Tests: add tests for leading (relative) slashes for BLI_path_join

Also note that leading slashes are kept in the doc-string.

3 files changed, 18 insertions, 3 deletions

diff --git a/source/blender/blenlib/BLI_path_util.h b/source/blender/blenlib/BLI_path_util.h
index 75002f52d94..136258e50f2 100644
--- a/source/blender/blenlib/BLI_path_util.h
+++ b/source/blender/blenlib/BLI_path_util.h
@@ -84,10 +84,18 @@ void BLI_join_dirfile(char *__restrict dst,
  * Join multiple strings into a path, ensuring only a single path separator between each,
  * and trailing slash is kept.
  *
+ * \param path: The first patch which has special treatment,
+ * allowing `//` prefix which is kept intact unlike double-slashes which are stripped
+ * from the bounds of all other paths passed in.
+ * Passing in the following paths all result in the same output (`//a/b/c`):
+ * - `"//", "a", "b", "c"`.
+ * - `"//", "/a/", "/b/", "/c"`.
+ * - `"//a", "b/c"`.
+ *
  * \note If you want a trailing slash, add `SEP_STR` as the last path argument,
  * duplicate slashes will be cleaned up.
  */
-size_t BLI_path_join(char *__restrict dst, size_t dst_len, const char *path_first, ...)
+size_t BLI_path_join(char *__restrict dst, size_t dst_len, const char *path, ...)
     ATTR_NONNULL(1, 3) ATTR_SENTINEL(0);
 /**
  * Like Python's `os.path.basename()`
diff --git a/source/blender/blenlib/intern/path_util.c b/source/blender/blenlib/intern/path_util.c
index 1e95aa3b7b0..c053c3907db 100644
--- a/source/blender/blenlib/intern/path_util.c
+++ b/source/blender/blenlib/intern/path_util.c
@@ -1505,8 +1505,8 @@ size_t BLI_path_join(char *__restrict dst, const size_t dst_len, const char *pat
     return ofs;
   }
 
-  /* remove trailing slashes, unless there are _only_ trailing slashes
-   * (allow "//" as the first argument). */
+  /* Remove trailing slashes, unless there are *only* trailing slashes
+   * (allow `//` or `//some_path` as the first argument). */
   bool has_trailing_slash = false;
   if (ofs != 0) {
     size_t len = ofs;
diff --git a/source/blender/blenlib/tests/BLI_path_util_test.cc b/source/blender/blenlib/tests/BLI_path_util_test.cc
index 4f6f4a5c413..54afc3d975d 100644
--- a/source/blender/blenlib/tests/BLI_path_util_test.cc
+++ b/source/blender/blenlib/tests/BLI_path_util_test.cc
@@ -298,6 +298,13 @@ TEST(path_util, JoinComplex)
   JOIN("1/2/3/", 100, "1", "////////", "", "2", "3\\");
 }
 
+TEST(path_util, JoinRelativePrefix)
+{
+  JOIN("//a/b/c", 100, "//a", "b", "c");
+  JOIN("//a/b/c", 100, "//", "//a//", "//b//", "//c");
+  JOIN("//a/b/c", 100, "//", "//", "a", "//", "b", "//", "c");
+}
+
 #undef JOIN
 
 /* BLI_path_frame */