Media: Keep PDF previews from overwriting files.

Since support for PDF previews were added in [38949], it's possible
that the generated image file could overwrite an existing image file
with the same name. This uses `wp_unique_filename()` to avoid this
issue and adds a '-pdf' identifier on the end of filenames.

Props gitlost, derosj, mikeschroder, joemcgill.
Fixes #39875. See #31050.
Built from https://develop.svn.wordpress.org/trunk@40130


git-svn-id: http://core.svn.wordpress.org/trunk@40067 1a063a9b-81f0-0310-95a4-ce76da25c4cd

wp-admin/includes/image.php

@@ -251,7 +251,15 @@ function wp_generate_attachment_metadata( $attachment_id, $file ) {
 			$editor = wp_get_image_editor( $file );
 
 			if ( ! is_wp_error( $editor ) ) { // No support for this type of file
-				$uploaded = $editor->save( $file, 'image/jpeg' );
+				/*
+				 * PDFs may have the same file filename as JPEGs.
+				 * Ensure the PDF preview image does not overwrite any JPEG images that already exist.
+				 */
+				$dirname = dirname( $file ) . '/';
+				$ext = '.' . pathinfo( $file, PATHINFO_EXTENSION );
+				$preview_file = $dirname . wp_unique_filename( $dirname, wp_basename( $file, $ext ) . '-pdf.jpg' );
+
+				$uploaded = $editor->save( $preview_file, 'image/jpeg' );
 				unset( $editor );
 
 				// Resize based on the full size image, rather than the source.

wp-includes/version.php

@@ -4,7 +4,7 @@
  *
  * @global string $wp_version
  */
-$wp_version = '4.8-alpha-40129';
+$wp_version = '4.8-alpha-40130';
 
 /**
  * Holds the WordPress DB revision, increments when changes are made to the WordPress DB schema.