servo/components/style/values/specified/align.rs
author Emilio Cobos Álvarez <emilio@crisal.io>
Sat, 10 Nov 2018 21:20:27 +0100
changeset 445809 8f4a9b61793ae1fed7ea246c42abc3df1cb8b1d8
parent 445807 a5a6ebd95c28652559571df953da5f9a2cf28d03
child 446794 c23d6003a3c3a37f523437afedc7e2914c9e194a
permissions -rw-r--r--
Bug 1506391 - Revert try -> r#try change. Since we're in an inconsistent state because mako files weren't updated, and it's really ugly.

/* 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 http://mozilla.org/MPL/2.0/. */

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

use crate::gecko_bindings::structs;
use crate::parser::{Parse, ParserContext};
use cssparser::Parser;
use std::fmt::{self, Write};
use style_traits::{CssWriter, KeywordsCollectFn, ParseError, SpecifiedValueInfo, ToCss};

bitflags! {
    /// Constants shared by multiple CSS Box Alignment properties
    ///
    /// These constants match Gecko's `NS_STYLE_ALIGN_*` constants.
    #[derive(MallocSizeOf, ToComputedValue)]
    pub struct AlignFlags: u8 {
        // Enumeration stored in the lower 5 bits:
        /// 'auto'
        const AUTO =            structs::NS_STYLE_ALIGN_AUTO as u8;
        /// 'normal'
        const NORMAL =          structs::NS_STYLE_ALIGN_NORMAL as u8;
        /// 'start'
        const START =           structs::NS_STYLE_ALIGN_START as u8;
        /// 'end'
        const END =             structs::NS_STYLE_ALIGN_END as u8;
        /// 'flex-start'
        const FLEX_START =      structs::NS_STYLE_ALIGN_FLEX_START as u8;
        /// 'flex-end'
        const FLEX_END =        structs::NS_STYLE_ALIGN_FLEX_END as u8;
        /// 'center'
        const CENTER =          structs::NS_STYLE_ALIGN_CENTER as u8;
        /// 'left'
        const LEFT =            structs::NS_STYLE_ALIGN_LEFT as u8;
        /// 'right'
        const RIGHT =           structs::NS_STYLE_ALIGN_RIGHT as u8;
        /// 'baseline'
        const BASELINE =        structs::NS_STYLE_ALIGN_BASELINE as u8;
        /// 'last-baseline'
        const LAST_BASELINE =   structs::NS_STYLE_ALIGN_LAST_BASELINE as u8;
        /// 'stretch'
        const STRETCH =         structs::NS_STYLE_ALIGN_STRETCH as u8;
        /// 'self-start'
        const SELF_START =      structs::NS_STYLE_ALIGN_SELF_START as u8;
        /// 'self-end'
        const SELF_END =        structs::NS_STYLE_ALIGN_SELF_END as u8;
        /// 'space-between'
        const SPACE_BETWEEN =   structs::NS_STYLE_ALIGN_SPACE_BETWEEN as u8;
        /// 'space-around'
        const SPACE_AROUND =    structs::NS_STYLE_ALIGN_SPACE_AROUND as u8;
        /// 'space-evenly'
        const SPACE_EVENLY =    structs::NS_STYLE_ALIGN_SPACE_EVENLY as u8;

        // Additional flags stored in the upper bits:
        /// 'legacy' (mutually exclusive w. SAFE & UNSAFE)
        const LEGACY =          structs::NS_STYLE_ALIGN_LEGACY as u8;
        /// 'safe'
        const SAFE =            structs::NS_STYLE_ALIGN_SAFE as u8;
        /// 'unsafe' (mutually exclusive w. SAFE)
        const UNSAFE =          structs::NS_STYLE_ALIGN_UNSAFE as u8;

