[PATCH v2 6/9] strbuf: introduce strbuf_strip_file_from_path()

["Derrick Stolee via GitGitGadget" <gitgitgadget@gmail.com>]

From: Derrick Stolee <derrickstolee@github.com>

The strbuf_parent_directory() method was added as a static method in
contrib/scalar by d0feac4e8c0 (scalar: 'register' sets recommended
config and starts maintenance, 2021-12-03) and then removed in
65f6a9eb0b9 (scalar: constrain enlistment search, 2022-08-18), but now
there is a need for a similar method in the bundle URI feature.

Re-add the method, this time in strbuf.c, but with a new name:
strbuf_strip_file_from_path(). The method requirements are slightly
modified to allow a trailing slash, in which case nothing is done, which
makes the name change valuable. The return value is the number of bytes
removed.

Signed-off-by: Derrick Stolee <derrickstolee@github.com>
---
 strbuf.c |  9 +++++++++
 strbuf.h | 12 ++++++++++++
 2 files changed, 21 insertions(+)

diff --git a/strbuf.c b/strbuf.c
index 0890b1405c5..8d1e2e8bb61 100644
--- a/strbuf.c
+++ b/strbuf.c
@@ -1200,3 +1200,12 @@ int strbuf_edit_interactively(struct strbuf *buffer, const char *path,
 	free(path2);
 	return res;
 }
+
+size_t strbuf_strip_file_from_path(struct strbuf *buf)
+{
+	size_t len = buf->len;
+	size_t offset = offset_1st_component(buf->buf);
+	char *path_sep = find_last_dir_sep(buf->buf + offset);
+	strbuf_setlen(buf, path_sep ? path_sep - buf->buf + 1 : offset);
+	return len - buf->len;
+}
diff --git a/strbuf.h b/strbuf.h
index 76965a17d44..4822b713786 100644
--- a/strbuf.h
+++ b/strbuf.h
@@ -664,6 +664,18 @@ int launch_sequence_editor(const char *path, struct strbuf *buffer,
 int strbuf_edit_interactively(struct strbuf *buffer, const char *path,
 			      const char *const *env);
 
+/*
+ * Remove the filename from the provided path string. If the path
+ * contains a trailing separator, then the path is considered a directory
+ * and nothing is modified. Returns the number of characters removed from
+ * the path.
+ *
+ * Examples:
+ * - "/path/to/file" -> "/path/to/" (returns: 4)
+ * - "/path/to/dir/" -> "/path/to/dir/" (returns: 0)
+ */
+size_t strbuf_strip_file_from_path(struct strbuf *buf);
+
 void strbuf_add_lines(struct strbuf *sb,
 		      const char *prefix,
 		      const char *buf,
-- 
gitgitgadget