Nested variables for "font-family" property will improperly lead to "unsupported computed value"

[Avlyssna]

This issue originally was noticed when using mkdocs-material. Fonts were not showing within the PDF, although they would render fine in the browser. Upon closer inspection, it appears that nested variables will break the font name resolution:

WARNING: Unsupported computed value "var(--md-text-font,_),-apple-system,BlinkMacSystemFont,Helvetica,Arial,sans-serif" set in variable '--md-text-font-family' for property 'font-family'.

This can be reproduced with the following CSS:

body {
  --md-text-font: Roboto;
  --md-text-font-family: var(--md-text-font, _), -apple-system, BlinkMacSystemFont, Helvetica, Arial, sans-serif;
  font-family: var(--md-text-font-family);
}

Ultimately, the font-family property validator does not have a case to handle when the list contains a FunctionBlock value.

[liZe]

Hi!

Thanks for the bug report.

The problem is not exactly caused by nested variables, it’s caused by variables in properties allowing multiple values. This bug is thus a duplicate of #1219.