BLI_path: add native path canonicalize function

This function handles cleaning valid system paths that are functional
when passed to `open(..)` but may be relative to the current working
directory or have redundant slashers that can be normalized.

source/blender/blenkernel/BKE_main.h

@@ -120,7 +120,18 @@ enum {
 
 typedef struct Main {
   struct Main *next, *prev;
-  /** The file-path of this blend file, an empty string indicates an unsaved file. */
+  /**
+   * The file-path of this blend file, an empty string indicates an unsaved file.
+   *
+   * \note For the current loaded blend file this path should be absolute & normalized
+   * to prevent redundant leading slashes or current-working-directory relative paths
+   * from causing problems with absolute/relative patch conversion that relies on this being
+   * an absolute path. See #BLI_path_canonicalize_native.
+   *
+   * This rule is not strictly enforced as in some cases loading a #Main is performed
+   * to read data temporarily (preferences & startup) for e.g.
+   * where the `filepath` is not persistent or used as a basis for other paths.
+   */
   char filepath[1024];               /* 1024 = FILE_MAX */
   short versionfile, subversionfile; /* see BLENDER_FILE_VERSION, BLENDER_FILE_SUBVERSION */
   short minversionfile, minsubversionfile;

source/blender/blenkernel/intern/appdir.c

@@ -897,8 +897,7 @@ void BKE_appdir_program_path_init(const char *argv0)
    * Otherwise other methods of detecting the binary that override this argument
    * which must point to the Python module for data-files to be detected. */
   STRNCPY(g_app.program_filepath, argv0);
-  BLI_path_abs_from_cwd(g_app.program_filepath, sizeof(g_app.program_filepath));
-  BLI_path_normalize_native(g_app.program_filepath);
+  BLI_path_canonicalize_native(g_app.program_filepath, sizeof(g_app.program_filepath));
 
   if (g_app.program_dirname[0] == '\0') {
     /* First time initializing, the file binary path isn't valid from a Python module.

source/blender/blenlib/BLI_path_util.h

@@ -185,6 +185,28 @@ void BLI_path_normalize_unc(char *path, int path_maxncpy);
 
 /** \} */
 
+/* -------------------------------------------------------------------- */
+/** \name Path Canonicalize
+ * \{ */
+
+/**
+ * Convert `path` to a canonical representation.
+ * This is intended for system paths (passed in as command-line arguments of via scripts)
+ * which are valid in that they resolve to a file/directory and but could be `CWD` relative or
+ * contain redundant slashes that cause absolute/relative conversion to fail.
+ * (specifically the "//" prefix used by Blender).
+ *
+ * Perform the following operations:
+ *
+ * - Make absolute (relative to the current working directory).
+ * - Convert slash direction (WIN32 only, as other systems may use back-slashes in filenames).
+ * - Normalize redundant slashes.
+ * - Strip trailing slashes.
+ */
+int BLI_path_canonicalize_native(char *path, int path_maxncpy);
+
+/** \} */
+
 /* -------------------------------------------------------------------- */
 /** \name Path FileName Manipulation
  * \{ */

source/blender/blenlib/intern/path_util.c

@@ -43,6 +43,7 @@ static int BLI_path_unc_prefix_len(const char *path);
 
 #ifdef WIN32
 static bool BLI_path_is_abs_win32(const char *path);
+static int BLI_path_win32_prefix_len(const char *path);
 #endif /* WIN32 */
 
 /**
@@ -384,6 +385,29 @@ int BLI_path_normalize_dir(char *dir, size_t dir_maxncpy)
   return BLI_path_slash_ensure_ex(dir, dir_maxncpy, dir_len);
 }
 