        /// Mask for the additional flags above.
        const FLAG_BITS =       structs::NS_STYLE_ALIGN_FLAG_BITS as u8;
    }
}

impl AlignFlags {
    /// Returns the enumeration value stored in the lower 5 bits.
    #[inline]
    fn value(&self) -> Self {
        *self & !AlignFlags::FLAG_BITS
    }
}

impl ToCss for AlignFlags {
    fn to_css<W>(&self, dest: &mut CssWriter<W>) -> fmt::Result
    where
        W: Write,
    {
        let extra_flags = *self & AlignFlags::FLAG_BITS;
        let value = self.value();

        match extra_flags {
            AlignFlags::LEGACY => {
                dest.write_str("legacy")?;
                if value.is_empty() {
                    return Ok(());
                }
                dest.write_char(' ')?;
            },
            AlignFlags::SAFE => dest.write_str("safe ")?,
            // Don't serialize "unsafe", since it's the default.
            AlignFlags::UNSAFE => {},
            _ => {
                debug_assert_eq!(extra_flags, AlignFlags::empty());
            },
        }

        dest.write_str(match value {
            AlignFlags::AUTO => "auto",
            AlignFlags::NORMAL => "normal",
            AlignFlags::START => "start",
            AlignFlags::END => "end",
            AlignFlags::FLEX_START => "flex-start",
            AlignFlags::FLEX_END => "flex-end",
            AlignFlags::CENTER => "center",
            AlignFlags::LEFT => "left",
            AlignFlags::RIGHT => "right",
            AlignFlags::BASELINE => "baseline",
            AlignFlags::LAST_BASELINE => "last baseline",
            AlignFlags::STRETCH => "stretch",
            AlignFlags::SELF_START => "self-start",
            AlignFlags::SELF_END => "self-end",
            AlignFlags::SPACE_BETWEEN => "space-between",
            AlignFlags::SPACE_AROUND => "space-around",
            AlignFlags::SPACE_EVENLY => "space-evenly",
            _ => unreachable!(),
        })
    }
}

/// An axis direction, either inline (for the `justify` properties) or block,
/// (for the `align` properties).
#[derive(Clone, Copy, PartialEq)]
pub enum AxisDirection {
    /// Block direction.
    Block,
    /// Inline direction.
    Inline,
}

/// Shared value for the `align-content` and `justify-content` properties.
///
/// <https://drafts.csswg.org/css-align/#content-distribution>
#[derive(Clone, Copy, Debug, Eq, MallocSizeOf, PartialEq, ToComputedValue, ToCss)]
#[cfg_attr(feature = "servo", derive(Deserialize, Serialize))]
pub struct ContentDistribution {
    primary: AlignFlags,
    // FIXME(https://github.com/w3c/csswg-drafts/issues/1002): This will need to
    // accept fallback alignment, eventually.
}

impl ContentDistribution {
    /// The initial value 'normal'
    #[inline]
    pub fn normal() -> Self {
        Self::new(AlignFlags::NORMAL)
    }

    /// `start`
    #[inline]
    pub fn start() -> Self {
        Self::new(AlignFlags::START)
    }

    /// The initial value 'normal'
    #[inline]
    pub fn new(primary: AlignFlags) -> Self {
        Self { primary }
    }

    fn from_bits(bits: u16) -> Self {
        Self {
            primary: AlignFlags::from_bits_truncate(bits as u8),
        }
    }

    fn as_bits(&self) -> u16 {
        self.primary.bits() as u16
    }

    /// Returns whether this value is a <baseline-position>.
    pub fn is_baseline_position(&self) -> bool {
        matches!(
            self.primary.value(),
            AlignFlags::BASELINE | AlignFlags::LAST_BASELINE
        )
    }

    /// The primary alignment
    #[inline]
    pub fn primary(self) -> AlignFlags {
        self.primary
    }

    /// Parse a value for align-content / justify-content.
    pub fn parse<'i, 't>(
        input: &mut Parser<'i, 't>,
        axis: AxisDirection,
    ) -> Result<Self, ParseError<'i>> {
        // NOTE Please also update the `list_keywords` function below
        //      when this function is updated.

        // Try to parse normal first
        if input.try(|i| i.expect_ident_matching("normal")).is_ok() {
            return Ok(ContentDistribution::normal());
        }

        // Parse <baseline-position>, but only on the block axis.
        if axis == AxisDirection::Block {
            if let Ok(value) = input.try(parse_baseline) {
                return Ok(ContentDistribution::new(value));
            }
        }

        // <content-distribution>
        if let Ok(value) = input.try(parse_content_distribution) {
            return Ok(ContentDistribution::new(value));
        }

        // <overflow-position>? <content-position>
        let overflow_position = input
            .try(parse_overflow_position)
            .unwrap_or(AlignFlags::empty());

        let content_position = try_match_ident_ignore_ascii_case! { input,
            "start" => AlignFlags::START,
            "end" => AlignFlags::END,
            "flex-start" => AlignFlags::FLEX_START,
            "flex-end" => AlignFlags::FLEX_END,
            "center" => AlignFlags::CENTER,
            "left" if axis == AxisDirection::Inline => AlignFlags::LEFT,
            "right" if axis == AxisDirection::Inline => AlignFlags::RIGHT,
        };

