Documentation/technical/api-gitattributes.txt

   1 gitattributes API
   2 =================
   3
   4 gitattributes mechanism gives a uniform way to associate various
   5 attributes to set of paths.
   6
   7
   8 Data Structure
   9 --------------
  10
  11 `struct git_attr`::
  12
  13         An attribute is an opaque object that is identified by its name.
  14         Pass the name to `git_attr()` function to obtain the object of
  15         this type.  The internal representation of this structure is
  16         of no interest to the calling programs.  The name of the
  17         attribute can be retrieved by calling `git_attr_name()`.
  18
  19 `struct attr_check_item`::
  20
  21         This structure represents one attribute and its value.
  22
  23 `struct attr_check`::
  24
  25         This structure represents a collection of `attr_check_item`.
  26         It is passed to `git_check_attr()` function, specifying the
  27         attributes to check, and receives their values.
  28
  29
  30 Attribute Values
  31 ----------------
  32
  33 An attribute for a path can be in one of four states: Set, Unset,
  34 Unspecified or set to a string, and `.value` member of `struct
  35 attr_check_item` records it.  There are three macros to check these:
  36
  37 `ATTR_TRUE()`::
  38
  39         Returns true if the attribute is Set for the path.
  40
  41 `ATTR_FALSE()`::
  42
  43         Returns true if the attribute is Unset for the path.
  44
  45 `ATTR_UNSET()`::
  46
  47         Returns true if the attribute is Unspecified for the path.
  48
  49 If none of the above returns true, `.value` member points at a string
  50 value of the attribute for the path.
  51
  52
  53 Querying Specific Attributes
  54 ----------------------------
  55
  56 * Prepare `struct attr_check` using attr_check_initl()
  57   function, enumerating the names of attributes whose values you are
  58   interested in, terminated with a NULL pointer.  Alternatively, an
  59   empty `struct attr_check` can be prepared by calling
  60   `attr_check_alloc()` function and then attributes you want to
  61   ask about can be added to it with `attr_check_append()`
  62   function.
  63
  64 * Call `git_check_attr()` to check the attributes for the path.
  65
  66 * Inspect `attr_check` structure to see how each of the
  67   attribute in the array is defined for the path.
  68
  69
  70 Example
  71 -------
  72
  73 To see how attributes "crlf" and "ident" are set for different paths.
  74
  75 . Prepare a `struct attr_check` with two elements (because
  76   we are checking two attributes):
  77
  78 ------------
  79 static struct attr_check *check;
  80 static void setup_check(void)
  81 {
  82         if (check)
  83                 return; /* already done */
  84         check = attr_check_initl("crlf", "ident", NULL);
  85 }
  86 ------------
  87
  88 . Call `git_check_attr()` with the prepared `struct attr_check`:
  89
  90 ------------
  91         const char *path;
  92
  93         setup_check();
  94         git_check_attr(path, check);
  95 ------------
  96
  97 . Act on `.value` member of the result, left in `check->items[]`:
  98
  99 ------------
 100         const char *value = check->items[0].value;
 101
 102         if (ATTR_TRUE(value)) {
 103                 The attribute is Set, by listing only the name of the
 104                 attribute in the gitattributes file for the path.
 105         } else if (ATTR_FALSE(value)) {
 106                 The attribute is Unset, by listing the name of the
 107                 attribute prefixed with a dash - for the path.
 108         } else if (ATTR_UNSET(value)) {
 109                 The attribute is neither set nor unset for the path.
 110         } else if (!strcmp(value, "input")) {
 111                 If none of ATTR_TRUE(), ATTR_FALSE(), or ATTR_UNSET() is
 112                 true, the value is a string set in the gitattributes
 113                 file for the path by saying "attr=value".
 114         } else if (... other check using value as string ...) {
 115                 ...
 116         }
 117 ------------
 118
 119 To see how attributes in argv[] are set for different paths, only
 120 the first step in the above would be different.
 121
 122 ------------
 123 static struct attr_check *check;
 124 static void setup_check(const char **argv)
 125 {
 126         check = attr_check_alloc();
 127         while (*argv) {
 128                 struct git_attr *attr = git_attr(*argv);
 129                 attr_check_append(check, attr);
 130                 argv++;
 131         }
 132 }
 133 ------------
 134
 135
 136 Querying All Attributes
 137 -----------------------
 138
 139 To get the values of all attributes associated with a file:
 140
 141 * Prepare an empty `attr_check` structure by calling
 142   `attr_check_alloc()`.
 143
 144 * Call `git_all_attrs()`, which populates the `attr_check`
 145   with the attributes attached to the path.
 146
 147 * Iterate over the `attr_check.items[]` array to examine
 148   the attribute names and values.  The name of the attribute
 149   described by an `attr_check.items[]` object can be retrieved via
 150   `git_attr_name(check->items[i].attr)`.  (Please note that no items
 151   will be returned for unset attributes, so `ATTR_UNSET()` will return
 152   false for all returned `attr_check.items[]` objects.)
 153
 154 * Free the `attr_check` struct by calling `attr_check_free()`.