[css-text-decor-4] Fix the expected serialization of text-decoration.

[BorisChiou]

We add some test cases for text-decoration-thickness in text-decoration.

Conceptually the process of serializing a shorthand in getComputedStyle should be something like:

• Calling to_resolved_value() on all the values for the properties of the shorthand. This should turn the color as an rgb(a) thing, as colors are always serialized as resolved from getComputedStyle().
• Going from the resolved value al the way to the specified value. This makes the color still an rgba color, not currentColor.
• Serialize the same way we serialize specified shorthands.

So we always serizlize text-decoration-color because it is impossible to be currentColor. For other keywords, if they are initial values, we omit them.

[BorisChiou]

@ericwilligers This may need your review.

cc @emilio

[ewilligers]

Are you suggesting the serialization of text-decoration from gCS should be different in the following two cases? Is there a precedent?

color: blue;
text-decoration-style: dotted;
text-decoration-color: currentColor;

color: blue;
text-decoration-style: dotted;
text-decoration-color: blue;

[BorisChiou]

Are you suggesting the serialization of text-decoration from gCS should be different in the following two cases? Is there a precedent?

This is a good example. I didn't notice any precedent, at least now. Emilio suggests to me that it'd be better to always serialize color because its resolved value is never currentColor. For other keywords, if they are default values, we omit them. I will update this patch to let you review again. Thanks for the question and example.

[BorisChiou]

Updated the description.

[ewilligers]

Serialize the same way we serialize specified shorthands.

Are you saying that for the specified value, none and solid should be omitted whenever a color is specified, or are none and solid always omitted, and currentcolor added if the result would otherwise be empty? For example, how should a specified value of none solid be serialized?

[BorisChiou]

Sorry for the confusing description. I reply these below.

Are you saying that for the specified value, none and solid should be omitted whenever a color is specified

For specified shorthand, we omit none and solid if the color is not currentcolor. For example:

div.style.textDecoration = "none rgb(0, 0, 255)";
console.log(div.style.textDecoration); // output is "rgb(0, 0, 255)"

div.style.textDecoration = "solid rgb(0, 0, 255)";
console.log(div.style.textDecoration); // output is "rgb(0, 0, 255)"

or are none and solid always omitted, and currentcolor added if the result would otherwise be empty? For example, how should a specified value of none solid be serialized?

For example:

div.style.textDecoration = "none solid";
console.log(div.style.textDecoration); // output is "none"

div.style.textDecoration = "none solid currentcolor";
console.log(div.style.textDecoration); // output is "none"

In this example, all keywords, including color, are default value, so we just serialize it as none.

Sorry, we landed this change into text-decoration-valid.html before discussing with you. Perhaps it's worth to write it down in the spec.

gCS() is a different case. currentcolor is always converted into an rgb value, so

div.style.textDecoration = "none solid currentcolor";
console.log(getComputedStyle(div).textDecoration);
// output is "rgb(0, 0, 255)", assume currentcolor is blue.

Note: I intend to land the serialization for gCS() on text-decoration in mozilla bug 1574222.

[ewilligers]

Do the specs specify where text-decoration-thickness appears in the text-decoration shorthand?

I only see "This property, which is also a sub-property of the text-decoration shorthand, ..."

[BorisChiou]

Do the specs specify where text-decoration-thickness appears in the text-decoration shorthand?

I only see "This property, which is also a sub-property of the text-decoration shorthand, ..."

I think the answer is no. This is another spec issue, so I need to file one for this. Anyway, I put it in the last one in the text-decoration shorthand for now.

BTW, I found there are some other test cases also need to be updated. I will upload an extra patch for review. Thanks.

[BorisChiou]

Rebased and try to rerun tests because we hit the Github API issue: #18704