rustc_attr_parsing/

context.rs

use std::cell::RefCell;
use std::collections::BTreeMap;
use std::ops::Deref;
use std::sync::LazyLock;

use rustc_ast as ast;
use rustc_attr_data_structures::AttributeKind;
use rustc_errors::{DiagCtxtHandle, Diagnostic};
use rustc_feature::Features;
use rustc_hir::{AttrArgs, AttrItem, AttrPath, Attribute, HashIgnoredAttrId};
use rustc_session::Session;
use rustc_span::{DUMMY_SP, ErrorGuaranteed, Span, Symbol, sym};

use crate::attributes::allow_unstable::{AllowConstFnUnstableParser, AllowInternalUnstableParser};
use crate::attributes::confusables::ConfusablesParser;
use crate::attributes::deprecation::DeprecationParser;
use crate::attributes::repr::ReprParser;
use crate::attributes::stability::{
    BodyStabilityParser, ConstStabilityIndirectParser, ConstStabilityParser, StabilityParser,
};
use crate::attributes::transparency::TransparencyParser;
use crate::attributes::{AttributeParser as _, Combine, Single};
use crate::parser::{ArgParser, MetaItemParser};

macro_rules! attribute_groups {
    (
        pub(crate) static $name: ident = [$($names: ty),* $(,)?];
    ) => {
        type Accepts = BTreeMap<
            &'static [Symbol],
            Box<dyn Send + Sync + Fn(&AcceptContext<'_>, &ArgParser<'_>)>
        >;
        type Finalizes = Vec<
            Box<dyn Send + Sync + Fn(&FinalizeContext<'_>) -> Option<AttributeKind>>
        >;
        pub(crate) static $name: LazyLock<(Accepts, Finalizes)> = LazyLock::new(|| {
            let mut accepts = Accepts::new();
            let mut finalizes = Finalizes::new();
            $(
                {
                    thread_local! {
                        static STATE_OBJECT: RefCell<$names> = RefCell::new(<$names>::default());
                    };

                    for (k, v) in <$names>::ATTRIBUTES {
                        let old = accepts.insert(*k, Box::new(|cx, args| {
                            STATE_OBJECT.with_borrow_mut(|s| {
                                v(s, cx, args)
                            })
                        }));
                        assert!(old.is_none());
                    }

                    finalizes.push(Box::new(|cx| {
                        let state = STATE_OBJECT.take();
                        state.finalize(cx)
                    }));
                }
            )*

            (accepts, finalizes)
        });
    };
}

attribute_groups!(
    pub(crate) static ATTRIBUTE_MAPPING = [
        // tidy-alphabetical-start
        BodyStabilityParser,
        ConfusablesParser,
        ConstStabilityParser,
        StabilityParser,
        // tidy-alphabetical-end

        // tidy-alphabetical-start
        Combine<AllowConstFnUnstableParser>,
        Combine<AllowInternalUnstableParser>,
        Combine<ReprParser>,
        // tidy-alphabetical-end

        // tidy-alphabetical-start
        Single<ConstStabilityIndirectParser>,
        Single<DeprecationParser>,
        Single<TransparencyParser>,
        // tidy-alphabetical-end
    ];
);

/// Context given to every attribute parser when accepting
///
/// Gives [`AttributeParser`]s enough information to create errors, for example.
pub(crate) struct AcceptContext<'a> {
    pub(crate) group_cx: &'a FinalizeContext<'a>,
    /// The span of the attribute currently being parsed
    pub(crate) attr_span: Span,
}

impl<'a> AcceptContext<'a> {
    pub(crate) fn emit_err(&self, diag: impl Diagnostic<'a>) -> ErrorGuaranteed {
        if self.limit_diagnostics {
            self.dcx().create_err(diag).delay_as_bug()
        } else {
            self.dcx().emit_err(diag)
        }
    }
}

impl<'a> Deref for AcceptContext<'a> {
    type Target = FinalizeContext<'a>;

    fn deref(&self) -> &Self::Target {
        &self.group_cx
    }
}

/// Context given to every attribute parser during finalization.
///
/// Gives [`AttributeParser`](crate::attributes::AttributeParser)s enough information to create
/// errors, for example.
pub(crate) struct FinalizeContext<'a> {
    /// The parse context, gives access to the session and the
    /// diagnostics context.
    pub(crate) cx: &'a AttributeParser<'a>,
    /// The span of the syntactical component this attribute was applied to
    pub(crate) target_span: Span,
}

impl<'a> Deref for FinalizeContext<'a> {
    type Target = AttributeParser<'a>;

    fn deref(&self) -> &Self::Target {
        &self.cx
    }
}

#[derive(PartialEq, Clone, Copy, Debug)]
pub enum OmitDoc {
    Lower,
    Skip,
}

