The first batch of topics after the 2.14 cycle
[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
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45* `show_all_errors` tells whether to stop at the first error or not.
46
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47Initializing
48------------
49
50`init_tree_desc`::
51
52 Initialize a `tree_desc` and decode its first entry. The buffer and
53 size parameters are assumed to be the same as the buffer and size
54 members of `struct tree`.
55
56`fill_tree_descriptor`::
57
58 Initialize a `tree_desc` and decode its first entry given the sha1 of
59 a tree. Returns the `buffer` member if the sha1 is a valid tree
60 identifier and NULL otherwise.
61
62`setup_traverse_info`::
63
64 Initialize a `traverse_info` given the pathname of the tree to start
65 traversing from. The `base` argument is assumed to be the `path`
66 member of the `name_entry` being recursed into unless the tree is a
67 top-level tree in which case the empty string ("") is used.
68
69Walking
70-------
71
72`tree_entry`::
73
74 Visit the next entry in a tree. Returns 1 when there are more entries
75 left to visit and 0 when all entries have been visited. This is
76 commonly used in the test of a while loop.
77
78`tree_entry_len`::
79
80 Calculate the length of a tree entry's pathname. This utilizes the
81 memory structure of a tree entry to avoid the overhead of using a
82 generic strlen().
83
84`update_tree_entry`::
85
86 Walk to the next entry in a tree. This is commonly used in conjunction
87 with `tree_entry_extract` to inspect the current entry.
88
89`tree_entry_extract`::
90
91 Decode the entry currently being visited (the one pointed to by
92 `tree_desc's` `entry` member) and return the sha1 of the entry. The
93 `pathp` and `modep` arguments are set to the entry's pathname and mode
94 respectively.
95
96`get_tree_entry`::
97
98 Find an entry in a tree given a pathname and the sha1 of a tree to
99 search. Returns 0 if the entry is found and -1 otherwise. The third
100 and fourth parameters are set to the entry's sha1 and mode
101 respectively.
102
103Traversing
104----------
105
106`traverse_trees`::
107
108 Traverse `n` number of trees in parallel. The `fn` callback member of
109 `traverse_info` is called once for each tree entry.
110
111`traverse_callback_t`::
112 The arguments passed to the traverse callback are as follows:
113+
114* `n` counts the number of trees being traversed.
115
116* `mask` has its nth bit set if something exists in the nth entry.
117
118* `dirmask` has its nth bit set if the nth tree's entry is a directory.
119
120* `entry` is an array of size `n` where the nth entry is from the nth tree.
121
122* `info` maintains the state of the traversal.
123
124+
125Returning a negative value will terminate the traversal. Otherwise the
126return value is treated as an update mask. If the nth bit is set the nth tree
127will be updated and if the bit is not set the nth tree entry will be the
128same in the next callback invocation.
129
130`make_traverse_path`::
131
132 Generate the full pathname of a tree entry based from the root of the
133 traversal. For example, if the traversal has recursed into another
134 tree named "bar" the pathname of an entry "baz" in the "bar"
135 tree would be "bar/baz".
136
137`traverse_path_len`::
138
139 Calculate the length of a pathname returned by `make_traverse_path`.
140 This utilizes the memory structure of a tree entry to avoid the
141 overhead of using a generic strlen().
142
143Authors
144-------
145
146Written by Junio C Hamano <gitster@pobox.com> and Linus Torvalds
147<torvalds@linux-foundation.org>