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diff --git a/tree-walk.h b/tree-walk.h
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+#ifndef TREE_WALK_H
+#define TREE_WALK_H
+
+#include "cache.h"
+
+#define MAX_TRAVERSE_TREES 8
+
+/**
+ * The tree walking API is used to traverse and inspect trees.
+ */
+
+/**
+ * An entry in a tree. Each entry has a sha1 identifier, pathname, and mode.
+ */
+struct name_entry {
+	struct object_id oid;
+	const char *path;
+	int pathlen;
+	unsigned int mode;
+};
+
+/**
+ * A semi-opaque data structure used to maintain the current state of the walk.
+ */
+struct tree_desc {
+	/*
+	 * pointer into the memory representation of the tree. It always
+	 * points at the current entry being visited.
+	 */
+	const void *buffer;
+
+	/* points to the current entry being visited. */
+	struct name_entry entry;
+
+	/* counts the number of bytes left in the `buffer`. */
+	unsigned int size;
+
+	/* option flags passed via init_tree_desc_gently() */
+	enum tree_desc_flags {
+		TREE_DESC_RAW_MODES = (1 << 0),
+	} flags;
+};
+
+/**
+ * Decode the entry currently being visited (the one pointed to by
+ * `tree_desc's` `entry` member) and return the sha1 of the entry. The
+ * `pathp` and `modep` arguments are set to the entry's pathname and mode
+ * respectively.
+ */
+static inline const struct object_id *tree_entry_extract(struct tree_desc *desc, const char **pathp, unsigned short *modep)
+{
+	*pathp = desc->entry.path;
+	*modep = desc->entry.mode;
+	return &desc->entry.oid;
+}
+
+/**
+ * Calculate the length of a tree entry's pathname. This utilizes the
+ * memory structure of a tree entry to avoid the overhead of using a
+ * generic strlen().
+ */
+static inline int tree_entry_len(const struct name_entry *ne)
+{
+	return ne->pathlen;
+}
+
+/*
+ * The _gently versions of these functions warn and return false on a
+ * corrupt tree entry rather than dying,
+ */
+
+/**
+ * Walk to the next entry in a tree. This is commonly used in conjunction
+ * with `tree_entry_extract` to inspect the current entry.
+ */
+void update_tree_entry(struct tree_desc *);
+
+int update_tree_entry_gently(struct tree_desc *);
+
+/**
+ * Initialize a `tree_desc` and decode its first entry. The buffer and
+ * size parameters are assumed to be the same as the buffer and size
+ * members of `struct tree`.
+ */
+void init_tree_desc(struct tree_desc *desc, const void *buf, unsigned long size);
+
+int init_tree_desc_gently(struct tree_desc *desc, const void *buf, unsigned long size,
+			  enum tree_desc_flags flags);
+
+/*
+ * Visit the next entry in a tree. Returns 1 when there are more entries
+ * left to visit and 0 when all entries have been visited. This is
+ * commonly used in the test of a while loop.
+ */
+int tree_entry(struct tree_desc *, struct name_entry *);
+
+int tree_entry_gently(struct tree_desc *, struct name_entry *);
+
+/**
+ * Initialize a `tree_desc` and decode its first entry given the
+ * object ID of a tree. Returns the `buffer` member if the latter
+ * is a valid tree identifier and NULL otherwise.
+ */
+void *fill_tree_descriptor(struct repository *r,
+			   struct tree_desc *desc,
+			   const struct object_id *oid);
+
+struct traverse_info;
+typedef int (*traverse_callback_t)(int n, unsigned long mask, unsigned long dirmask, struct name_entry *entry, struct traverse_info *);
+
+/**
+ * Traverse `n` number of trees in parallel. The `fn` callback member of
+ * `traverse_info` is called once for each tree entry.
