src/librustdoc/clean/cfg.rs

//! The representation of a `#[doc(cfg(...))]` attribute.

// FIXME: Once the portability lint RFC is implemented (see tracking issue #41619),
// switch to use those structures instead.

use std::str::FromStr;
use std::sync::Arc;
use std::{fmt, mem, ops};

use itertools::Either;
use rustc_data_structures::fx::FxHashMap;
use rustc_data_structures::thin_vec::{ThinVec, thin_vec};
use rustc_hir as hir;
use rustc_hir::Attribute;
use rustc_hir::attrs::{
    AttributeKind, CfgEntry, CfgHideShow, DocCfgHideShow, DocCfgHideShowValue, HideOrShow,
};
use rustc_middle::ty::TyCtxt;
use rustc_span::symbol::{Symbol, sym};
use rustc_span::{DUMMY_SP, Span};
use rustc_target::spec;

use crate::display::{Joined as _, MaybeDisplay, Wrapped};
use crate::html::escape::Escape;

#[cfg(test)]
mod tests;

#[derive(Clone, Debug, Hash)]
// Because `CfgEntry` includes `Span`, we must NEVER use `==`/`!=` operators on `Cfg` and instead
// use `is_equivalent_to`.
#[cfg_attr(test, derive(PartialEq))]
pub(crate) struct Cfg(CfgEntry);

// Similar to `hir::DocCfgHideShow` but allows to handle both `show` and `hide` as with the `except`
// field in `Any` variant.
#[derive(Clone, Debug)]
enum DocCfgHide {
    Any { except: ThinVec<DocCfgHideShowValue> },
    List(ThinVec<DocCfgHideShowValue>),
}

impl DocCfgHide {
    fn new() -> Self {
        Self::List([DocCfgHideShowValue::new_none(DUMMY_SP)].into())
    }

    fn contains(&self, value: Option<Symbol>) -> bool {
        match self {
            // Contains any values except the ones listed in `except`.
            Self::Any { except } => !except.iter().any(|e| e.value == value),
            Self::List(values) => values.iter().any(|v| v.value == value),
        }
    }

    fn merge_with(&mut self, other: &DocCfgHideShow) {
        match (self, other) {
            (Self::Any { except }, DocCfgHideShow::Any(_)) => {
                except.clear();
            }
            (s, DocCfgHideShow::Any(_)) => {
                // We "upgrade" the list values to "all".
                *s = Self::Any { except: ThinVec::new() };
            }
            (Self::Any { except }, DocCfgHideShow::List(values)) => {
                for other in values {
                    if let Some(index) = except.iter().position(|value| value.value == other.value)
                    {
                        except.remove(index);
                    }
                }
            }
            (Self::List(values), DocCfgHideShow::List(other_values)) => {
                for other in other_values {
                    if !values.iter().any(|value| value.value == other.value) {
                        values.push(*other);
                    }
                }
            }
        }
    }

    fn remove(&mut self, other: &DocCfgHideShow) {
        match (self, other) {
            (s, DocCfgHideShow::Any(_)) => {
                *s = Self::List(ThinVec::new());
            }
            (Self::Any { except }, DocCfgHideShow::List(other_values)) => {
                for other in other_values {
                    if !except.iter().any(|value| value.value == other.value) {
                        except.push(*other);
                    }
                }
            }
            (Self::List(values), DocCfgHideShow::List(other_values)) => {
                for other in other_values {
                    if let Some(index) = values.iter().position(|value| value.value == other.value)
                    {
                        values.remove(index);
                    }
                }
            }
        }
    }
}

impl From<&DocCfgHideShow> for DocCfgHide {
    fn from(from: &DocCfgHideShow) -> Self {
        match from {
            DocCfgHideShow::Any(_) => Self::Any { except: ThinVec::new() },
            DocCfgHideShow::List(values) => Self::List(values.clone()),
        }
    }
}

/// Whether the configuration consists of just `Cfg` or `Not`.
fn is_simple_cfg(cfg: &CfgEntry) -> bool {
    match cfg {
        CfgEntry::Bool(..)
        | CfgEntry::NameValue { .. }
        | CfgEntry::Not(..)
        | CfgEntry::Version(..) => true,
        CfgEntry::All(..) | CfgEntry::Any(..) => false,
    }
}

