Fix immediate exit when displaying an invalid UTF8 title on Wayland

A non UTF8 title on Wayland causes disconnection from the server.
Resolve by using the path as-is unless invalid UTF8 byte sequences
are found, in that case they're replaced by `?`.

This is skipped on WIN32 & macOS since the issue only exists on Wayland.

source/blender/blenlib/BLI_string_utf8.h

@@ -49,6 +49,18 @@ int BLI_str_utf8_invalid_strip(char *str, size_t str_len) ATTR_NONNULL(1);
 int BLI_str_utf8_invalid_substitute(char *str, size_t str_len, const char substitute)
     ATTR_NONNULL(1);
 
+/**
+ * A utility for #BLI_str_utf8_invalid_substitute that returns `str` when it contains a
+ * valid UTF8 string. Otherwise it is copied into `buf` with invalid byte sequences
+ * substituted for `substitute`.
+ *
+ * \note This is intended for situations when the string is expected to be valid,
+ * where copying and substituting values is typically not needed.
+ */
+[[nodiscard]] const char *BLI_str_utf8_invalid_substitute_as_needed(
+    const char *str, size_t str_len, const char substitute, char *buf, const size_t buf_maxncpy)
+    ATTR_NONNULL(1, 4);
+
 /**
  * \return The size (in bytes) of a single UTF8 char.
  * \warning Can return -1 on bad chars.

source/blender/blenlib/intern/string_utf8.cc

@@ -326,6 +326,40 @@ int BLI_str_utf8_invalid_substitute(char *str, size_t str_len, const char substi
   return tot;
 }
 
+const char *BLI_str_utf8_invalid_substitute_as_needed(const char *str,
+                                                      const size_t str_len,
+                                                      const char substitute,
+                                                      char *buf,
+                                                      const size_t buf_maxncpy)
+{
+  BLI_assert(str[str_len] == '\0');
+  const ptrdiff_t bad_char = BLI_str_utf8_invalid_byte(str, str_len);
+  if (LIKELY(bad_char == -1)) {
+    return str;
+  }
+  BLI_assert(bad_char >= 0);
+
+  /* In the case a bad character is outside the buffer limit,
+   * simply perform a truncating UTF8 copy into the buffer and return that. */
+  if (UNLIKELY(size_t(bad_char) >= buf_maxncpy)) {
+    BLI_strncpy_utf8(buf, str, buf_maxncpy);
+    return buf;
+  }
+
+  size_t buf_len;
+  if (str_len < buf_maxncpy) {
+    memcpy(buf, str, str_len + 1);
+    buf_len = str_len;
+  }
+  else {
+    buf_len = BLI_strncpy_rlen(buf, str, buf_maxncpy);
+  }
+
+  /* Skip the good characters. */
+  BLI_str_utf8_invalid_substitute(buf + bad_char, buf_len - size_t(bad_char), substitute);
+  return buf;
+}
+
 /**
  * Internal utility for implementing #BLI_strncpy_utf8 / #BLI_strncpy_utf8_rlen.
  *

source/blender/windowmanager/intern/wm_window.cc

@@ -512,11 +512,26 @@ void WM_window_title(wmWindowManager *wm, wmWindow *win, const char *title)
     return;
   }
 
-  const char *filepath = BKE_main_blendfile_path_from_global();
-  const char *filename = BLI_path_basename(filepath);
+  /* This path may contain invalid UTF8 byte sequences on UNIX systems,
+   * use `filepath` for display which is sanitized as needed. */
+  const char *filepath_as_bytes = BKE_main_blendfile_path_from_global();
 
+  char _filepath_utf8_buf[FILE_MAX];
+  /* Allow non-UTF8 characters on systems that support it.
+   *
+   * On Wayland, invalid UTF8 characters will disconnect
+   * from the server - exiting immediately. */
+  const char *filepath = (OS_MAC || OS_WINDOWS) ?
+                             filepath_as_bytes :
+                             BLI_str_utf8_invalid_substitute_as_needed(filepath_as_bytes,
+                                                                       strlen(filepath_as_bytes),
+                                                                       '?',
+                                                                       _filepath_utf8_buf,
+                                                                       sizeof(_filepath_utf8_buf));
+
+  const char *filename = BLI_path_basename(filepath);
   const bool has_filepath = filepath[0] != '\0';
-  const bool native_filepath_display = GHOST_SetPath(handle, filepath) == GHOST_kSuccess;
+  const bool native_filepath_display = GHOST_SetPath(handle, filepath_as_bytes) == GHOST_kSuccess;
   const bool include_filepath = has_filepath && (filepath != filename) && !native_filepath_display;
 
   /* File saved state. */