        Ok(ContentDistribution::new(
            content_position | overflow_position,
        ))
    }

    fn list_keywords(f: KeywordsCollectFn, axis: AxisDirection) {
        f(&["normal"]);
        if axis == AxisDirection::Block {
            list_baseline_keywords(f);
        }
        list_content_distribution_keywords(f);
        list_overflow_position_keywords(f);
        f(&["start", "end", "flex-start", "flex-end", "center"]);
        if axis == AxisDirection::Inline {
            f(&["left", "right"]);
        }
    }
}

/// Value for the `align-content` property.
///
/// <https://drafts.csswg.org/css-align/#propdef-align-content>
#[derive(Clone, Copy, Debug, Eq, MallocSizeOf, PartialEq, ToComputedValue, ToCss)]
pub struct AlignContent(pub ContentDistribution);

impl Parse for AlignContent {
    fn parse<'i, 't>(
        _: &ParserContext,
        input: &mut Parser<'i, 't>,
    ) -> Result<Self, ParseError<'i>> {
        // NOTE Please also update `impl SpecifiedValueInfo` below when
        //      this function is updated.
        Ok(AlignContent(ContentDistribution::parse(
            input,
            AxisDirection::Block,
        )?))
    }
}

impl SpecifiedValueInfo for AlignContent {
    fn collect_completion_keywords(f: KeywordsCollectFn) {
        ContentDistribution::list_keywords(f, AxisDirection::Block);
    }
}

#[cfg(feature = "gecko")]
impl From<u16> for AlignContent {
    fn from(bits: u16) -> Self {
        AlignContent(ContentDistribution::from_bits(bits))
    }
}

#[cfg(feature = "gecko")]
impl From<AlignContent> for u16 {
    fn from(v: AlignContent) -> u16 {
        v.0.as_bits()
    }
}

/// Value for the `justify-content` property.
///
/// <https://drafts.csswg.org/css-align/#propdef-align-content>
#[derive(Clone, Copy, Debug, Eq, MallocSizeOf, PartialEq, ToComputedValue, ToCss)]
pub struct JustifyContent(pub ContentDistribution);

impl Parse for JustifyContent {
    fn parse<'i, 't>(
        _: &ParserContext,
        input: &mut Parser<'i, 't>,
    ) -> Result<Self, ParseError<'i>> {
        // NOTE Please also update `impl SpecifiedValueInfo` below when
        //      this function is updated.
        Ok(JustifyContent(ContentDistribution::parse(
            input,
            AxisDirection::Inline,
        )?))
    }
}

impl SpecifiedValueInfo for JustifyContent {
    fn collect_completion_keywords(f: KeywordsCollectFn) {
        ContentDistribution::list_keywords(f, AxisDirection::Inline);
    }
}

#[cfg(feature = "gecko")]
impl From<u16> for JustifyContent {
    fn from(bits: u16) -> Self {
        JustifyContent(ContentDistribution::from_bits(bits))
    }
}

#[cfg(feature = "gecko")]
impl From<JustifyContent> for u16 {
    fn from(v: JustifyContent) -> u16 {
        v.0.as_bits()
    }
}

/// <https://drafts.csswg.org/css-align/#self-alignment>
#[derive(Clone, Copy, Debug, Eq, MallocSizeOf, PartialEq, ToComputedValue, ToCss)]
pub struct SelfAlignment(pub AlignFlags);

impl SelfAlignment {
    /// The initial value 'auto'
    #[inline]
    pub fn auto() -> Self {
        SelfAlignment(AlignFlags::AUTO)
    }

    /// Returns whether this value is valid for both axis directions.
    pub fn is_valid_on_both_axes(&self) -> bool {
        match self.0.value() {
            // left | right are only allowed on the inline axis.
            AlignFlags::LEFT | AlignFlags::RIGHT => false,

            _ => true,
        }
    }

    /// Parse a self-alignment value on one of the axis.
    pub fn parse<'i, 't>(
        input: &mut Parser<'i, 't>,
        axis: AxisDirection,
    ) -> Result<Self, ParseError<'i>> {
        // NOTE Please also update the `list_keywords` function below
        //      when this function is updated.