/// Returns `true` if is [`CfgEntry::Any`], otherwise returns `false`.
fn is_any_cfg(cfg: &CfgEntry) -> bool {
    match cfg {
        CfgEntry::Bool(..)
        | CfgEntry::NameValue { .. }
        | CfgEntry::Not(..)
        | CfgEntry::Version(..)
        | CfgEntry::All(..) => false,
        CfgEntry::Any(..) => true,
    }
}

fn strip_hidden(cfg: &CfgEntry, hidden: &FxHashMap<Symbol, DocCfgHide>) -> Option<CfgEntry> {
    match cfg {
        CfgEntry::Bool(..) => Some(cfg.clone()),
        CfgEntry::NameValue { name, value, .. } => {
            if hidden.get(name).is_some_and(|values| values.contains(*value)) {
                None
            } else {
                Some(cfg.clone())
            }
        }
        CfgEntry::Not(cfg, _) => {
            if let Some(cfg) = strip_hidden(cfg, hidden) {
                Some(CfgEntry::Not(Box::new(cfg), DUMMY_SP))
            } else {
                None
            }
        }
        CfgEntry::Any(cfgs, _) => {
            let cfgs =
                cfgs.iter().filter_map(|cfg| strip_hidden(cfg, hidden)).collect::<ThinVec<_>>();
            if cfgs.is_empty() { None } else { Some(CfgEntry::Any(cfgs, DUMMY_SP)) }
        }
        CfgEntry::All(cfgs, _) => {
            let cfgs =
                cfgs.iter().filter_map(|cfg| strip_hidden(cfg, hidden)).collect::<ThinVec<_>>();
            if cfgs.is_empty() { None } else { Some(CfgEntry::All(cfgs, DUMMY_SP)) }
        }
        CfgEntry::Version(..) => {
            // FIXME: Should be handled.
            Some(cfg.clone())
        }
    }
}

fn should_capitalize_first_letter(cfg: &CfgEntry) -> bool {
    match cfg {
        CfgEntry::Bool(..) | CfgEntry::Not(..) | CfgEntry::Version(..) => true,
        CfgEntry::Any(sub_cfgs, _) | CfgEntry::All(sub_cfgs, _) => {
            sub_cfgs.first().map(should_capitalize_first_letter).unwrap_or(false)
        }
        CfgEntry::NameValue { name, .. } => {
            *name == sym::debug_assertions || *name == sym::target_endian
        }
    }
}

impl Cfg {
    /// Renders the configuration for human display, as a short HTML description.
    pub(crate) fn render_short_html(&self) -> String {
        let mut msg = Display(&self.0, Format::ShortHtml).to_string();
        if should_capitalize_first_letter(&self.0)
            && let Some(i) = msg.find(|c: char| c.is_ascii_alphanumeric())
        {
            msg[i..i + 1].make_ascii_uppercase();
        }
        msg
    }

    fn render_long_inner(&self, format: Format) -> String {
        let on = if self.omit_preposition() {
            " "
        } else if self.should_use_with_in_description() {
            " with "
        } else {
            " on "
        };

        let mut msg = if matches!(format, Format::LongHtml) {
            format!("Available{on}<strong>{}</strong>", Display(&self.0, format))
        } else {
            format!("Available{on}{}", Display(&self.0, format))
        };
        if self.should_append_only_to_description() {
            msg.push_str(" only");
        }
        msg
    }

    /// Renders the configuration for long display, as a long HTML description.
    pub(crate) fn render_long_html(&self) -> String {
        let mut msg = self.render_long_inner(Format::LongHtml);
        msg.push('.');
        msg
    }

    /// Renders the configuration for long display, as a long plain text description.
    pub(crate) fn render_long_plain(&self) -> String {
        self.render_long_inner(Format::LongPlain)
    }

    fn should_append_only_to_description(&self) -> bool {
        match self.0 {
            CfgEntry::Any(..)
            | CfgEntry::All(..)
            | CfgEntry::NameValue { .. }
            | CfgEntry::Version(..)
            | CfgEntry::Not(CfgEntry::NameValue { .. }, _) => true,
            CfgEntry::Not(..) | CfgEntry::Bool(..) => false,
        }
    }

    fn should_use_with_in_description(&self) -> bool {
        matches!(self.0, CfgEntry::NameValue { name, .. } if name == sym::target_feature)
    }

