1 files changed, 122 insertions, 2 deletions

diff --git a/tree-walk.h b/tree-walk.h
index abe2caf4e0..a5058469e9 100644
--- a/tree-walk.h
+++ b/tree-walk.h
@@ -3,6 +3,15 @@
 
 #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;
@@ -10,12 +19,29 @@ struct name_entry {
 	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;
 };
 
+/**
+ * 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;
@@ -23,6 +49,11 @@ static inline const struct object_id *tree_entry_extract(struct tree_desc *desc,
 	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;
@@ -33,52 +64,141 @@ static inline int tree_entry_len(const struct name_entry *ne)
  * 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);
 
 /*
- * Helper function that does both tree_entry_extract() and update_tree_entry()
- * and returns true for success
+ * 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)
 {