        // <baseline-position>
        //
        // It's weird that this accepts <baseline-position>, but not
        // justify-content...
        if let Ok(value) = input.try(parse_baseline) {
            return Ok(SelfAlignment(value));
        }

        // auto | normal | stretch
        if let Ok(value) = input.try(parse_auto_normal_stretch) {
            return Ok(SelfAlignment(value));
        }

        // <overflow-position>? <self-position>
        let overflow_position = input
            .try(parse_overflow_position)
            .unwrap_or(AlignFlags::empty());
        let self_position = parse_self_position(input, axis)?;
        Ok(SelfAlignment(overflow_position | self_position))
    }

    fn list_keywords(f: KeywordsCollectFn, axis: AxisDirection) {
        list_baseline_keywords(f);
        list_auto_normal_stretch(f);
        list_overflow_position_keywords(f);
        list_self_position_keywords(f, axis);
    }
}

/// The specified value of the align-self property.
///
/// <https://drafts.csswg.org/css-align/#propdef-align-self>
#[derive(Clone, Copy, Debug, Eq, MallocSizeOf, PartialEq, ToComputedValue, ToCss)]
pub struct AlignSelf(pub SelfAlignment);

impl Parse for AlignSelf {
    fn parse<'i, 't>(
        _: &ParserContext,
        input: &mut Parser<'i, 't>,
    ) -> Result<Self, ParseError<'i>> {
        // NOTE Please also update `impl SpecifiedValueInfo` below when
        //      this function is updated.
        Ok(AlignSelf(SelfAlignment::parse(
            input,
            AxisDirection::Block,
        )?))
    }
}

impl SpecifiedValueInfo for AlignSelf {
    fn collect_completion_keywords(f: KeywordsCollectFn) {
        SelfAlignment::list_keywords(f, AxisDirection::Block);
    }
}

impl From<u8> for AlignSelf {
    fn from(bits: u8) -> Self {
        AlignSelf(SelfAlignment(AlignFlags::from_bits_truncate(bits)))
    }
}

impl From<AlignSelf> for u8 {
    fn from(align: AlignSelf) -> u8 {
        (align.0).0.bits()
    }
}

/// The specified value of the justify-self property.
///
/// <https://drafts.csswg.org/css-align/#propdef-justify-self>
#[derive(Clone, Copy, Debug, Eq, MallocSizeOf, PartialEq, ToComputedValue, ToCss)]
pub struct JustifySelf(pub SelfAlignment);

impl Parse for JustifySelf {
    fn parse<'i, 't>(
        _: &ParserContext,
        input: &mut Parser<'i, 't>,
    ) -> Result<Self, ParseError<'i>> {
        // NOTE Please also update `impl SpecifiedValueInfo` below when
        //      this function is updated.
        Ok(JustifySelf(SelfAlignment::parse(
            input,
            AxisDirection::Inline,
        )?))
    }
}

impl SpecifiedValueInfo for JustifySelf {
    fn collect_completion_keywords(f: KeywordsCollectFn) {
        SelfAlignment::list_keywords(f, AxisDirection::Inline);
    }
}

impl From<u8> for JustifySelf {
    fn from(bits: u8) -> Self {
        JustifySelf(SelfAlignment(AlignFlags::from_bits_truncate(bits)))
    }
}

impl From<JustifySelf> for u8 {
    fn from(justify: JustifySelf) -> u8 {
        (justify.0).0.bits()
    }
}

/// Value of the `align-items` property
///
/// <https://drafts.csswg.org/css-align/#self-alignment>
#[derive(Clone, Copy, Debug, Eq, MallocSizeOf, PartialEq, ToComputedValue, ToCss)]
pub struct AlignItems(pub AlignFlags);

impl AlignItems {
    /// The initial value 'normal'
    #[inline]
    pub fn normal() -> Self {
        AlignItems(AlignFlags::NORMAL)
    }
}

impl Parse for AlignItems {
    // normal | stretch | <baseline-position> |
    // <overflow-position>? <self-position>
    fn parse<'i, 't>(
        _: &ParserContext,
        input: &mut Parser<'i, 't>,
    ) -> Result<Self, ParseError<'i>> {
        // NOTE Please also update `impl SpecifiedValueInfo` below when
        //      this function is updated.