    /// Attempt to simplify this cfg by assuming that `assume` is already known to be true, will
    /// return `None` if simplification managed to completely eliminate any requirements from this
    /// `Cfg`.
    ///
    /// See `tests::test_simplify_with` for examples.
    pub(crate) fn simplify_with(&self, assume: &Self) -> Option<Self> {
        if self.0.is_equivalent_to(&assume.0) {
            None
        } else if let CfgEntry::All(a, _) = &self.0 {
            let mut sub_cfgs: ThinVec<CfgEntry> = if let CfgEntry::All(b, _) = &assume.0 {
                a.iter().filter(|a| !b.iter().any(|b| a.is_equivalent_to(b))).cloned().collect()
            } else {
                a.iter().filter(|&a| !a.is_equivalent_to(&assume.0)).cloned().collect()
            };
            let len = sub_cfgs.len();
            match len {
                0 => None,
                1 => sub_cfgs.pop().map(Cfg),
                _ => Some(Cfg(CfgEntry::All(sub_cfgs, DUMMY_SP))),
            }
        } else if let CfgEntry::All(b, _) = &assume.0
            && b.iter().any(|b| b.is_equivalent_to(&self.0))
        {
            None
        } else {
            Some(self.clone())
        }
    }

    /// Recursively sorts the configuration tree to ensure deterministic rendering.
    ///
    /// Sorting groups predicates logically: Targets first, then Target Features,
    /// then Crate Features, and finally nested Any/All/Not groupings.
    /// Within each group, a fallback alphabetical sort is applied.
    pub(crate) fn sort_for_rendering(&mut self) {
        fn sort_cfg_entry(cfg: &mut CfgEntry) {
            match cfg {
                CfgEntry::Any(sub_cfgs, _) | CfgEntry::All(sub_cfgs, _) => {
                    for sub_cfg in sub_cfgs.iter_mut() {
                        sort_cfg_entry(sub_cfg);
                    }

                    sub_cfgs.sort_by_cached_key(|a| {
                        (
                            cfg_category(a),
                            Display(a, Format::LongPlain).to_string().to_ascii_lowercase(),
                        )
                    });
                }
                CfgEntry::Not(box_cfg, _) => sort_cfg_entry(box_cfg),
                _ => {}
            }
        }

        fn cfg_category(cfg: &CfgEntry) -> u8 {
            match cfg {
                CfgEntry::NameValue { name, .. } if *name == sym::feature => 2,
                CfgEntry::NameValue { name, .. } if *name == sym::target_feature => 1,
                CfgEntry::NameValue { .. } | CfgEntry::Bool(..) => 0,
                CfgEntry::Any(..) | CfgEntry::All(..) | CfgEntry::Not(..) => 3,
                _ => 4,
            }
        }

        sort_cfg_entry(&mut self.0);
    }

    fn omit_preposition(&self) -> bool {
        matches!(self.0, CfgEntry::Bool(..))
    }

    pub(crate) fn inner(&self) -> &CfgEntry {
        &self.0
    }
}

impl ops::Not for Cfg {
    type Output = Cfg;
    fn not(self) -> Cfg {
        Cfg(match self.0 {
            CfgEntry::Bool(v, s) => CfgEntry::Bool(!v, s),
            CfgEntry::Not(cfg, _) => *cfg,
            s => CfgEntry::Not(Box::new(s), DUMMY_SP),
        })
    }
}