+int BLI_path_canonicalize_native(char *path, int path_maxncpy)
+{
+  BLI_path_abs_from_cwd(path, path_maxncpy);
+  /* As these are system level paths, only convert slashes
+   * if the alternate direction is accepted as a slash. */
+  if (BLI_path_slash_is_native_compat(ALTSEP)) {
+    BLI_path_slash_native(path);
+  }
+  int path_len = BLI_path_normalize_native(path);
+  /* Strip trailing slash but don't strip `/` away to nothing. */
+  if (path_len > 1 && path[path_len - 1] == SEP) {
+#ifdef WIN32
+    /* Don't strip `C:\` -> `C:` as this is no longer a valid directory. */
+    if (BLI_path_win32_prefix_len(path) + 1 < path_len)
+#endif
+    {
+      path_len -= 1;
+      path[path_len] = '\0';
+    }
+  }
+  return path_len;
+}
+
 bool BLI_path_make_safe_filename_ex(char *fname, bool allow_tokens)
 {
 #define INVALID_CHARS \
@@ -529,6 +553,16 @@ static int BLI_path_unc_prefix_len(const char *path)
   return 0;
 }
 
+#ifdef WIN32
+static int BLI_path_win32_prefix_len(const char *path)
+{
+  if (BLI_path_is_win32_drive(path)) {
+    return 2;
+  }
+  return BLI_path_unc_prefix_len(path);
+}
+#endif
+
 bool BLI_path_is_win32_drive(const char *path)
 {
   return isalpha(path[0]) && (path[1] == ':');

source/blender/windowmanager/intern/wm_files.cc

@@ -2797,8 +2797,7 @@ static int wm_open_mainfile__open(bContext *C, wmOperator *op)
   bool success;
 
   RNA_string_get(op->ptr, "filepath", filepath);
-  BLI_path_abs_from_cwd(filepath, sizeof(filepath));
-  BLI_path_normalize_native(filepath);
+  BLI_path_canonicalize_native(filepath, sizeof(filepath));
 
   /* re-use last loaded setting so we can reload a file without changing */
   wm_open_init_load_ui(op, false);
@@ -3103,8 +3102,7 @@ static int wm_recover_auto_save_exec(bContext *C, wmOperator *op)
   bool success;
 
   RNA_string_get(op->ptr, "filepath", filepath);
-  BLI_path_abs_from_cwd(filepath, sizeof(filepath));
-  BLI_path_normalize_native(filepath);
+  BLI_path_canonicalize_native(filepath, sizeof(filepath));
 
   wm_open_init_use_scripts(op, true);
   SET_FLAG_FROM_TEST(G.f, RNA_boolean_get(op->ptr, "use_scripts"), G_FLAG_SCRIPT_AUTOEXEC);
@@ -3246,8 +3244,7 @@ static int wm_save_as_mainfile_exec(bContext *C, wmOperator *op)
   const bool is_filepath_set = RNA_struct_property_is_set(op->ptr, "filepath");
   if (is_filepath_set) {
     RNA_string_get(op->ptr, "filepath", filepath);
-    BLI_path_abs_from_cwd(filepath, sizeof(filepath));
-    BLI_path_normalize_native(filepath);
+    BLI_path_canonicalize_native(filepath, sizeof(filepath));
   }
   else {
     STRNCPY(filepath, BKE_main_blendfile_path(bmain));

source/creator/creator_args.c

@@ -1866,7 +1866,7 @@ static int arg_handle_python_file_run(int argc, const char **argv, void *data)
     /* Make the path absolute because its needed for relative linked blends to be found */
     char filepath[FILE_MAX];
     STRNCPY(filepath, argv[1]);
-    BLI_path_abs_from_cwd(filepath, sizeof(filepath));
+    BLI_path_canonicalize_native(filepath, sizeof(filepath));
 
     bool ok;
     BPY_CTX_SETUP(ok = BPY_run_filepath(C, filepath, NULL));
@@ -2063,9 +2063,7 @@ static int arg_handle_load_file(int UNUSED(argc), const char **argv, void *data)
   }
 
   STRNCPY(filepath, argv[0]);
-  BLI_path_slash_native(filepath);
-  BLI_path_abs_from_cwd(filepath, sizeof(filepath));
-  BLI_path_normalize_native(filepath);
+  BLI_path_canonicalize_native(filepath, sizeof(filepath));
 
   /* load the file */
   BKE_reports_init(&reports, RPT_PRINT);