1459570 - Remove checks for CSS Colors Level 4 support

Status: NEW

(DevTools :: Inspector, task, P3)

Description

[Razvan Caliman [:rcaliman]]

There are guards in the code to check for CSS Colors Level 4 platform support. They are used when doing color format conversions in the Inspector and when instantiating SwatchColorPickerTooltip. 

Bug 1295456 has implemented this feature since Firefox 52. The ESR is planned to switch from Firefox 52 to Firefox 60 in May 2018. (https://www.mozilla.org/en-US/firefox/organizations/)

It seems like a good time to remove the checks for CSS Colors Level 4 given the established platform support across Firefox versions.


Places where code or checks can be removed:

- In devtools/shared/fronts/css-properties.js
`CssProperties.upportsCssColor4ColorFunction`
`CSSProperties.cssColor4ColorFunction`

- In devtools/server/actors/css-properties.js
```
const supportedFeature = {
      // checking for css-color-4 color function support.
      "css-color-4-color-function": InspectorUtils.isValidCSSColor("rgb(1 1 1 / 100%)"),
    };
```

- In devtools/client/shared/widgets/tooltip/SwatchColorPickerTooltip.js
`this.cssColor4 = supportsCssColor4ColorFunction();`


- In devtools/client/shared/output-parser.js
`this.cssColor4 = supportsCssColor4ColorFunction();`

Comment 1

[Razvan Caliman [:rcaliman]]

@Tom, since you reviewed the patches that introduced these checks for CSS Colors Level 4, do you see any issues with removing these checks now, given the platform support. Are there other reasons for keeping them in?

Comment 2

[Tom Tromey :tromey]

(In reply to Razvan Caliman [:rcaliman][@rcaliman] from comment #1)
> @Tom, since you reviewed the patches that introduced these checks for CSS
> Colors Level 4, do you see any issues with removing these checks now, given
> the platform support. Are there other reasons for keeping them in?

I think the underlying question here is about devtools policy, namely, what
versions of FF should be supported as debugging targets.  So, I'm redirecting
the NI to someone who might know the answer, or at least will know who will.

I don't recall if this code is checking server capabilities -- if not, then
it's already incorrect and IMO there would be no barrier to removing the checks.

Comment 3

[J. Ryan Stinnett [:jryans] (Use needinfo, replies may be slow)]

The backward compatibility[1] page attempts to describe our policy for things like this (though admittedly it could probably use more detail on the finer points, so please let me know if you have questions so that it can be expanded).

For the code in question here, it looks like we are detecting server feature support.  The compatibility range goes back to Release, so currently 59 and later (soon 60 and later).  Since the feature was added in 52, we're well beyond that range, so it appears safe to remove the checks.

[1]: http://docs.firefox-dev.tools/backend/backward-compatibility.html

Comment 4

[Razvan Caliman [:rcaliman]]

Thank you both for the answers! I will proceed with the removal of the checks and related code.