Cleanup: minor changes to BKE_appdir_font_folder_default

- Ensure a trailing slash in BKE_blendfile_userdef_from_defaults
  instead of in-line platform specific checks.
- Take a buffer size argument for the directory.
- Use the documented size for SHGetSpecialFolderPathW wchar_t argument.
- Remove use of unsafe `wcscat` on WIN32

release/datafiles/userdef/userdef_default.c

@@ -32,6 +32,8 @@ const UserDef U_default = {
     .pref_flag = USER_PREF_FLAG_SAVE,
     .savetime = 2,
     .tempdir = "",
+    /* Overwritten by #BKE_appdir_font_folder_default(..)
+     * unless the system font's cannot be found. */
     .fontdir = "//",
     .renderdir = "//",
     .render_cachedir = "",

source/blender/blenkernel/BKE_appdir.h

@@ -131,7 +131,7 @@ const char *BKE_appdir_program_dir(void) ATTR_WARN_UNUSED_RESULT ATTR_RETURNS_NO
 /**
  * Gets a good default directory for fonts.
  */
-bool BKE_appdir_font_folder_default(char *dir);
+bool BKE_appdir_font_folder_default(char *dir, size_t dir_maxncpy);
 
 /**
  * Find Python executable.

source/blender/blenkernel/intern/appdir.c

@@ -227,26 +227,24 @@ bool BKE_appdir_folder_caches(char *path, const size_t path_maxncpy)
   return true;
 }
 
-bool BKE_appdir_font_folder_default(char *dir)
+bool BKE_appdir_font_folder_default(char *dir, size_t dir_maxncpy)
 {
   char test_dir[FILE_MAXDIR];
   test_dir[0] = '\0';
 
 #ifdef WIN32
-  wchar_t wpath[FILE_MAXDIR];
+  wchar_t wpath[MAX_PATH];
   if (SHGetSpecialFolderPathW(0, wpath, CSIDL_FONTS, 0)) {
-    wcscat(wpath, L"\\");
     BLI_strncpy_wchar_as_utf8(test_dir, wpath, sizeof(test_dir));
   }
 #elif defined(__APPLE__)
-  STRNCPY(test_dir, BLI_expand_tilde("~/Library/Fonts/"));
-  BLI_path_slash_ensure(test_dir, sizeof(test_dir));
+  STRNCPY(test_dir, BLI_expand_tilde("~/Library/Fonts"));
 #else
   STRNCPY(test_dir, "/usr/share/fonts");
 #endif
 
   if (test_dir[0] && BLI_exists(test_dir)) {
-    BLI_strncpy(dir, test_dir, FILE_MAXDIR);
+    BLI_strncpy(dir, test_dir, dir_maxncpy);
     return true;
   }
   return false;

source/blender/blenkernel/intern/blendfile.cc

@@ -1214,8 +1214,13 @@ UserDef *BKE_blendfile_userdef_from_defaults(void)
   userdef->flag &= ~USER_SCRIPT_AUTOEXEC_DISABLE;
 #endif
 
-  /* System-specific fonts directory. */
-  BKE_appdir_font_folder_default(userdef->fontdir);
+  /* System-specific fonts directory.
+   * NOTE: when not found, leaves as-is (`//` for the blend-file directory). */
+  if (BKE_appdir_font_folder_default(userdef->fontdir, sizeof(userdef->fontdir))) {
+    /* Not actually needed, just a convention that directory selection
+     * adds a trailing slash. */
+    BLI_path_slash_ensure(userdef->fontdir, sizeof(userdef->fontdir));
+  }
 
   userdef->memcachelimit = min_ii(BLI_system_memory_max_in_megabytes_int() / 2,
                                   userdef->memcachelimit);