impl ops::BitAndAssign for Cfg {
    fn bitand_assign(&mut self, other: Cfg) {
        match (&mut self.0, other.0) {
            (CfgEntry::Bool(false, _), _) | (_, CfgEntry::Bool(true, _)) => {}
            (s, CfgEntry::Bool(false, _)) => *s = CfgEntry::Bool(false, DUMMY_SP),
            (s @ CfgEntry::Bool(true, _), b) => *s = b,
            (CfgEntry::All(a, _), CfgEntry::All(ref mut b, _)) => {
                for c in b.drain(..) {
                    if !a.iter().any(|a| a.is_equivalent_to(&c)) {
                        a.push(c);
                    }
                }
            }
            (CfgEntry::All(a, _), ref mut b) => {
                if !a.iter().any(|a| a.is_equivalent_to(b)) {
                    a.push(mem::replace(b, CfgEntry::Bool(true, DUMMY_SP)));
                }
            }
            (s, CfgEntry::All(mut a, _)) => {
                let b = mem::replace(s, CfgEntry::Bool(true, DUMMY_SP));
                if !a.iter().any(|a| a.is_equivalent_to(&b)) {
                    a.push(b);
                }
                *s = CfgEntry::All(a, DUMMY_SP);
            }
            (s, b) => {
                if !s.is_equivalent_to(&b) {
                    let a = mem::replace(s, CfgEntry::Bool(true, DUMMY_SP));
                    *s = CfgEntry::All(thin_vec![a, b], DUMMY_SP);
                }
            }
        }
    }
}

impl ops::BitAnd for Cfg {
    type Output = Cfg;
    fn bitand(mut self, other: Cfg) -> Cfg {
        self &= other;
        self
    }
}

impl ops::BitOrAssign for Cfg {
    fn bitor_assign(&mut self, other: Cfg) {
        match (&mut self.0, other.0) {
            (CfgEntry::Bool(true, _), _)
            | (_, CfgEntry::Bool(false, _))
            | (_, CfgEntry::Bool(true, _)) => {}
            (s @ CfgEntry::Bool(false, _), b) => *s = b,
            (CfgEntry::Any(a, _), CfgEntry::Any(ref mut b, _)) => {
                for c in b.drain(..) {
                    if !a.iter().any(|a| a.is_equivalent_to(&c)) {
                        a.push(c);
                    }
                }
            }
            (CfgEntry::Any(a, _), ref mut b) => {
                if !a.iter().any(|a| a.is_equivalent_to(b)) {
                    a.push(mem::replace(b, CfgEntry::Bool(true, DUMMY_SP)));
                }
            }
            (s, CfgEntry::Any(mut a, _)) => {
                let b = mem::replace(s, CfgEntry::Bool(true, DUMMY_SP));
                if !a.iter().any(|a| a.is_equivalent_to(&b)) {
                    a.push(b);
                }
                *s = CfgEntry::Any(a, DUMMY_SP);
            }
            (s, b) => {
                if !s.is_equivalent_to(&b) {
                    let a = mem::replace(s, CfgEntry::Bool(true, DUMMY_SP));
                    *s = CfgEntry::Any(thin_vec![a, b], DUMMY_SP);
                }
            }
        }
    }
}

impl ops::BitOr for Cfg {
    type Output = Cfg;
    fn bitor(mut self, other: Cfg) -> Cfg {
        self |= other;
        self
    }
}

#[derive(Clone, Copy)]
enum Format {
    LongHtml,
    LongPlain,
    ShortHtml,
}

impl Format {
    fn is_long(self) -> bool {
        match self {
            Format::LongHtml | Format::LongPlain => true,
            Format::ShortHtml => false,
        }
    }

    fn is_html(self) -> bool {
        match self {
            Format::LongHtml | Format::ShortHtml => true,
            Format::LongPlain => false,
        }
    }

    fn escape(self, s: &str) -> impl fmt::Display {
        if self.is_html() { Either::Left(Escape(s)) } else { Either::Right(s) }
    }
}

/// Pretty-print wrapper for a `Cfg`. Also indicates what form of rendering should be used.
struct Display<'a>(&'a CfgEntry, Format);

impl Display<'_> {
    fn code_wrappers(&self) -> Wrapped<&'static str> {
        if self.1.is_html() { Wrapped::with("<code>", "</code>") } else { Wrapped::with("`", "`") }
    }

    fn display_sub_cfgs(
        &self,
        fmt: &mut fmt::Formatter<'_>,
        sub_cfgs: &[CfgEntry],
        separator: &str,
    ) -> fmt::Result {
        use fmt::Display as _;