        // <baseline-position>
        if let Ok(baseline) = input.try(parse_baseline) {
            return Ok(AlignItems(baseline));
        }

        // normal | stretch
        if let Ok(value) = input.try(parse_normal_stretch) {
            return Ok(AlignItems(value));
        }
        // <overflow-position>? <self-position>
        let overflow = input
            .try(parse_overflow_position)
            .unwrap_or(AlignFlags::empty());
        let self_position = parse_self_position(input, AxisDirection::Block)?;
        Ok(AlignItems(self_position | overflow))
    }
}

impl SpecifiedValueInfo for AlignItems {
    fn collect_completion_keywords(f: KeywordsCollectFn) {
        list_baseline_keywords(f);
        list_normal_stretch(f);
        list_overflow_position_keywords(f);
        list_self_position_keywords(f, AxisDirection::Block);
    }
}

/// Value of the `justify-items` property
///
/// <https://drafts.csswg.org/css-align/#justify-items-property>
#[derive(Clone, Copy, Debug, Eq, MallocSizeOf, PartialEq, ToCss)]
pub struct JustifyItems(pub AlignFlags);

impl JustifyItems {
    /// The initial value 'legacy'
    #[inline]
    pub fn legacy() -> Self {
        JustifyItems(AlignFlags::LEGACY)
    }

    /// The value 'normal'
    #[inline]
    pub fn normal() -> Self {
        JustifyItems(AlignFlags::NORMAL)
    }
}

impl Parse for JustifyItems {
    fn parse<'i, 't>(
        _: &ParserContext,
        input: &mut Parser<'i, 't>,
    ) -> Result<Self, ParseError<'i>> {
        // NOTE Please also update `impl SpecifiedValueInfo` below when
        //      this function is updated.

        // <baseline-position>
        //
        // It's weird that this accepts <baseline-position>, but not
        // justify-content...
        if let Ok(baseline) = input.try(parse_baseline) {
            return Ok(JustifyItems(baseline));
        }

        // normal | stretch
        if let Ok(value) = input.try(parse_normal_stretch) {
            return Ok(JustifyItems(value));
        }

        // legacy | [ legacy && [ left | right | center ] ]
        if let Ok(value) = input.try(parse_legacy) {
            return Ok(JustifyItems(value));
        }

        // <overflow-position>? <self-position>
        let overflow = input
            .try(parse_overflow_position)
            .unwrap_or(AlignFlags::empty());
        let self_position = parse_self_position(input, AxisDirection::Inline)?;
        Ok(JustifyItems(overflow | self_position))
    }
}

impl SpecifiedValueInfo for JustifyItems {
    fn collect_completion_keywords(f: KeywordsCollectFn) {
        list_baseline_keywords(f);
        list_normal_stretch(f);
        list_legacy_keywords(f);
        list_overflow_position_keywords(f);
        list_self_position_keywords(f, AxisDirection::Inline);
    }
}

// auto | normal | stretch
fn parse_auto_normal_stretch<'i, 't>(
    input: &mut Parser<'i, 't>,
) -> Result<AlignFlags, ParseError<'i>> {
    // NOTE Please also update the `list_auto_normal_stretch` function
    //      below when this function is updated.
    try_match_ident_ignore_ascii_case! { input,
        "auto" => Ok(AlignFlags::AUTO),
        "normal" => Ok(AlignFlags::NORMAL),
        "stretch" => Ok(AlignFlags::STRETCH),
    }
}

fn list_auto_normal_stretch(f: KeywordsCollectFn) {
    f(&["auto", "normal", "stretch"]);
}

// normal | stretch
fn parse_normal_stretch<'i, 't>(input: &mut Parser<'i, 't>) -> Result<AlignFlags, ParseError<'i>> {
    // NOTE Please also update the `list_normal_stretch` function below
    //      when this function is updated.
    try_match_ident_ignore_ascii_case! { input,
        "normal" => Ok(AlignFlags::NORMAL),
        "stretch" => Ok(AlignFlags::STRETCH),
    }
}

fn list_normal_stretch(f: KeywordsCollectFn) {
    f(&["normal", "stretch"]);
}

// <baseline-position>
fn parse_baseline<'i, 't>(input: &mut Parser<'i, 't>) -> Result<AlignFlags, ParseError<'i>> {
    // NOTE Please also update the `list_baseline_keywords` function
    //      below when this function is updated.
    try_match_ident_ignore_ascii_case! { input,
        "baseline" => Ok(AlignFlags::BASELINE),
        "first" => {
            input.expect_ident_matching("baseline")?;
            Ok(AlignFlags::BASELINE)
        }
        "last" => {
            input.expect_ident_matching("baseline")?;
            Ok(AlignFlags::LAST_BASELINE)
        }
    }
}

fn list_baseline_keywords(f: KeywordsCollectFn) {
    f(&["baseline", "first baseline", "last baseline"]);
}

