@Kghbln: Did @Pastakhov explicitly agree to work on fixing this task? Asking as you set Pastakhov as task assignee.

He is the only one working on the extension. However ...

yes, I'm one, I'll fix it when I get some time

@Pastakhov I will be great if you could have a peep.

Still remains for this new setup:

• Mpdf 1.0 (3ac9540) 11:00, 12 July 2020
• MediaWiki 1.35.0-rc.2 (37ef236) 17:21, 22 August 2020
• PHP 7.2.24-0ubuntu0.18.04.6 (apache2handler)
• mpdf/mpdf 6.1.3 GPL-2.0

I just saw this error with PHP 7.3.19 and it can be resolved by using mPDF v7 or v8. I tested quickly with v7, at first sight it mostly work except the constructor whose the signature changed:

diff --git a/MpdfAction.php b/MpdfAction.php
index c68a8d4..bca1249 100644
--- a/MpdfAction.php
+++ b/MpdfAction.php
@@ -95 +95 @@ class MpdfAction extends Action {
-                       $mpdf = new mPDF( $mode, $format, 0, '', $marginLeft, $marginRight, $marginTop, $marginBottom, $marginHeader, $marginFooter, $orientation );
+                       $mpdf = new \Mpdf\Mpdf( [ 'mode' => $mode, 'format' => $format, 'default_font_size' => 0, 'default_font' => '', 'margin_left' => $marginLeft, 'margin_right' => $marginRight, 'margin_top' => $marginTop, 'margin_bottom' => $marginBottom, 'margin_header' => $marginHeader, 'margin_footer' => $marginFooter, 'orientation' => $orientation ] );

According to requirements with PHP versions, the v8 also supports PHP 7.4, it could be worth testing if it works with the minimal patch above.

Change #1041660 had a related patch set uploaded (by Seb35; author: Seb35):

[mediawiki/extensions/Mpdf@master] Upgrade the library mPDF to 8.0.13

https://gerrit.wikimedia.org/r/1041660

The linked patch should work on PHP 5.6 → 8.1 according to the requirements of the library mPDF and I tested it on PHP 7.4. I will test it on PHP 8.1 in a few days.

Also, I link this task to T323797, which is similar in the sense "Upgrade the underlying library mPDF".

The patch from @Seb35 worked well until MediaWiki 1.43.5 - however, the MediaWiki Docker images for 1.43 (.6) are based on PHP 8.3.29, which is supported since mpdf 8.2.1

So I think, we would need to upgrade mpdf to 8.2.1.

I can file a patch for review, but unfortunately can only test on MediaWiki 1.43.6. @Pastakhov Do you have better testing capabilities? :)