[wp-trac] [WordPress Trac] #62083: Text_Diff::_check() throws a fatal error when $prevtype is null.

[WordPress Trac]

#62083: Text_Diff::_check() throws a fatal error when $prevtype is null.
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 Reporter:  hellofromTonya      |      Owner:  (none)
     Type:  defect (bug)        |     Status:  assigned
 Priority:  normal              |  Milestone:  6.7
Component:  External Libraries  |    Version:  5.6
 Severity:  normal              |   Keywords:
  Focuses:                      |
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 `Text_Diff::_check()` will throw a fatal error when `$prevtype` is null.

 >Fatal error: Uncaught Error: Class name must be a valid object or a
 string

 `instanceof` requires the class name's term to be an object or string.

 See it in action here https://3v4l.org/rQ0s4#veol.

 Looking at the existing code (using
 [https://core.trac.wordpress.org/browser/trunk/src/wp-
 includes/Text/Diff.php?annotate=blame#L279 the 6.6.2 tagged version as its
 the latest release as of this ticket]),

 {{{
 $prevtype = null;
 foreach ($this->_edits as $edit) {
     if ($edit instanceof $prevtype) {
         trigger_error("Edit sequence is non-optimal", E_USER_ERROR);
     }
     $prevtype = get_class($edit);
 }
 }}}

 this means `$prevtype` must be an object or string. On the first loop,
 `$prevtype` is `null`.

 For contextual history, [49194] changed from `get_class()` to
 `instanceof`.

 Reference:
 * https://www.php.net/manual/en/language.operators.type.php

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Ticket URL: <https://core.trac.wordpress.org/ticket/62083>
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