From 638bf05a23e1ef7dddd3b5d42d9521d8849a4375 Mon Sep 17 00:00:00 2001
From: Campbell Barton <campbell@blender.org>
Date: Wed, 2 Nov 2022 16:56:37 +1100
Subject: Fix BLI_path_parent_dir returning success with a single period as
 input

While relatively harmless, BLI_path_parent_dir wasn't returning failure
when passed in "./" which wouldn't succeed.

Instead of adding a ".." and normalizing, normalize the path and remove
the last directly. This is simpler than inspecting the resulting path
to see if normalize removed it or not.

Add additional tests which failed previously.
---
 source/blender/blenlib/intern/path_util.c          | 18 ++++++++++------
 source/blender/blenlib/tests/BLI_path_util_test.cc | 25 +++++++++++++++++++---
 2 files changed, 34 insertions(+), 9 deletions(-)

diff --git a/source/blender/blenlib/intern/path_util.c b/source/blender/blenlib/intern/path_util.c
index 7c08eeedaa2..3a87b39a446 100644
--- a/source/blender/blenlib/intern/path_util.c
+++ b/source/blender/blenlib/intern/path_util.c
@@ -626,10 +626,9 @@ bool BLI_path_suffix(char *string, size_t maxlen, const char *suffix, const char
 
 bool BLI_path_parent_dir(char *path)
 {
-  const char parent_dir[] = {'.', '.', SEP, '\0'}; /* "../" or "..\\" */
-  char tmp[FILE_MAX + 4];
+  char tmp[FILE_MAX];
 
-  BLI_path_join(tmp, sizeof(tmp), path, parent_dir);
+  STRNCPY(tmp, path);
   /* Does all the work of normalizing the path for us.
    *
    * NOTE(@campbellbarton): While it's possible strip text after the second last slash,
@@ -645,12 +644,19 @@ bool BLI_path_parent_dir(char *path)
    *   which would cause checking for a tailing `/../` fail.
    * Extracting the span of the final directory avoids both these issues. */
   int tail_ofs = 0, tail_len = 0;
-  if (BLI_path_name_at_index(tmp, -1, &tail_ofs, &tail_len) && (tail_len == 2) &&
-      (memcmp(&tmp[tail_ofs], "..", 2) == 0)) {
+  if (!BLI_path_name_at_index(tmp, -1, &tail_ofs, &tail_len)) {
     return false;
   }
+  if (tail_len == 1) {
+    /* Last path is ".", as normalize should remove this, it's safe to assume failure.
+     * This happens when the input a single period (possibly with slashes before or after). */
+    if (tmp[tail_ofs] == '.') {
+      return false;
+    }
+  }
 
-  strcpy(path, tmp); /* We assume the parent directory is always shorter. */
+  memcpy(path, tmp, tail_ofs);
+  path[tail_ofs] = '\0';
   return true;
 }
 
diff --git a/source/blender/blenlib/tests/BLI_path_util_test.cc b/source/blender/blenlib/tests/BLI_path_util_test.cc
index 379ff432988..293d353efcc 100644
--- a/source/blender/blenlib/tests/BLI_path_util_test.cc
+++ b/source/blender/blenlib/tests/BLI_path_util_test.cc
@@ -102,8 +102,6 @@ TEST(path_util, Clean_Parent)
 /** \name Tests for: #BLI_path_parent_dir
  * \{ */
 
-TEST(path_util, ParentDir)
-{
 #define PARENT_DIR(input, output) \
   { \
     char path[FILE_MAX] = input; \
@@ -118,12 +116,25 @@ TEST(path_util, ParentDir)
   } \
   ((void)0)
 
+TEST(path_util, ParentDir_Simple)
+{
   PARENT_DIR("/a/b/", "/a/");
   PARENT_DIR("/a/b", "/a/");
   PARENT_DIR("/a", "/");
+}
+
+TEST(path_util, ParentDir_NOP)
+{
   PARENT_DIR("/", "/");
   PARENT_DIR("", "");
+  PARENT_DIR(".", ".");
+  PARENT_DIR("./", "./");
+  PARENT_DIR(".//", ".//");
+  PARENT_DIR("./.", "./.");
+}
 
+TEST(path_util, ParentDir_TrailingPeriod)
+{
   /* Ensure trailing dots aren't confused with parent path. */
   PARENT_DIR("/.../.../.../", "/.../.../");
   PARENT_DIR("/.../.../...", "/.../.../");
@@ -133,10 +144,18 @@ TEST(path_util, ParentDir)
 
   PARENT_DIR("/a./b./c./", "/a./b./");
   PARENT_DIR("/a./b./c.", "/a./b./");
+}
 
-#undef PARENT_DIR
+TEST(path_util, ParentDir_Complex)
+{
+  PARENT_DIR("./a/", "./");
+  PARENT_DIR("./a", "./");
+  PARENT_DIR("../a/", "../");
+  PARENT_DIR("../a", "../");
 }
 
+#undef PARENT_DIR
+
 /** \} */
 
 /* -------------------------------------------------------------------- */
-- 
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