        let short_longhand = self.1.is_long() && {
            let all_crate_features = sub_cfgs.iter().all(|sub_cfg| {
                matches!(sub_cfg, CfgEntry::NameValue { name: sym::feature, value: Some(_), .. })
            });
            let all_target_features = sub_cfgs.iter().all(|sub_cfg| {
                matches!(
                    sub_cfg,
                    CfgEntry::NameValue { name: sym::target_feature, value: Some(_), .. }
                )
            });

            if all_crate_features {
                fmt.write_str("crate features ")?;
                true
            } else if all_target_features {
                fmt.write_str("target features ")?;
                true
            } else {
                false
            }
        };

        fmt::from_fn(|f| {
            sub_cfgs
                .iter()
                .map(|sub_cfg| {
                    if let CfgEntry::NameValue { value: Some(feat), .. } = sub_cfg
                        && short_longhand
                    {
                        Either::Left(self.code_wrappers().wrap(feat))
                    } else {
                        Either::Right(
                            Wrapped::with_parens()
                                .when(is_any_cfg(sub_cfg))
                                .wrap(Display(sub_cfg, self.1)),
                        )
                    }
                })
                .joined(separator, f)
        })
        .fmt(fmt)?;

        Ok(())
    }
}

impl fmt::Display for Display<'_> {
    fn fmt(&self, fmt: &mut fmt::Formatter<'_>) -> fmt::Result {
        match &self.0 {
            CfgEntry::Not(CfgEntry::Any(sub_cfgs, _), _) => {
                let separator = if sub_cfgs.iter().all(is_simple_cfg) { " nor " } else { ", nor " };
                fmt.write_str("neither ")?;

                sub_cfgs
                    .iter()
                    .map(|sub_cfg| {
                        Wrapped::with_parens()
                            .when(is_any_cfg(sub_cfg))
                            .wrap(Display(sub_cfg, self.1))
                    })
                    .joined(separator, fmt)
            }
            CfgEntry::Not(simple @ CfgEntry::NameValue { .. }, _) => {
                write!(fmt, "non-{}", Display(simple, self.1))
            }
            CfgEntry::Not(c, _) => write!(fmt, "not ({})", Display(c, self.1)),

            CfgEntry::Any(sub_cfgs, _) => {
                let separator = if sub_cfgs.iter().all(is_simple_cfg) { " or " } else { ", or " };
                self.display_sub_cfgs(fmt, sub_cfgs.as_slice(), separator)
            }
            CfgEntry::All(sub_cfgs, _) => self.display_sub_cfgs(fmt, sub_cfgs.as_slice(), " and "),

            CfgEntry::Bool(v, _) => {
                if *v {
                    fmt.write_str("everywhere")
                } else {
                    fmt.write_str("nowhere")
                }
            }

            &CfgEntry::NameValue { name, value, .. } => {
                let human_readable = match (*name, value) {
                    (sym::unix, None) => "Unix",
                    (sym::windows, None) => "Windows",
                    (sym::debug_assertions, None) => "debug-assertions enabled",
                    (sym::target_object_format, Some(format)) => match self.1 {
                        Format::LongHtml => {
                            return write!(fmt, "object format <code>{format}</code>");
                        }
                        Format::LongPlain => return write!(fmt, "object format `{format}`"),
                        Format::ShortHtml => return write!(fmt, "<code>{format}</code>"),
                    },
                    (sym::target_os, Some(os)) => human_readable_target_os(*os).unwrap_or_default(),
                    (sym::target_arch, Some(arch)) => {
                        human_readable_target_arch(*arch).unwrap_or_default()
                    }
                    (sym::target_vendor, Some(vendor)) => match vendor.as_str() {
                        "apple" => "Apple",
                        "pc" => "PC",
                        "sun" => "Sun",
                        "fortanix" => "Fortanix",
                        _ => "",
                    },
                    (sym::target_env, Some(env)) => {
                        human_readable_target_env(*env).unwrap_or_default()
                    }
                    (sym::target_endian, Some(endian)) => {
                        return write!(fmt, "{endian}-endian");
                    }
                    (sym::target_pointer_width, Some(bits)) => {
                        return write!(fmt, "{bits}-bit");
                    }
                    (sym::target_feature, Some(feat)) => match self.1 {
                        Format::LongHtml => {
                            return write!(fmt, "target feature <code>{feat}</code>");
                        }
                        Format::LongPlain => return write!(fmt, "target feature `{feat}`"),
                        Format::ShortHtml => return write!(fmt, "<code>{feat}</code>"),
                    },
                    (sym::feature, Some(feat)) => match self.1 {
                        Format::LongHtml => {
                            return write!(fmt, "crate feature <code>{feat}</code>");
                        }
                        Format::LongPlain => return write!(fmt, "crate feature `{feat}`"),
                        Format::ShortHtml => return write!(fmt, "<code>{feat}</code>"),
                    },
                    _ => "",
                };
                if !human_readable.is_empty() {
                    fmt.write_str(human_readable)
                } else {
                    let value = value
                        .map(|v| fmt::from_fn(move |f| write!(f, "={}", self.1.escape(v.as_str()))))
                        .maybe_display();
                    self.code_wrappers()
                        .wrap(format_args!("{}{value}", self.1.escape(name.as_str())))
                        .fmt(fmt)
                }
            }

