stylo 0.17.0

The Stylo CSS engine
Documentation 
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89

/* This Source Code Form is subject to the terms of the Mozilla Public
 * License, v. 2.0. If a copy of the MPL was not distributed with this
 * file, You can obtain one at https://mozilla.org/MPL/2.0/. */

//! Values for CSS Box Alignment properties
//!
//! https://drafts.csswg.org/css-align/

use crate::derives::*;
use crate::values::computed::{Context, ToComputedValue};
use crate::values::specified;

pub use super::specified::{ContentDistribution, ItemPlacement, SelfAlignment};

/// The computed value for the `justify-items` property.
///
/// Need to carry around both the specified and computed value to handle the
/// special legacy keyword without destroying style sharing.
///
/// In particular, `justify-items` is a reset property, so we ought to be able
/// to share its computed representation across elements as long as they match
/// the same rules. Except that it's not true if the specified value for
/// `justify-items` is `legacy` and the computed value of the parent has the
/// `legacy` modifier.
///
/// So instead of computing `legacy` "normally" looking at get_parent_position(),
/// marking it as uncacheable, we carry the specified value around and handle
/// the special case in `StyleAdjuster` instead, only when the result of the
/// computation would vary.
///
/// Note that we also need to special-case this property in matching.rs, in
/// order to properly handle changes to the legacy keyword... This all kinda
/// sucks :(.
///
/// See the discussion in https://bugzil.la/1384542.
#[derive(Clone, Copy, Debug, Eq, MallocSizeOf, PartialEq, ToCss, ToResolvedValue, ToTyped)]
#[repr(C)]
#[typed(todo_derive_fields)]
pub struct ComputedJustifyItems {
    /// The specified value for the property. Can contain the bare `legacy`
    /// keyword.
    #[css(skip)]
    pub specified: specified::JustifyItems,
    /// The computed value for the property. Cannot contain the bare `legacy`
    /// keyword, but note that it could contain it in combination with other
    /// keywords like `left`, `right` or `center`.
    pub computed: specified::JustifyItems,
}

pub use self::ComputedJustifyItems as JustifyItems;

impl JustifyItems {
    /// Returns the `legacy` value.
    pub fn legacy() -> Self {
        Self {
            specified: specified::JustifyItems::legacy(),
            computed: specified::JustifyItems::normal(),
        }
    }
}

impl ToComputedValue for specified::JustifyItems {
    type ComputedValue = JustifyItems;

    /// <https://drafts.csswg.org/css-align/#valdef-justify-items-legacy>
    fn to_computed_value(&self, _context: &Context) -> JustifyItems {
        use crate::values::specified::align;
        let specified = *self;
        let computed = if (self.0).0 != align::AlignFlags::LEGACY {
            *self
        } else {
            // If the inherited value of `justify-items` includes the
            // `legacy` keyword, `legacy` computes to the inherited value, but
            // we assume it computes to `normal`, and handle that special-case
            // in StyleAdjuster.
            Self::normal()
        };

        JustifyItems {
            specified,
            computed,
        }
    }

    #[inline]
    fn from_computed_value(computed: &JustifyItems) -> Self {
        computed.specified
    }
}