Twenty Thirteen: Fix post navigation to respect sort order.

Change the labels on post navigation links when the sort order is changed so the labels accurately reflect the target entries.

Previously, if the sort order was reversed, 'Older' or 'Previous' links would navigate to newer entries and 'Newer' or 'Next' links would navigate to older entries.

Props jikamens, dancameron, obenland, shrey0shrivastava, sirlouen, sabernhardt, shailu25, westonruter, joedolson.
See #10219.

git-svn-id: https://develop.svn.wordpress.org/trunk@61094 602fd350-edb4-49c9-b593-d223f7449a82

Author: joedolson

src/wp-content/themes/twentythirteen/functions.php

@@ -494,7 +494,17 @@ function twentythirteen_paging_nav() {
 		if ( $wp_query->max_num_pages < 2 ) {
 			return;
 		}
+
+		$order   = get_query_var( 'order', 'DESC' );
+		$is_desc = 'DESC' === $order;
+
+		$new_posts_text = __( 'Newer posts <span class="meta-nav">&rarr;</span>', 'twentythirteen' );
+		$old_posts_text = __( '<span class="meta-nav">&larr;</span> Older posts', 'twentythirteen' );
+
+		$prev_link = $is_desc ? get_next_posts_link( $old_posts_text ) : get_previous_posts_link( $old_posts_text );
+		$next_link = $is_desc ? get_previous_posts_link( $new_posts_text ) : get_next_posts_link( $new_posts_text );
 		?>
+
 		<nav class="navigation paging-navigation">
 		<h1 class="screen-reader-text">
 			<?php
@@ -503,14 +513,19 @@ function twentythirteen_paging_nav() {
 			?>
 		</h1>
 		<div class="nav-links">
+		<?php if ( $prev_link ) : ?>
+			<div class="nav-previous">
+				<?php echo $prev_link; ?>
+			</div>
+			<?php
+		endif;
 
-			<?php if ( get_next_posts_link() ) : ?>
-			<div class="nav-previous"><?php next_posts_link( __( '<span class="meta-nav">&larr;</span> Older posts', 'twentythirteen' ) ); ?></div>
-			<?php endif; ?>
-
-			<?php if ( get_previous_posts_link() ) : ?>
-			<div class="nav-next"><?php previous_posts_link( __( 'Newer posts <span class="meta-nav">&rarr;</span>', 'twentythirteen' ) ); ?></div>
-			<?php endif; ?>
+		if ( $next_link ) :
+			?>
+			<div class="nav-next">
+				<?php echo $next_link; ?>
+			</div>
+		<?php endif; ?>
 
 		</div><!-- .nav-links -->
 	</nav><!-- .navigation -->