[PATCH v2 1/2] Introduce the function strip_path_suffix()

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The function strip_path_suffix() will try to strip a given suffix from 
a given path.  The suffix must start at a directory boundary (i.e. "core" 
is not a path suffix of "libexec/git-core", but "git-core" is).

Arbitrary runs of directory separators ("slashes") are assumed identical.

Example:

	strip_path_suffix("C:\\msysgit/\\libexec\\git-core",
		"libexec///git-core", &prefix)

will set prefix to "C:\\msysgit" and return 0.

Signed-off-by: Johannes Schindelin <johannes.schindelin@xxxxxx>
---
 cache.h               |    1 +
 path.c                |   32 ++++++++++++++++++++++++++++++++
 t/t0060-path-utils.sh |    4 ++++
 test-path-utils.c     |    6 ++++++
 4 files changed, 43 insertions(+), 0 deletions(-)

diff --git a/cache.h b/cache.h
index c926bc7..1fa184d 100644
--- a/cache.h
+++ b/cache.h
@@ -630,6 +630,7 @@ const char *make_nonrelative_path(const char *path);
 const char *make_relative_path(const char *abs, const char *base);
 int normalize_path_copy(char *dst, const char *src);
 int longest_ancestor_length(const char *path, const char *prefix_list);
+char *strip_path_suffix(const char *path, const char *suffix);
 
 /* Read and unpack a sha1 file into memory, write memory to a sha1 file */
 extern int sha1_object_info(const unsigned char *, unsigned long *);
diff --git a/path.c b/path.c
index 4b9107f..2030bf1 100644
--- a/path.c
+++ b/path.c
@@ -499,3 +499,35 @@ int longest_ancestor_length(const char *path, const char *prefix_list)
 
 	return max_len;
 }
+
+/* strip arbitrary amount of directory separators at end of path */
+static inline int chomp_trailing_dir_sep(const char *path, int len)
+{
+	while (len && is_dir_sep(path[len - 1]))
+		len--;
+	return len;
+}
+
+/* sets prefix if the suffix matches */
+char *strip_path_suffix(const char *path, const char *suffix)
+{
+	int path_len = strlen(path), suffix_len = strlen(suffix);
+
+	while (suffix_len) {
+		if (!path_len)
+			return NULL;
+
+		if (is_dir_sep(path[path_len - 1])) {
+			if (!is_dir_sep(suffix[suffix_len - 1]))
+				return NULL;
+			path_len = chomp_trailing_dir_sep(path, path_len);
+			suffix_len = chomp_trailing_dir_sep(suffix, suffix_len);
+		}
+		else if (path[--path_len] != suffix[--suffix_len])
+			return NULL;
+	}
+
+	if (path_len && !is_dir_sep(path[path_len - 1]))
+		return NULL;
+	return xstrndup(path, chomp_trailing_dir_sep(path, path_len));
+}
diff --git a/t/t0060-path-utils.sh b/t/t0060-path-utils.sh
index 4ed1f0b..8336114 100755
--- a/t/t0060-path-utils.sh
+++ b/t/t0060-path-utils.sh
@@ -85,4 +85,8 @@ ancestor /foo/bar :://foo/.:: 4
 ancestor /foo/bar //foo/./::/bar 4
 ancestor /foo/bar ::/bar -1
 
+test_expect_success 'strip_path_suffix' '
+	test c:/msysgit = $(test-path-utils strip_path_suffix \
+		c:/msysgit/libexec//git-core libexec/git-core)
+'
 test_done
diff --git a/test-path-utils.c b/test-path-utils.c
index 5168a8e..d261398 100644
--- a/test-path-utils.c
+++ b/test-path-utils.c
@@ -26,6 +26,12 @@ int main(int argc, char **argv)
 		return 0;
 	}
 
+	if (argc == 4 && !strcmp(argv[1], "strip_path_suffix")) {
+		char *prefix = strip_path_suffix(argv[2], argv[3]);
+		printf("%s\n", prefix ? prefix : "(null)");
+		return 0;
+	}
+
 	fprintf(stderr, "%s: unknown function name: %s\n", argv[0],
 		argv[1] ? argv[1] : "(there was none)");
 	return 1;
-- 
1.6.2.rc1.380.g0299c

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