/// Context created once, for example as part of the ast lowering
/// context, through which all attributes can be lowered.
pub struct AttributeParser<'sess> {
    #[expect(dead_code)] // FIXME(jdonszelmann): needed later to verify we parsed all attributes
    tools: Vec<Symbol>,
    sess: &'sess Session,
    features: Option<&'sess Features>,

    /// *Only* parse attributes with this symbol.
    ///
    /// Used in cases where we want the lowering infrastructure for parse just a single attribute.
    parse_only: Option<Symbol>,

    /// Can be used to instruct parsers to reduce the number of diagnostics it emits.
    /// Useful when using `parse_limited` and you know the attr will be reparsed later.
    pub(crate) limit_diagnostics: bool,
}

impl<'sess> AttributeParser<'sess> {
    /// This method allows you to parse attributes *before* you have access to features or tools.
    /// One example where this is necessary, is to parse `feature` attributes themselves for
    /// example.
    ///
    /// Try to use this as little as possible. Attributes *should* be lowered during
    /// `rustc_ast_lowering`. Some attributes require access to features to parse, which would
    /// crash if you tried to do so through [`parse_limited`](Self::parse_limited).
    ///
    /// To make sure use is limited, supply a `Symbol` you'd like to parse. Only attributes with
    /// that symbol are picked out of the list of instructions and parsed. Those are returned.
    pub fn parse_limited(
        sess: &'sess Session,
        attrs: &[ast::Attribute],
        sym: Symbol,
        target_span: Span,
        limit_diagnostics: bool,
    ) -> Option<Attribute> {
        let mut parsed = Self {
            sess,
            features: None,
            tools: Vec::new(),
            parse_only: Some(sym),
            limit_diagnostics,
        }
        .parse_attribute_list(attrs, target_span, OmitDoc::Skip, std::convert::identity);

        assert!(parsed.len() <= 1);

        parsed.pop()
    }

    pub fn new(sess: &'sess Session, features: &'sess Features, tools: Vec<Symbol>) -> Self {
        Self { sess, features: Some(features), tools, parse_only: None, limit_diagnostics: false }
    }

    pub(crate) fn sess(&self) -> &'sess Session {
        self.sess
    }

    pub(crate) fn features(&self) -> &'sess Features {
        self.features.expect("features not available at this point in the compiler")
    }

    pub(crate) fn dcx(&self) -> DiagCtxtHandle<'sess> {
        self.sess.dcx()
    }

    /// Parse a list of attributes.
    ///
    /// `target_span` is the span of the thing this list of attributes is applied to,
    /// and when `omit_doc` is set, doc attributes are filtered out.
    pub fn parse_attribute_list<'a>(
        &'a self,
        attrs: &'a [ast::Attribute],
        target_span: Span,
        omit_doc: OmitDoc,

        lower_span: impl Copy + Fn(Span) -> Span,
    ) -> Vec<Attribute> {
        let mut attributes = Vec::new();

        let group_cx = FinalizeContext { cx: self, target_span };

        for attr in attrs {
            // If we're only looking for a single attribute, skip all the ones we don't care about.
            if let Some(expected) = self.parse_only {
                if !attr.has_name(expected) {
                    continue;
                }
            }

