technical-docs: document tree-walking API
[git/git.git] / Documentation / technical / api-tree-walking.txt
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1tree walking API
2================
3
6639ffc2 4The tree walking API is used to traverse and inspect trees.
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6Data Structures
7---------------
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9`struct name_entry`::
10
11 An entry in a tree. Each entry has a sha1 identifier, pathname, and
12 mode.
13
14`struct tree_desc`::
15
16 A semi-opaque data structure used to maintain the current state of the
17 walk.
18+
19* `buffer` is a pointer into the memory representation of the tree. It always
20points at the current entry being visited.
21
22* `size` counts the number of bytes left in the `buffer`.
23
24* `entry` points to the current entry being visited.
25
26`struct traverse_info`::
27
28 A structure used to maintain the state of a traversal.
29+
30* `prev` points to the traverse_info which was used to descend into the
31current tree. If this is the top-level tree `prev` will point to
32a dummy traverse_info.
33
34* `name` is the entry for the current tree (if the tree is a subtree).
35
36* `pathlen` is the length of the full path for the current tree.
37
38* `conflicts` can be used by callbacks to maintain directory-file conflicts.
39
40* `fn` is a callback called for each entry in the tree. See Traversing for more
41information.
42
43* `data` can be anything the `fn` callback would want to use.
44
45Initializing
46------------
47
48`init_tree_desc`::
49
50 Initialize a `tree_desc` and decode its first entry. The buffer and
51 size parameters are assumed to be the same as the buffer and size
52 members of `struct tree`.
53
54`fill_tree_descriptor`::
55
56 Initialize a `tree_desc` and decode its first entry given the sha1 of
57 a tree. Returns the `buffer` member if the sha1 is a valid tree
58 identifier and NULL otherwise.
59
60`setup_traverse_info`::
61
62 Initialize a `traverse_info` given the pathname of the tree to start
63 traversing from. The `base` argument is assumed to be the `path`
64 member of the `name_entry` being recursed into unless the tree is a
65 top-level tree in which case the empty string ("") is used.
66
67Walking
68-------
69
70`tree_entry`::
71
72 Visit the next entry in a tree. Returns 1 when there are more entries
73 left to visit and 0 when all entries have been visited. This is
74 commonly used in the test of a while loop.
75
76`tree_entry_len`::
77
78 Calculate the length of a tree entry's pathname. This utilizes the
79 memory structure of a tree entry to avoid the overhead of using a
80 generic strlen().
81
82`update_tree_entry`::
83
84 Walk to the next entry in a tree. This is commonly used in conjunction
85 with `tree_entry_extract` to inspect the current entry.
86
87`tree_entry_extract`::
88
89 Decode the entry currently being visited (the one pointed to by
90 `tree_desc's` `entry` member) and return the sha1 of the entry. The
91 `pathp` and `modep` arguments are set to the entry's pathname and mode
92 respectively.
93
94`get_tree_entry`::
95
96 Find an entry in a tree given a pathname and the sha1 of a tree to
97 search. Returns 0 if the entry is found and -1 otherwise. The third
98 and fourth parameters are set to the entry's sha1 and mode
99 respectively.
100
101Traversing
102----------
103
104`traverse_trees`::
105
106 Traverse `n` number of trees in parallel. The `fn` callback member of
107 `traverse_info` is called once for each tree entry.
108
109`traverse_callback_t`::
110 The arguments passed to the traverse callback are as follows:
111+
112* `n` counts the number of trees being traversed.
113
114* `mask` has its nth bit set if something exists in the nth entry.
115
116* `dirmask` has its nth bit set if the nth tree's entry is a directory.
117
118* `entry` is an array of size `n` where the nth entry is from the nth tree.
119
120* `info` maintains the state of the traversal.
121
122+
123Returning a negative value will terminate the traversal. Otherwise the
124return value is treated as an update mask. If the nth bit is set the nth tree
125will be updated and if the bit is not set the nth tree entry will be the
126same in the next callback invocation.
127
128`make_traverse_path`::
129
130 Generate the full pathname of a tree entry based from the root of the
131 traversal. For example, if the traversal has recursed into another
132 tree named "bar" the pathname of an entry "baz" in the "bar"
133 tree would be "bar/baz".
134
135`traverse_path_len`::
136
137 Calculate the length of a pathname returned by `make_traverse_path`.
138 This utilizes the memory structure of a tree entry to avoid the
139 overhead of using a generic strlen().
140
141Authors
142-------
143
144Written by Junio C Hamano <gitster@pobox.com> and Linus Torvalds
145<torvalds@linux-foundation.org>