Phpstan hasn't identified any errors in Samples in a long time. But, as it turns out, one particular error is suppressed:
```
Variable $helper might not be defined.
```
This error would be generated by almost all samples, and the errors that it suppresses will become problematic if we move to Level 10. We are not yet committed to doing that, but it is pretty easy to write a script to change the samples so that error no longer happens, and there isn't really any reason to delay doing so. The results of that script constitute this PR.
* Let Phpstan Run on Samples
Phpstan currently analyzes all source and test members. We already run phpcs and php-cs-fixer on samples as well. I would expect that samples are often used as templates for code in userland; it behooves us to be at least as careful with those members as for the others which are already being analyzed. Aside from 1300+ messages `Variable $helper might not be defined.`, which will be suppressed in phpstan.neon.dist, there are really only a few changes needed for sample members, so that part of the code base was already in good shape, and is now even better. No annotations were needed.
* Scrutinizer 2 out of 3
1 false positive, now suppressed; fix other 2.
* Remove Dead Code
* Very Minor Changes
* Add infra
Fix#3015. Fix#2766. Both issues requested a way to set Mpdf configuration parameters. I explained this could be done by extending class Mpdf and overriding protected function createExternalWriterInstance. So, no change is needed to PhpSpreadsheet. The parameters they wanted to override didn't seem interesting from a PhpSpreadsheet perspective. However, the configuration parameters include the ability to add fonts on the fly to those distributed by Mpdf, and that does sound useful. Normally, Mpdf (and Dompdf and Tcpdf) support a limited number of fonts, and will substitute for fonts they don't know (most fonts, even commonly used one, wind up using a DejaVu variant). Using these configuration options can lead to a more faithful Pdf representation of the spreadsheet.
In order to demonstrate this in action, I've added a new sample, a new class extending Mpdf, and a distinctive small font file from Google fonts with its (SIL Open Font) license. IANAL, but I can't see how this wouldn't be permitted use. There are no source code changes.
An alternate approach would be to add a callback to Writer/Pdf/Mpdf. It seems that this would be at least as much effort for the end-user as extending the class, and more effort for us.
It appears that Dompdf and Tcpdf need prep work to achieve the same end, and are thus less suitable for demonstrating via an example. I will continue to research.
oleibman