            // Sometimes, for example for `#![doc = include_str!("readme.md")]`,
            // doc still contains a non-literal. You might say, when we're lowering attributes
            // that's expanded right? But no, sometimes, when parsing attributes on macros,
            // we already use the lowering logic and these are still there. So, when `omit_doc`
            // is set we *also* want to ignore these.
            if omit_doc == OmitDoc::Skip && attr.has_name(sym::doc) {
                continue;
            }

            match &attr.kind {
                ast::AttrKind::DocComment(comment_kind, symbol) => {
                    if omit_doc == OmitDoc::Skip {
                        continue;
                    }

                    attributes.push(Attribute::Parsed(AttributeKind::DocComment {
                        style: attr.style,
                        kind: *comment_kind,
                        span: lower_span(attr.span),
                        comment: *symbol,
                    }))
                }
                // // FIXME: make doc attributes go through a proper attribute parser
                // ast::AttrKind::Normal(n) if n.has_name(sym::doc) => {
                //     let p = GenericMetaItemParser::from_attr(&n, self.dcx());
                //
                //     attributes.push(Attribute::Parsed(AttributeKind::DocComment {
                //         style: attr.style,
                //         kind: CommentKind::Line,
                //         span: attr.span,
                //         comment: p.args().name_value(),
                //     }))
                // }
                ast::AttrKind::Normal(n) => {
                    let parser = MetaItemParser::from_attr(n, self.dcx());
                    let (path, args) = parser.deconstruct();
                    let parts = path.segments().map(|i| i.name).collect::<Vec<_>>();

                    if let Some(accept) = ATTRIBUTE_MAPPING.0.get(parts.as_slice()) {
                        let cx =
                            AcceptContext { group_cx: &group_cx, attr_span: lower_span(attr.span) };

                        accept(&cx, &args)
                    } else {
                        // If we're here, we must be compiling a tool attribute... Or someone
                        // forgot to parse their fancy new attribute. Let's warn them in any case.
                        // If you are that person, and you really think your attribute should
                        // remain unparsed, carefully read the documentation in this module and if
                        // you still think so you can add an exception to this assertion.

                        // FIXME(jdonszelmann): convert other attributes, and check with this that
                        // we caught em all
                        // const FIXME_TEMPORARY_ATTR_ALLOWLIST: &[Symbol] = &[sym::cfg];
                        // assert!(
                        //     self.tools.contains(&parts[0]) || true,
                        //     // || FIXME_TEMPORARY_ATTR_ALLOWLIST.contains(&parts[0]),
                        //     "attribute {path} wasn't parsed and isn't a know tool attribute",
                        // );

                        attributes.push(Attribute::Unparsed(Box::new(AttrItem {
                            path: AttrPath::from_ast(&n.item.path),
                            args: self.lower_attr_args(&n.item.args, lower_span),
                            id: HashIgnoredAttrId { attr_id: attr.id },
                            style: attr.style,
                            span: lower_span(attr.span),
                        })));
                    }
                }
            }
        }

        let mut parsed_attributes = Vec::new();
        for f in &ATTRIBUTE_MAPPING.1 {
            if let Some(attr) = f(&group_cx) {
                parsed_attributes.push(Attribute::Parsed(attr));
            }
        }

        attributes.extend(parsed_attributes);

        attributes
    }

    fn lower_attr_args(&self, args: &ast::AttrArgs, lower_span: impl Fn(Span) -> Span) -> AttrArgs {
        match args {
            ast::AttrArgs::Empty => AttrArgs::Empty,
            ast::AttrArgs::Delimited(args) => AttrArgs::Delimited(args.clone()),
            // This is an inert key-value attribute - it will never be visible to macros
            // after it gets lowered to HIR. Therefore, we can extract literals to handle
            // nonterminals in `#[doc]` (e.g. `#[doc = $e]`).
            ast::AttrArgs::Eq { eq_span, expr } => {
                // In valid code the value always ends up as a single literal. Otherwise, a dummy
                // literal suffices because the error is handled elsewhere.
                let lit = if let ast::ExprKind::Lit(token_lit) = expr.kind
                    && let Ok(lit) =
                        ast::MetaItemLit::from_token_lit(token_lit, lower_span(expr.span))
                {
                    lit
                } else {
                    let guar = self.dcx().span_delayed_bug(
                        args.span().unwrap_or(DUMMY_SP),
                        "expr in place where literal is expected (builtin attr parsing)",
                    );
                    ast::MetaItemLit {
                        symbol: sym::dummy,
                        suffix: None,
                        kind: ast::LitKind::Err(guar),
                        span: DUMMY_SP,
                    }
                };
                AttrArgs::Eq { eq_span: lower_span(*eq_span), expr: lit }
            }
        }
    }
}