Use is_string in wp_title to prevent deprecation notice

[sabernhardt]

Checks whether $title is a string and then checks whether it equals an empty string before adding the separator.

Trac 61352

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Props sabernhardt, mukesh27, joedolson.

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[sabernhardt]

While I often create untitled posts on local sites and I expect that sometimes they are appropriate on live sites too, an empty $title string is hopefully uncommon. Also, even an empty array would run through implode() later anyway.

If skipping explode() is important, however, I think that parentheses make the condition a little easier to read.

Suggested change

	$title_array = apply_filters( 'wp_title_parts', explode( $t_sep, $title ) );
	$title_array = apply_filters( 'wp_title_parts', ( '' !== $title ) ? explode( $t_sep, $title ) : array() );

[mukeshpanchal27]

Suggest moving the conditional logic before apply_filters and passing the variable for better readability.

[sabernhardt]

This could be more readable:

	if ( ! is_string( $title ) ) {
		$title = '';
	}

	$prefix      = '';
	$title_array = array();
	if ( '' !== $title ) {
		$prefix      = " $sep ";
		$title_array = explode( $t_sep, $title );
	}

	/**
	 * Filters the parts of the page title.
	 *
	 * @since 4.0.0
	 *
	 * @param string[] $title_array Array of parts of the page title.
	 */
	$title_array = apply_filters( 'wp_title_parts', $title_array );

We probably should change the $sep and/or $t_sep names too, but not for this release.

[sabernhardt]

If the apply_filters( 'wp_title_parts', $title_array ) direction above is worth pursuing, it might be better in a separate PR.

[joedolson]

I don't think there's any need to go to a new PR for that change. It looks good to me.

[sabernhardt]

I switched this PR to the more readable concept and checked the following URLs with the updated .diff and Twenty Fourteen.

• http://localhost/svn/src/0-2/ (with 0 as the post title): <title>0 | Trunk (SVN)</title>
• http://localhost/svn/src/ (front page, without a static front page): <title>Trunk (SVN)</title>
• http://localhost/svn/src/sample-page/ (page of posts): <title>Sample Page | Trunk (SVN)</title>

[joedolson]

Duplicated the same tests with Twenty Twenty, and confirmed same behavior.

[github-actions]

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