Handle functions (var, attr…) in properties with multiple values

[oussama-he]

I'm using weasyprint in one of my projects and I would like to use CSS variables but they don't work correctly. I have these rules like these in my style.css:

:root {
  --primary-color: #2ea44f;
}

.table thead {
    background-color: var(--primary-color);
    color: #fff;
    text-align: left;
}

.table tbody tr:last-child {
    border-bottom: 2px solid var(--primary-color);
}

The rule .table thead {...} works normally and this rule .table tbody tr:last-child{...} doesn't work and I get a message in the terminal:

WARNING: Ignored `border-bottom: 2px solid var(--primary-color)` at 90:5, invalid value.

Any help, please? Thank you in advance.

[liZe]

The problem is that var (and other functions such as attr) don’t work when properties have multiple values.

A workaround for now is to use border-bottom-color: var(--primary-color).

As said in #1165, we have to fully rewrite the way values are calculated, and that’s a lot of work…

[aleho]

Just a quick note, this also breaks font-variation-settings: "wght" var(--font-weight-light); where there's not work-around (as far as I know) because the settings have to be written that way.

[liZe]

Just a quick note, this also breaks font-variation-settings: "wght" var(--font-weight-light); where there's not work-around (as far as I know) because the settings have to be written that way.

Oh, thanks for this quick note. I was happy because we’re close to get var working on shorthand properties, but I "forgot" that some normal properties can also get multiple values.

So, let’s not forget font-variation-settings and its friends (at least font-family, display, some of background-*, border-*-*-radius, border-spacing, bookmark-label, quotes, object-position, marks, hyphenate-limit-chars, transform-origin.)

"Good" news is that attr is not supported by other browsers in properties other than content, so we can safely forget this part for now.

[Dano507]

Hi, I discovered this issue yesterday. From then, I've been looking through the source to find potential fixes.

If I'm understanding correctly, the issue is in the weasyprint/css/validation package, and occurs whenever a css var() function in a property with multiple values is passed to the expander_() call in __init__.py.

expander_ = EXPANDERS.get(name, validate_non_shorthand)
tokens = remove_whitespace(declaration.value)
try:
    # Use list() to consume generators now and catch any error.
    result = list(expander_(base_url, name, tokens))  # ERROR HERE
except InvalidValues as exc:
    validation_error(
        'warning',
        exc.args[0] if exc.args and exc.args[0] else 'invalid value')
    continue

Would evaluating all function tokens (in the tokens array) before the expander_() call be feasible? It seems like a sensible solution, but I don't know how implementing it would work.

[liZe]

Hi, I discovered this issue yesterday. From then, I've been looking through the source to find potential fixes.

Hi, thanks for the comment!

We’re currently working on this on the functions branch. And you’re right: there were limitations with validators … and a lot of other problems!

The current code (in functions) should work with shorthand properties for "normal" cases. We still have to fix other properties with multiple values (font-variation-settings for example, as explained above) and possibly in other functions. Then we’ll merge and close this issue, hopefully before version 61!

(Now that the code is cleaner, we also secretly hope that it will give us the possibility to handle other functions such as calc() #357, but that’s a secret.)

[Dano507]

The progress looks pretty good so far. I didn't realize that it was this far into being fixed.

we also secretly hope that it will give us the possibility to handle other functions such as calc() https://github.com/Kozea/WeasyPrint/issues/357, but that’s a secret.

(That sounds great. And no worries, I'll keep it a secret)

Thanks for the informative reply, great work so far, and good luck.

[liZe]

Anyone interested in this feature can test #2017. Feedback is welcome!