WIP: a solution for multi label printing

[nwns]

A hack and slash solution to multi-label printing (note that this is against stable not master, though it looks like it will auto merge against master as well).

A proposed fix for #3528

TODO:

• Determine how this affects the plugin system. Will require understanding what the plugin system is accomplishing in the first place.
• Template debug mode is ignored. Labels are always rendered as pdf.
• PDF inline is ignored. File is always downloaded.

A, likely breaking, refactor of the label templates would probably be required to clean this up.

[matmair]

While I applaude the effort this breaks nearly every feature of labels and sets us back a year in that area. @SchrodingersGat any insights into reports/how that could be done while keeping the current featureset?

[nwns]

@matmair I am not sure I follow how it breaks nearly everything?

There will be breaking changes for the templates themselves, but everything in the documentation should be possible how I proposed it.

Alternatively, assuming I understand what the BarcodePlugins are supposed to do, we always use the plugin path and convert every label to a png first, then using my new template, create the pdf for the user from the list of images as a single pdf document.

[SchrodingersGat]

@nwns this is actually an issue with the weasyprint library we use for PDF generation. I've tracked it down to a known issue: Kozea/WeasyPrint#1517

I'll pin the library to a version that works and that will address the issue.

[nwns]

@SchrodingersGat awesome. Downgrading weasyprint fixed it for me.

[SchrodingersGat]

Good to hear!