[Bug ?] Conflict between 2 cosmetic filters

[Procyon-b]

https://new.reddit.com/r/uBlockOrigin/comments/1hbit6l/elementsads_on_raiderio_refuse_to_stay_blocked/

Yesterday a user came on reddit with a problem with a userfilter that isn't applied by uBO. I was unable to reproduce, and since the user has enabled many extra lists (43) I was unable to continue debugging. He later came back after identifying the list which was causing the issue ("AdGuard – Social Widgets").

website: raider.io
userfilter: raider.io##.slds-size--1-of-1.slds-col > div.fresnel-greaterThan-sm.fresnel-container
targets at least 2 blocks on the index page (The top one contains "New: Recruitment system")

Test:
Disabling all lists except "My filters" and "AdGuard – Social Widgets", enable "Ignore generic cosmetic filters", add the userfilter and reload the page. The top block isn't hidden.

Using raider.io##.slds-size--1-of-1.slds-col > div.fresnel-greaterThan-sm.fresnel-container:style(opacity: .2; outline: 2px solid red;) instead marks the block correctly.

Using raider.io##.slds-size--1-of-1.slds-col > div.fresnel-greaterThan-sm.fresnel-container:style(display: none;) also works as expected.

Only 3 cosmetic filters in the list are targeting this site. And one is responsible. After simplification, it is:
raider.io##.twitter-timeline|blog.jp

Now, disable the list, and run uBO with only that filter and the user's filter. The userfilter won't be applied, but styling the target works.

TLDR:
a (hiding) cosmetic filter prevents hiding an element with another (hiding) userfilter
but you can style the target element with :style()
and you can even hide it with :style(display: none;)

[gorhill]

I will need to investigate more but my first guess is that there is an invalid cosmetic filter in the AdGuard list, undetected by uBO, which breaks cosmetic filtering.

[Yuki2718]

It looks to be a typo in AdguardTeam/AdguardFilters@051ef5a
Corrected AdguardTeam/AdguardFilters@6e2aa19

[gorhill]

The selector is seen as valid by uBO since | is a valid namespace operator.

[Procyon-b]

@gorhill but why does it make the other filter irrelevant ? Is it only a browser bug ?

[gorhill]

Because all plain CSS cosmetic filters are injected as a single CSS declaration. If one selector is bad, the whole CSS declaration is bad and ignored by the browser.

[Procyon-b]

Edit:
scratch that. The 2 cents just dropped. ;)
/edit:

OK. I assume that the filters with :style() are injected in a separate declaration ?
Thanks

[uBlock-user]

raider.io##.twitter-timeline|blog.jp

invalid filter

[Procyon-b]

I know that it's an invalid filter. But why does it prevent uBO to use the other filter (except when :style() is used) ?

[uBlock-user]

@gorhill uBO is unable to handle syntax error gracefully it seems

[uBlock-user]

@Procyon-b If you remove the |blog.jp part, from the filter then the issue doesn't occur

[gorhill]

unable to handle syntax error gracefully it seems

It's from the logger related-code specifically. The error can be caught, and might be good to report the error to the logger so that it becomes easier to spot invalid selectors.

[u-RraaLL]

Just referencing the previous case/discussion so it's easier to find them in the future: https://github.com/uBlockOrigin/uBlock-discussions/discussions/833#discussioncomment-8669882