958118 - getAuthoredPropertyValue() returns computed value when object obtained using getComputedStyle()

Status: RESOLVED WONTFIX

(Core :: DOM: CSS Object Model, defect)

Description

[Mike Ratcliffe [:miker] [:mratcliffe] [:mikeratcliffe]]

getAuthoredPropertyValue() returns the computed value when style object is obtained using getComputedStyle(). It would be far more useful for us if this would return the authored property value (we only really care about authored colors).

Run the following in a scratchpad in browser context:

let span = content.document.createElement("span");
span.setAttribute("style", "color: #F00");

span.style.getAuthoredPropertyValue("color"); // Correctly returns #F00

let computed = content.window.getComputedStyle(span);
computed.getAuthoredPropertyValue("color"); // Incorrectly returns rgb(255, 0, 0)

Comment 1

[Boris Zbarsky [:bzbarsky]]

Uh... why would you ever call getAuthoredPropertyValue on computed style?  What exactly do you expect it to return???  The whole operation is nonsensical, like the code comments in nsComputedDOMStyle::GetAuthoredPropertyValue say.

Comment 2

[Boris Zbarsky [:bzbarsky]]

And in particular, computed values are synthesized out of thin air in many cases and don't correspond to any specified, much less authored, value.

Arguably we should have made getAuthoredPropertyValue just throw on computed style.

Comment 3

[Mike Ratcliffe [:miker] [:mratcliffe] [:mikeratcliffe]]

Attachment: Authored.PNG

(In reply to Boris Zbarsky [:bz] from comment #1)
> Uh... why would you ever call getAuthoredPropertyValue on computed style? 
> What exactly do you expect it to return???  The whole operation is
> nonsensical, like the code comments in
> nsComputedDOMStyle::GetAuthoredPropertyValue say.

Out of context it probably is nonsensical.

We have a computed style panel and would like the styles containing colors to show the authored style. It wouldn't make sense to display them as authored in the rule view and when a computed style is expanded but use rgb(r, g, b) in the rest of the computed view (see image).

Comment 4

[Boris Zbarsky [:bzbarsky]]

Computed style data simply doesn't have that information.  For example, if your computed color is rgb(255, 0, 0) then the authored style could have been any of a variety of things, but all the layout data structures contain is a single 32-bit integer representing the color....

Given how common the color struct is, I'm not sure we want to pay the memory cost of storing the authored representation in it.

Comment 5

[Mike Ratcliffe [:miker] [:mratcliffe] [:mikeratcliffe]]

Fair enough, we can compute these values ourselves by looping through the DOM rules.