1264520 - Support mixed number, unit value, and percent for calc() parser including type checking

Status: RESOLVED DUPLICATE of bug 1827404

(Core :: CSS Parsing and Computation, defect, P3)

Description

[Boris Chiou [:boris]]

According to Bug 594933 comment 28 and 29, the unit checking in the parsing code needs additional changes. For example, our code can parse calc(1 + 2) and calc(1px + 2px),

but doesn't accept calc(1 + 2px),

which ought to be accepted for line-height, stroke-dashoffset, and stroke-width. There is various code in the functions inside of ParseCalc that needs updating, and some comments also need updating. There's currently no spec for it, but it's better to handle this case.

Comment 1

[David Baron :dbaron: (⌚️UTC-5, no longer working on Mozilla)]

Also, my understanding from bug 594933 is that other browser engines don't currently support this (I think that's silly, but it's also the reason I said fixing bug 594933 without this was OK).  If that changes, somebody should update this bug to say so!

Comment 3

[Daniel Holbert [:dholbert]]

(In reply to Boris Chiou [:boris] from comment #0)
> For example, our code can parse calc(1 + 2)

(To clarify something that confused me initially -- so, you're right that we do support that expression *for line-height*, but we don't support calc(number+number) or calc(integer+integer) in general, e.g. in the number-valued "opacity" property or the integer-valued "z-index" property.  Bug 1296209 partly covers that.  calc(1+2) only works for "line-height" via a custom "SetLineHeightCalcOps" calc-handling class that lives in nsRuleNode.cpp right now.)

Comment 4

[Sebastian Zartner [:sebo]]

What's possible for calc() and what not is outlined in https://drafts.csswg.org/css-values-3/#calc-notation.

Sebastian

Comment 5

[David Baron :dbaron: (⌚️UTC-5, no longer working on Mozilla)]

I believe that's extended in https://drafts.csswg.org/css-values-4/#calc-notation

Comment 6

[Sebastian Zartner [:sebo]]

Does this bug cover type checking as defined in CSS Values 4? I.e. will it be used to cover unit algebra with multiplication and division like calc(3rem / 2rem)?

Sebastian

Comment 7

[Boris Chiou [:boris]]

This bug was filed for the legacy implementation of calc(). Now we are using Rust to parse calc(), so I think we definitely can extend this bug to cover the case you mentioned (i.e. including all the type checking for calc()). Feel free to update the title if needed.

Comment 8

[Oskar Larsson Högfeldt]

Hi! I had a use for this recently: I wanted to use this on a page to fade out a decorative element (using opacity) based on the viewport width. For that to work I would need to use a calc with the pagelength and divide it and get a unitless number. This is supported in other web browsers

Comment 9

[Emilio Cobos Álvarez [:emilio]]

There's some relevant work ongoing in bug 2035572.

Comment 10

[David Shin[:dshin]]

Part of :janv's Typed OM work (Bug 2046802) does a lot of similar (Identical?) work that hopefully we can reuse.

Comment 11

[Sajid Anwar [:sajidanwar]]

Going to close this as a duplicate of Bug 1827404, which is where typed arithmetic has been implemented behind a pref for now. (Also because the calc(1 + 2px) example which was the original source of this bug is explicitly disallowed by the spec.)