// <content-distribution>
fn parse_content_distribution<'i, 't>(
    input: &mut Parser<'i, 't>,
) -> Result<AlignFlags, ParseError<'i>> {
    // NOTE Please also update the `list_content_distribution_keywords`
    //      function below when this function is updated.
    try_match_ident_ignore_ascii_case! { input,
        "stretch" => Ok(AlignFlags::STRETCH),
        "space-between" => Ok(AlignFlags::SPACE_BETWEEN),
        "space-around" => Ok(AlignFlags::SPACE_AROUND),
        "space-evenly" => Ok(AlignFlags::SPACE_EVENLY),
    }
}

fn list_content_distribution_keywords(f: KeywordsCollectFn) {
    f(&["stretch", "space-between", "space-around", "space-evenly"]);
}

// <overflow-position>
fn parse_overflow_position<'i, 't>(
    input: &mut Parser<'i, 't>,
) -> Result<AlignFlags, ParseError<'i>> {
    // NOTE Please also update the `list_overflow_position_keywords`
    //      function below when this function is updated.
    try_match_ident_ignore_ascii_case! { input,
        "safe" => Ok(AlignFlags::SAFE),
        "unsafe" => Ok(AlignFlags::UNSAFE),
    }
}

fn list_overflow_position_keywords(f: KeywordsCollectFn) {
    f(&["safe", "unsafe"]);
}

// <self-position> | left | right in the inline axis.
fn parse_self_position<'i, 't>(
    input: &mut Parser<'i, 't>,
    axis: AxisDirection,
) -> Result<AlignFlags, ParseError<'i>> {
    // NOTE Please also update the `list_self_position_keywords`
    //      function below when this function is updated.
    Ok(try_match_ident_ignore_ascii_case! { input,
        "start" => AlignFlags::START,
        "end" => AlignFlags::END,
        "flex-start" => AlignFlags::FLEX_START,
        "flex-end" => AlignFlags::FLEX_END,
        "center" => AlignFlags::CENTER,
        "self-start" => AlignFlags::SELF_START,
        "self-end" => AlignFlags::SELF_END,
        "left" if axis == AxisDirection::Inline => AlignFlags::LEFT,
        "right" if axis == AxisDirection::Inline => AlignFlags::RIGHT,
    })
}

fn list_self_position_keywords(f: KeywordsCollectFn, axis: AxisDirection) {
    f(&[
        "start",
        "end",
        "flex-start",
        "flex-end",
        "center",
        "self-start",
        "self-end",
    ]);
    if axis == AxisDirection::Inline {
        f(&["left", "right"]);
    }
}

fn parse_left_right_center<'i, 't>(
    input: &mut Parser<'i, 't>,
) -> Result<AlignFlags, ParseError<'i>> {
    // NOTE Please also update the `list_legacy_keywords` function below
    //      when this function is updated.
    Ok(try_match_ident_ignore_ascii_case! { input,
        "left" => AlignFlags::LEFT,
        "right" => AlignFlags::RIGHT,
        "center" => AlignFlags::CENTER,
    })
}

// legacy | [ legacy && [ left | right | center ] ]
fn parse_legacy<'i, 't>(input: &mut Parser<'i, 't>) -> Result<AlignFlags, ParseError<'i>> {
    // NOTE Please also update the `list_legacy_keywords` function below
    //      when this function is updated.
    let flags = try_match_ident_ignore_ascii_case! { input,
        "legacy" => {
            let flags = input.try(parse_left_right_center)
                .unwrap_or(AlignFlags::empty());

            return Ok(AlignFlags::LEGACY | flags)
        }
        "left" => AlignFlags::LEFT,
        "right" => AlignFlags::RIGHT,
        "center" => AlignFlags::CENTER,
    };

    input.expect_ident_matching("legacy")?;
    Ok(AlignFlags::LEGACY | flags)
}

fn list_legacy_keywords(f: KeywordsCollectFn) {
    f(&["legacy", "left", "right", "center"]);
}