bit integer.

   465     Always greater than or equal to zero, and strictly less than a billion.

   466 

   467   The presence of a directory modification time means that at some point,

   468   this path in the working directory was observed:

   469 

   470   - To be a directory

   471   - With the given modification time

   472   - That time was already strictly in the past when observed,

   473     meaning that later changes cannot happen in the same clock tick

   474     and must cause a different modification time

   475     (unless the system clock jumps back and we get unlucky,

   476     which is not impossible but deemed unlikely enough).

   477   - All direct children of this directory

   478     (as returned by `std::fs::read_dir`)

   479     either have a corresponding dirstate node,

   480     or are ignored by ignore patterns whose hash is in tree metadata.

   481 

   482   This means that if `std::fs::symlink_metadata` later reports

   483   the same modification time

   484   and ignored patterns haven’t changed,

   485   a run of status that is not listing ignored files

   486   can skip calling `std::fs::read_dir` again for this directory,

   487   and iterate child dirstate nodes instead.

   488