Reduce usage of fmt in serialization and error reporting
`format!` and `write!` create a somewhat-heavyweight `Formatting` struct and use dynamic dispatch to call into impls of `Dispaly` and related traits. The former also allocates an intermediate string that is sometimes unnecessary.
I started looking into this from https://bugzilla.mozilla.org/show_bug.cgi?id=1355599, but I expect the impact there will be small to insignificant. It might be a slightly less so on parsing (error reporting).
<!-- Reviewable:start -->
---
This change is [<img src="https://reviewable.io/review_button.svg" height="34" align="absmiddle" alt="Reviewable"/>](https://reviewable.io/reviews/servo/servo/18355)
<!-- Reviewable:end -->
I want to play with autogenerating style structs, and color is the smallest
struct out there.
However, moving it out of the mako file is a requirement. This patch does that.
Properly set default direction of prefixed linear gradients
The default linear gradient direction is `to bottom`. This correspondes to
`top` keyword in prefixed linear gradients. We should preserve the default value.
---
<!-- Thank you for contributing to Servo! Please replace each `[ ]` by `[X]` when the step is complete, and replace `__` with appropriate data: -->
- [X] `./mach build -d` does not report any errors
- [X] `./mach test-tidy` does not report any errors
- [X] These changes fix [Bug 1395189](https://bugzilla.mozilla.org/show_bug.cgi?id=1395189)
<!-- Reviewable:start -->
---
This change is [<img src="https://reviewable.io/review_button.svg" height="34" align="absmiddle" alt="Reviewable"/>](https://reviewable.io/reviews/servo/servo/18321)
<!-- Reviewable:end -->
The default linear gradient direction is `to bottom`. This correspondes to
`top` keyword in prefixed linear gradients. We should preserve the default value.
Handle single X keyword value in LegacyPosition
This is reviewed by emilio in bugzilla.
---
<!-- Thank you for contributing to Servo! Please replace each `[ ]` by `[X]` when the step is complete, and replace `__` with appropriate data: -->
- [X] `./mach build -d` does not report any errors
- [X] `./mach test-tidy` does not report any errors
- [X] These changes fix [Bug 1391432](https://bugzilla.mozilla.org/show_bug.cgi?id=1391432)
<!-- Reviewable:start -->
---
This change is [<img src="https://reviewable.io/review_button.svg" height="34" align="absmiddle" alt="Reviewable"/>](https://reviewable.io/reviews/servo/servo/18144)
<!-- Reviewable:end -->
We need to use enum instead of Either since we can't interpolate stroke-* between
unitless length and unit length(e.g. '5' -> '10px').
This coomit make following:
* Introduce SVGLengthOrPercentageOrNumber on computed and specified values.
* Make SVGLengthOrPercentageOrNumber animatable.
* Make stroke-dasharray not-accumulate.
Introduce ComputedUrl
<!-- Please describe your changes on the following line: -->
Use the new `ComputedUrl` type for computed types and `SpecifiedUrl` for specified types instead of using the `SpecifiedUrl` implementation for both.
---
<!-- Thank you for contributing to Servo! Please replace each `[ ]` by `[X]` when the step is complete, and replace `__` with appropriate data: -->
- [x] `./mach build -d` does not report any errors
- [x] `./mach test-tidy` does not report any errors
- [x] These changes fix#17625 (github issue number if applicable).
<!-- Either: -->
- [ ] There are tests for these changes OR
- [x] These changes do not require tests because this is an implementation change and tests already exist.
<!-- Also, please make sure that "Allow edits from maintainers" checkbox is checked, so that we can help you if you get stuck somewhere along the way.-->
<!-- Pull requests that do not address these steps are welcome, but they will require additional verification as part of the review process. -->
<!-- Reviewable:start -->
---
This change is [<img src="https://reviewable.io/review_button.svg" height="34" align="absmiddle" alt="Reviewable"/>](https://reviewable.io/reviews/servo/servo/17812)
<!-- Reviewable:end -->
As silly as it may seem to specify font-sizes using viewport units, we weren't
handling zoom for them correctly either.
Bug: 1388588
Reviewed-by: Manishearth
MozReview-Commit-ID: 3Q6phYAu5CE
stylo: Bug 1374233 - Clamp interpolated values for properties which need to be restricted
Some properties only accept non-negative values, or values greater than or equal to one. It is possible to produce an negative interpolated values while using negative timing functions, so we have to apply a restriction to these values to avoid getting invalid values.
For example, line-height must be non-negative, but the output progress of some timing functions (e,g. cubic-bezier(0.25, -2, 0.75, 1)) may be a negative value, so the interpolated result of line-height is also negative.
---
- [X] `./mach build -d` does not report any errors
- [X] `./mach test-tidy` does not report any errors
- [X] These changes fix Bug 1374233.
- [X] These changes do not require tests because we have tests in Gecko side already.
<!-- Reviewable:start -->
---
This change is [<img src="https://reviewable.io/review_button.svg" height="34" align="absmiddle" alt="Reviewable"/>](https://reviewable.io/reviews/servo/servo/17783)
<!-- Reviewable:end -->
We already have NonNegativeLength and NonNegativeAu, so we can re-use it
to define the specified value and the computed value of border-spacing.
And then implement ToAnimatedValue for it.
MozReview-Commit-ID: CLckpKMYVXU
Add NonNegativeLength, which could be computed to NonNegativeAu. So we
can declare Either<NonNegativeLength, X>, X=Auto, Normal, or Number.
NonNegativeLengthOrAuto is for column-width.
NonNegativeLengthOrNormal is for column-gap.
NonNegativeLengthOrNumber is for -moz-tab-size.
MozReview-Commit-ID: AfU8XpA1um0
Add values::computed::NonNegativeAu, so BorderSideWith could be computed
to this non-negative Au, for the following properties:
1. outline-width
2. border-{*}-width
3. column-rule-width
4. -webkit-text-stroke-width
MozReview-Commit-ID: ASHaB2F7VtM
NonNegativeNumber: for -moz-box-flex, flex-grow, and flex-shrink.
GreaterThanOrEqualToOneNumber: for stroke-miterlimit.
MozReview-Commit-ID: Kgbt99BPdVA
