gitattributes API

gitattributes mechanism gives a uniform way to associate various attributes to set of paths.

Data Structure

struct git_attr: An attribute is an opaque object that is identified by its name. Pass the name to git_attr() function to obtain the object of this type. The internal representation of this structure is of no interest to the calling programs. The name of the attribute can be retrieved by calling git_attr_name().
struct attr_check_item: This structure represents one attribute and its value.
struct attr_check: This structure represents a collection of attr_check_item. It is passed to git_check_attr() function, specifying the attributes to check, and receives their values.

Attribute Values

An attribute for a path can be in one of four states: Set, Unset, Unspecified or set to a string, and .value member of struct attr_check_item records it. There are three macros to check these:

ATTR_TRUE(): Returns true if the attribute is Set for the path.
ATTR_FALSE(): Returns true if the attribute is Unset for the path.
ATTR_UNSET(): Returns true if the attribute is Unspecified for the path.

If none of the above returns true, .value member points at a string value of the attribute for the path.

Querying Specific Attributes

Prepare struct attr_check using attr_check_initl() function, enumerating the names of attributes whose values you are interested in, terminated with a NULL pointer. Alternatively, an empty struct attr_check can be prepared by calling attr_check_alloc() function and then attributes you want to ask about can be added to it with attr_check_append() function.
Call git_check_attr() to check the attributes for the path.
Inspect attr_check structure to see how each of the attribute in the array is defined for the path.

Example

To see how attributes "crlf" and "ident" are set for different paths.

Prepare a struct attr_check with two elements (because we are checking two attributes):

static struct attr_check *check;
static void setup_check(void)
{
        if (check)
                return; /* already done */
        check = attr_check_initl("crlf", "ident", NULL);
}

Call git_check_attr() with the prepared struct attr_check:

        const char *path;

        setup_check();
        git_check_attr(path, check);

Act on .value member of the result, left in check->items[]:

        const char *value = check->items[0].value;

        if (ATTR_TRUE(value)) {
                The attribute is Set, by listing only the name of the
                attribute in the gitattributes file for the path.
        } else if (ATTR_FALSE(value)) {
                The attribute is Unset, by listing the name of the
                attribute prefixed with a dash - for the path.
        } else if (ATTR_UNSET(value)) {
                The attribute is neither set nor unset for the path.
        } else if (!strcmp(value, "input")) {
                If none of ATTR_TRUE(), ATTR_FALSE(), or ATTR_UNSET() is
                true, the value is a string set in the gitattributes
                file for the path by saying "attr=value".
        } else if (... other check using value as string ...) {
                ...
        }

To see how attributes in argv[] are set for different paths, only the first step in the above would be different.

static struct attr_check *check;
static void setup_check(const char **argv)
{
        check = attr_check_alloc();
        while (*argv) {
                struct git_attr *attr = git_attr(*argv);
                attr_check_append(check, attr);
                argv++;
        }
}

Querying All Attributes

To get the values of all attributes associated with a file:

Prepare an empty attr_check structure by calling attr_check_alloc().
Call git_all_attrs(), which populates the attr_check with the attributes attached to the path.
Iterate over the attr_check.items[] array to examine the attribute names and values. The name of the attribute described by an attr_check.items[] object can be retrieved via git_attr_name(check->items[i].attr). (Please note that no items will be returned for unset attributes, so ATTR_UNSET() will return false for all returned attr_check.items[] objects.)
Free the attr_check struct by calling attr_check_free().