# Path-Walk API

The path-walk API is used to walk reachable objects, but to visit objects in batches based on a common path they appear in, or by type.

For example, all reachable commits are visited in a group. All tags are visited in a group. Then, all root trees are visited. At some point, all blobs reachable via a path `my/dir/to/A` are visited. When there are multiple paths possible to reach the same object, then only one of those paths is used to visit the object.

## Basics

To use the path-walk API, include `path-walk.h` and call `walk_objects_by_path`() with a customized `path_walk_info` struct. The struct is used to set all of the options for how the walk should proceed. Let’s dig into the different options and their use.

`path_fn` and `path_fn_data`

  The most important option is the `path_fn` option, which is a function pointer to the callback that can execute logic on the object IDs for objects grouped by type and path. This function also receives a `data` value that corresponds to the `path_fn_data` member, for providing custom data structures to this callback function.

`revs`

  To configure the exact details of the reachable set of objects, use the `revs` member and initialize it using the revision machinery in `revision.h`. Initialize `revs` using calls such as `setup_revisions`() or `parse_revision_opt`(). Do not call `prepare_revision_walk`(), as that will be called within `walk_objects_by_path`().

  It is also important that you do not specify the `--objects` flag for the `revs` struct. The revision walk should only be used to walk commits, and the objects will be walked in a separate way based on those starting commits.

`commits`, `blobs`, `trees`, `tags`

  By default, these members are enabled and signal that the path-walk API should call the `path_fn` on objects of these types. Specialized applications could disable some options to make it simpler to walk the objects or to have fewer calls to `path_fn`.

  While it is possible to walk only commits in this way, consumers would be better off using the revision walk API instead.

`prune_all_uninteresting`

  By default, all reachable paths are emitted by the path-walk API. This option allows consumers to declare that they are not interested in paths where all included objects are marked with the `UNINTERESTING` flag. This requires using the `boundary` option in the revision walk so that the walk emits commits marked with the `UNINTERESTING` flag.

`pl`

  This pattern list pointer allows focusing the path-walk search to a set of patterns, only emitting paths that match the given patterns. See gitignore(5) or git-sparse-checkout(1) for details about pattern lists. When the pattern list uses cone-mode patterns, then the path-walk API can prune the set of paths it walks to improve performance.

## Examples

See example usages in: `t/helper/test-path-walk.c`, `builtin/backfill.c`