Improper css var() causes crash

[sureshvv]

Getting this error when I process this html file
yy1.txt

[Tontyna]

That's a crash with announcement -- do you see the WARNING Unsupported computed value `calc(var(--line-height) / var(--line-height-ratio))` set in variable `--font-size` for property `font-size`.?

That's because calc() isn't implemented in WeasyPrint. Although this shouldn't crash WeasyPrint.

And indeed, it's not the unsupported calc, that crashes WeasyPrint, but the fallback value -- WeasyPrint's compute function detects that it cannot replace the var(--font-size) and falls back to the font-size of the parent. Which happens to be a unit-less simple integer or float.
And crashes in the font_size() function. We could make font_size aware for simple numbers, but then the length() function will crash.

@liZe - this fallback to a unit-less parent property is fatal for all css properties that designate a length, didn't count the COMPUTER_FUNCTIONS that call the length() method and the css properties that directly call length()... Assuming a Dimension wasn't a problem until var() was implemented -- regular unit-less lengths are rejected in "Step 2 - Fetching and parsing CSS"

@sureshvv - even if WeasyPrint was able to calculate your --font-size variable it would crash because the calc() in your css doesn't supply a unit, just plain numbers.

[sureshvv]

Browsers seem to handle it well. The html file displays perfectly in all the browsers that I have tested on. wkhtmltopdf also handles the same html file but not as well ;)

Won't the default unit be "px"?

[Tontyna]

Browsers seem to handle it well.

Yes, they dont crash. My Browser ignores the calculated dimension-less values and falls back to the initial or inherited value.

[Tontyna]

this fallback to a unit-less parent property is fatal for all css properties ...

That's not true. Almost all of the 'lengthy' properties get a sane value from INITIAL_VALUES and/or the responsible @register_computer function handles the case when this value is a deliberate integer.

Looks like only font-size and word-spacing are affected by the unit-less fallback crash.

[Tontyna]

Looks like only font-size and word-spacing are affected by the unit-less fallback crash.

Minimal example to crash WeasyPrint by var():

<style>
div {
  --value: invalidValue;
  border-spacing: var(--value);
}
</style>
<div>crash</div>

The complete list of properties that kill WeasyPrint when defined via an invalid var() value is:

• word-spacing
• font-size
• border-spacing
• size
• content
• string-set
• anchor
• link
• lang
• transform

[Tontyna]

@sureshvv would you be so kind and rename this issue to sth like "improper css var() causes crash"?

[sureshvv]

Done. Now who wlll fix this? ;)

[Tontyna]

Now who wlll fix this?

• I'm currently preparing a PR to prevent the crash.
• AFAIK nobody is working on Implement calc() and other math functions #357

[Tontyna]

@liZe -- your commit is a lot more elegant than #977 👍

But it doesn't survive invalid values for font-size (fixed in font_size() by af78171) and transform (fixed with try..except by 0bb4e2c).

Cf. f0a432f, the full test for all KNOWN_VALUES.

[liZe]

@liZe -- your commit is a lot more elegant than #977

I’ve missed your PR, even with your comment and the bold title below. I don’t know how it’s possible. Maybe it’s time to sleep.

👓

(I’m really sorry…)

But it doesn't survive invalid values for font-size (fixed in font_size() by af78171) and transform (fixed with try..except by 0bb4e2c).

😞

Cf. f0a432f, the full test for all KNOWN_VALUES.

It’s much better than my little test.

I’ll cherry-pick some of your commits for sure, thanks a lot.

[liZe]

I’ve cherry-picked your test (and "parametrize" it, it’s easier to debug).

As you said, transform was crashing. I’ve removed (in c21028e) the InvalidValues exception from this validator, as it was the only one doing this.

(But we should probably call validate_non_shorthand instead of calling PROPERTIES[…], I don’t know how initial/inherit are handled now. In this case, we’ll have to cherry-pick 0bb4e2c too.)

font-size works well, even without af78171. As the value is already computed, we never call the computer function with integers.

[Tontyna]

font-size works well, even without af78171

You're right, of course -- me needing more sleep, too