[PATCH 2/4] tree-walk: copy tree_entry_interesting() as is from tree-diff.c

["Nguyễn Thái Ngọc Duy" <pclouds@gmail.com>]

Just a straight copy. The function is not used anywhere. It is to
separate changes that will be made to this function in the next patch.

Signed-off-by: Nguyễn Thái Ngọc Duy <pclouds@gmail.com>
---
 tree-walk.c |  115 +++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 files changed, 115 insertions(+), 0 deletions(-)

diff --git a/tree-walk.c b/tree-walk.c
index a9bbf4e..bc83fa3 100644
--- a/tree-walk.c
+++ b/tree-walk.c
@@ -2,6 +2,7 @@
 #include "tree-walk.h"
 #include "unpack-trees.h"
 #include "tree.h"
+#include "diff.h"
 
 static const char *get_mode(const char *str, unsigned int *modep)
 {
@@ -455,3 +456,117 @@ int get_tree_entry(const unsigned char *tree_sha1, const char *name, unsigned ch
 	free(tree);
 	return retval;
 }
+
+/*
+ * Is a tree entry interesting given the pathspec we have?
+ *
+ * Return:
+ *  - 2 for "yes, and all subsequent entries will be"
+ *  - 1 for yes
+ *  - zero for no
+ *  - negative for "no, and no subsequent entries will be either"
+ */
+static int tree_entry_interesting(struct tree_desc *desc, const char *base, int baselen, struct diff_options *opt)
+{
+	const char *path;
+	const unsigned char *sha1;
+	unsigned mode;
+	int i;
+	int pathlen;
+	int never_interesting = -1;
+
+	if (!opt->nr_paths)
+		return 1;
+
+	sha1 = tree_entry_extract(desc, &path, &mode);
+
+	pathlen = tree_entry_len(path, sha1);
+
+	for (i = 0; i < opt->nr_paths; i++) {
+		const char *match = opt->paths[i];
+		int matchlen = opt->pathlens[i];
+		int m = -1; /* signals that we haven't called strncmp() */
+
+		if (baselen >= matchlen) {
+			/* If it doesn't match, move along... */
+			if (strncmp(base, match, matchlen))
+				continue;
+
+			/*
+			 * If the base is a subdirectory of a path which
+			 * was specified, all of them are interesting.
+			 */
+			if (!matchlen ||
+			    base[matchlen] == '/' ||
+			    match[matchlen - 1] == '/')
+				return 2;
+
+			/* Just a random prefix match */
+			continue;
+		}
+
+		/* Does the base match? */
+		if (strncmp(base, match, baselen))
+			continue;
+
+		match += baselen;
+		matchlen -= baselen;
+
+		if (never_interesting) {
+			/*
+			 * We have not seen any match that sorts later
+			 * than the current path.
+			 */
+
+			/*
+			 * Does match sort strictly earlier than path
+			 * with their common parts?
+			 */
+			m = strncmp(match, path,
+				    (matchlen < pathlen) ? matchlen : pathlen);
+			if (m < 0)
+				continue;
+
+			/*
+			 * If we come here even once, that means there is at
+			 * least one pathspec that would sort equal to or
+			 * later than the path we are currently looking at.
+			 * In other words, if we have never reached this point
+			 * after iterating all pathspecs, it means all
+			 * pathspecs are either outside of base, or inside the
+			 * base but sorts strictly earlier than the current
+			 * one.  In either case, they will never match the
+			 * subsequent entries.  In such a case, we initialized
+			 * the variable to -1 and that is what will be
+			 * returned, allowing the caller to terminate early.
+			 */
+			never_interesting = 0;
+		}
+
+		if (pathlen > matchlen)
+			continue;
+
+		if (matchlen > pathlen) {
+			if (match[pathlen] != '/')
+				continue;
+			if (!S_ISDIR(mode))
+				continue;
+		}
+
+		if (m == -1)
+			/*
+			 * we cheated and did not do strncmp(), so we do
+			 * that here.
+			 */
+			m = strncmp(match, path, pathlen);
+
+		/*
+		 * If common part matched earlier then it is a hit,
+		 * because we rejected the case where path is not a
+		 * leading directory and is shorter than match.
+		 */
+		if (!m)
+			return 1;
+	}
+	return never_interesting; /* No matches */
+}
-- 
1.7.1.rc1.69.g24c2f7