            CfgEntry::Version(..) => {
                // FIXME: Should we handle it?
                Ok(())
            }
        }
    }
}

fn human_readable_target_os(os: Symbol) -> Option<&'static str> {
    let os = spec::Os::from_str(os.as_str()).ok()?;

    use spec::Os::*;
    Some(match os {
        // tidy-alphabetical-start
        Aix => "AIX",
        AmdHsa => "AMD HSA",
        Android => "Android",
        Cuda => "CUDA",
        Cygwin => "Cygwin",
        Dragonfly => "DragonFly BSD",
        Emscripten => "Emscripten",
        EspIdf => "ESP-IDF",
        FreeBsd => "FreeBSD",
        Fuchsia => "Fuchsia",
        Haiku => "Haiku",
        HelenOs => "HelenOS",
        Hermit => "Hermit",
        Horizon => "Horizon",
        Hurd => "GNU/Hurd",
        IOs => "iOS",
        Illumos => "illumos",
        L4Re => "L4Re",
        Linux => "Linux",
        LynxOs178 => "LynxOS-178",
        MacOs => "macOS",
        Managarm => "Managarm",
        Motor => "Motor OS",
        NetBsd => "NetBSD",
        None => "bare-metal",
        Nto => "QNX Neutrino",
        NuttX => "NuttX",
        OpenBsd => "OpenBSD",
        Psp => "Play Station Portable",
        Psx => "Play Station 1",
        Qurt => "QuRT",
        Redox => "Redox OS",
        Rtems => "RTEMS OS",
        Solaris => "Solaris",
        SolidAsp3 => "SOLID ASP3",
        TeeOs => "TEEOS",
        Trusty => "Trusty",
        TvOs => "tvOS",
        Uefi => "UEFI",
        VexOs => "VEXos",
        VisionOs => "visionOS",
        Vita => "Play Station Vita",
        VxWorks => "VxWorks",
        Wasi => "WASI",
        WatchOs => "watchOS",
        Windows => "Windows",
        Xous => "Xous",
        Zkvm => "zero knowledge Virtual Machine",
        // tidy-alphabetical-end
        Unknown | Other(_) => return Option::None,
    })
}

fn human_readable_target_arch(os: Symbol) -> Option<&'static str> {
    let arch = spec::Arch::from_str(os.as_str()).ok()?;

    use spec::Arch::*;
    Some(match arch {
        // tidy-alphabetical-start
        AArch64 => "AArch64",
        AmdGpu => "AMD GPU",
        Arm => "ARM",
        Arm64EC => "ARM64EC",
        Avr => "AVR",
        Bpf => "BPF",
        CSky => "C-SKY",
        Hexagon => "Hexagon",
        LoongArch32 => "LoongArch32",
        LoongArch64 => "LoongArch64",
        M68k => "Motorola 680x0",
        Mips => "MIPS",
        Mips32r6 => "MIPS release 6",
        Mips64 => "MIPS-64",
        Mips64r6 => "MIPS-64 release 6",
        Msp430 => "MSP430",
        Nvptx64 => "NVidia GPU",
        PowerPC => "PowerPC",
        PowerPC64 => "PowerPC64",
        RiscV32 => "RISC-V RV32",
        RiscV64 => "RISC-V RV64",
        S390x => "s390x",
        Sparc => "SPARC",
        Sparc64 => "SPARC-64",
        SpirV => "SPIR-V",
        Wasm32 | Wasm64 => "WebAssembly",
        X86 => "x86",
        X86_64 => "x86-64",
        Xtensa => "Xtensa",
        // tidy-alphabetical-end
        Other(_) => return None,
    })
}

