tree walking API
================
-Talk about <tree-walk.h>, things like
+The tree walking API is used to traverse and inspect trees.
-* struct tree_desc
-* init_tree_desc
-* tree_entry_extract
-* update_tree_entry
-* get_tree_entry
+Data Structures
+---------------
-(JC, Linus)
+`struct name_entry`::
+
+ An entry in a tree. Each entry has a sha1 identifier, pathname, and
+ mode.
+
+`struct tree_desc`::
+
+ A semi-opaque data structure used to maintain the current state of the
+ walk.
++
+* `buffer` is a pointer into the memory representation of the tree. It always
+points at the current entry being visited.
+
+* `size` counts the number of bytes left in the `buffer`.
+
+* `entry` points to the current entry being visited.
+
+`struct traverse_info`::
+
+ A structure used to maintain the state of a traversal.
++
+* `prev` points to the traverse_info which was used to descend into the
+current tree. If this is the top-level tree `prev` will point to
+a dummy traverse_info.
+
+* `name` is the entry for the current tree (if the tree is a subtree).
+
+* `pathlen` is the length of the full path for the current tree.
+
+* `conflicts` can be used by callbacks to maintain directory-file conflicts.
+
+* `fn` is a callback called for each entry in the tree. See Traversing for more
+information.
+
+* `data` can be anything the `fn` callback would want to use.
+
+Initializing
+------------
+
+`init_tree_desc`::
+
+ Initialize a `tree_desc` and decode its first entry. The buffer and
+ size parameters are assumed to be the same as the buffer and size
+ members of `struct tree`.
+
+`fill_tree_descriptor`::
+
+ Initialize a `tree_desc` and decode its first entry given the sha1 of
+ a tree. Returns the `buffer` member if the sha1 is a valid tree
+ identifier and NULL otherwise.
+
+`setup_traverse_info`::
+
+ Initialize a `traverse_info` given the pathname of the tree to start
+ traversing from. The `base` argument is assumed to be the `path`
+ member of the `name_entry` being recursed into unless the tree is a
+ top-level tree in which case the empty string ("") is used.
+
+Walking
+-------
+
+`tree_entry`::
+
+ Visit the next entry in a tree. Returns 1 when there are more entries
+ left to visit and 0 when all entries have been visited. This is
+ commonly used in the test of a while loop.
+
+`tree_entry_len`::
+
+ Calculate the length of a tree entry's pathname. This utilizes the
+ memory structure of a tree entry to avoid the overhead of using a
+ generic strlen().
+
+`update_tree_entry`::
+
+ Walk to the next entry in a tree. This is commonly used in conjunction
+ with `tree_entry_extract` to inspect the current entry.
+
+`tree_entry_extract`::
+
+ Decode the entry currently being visited (the one pointed to by
+ `tree_desc's` `entry` member) and return the sha1 of the entry. The
+ `pathp` and `modep` arguments are set to the entry's pathname and mode
+ respectively.
+
+`get_tree_entry`::
+
+ Find an entry in a tree given a pathname and the sha1 of a tree to
+ search. Returns 0 if the entry is found and -1 otherwise. The third
+ and fourth parameters are set to the entry's sha1 and mode
+ respectively.
+
+Traversing
+----------
+
+`traverse_trees`::
+
+ Traverse `n` number of trees in parallel. The `fn` callback member of
+ `traverse_info` is called once for each tree entry.
+
+`traverse_callback_t`::
+ The arguments passed to the traverse callback are as follows:
++
+* `n` counts the number of trees being traversed.
+
+* `mask` has its nth bit set if something exists in the nth entry.
+
+* `dirmask` has its nth bit set if the nth tree's entry is a directory.
+
+* `entry` is an array of size `n` where the nth entry is from the nth tree.
+
+* `info` maintains the state of the traversal.
+
++
+Returning a negative value will terminate the traversal. Otherwise the
+return value is treated as an update mask. If the nth bit is set the nth tree
+will be updated and if the bit is not set the nth tree entry will be the
+same in the next callback invocation.
+
+`make_traverse_path`::
+
+ Generate the full pathname of a tree entry based from the root of the
+ traversal. For example, if the traversal has recursed into another
+ tree named "bar" the pathname of an entry "baz" in the "bar"
+ tree would be "bar/baz".
+
+`traverse_path_len`::
+
+ Calculate the length of a pathname returned by `make_traverse_path`.
+ This utilizes the memory structure of a tree entry to avoid the
+ overhead of using a generic strlen().
+
+Authors
+-------
+
+Written by Junio C Hamano <gitster@pobox.com> and Linus Torvalds
+<torvalds@linux-foundation.org>