+ */
+int traverse_trees(struct index_state *istate, int n, struct tree_desc *t, struct traverse_info *info);
+
+enum get_oid_result get_tree_entry_follow_symlinks(struct repository *r, struct object_id *tree_oid, const char *name, struct object_id *result, struct strbuf *result_path, unsigned short *mode);
+
+/**
+ * A structure used to maintain the state of a traversal.
+ */
+struct traverse_info {
+	const char *traverse_path;
+
+	/*
+	 * points to the traverse_info which was used to descend into the
+	 * current tree. If this is the top-level tree `prev` will point to
+	 * a dummy traverse_info.
+	 */
+	struct traverse_info *prev;
+
+	/* is the entry for the current tree (if the tree is a subtree). */
+	const char *name;
+
+	size_t namelen;
+	unsigned mode;
+
+	/* is the length of the full path for the current tree. */
+	size_t pathlen;
+
+	struct pathspec *pathspec;
+
+	/* can be used by callbacks to maintain directory-file conflicts. */
+	unsigned long df_conflicts;
+
+	/* a callback called for each entry in the tree.
+	 *
+	 * The arguments passed to the traverse callback are as follows:
+	 *
+	 * - `n` counts the number of trees being traversed.
+	 *
+	 * - `mask` has its nth bit set if something exists in the nth entry.
+	 *
+	 * - `dirmask` has its nth bit set if the nth tree's entry is a directory.
+	 *
+	 * - `entry` is an array of size `n` where the nth entry is from the nth tree.
+	 *
+	 * - `info` maintains the state of the traversal.
+	 *
+	 * Returning a negative value will terminate the traversal. Otherwise the
+	 * return value is treated as an update mask. If the nth bit is set the nth tree
+	 * will be updated and if the bit is not set the nth tree entry will be the
+	 * same in the next callback invocation.
+	 */
+	traverse_callback_t fn;
+
+	/* can be anything the `fn` callback would want to use. */
+	void *data;
+
+	/* tells whether to stop at the first error or not. */
+	int show_all_errors;
+};
+
+/**
+ * Find an entry in a tree given a pathname and the sha1 of a tree to
+ * search. Returns 0 if the entry is found and -1 otherwise. The third
+ * and fourth parameters are set to the entry's sha1 and mode respectively.
+ */
+int get_tree_entry(struct repository *, const struct object_id *, const char *, struct object_id *, unsigned short *);
+
+/**
+ * Generate the full pathname of a tree entry based from the root of the
+ * traversal. For example, if the traversal has recursed into another
+ * tree named "bar" the pathname of an entry "baz" in the "bar"
+ * tree would be "bar/baz".
+ */
+char *make_traverse_path(char *path, size_t pathlen, const struct traverse_info *info,
+			 const char *name, size_t namelen);
+
+/**
+ * Convenience wrapper to `make_traverse_path` into a strbuf.
+ */
+void strbuf_make_traverse_path(struct strbuf *out,
+			       const struct traverse_info *info,
+			       const char *name, size_t namelen);
+
+/**
+ * Initialize a `traverse_info` given the pathname of the tree to start
+ * traversing from.
+ */
+void setup_traverse_info(struct traverse_info *info, const char *base);
+
+/**
+ * Calculate the length of a pathname returned by `make_traverse_path`.
+ * This utilizes the memory structure of a tree entry to avoid the
+ * overhead of using a generic strlen().
+ */
+static inline size_t traverse_path_len(const struct traverse_info *info,
+				       size_t namelen)
+{
+	return st_add(info->pathlen, namelen);
+}
+
+/* in general, positive means "kind of interesting" */
+enum interesting {
+	all_entries_not_interesting = -1, /* no, and no subsequent entries will be either */
+	entry_not_interesting = 0,
+	entry_interesting = 1,
+	all_entries_interesting = 2 /* yes, and all subsequent entries will be */
+};
+
+enum interesting tree_entry_interesting(struct index_state *istate,
+					const struct name_entry *,
+					struct strbuf *, int,
+					const struct pathspec *ps);
+
+#endif