fn human_readable_target_env(env: Symbol) -> Option<&'static str> {
    let env = spec::Env::from_str(env.as_str()).ok()?;

    use spec::Env::*;
    Some(match env {
        // tidy-alphabetical-start
        Gnu => "GNU",
        MacAbi => "Catalyst",
        Mlibc => "Managarm C Library",
        Msvc => "MSVC",
        Musl => "musl",
        Newlib => "Newlib",
        Nto70 => "Neutrino 7.0",
        Nto71 => "Neutrino 7.1",
        Nto71IoSock => "Neutrino 7.1 with io-sock",
        Nto80 => "Neutrino 8.0",
        Ohos => "OpenHarmony",
        P1 => "WASIp1",
        P2 => "WASIp2",
        P3 => "WASIp3",
        Relibc => "relibc",
        Sgx => "SGX",
        Sim => "Simulator",
        Uclibc => "uClibc",
        V5 => "V5",
        // tidy-alphabetical-end
        Unspecified | Other(_) => return None,
    })
}

/// This type keeps track of (doc) cfg information as we go down the item tree.
#[derive(Clone, Debug)]
pub(crate) struct CfgInfo {
    /// List of currently active `doc(auto_cfg(hide(...)))` cfgs, minus currently active
    /// `doc(auto_cfg(show(...)))` cfgs.
    hidden_cfg: FxHashMap<Symbol, DocCfgHide>,
    /// Current computed `cfg`. Each time we enter a new item, this field is updated as well while
    /// taking into account the `hidden_cfg` information.
    current_cfg: Cfg,
    /// Whether the `doc(auto_cfg())` feature is enabled or not at this point.
    auto_cfg_active: bool,
    /// If the parent item used `doc(cfg(...))`, then we don't want to overwrite `current_cfg`,
    /// instead we will concatenate with it. However, if it's not the case, we need to overwrite
    /// `current_cfg`.
    parent_is_doc_cfg: bool,
}

impl Default for CfgInfo {
    fn default() -> Self {
        Self {
            hidden_cfg: FxHashMap::from_iter([
                (sym::test, DocCfgHide::new()),
                (sym::doc, DocCfgHide::new()),
                (sym::doctest, DocCfgHide::new()),
            ]),
            current_cfg: Cfg(CfgEntry::Bool(true, DUMMY_SP)),
            auto_cfg_active: true,
            parent_is_doc_cfg: false,
        }
    }
}

/// This functions updates the `hidden_cfg` field of the provided `cfg_info` argument.
///
/// Because we go through a list of `cfg`s, we keep track of the `cfg`s we saw in `new_show_attrs`
/// and in `new_hide_attrs` arguments.
fn handle_auto_cfg_hide_show(cfg_info: &mut CfgInfo, attr: &CfgHideShow) {
    for (cfg_name, value) in &attr.values {
        if attr.kind == HideOrShow::Show {
            cfg_info
                .hidden_cfg
                .entry(*cfg_name)
                .and_modify(|entry| entry.remove(value))
                .or_insert_with(|| value.into());
        } else {
            cfg_info
                .hidden_cfg
                .entry(*cfg_name)
                .and_modify(|entry| entry.merge_with(value))
                .or_insert_with(|| value.into());
        }
    }
}

