crates/hir-expand/src/hygiene.rs

//! Machinery for hygienic macros.
//!
//! Inspired by Matthew Flatt et al., “Macros That Work Together: Compile-Time Bindings, Partial
//! Expansion, and Definition Contexts,” *Journal of Functional Programming* 22, no. 2
//! (March 1, 2012): 181–216, <https://doi.org/10.1017/S0956796812000093>.
//!
//! Also see <https://rustc-dev-guide.rust-lang.org/macro-expansion.html#hygiene-and-hierarchies>
//!
//! # The Expansion Order Hierarchy
//!
//! `ExpnData` in rustc, rust-analyzer's version is [`MacroCallLoc`]. Traversing the hierarchy
//! upwards can be achieved by walking up [`MacroCallLoc::kind`]'s contained file id, as
//! [`MacroFile`]s are interned [`MacroCallLoc`]s.
//!
//! # The Macro Definition Hierarchy
//!
//! `SyntaxContextData` in rustc and rust-analyzer. Basically the same in both.
//!
//! # The Call-site Hierarchy
//!
//! `ExpnData::call_site` in rustc, [`MacroCallLoc::call_site`] in rust-analyzer.
// FIXME: Move this into the span crate? Not quite possible today as that depends on `MacroCallLoc`
// which contains a bunch of unrelated things

use std::convert::identity;

use span::{Edition, MacroCallId, Span, SyntaxContext};

use crate::db::ExpandDatabase;

pub use span::Transparency;

pub fn span_with_def_site_ctxt(
    db: &dyn ExpandDatabase,
    span: Span,
    expn_id: MacroCallId,
    edition: Edition,
) -> Span {
    span_with_ctxt_from_mark(db, span, expn_id, Transparency::Opaque, edition)
}

pub fn span_with_call_site_ctxt(
    db: &dyn ExpandDatabase,
    span: Span,
    expn_id: MacroCallId,
    edition: Edition,
) -> Span {
    span_with_ctxt_from_mark(db, span, expn_id, Transparency::Transparent, edition)
}

pub fn span_with_mixed_site_ctxt(
    db: &dyn ExpandDatabase,
    span: Span,
    expn_id: MacroCallId,
    edition: Edition,
) -> Span {
    span_with_ctxt_from_mark(db, span, expn_id, Transparency::SemiTransparent, edition)
}

fn span_with_ctxt_from_mark(
    db: &dyn ExpandDatabase,
    span: Span,
    expn_id: MacroCallId,
    transparency: Transparency,
    edition: Edition,
) -> Span {
    Span {
        ctx: apply_mark(db, SyntaxContext::root(edition), expn_id, transparency, edition),
        ..span
    }
}

pub(super) fn apply_mark(
    db: &dyn ExpandDatabase,
    ctxt: span::SyntaxContext,
    call_id: span::MacroCallId,
    transparency: Transparency,
    edition: Edition,
) -> SyntaxContext {
    if transparency == Transparency::Opaque {
        return apply_mark_internal(db, ctxt, call_id, transparency, edition);
    }

    let call_site_ctxt = db.lookup_intern_macro_call(call_id.into()).ctxt;
    let mut call_site_ctxt = if transparency == Transparency::SemiTransparent {
        call_site_ctxt.normalize_to_macros_2_0(db)
    } else {
        call_site_ctxt.normalize_to_macro_rules(db)
    };

    if call_site_ctxt.is_root() {
        return apply_mark_internal(db, ctxt, call_id, transparency, edition);
    }

    // Otherwise, `expn_id` is a macros 1.0 definition and the call site is in a
    // macros 2.0 expansion, i.e., a macros 1.0 invocation is in a macros 2.0 definition.
    //
    // In this case, the tokens from the macros 1.0 definition inherit the hygiene
    // at their invocation. That is, we pretend that the macros 1.0 definition
    // was defined at its invocation (i.e., inside the macros 2.0 definition)
    // so that the macros 2.0 definition remains hygienic.
    //
    // See the example at `test/ui/hygiene/legacy_interaction.rs`.
    for (call_id, transparency) in ctxt.marks(db) {
        call_site_ctxt = apply_mark_internal(db, call_site_ctxt, call_id, transparency, edition);
    }
    apply_mark_internal(db, call_site_ctxt, call_id, transparency, edition)
}

fn apply_mark_internal(
    db: &dyn ExpandDatabase,
    ctxt: SyntaxContext,
    call_id: MacroCallId,
    transparency: Transparency,
    edition: Edition,
) -> SyntaxContext {
    let call_id = Some(call_id);

    let mut opaque = ctxt.opaque(db);
    let mut opaque_and_semitransparent = ctxt.opaque_and_semitransparent(db);

    if transparency >= Transparency::Opaque {
        let parent = opaque;
        opaque = SyntaxContext::new(db, call_id, transparency, edition, parent, identity, identity);
    }

    if transparency >= Transparency::SemiTransparent {
        let parent = opaque_and_semitransparent;
        opaque_and_semitransparent =
            SyntaxContext::new(db, call_id, transparency, edition, parent, |_| opaque, identity);
    }

    let parent = ctxt;
    SyntaxContext::new(
        db,
        call_id,
        transparency,
        edition,
        parent,
        |_| opaque,
        |_| opaque_and_semitransparent,
    )
}