pub(crate) fn extract_cfg_from_attrs<'a, I: Iterator<Item = &'a hir::Attribute> + Clone>(
    attrs: I,
    tcx: TyCtxt<'_>,
    cfg_info: &mut CfgInfo,
) -> Option<Arc<Cfg>> {
    fn check_changed_auto_active_status(
        changed_auto_active_status: &mut Option<rustc_span::Span>,
        attr_span: Span,
        cfg_info: &mut CfgInfo,
        tcx: TyCtxt<'_>,
        new_value: bool,
    ) -> bool {
        if let Some(first_change) = changed_auto_active_status {
            if cfg_info.auto_cfg_active != new_value {
                tcx.sess
                    .dcx()
                    .struct_span_err(
                        vec![*first_change, attr_span],
                        "`auto_cfg` was disabled and enabled more than once on the same item",
                    )
                    .emit();
                return true;
            }
        } else {
            *changed_auto_active_status = Some(attr_span);
        }
        cfg_info.auto_cfg_active = new_value;
        false
    }

    let mut doc_cfg = attrs
        .clone()
        .filter_map(|attr| match attr {
            Attribute::Parsed(AttributeKind::Doc(d)) if !d.cfg.is_empty() => Some(d),
            _ => None,
        })
        .peekable();
    // If the item uses `doc(cfg(...))`, then we ignore the other `cfg(...)` attributes.
    if doc_cfg.peek().is_some() {
        // We overwrite existing `cfg`.
        if !cfg_info.parent_is_doc_cfg {
            cfg_info.current_cfg = Cfg(CfgEntry::Bool(true, DUMMY_SP));
            cfg_info.parent_is_doc_cfg = true;
        }
        for attr in doc_cfg {
            for new_cfg in attr.cfg.clone() {
                cfg_info.current_cfg &= Cfg(new_cfg);
            }
        }
    } else {
        cfg_info.parent_is_doc_cfg = false;
    }

    let mut changed_auto_active_status = None;

    // We get all `doc(auto_cfg)`, `cfg` and `target_feature` attributes.
    for attr in attrs {
        if let Attribute::Parsed(AttributeKind::Doc(d)) = attr {
            for (new_value, span) in &d.auto_cfg_change {
                if check_changed_auto_active_status(
                    &mut changed_auto_active_status,
                    *span,
                    cfg_info,
                    tcx,
                    *new_value,
                ) {
                    return None;
                }
            }
            if let Some((_, span)) = d.auto_cfg.first() {
                if check_changed_auto_active_status(
                    &mut changed_auto_active_status,
                    *span,
                    cfg_info,
                    tcx,
                    true,
                ) {
                    return None;
                }
                for (value, _) in &d.auto_cfg {
                    handle_auto_cfg_hide_show(cfg_info, value);
                }
            }
        } else if let hir::Attribute::Parsed(AttributeKind::TargetFeature { features, .. }) = attr {
            // Treat `#[target_feature(enable = "feat")]` attributes as if they were
            // `#[doc(cfg(target_feature = "feat"))]` attributes as well.
            for (feature, _) in features {
                cfg_info.current_cfg &= Cfg(CfgEntry::NameValue {
                    name: sym::target_feature,
                    value: Some(*feature),
                    span: DUMMY_SP,
                });
            }
            continue;
        } else if !cfg_info.parent_is_doc_cfg
            && let hir::Attribute::Parsed(AttributeKind::CfgTrace(cfgs)) = attr
        {
            for (new_cfg, _) in cfgs {
                cfg_info.current_cfg &= Cfg(new_cfg.clone());
            }
        }
    }

    // If `doc(auto_cfg)` feature is disabled and `doc(cfg())` wasn't used, there is nothing
    // to be done here.
    if !cfg_info.auto_cfg_active && !cfg_info.parent_is_doc_cfg {
        None
    } else if cfg_info.parent_is_doc_cfg {
        if matches!(cfg_info.current_cfg.0, CfgEntry::Bool(true, _)) {
            None
        } else {
            let mut cfg = cfg_info.current_cfg.clone();
            cfg.sort_for_rendering();
            Some(Arc::new(cfg))
        }
    } else {
        // If `doc(auto_cfg)` feature is enabled, we want to collect all `cfg` items, we remove the
        // hidden ones afterward.
        match strip_hidden(&cfg_info.current_cfg.0, &cfg_info.hidden_cfg) {
            None | Some(CfgEntry::Bool(true, _)) => None,
            Some(cfg_entry) => {
                let mut cfg = Cfg(cfg_entry);
                cfg.sort_for_rendering();
                Some(Arc::new(cfg))
            }
        }
    }
}