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Some hygiene doc improvements #146159

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Merged
bors merged 1 commit into rust-lang:master from camsteffen:hygiene-docs
Sep 14, 2025
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30 changes: 20 additions & 10 deletions compiler/rustc_span/src/hygiene.rs
View file Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -46,6 +46,8 @@ use crate::symbol::{Symbol, kw, sym};
use crate::{DUMMY_SP, HashStableContext, Span, SpanDecoder, SpanEncoder, with_session_globals};

/// A `SyntaxContext` represents a chain of pairs `(ExpnId, Transparency)` named "marks".
///
/// See <https://rustc-dev-guide.rust-lang.org/macro-expansion.html> for more explanation.
#[derive(Clone, Copy, PartialEq, Eq, Hash)]
pub struct SyntaxContext(u32);

Expand All @@ -61,7 +63,10 @@ pub type SyntaxContextKey = (SyntaxContext, ExpnId, Transparency);

#[derive(Clone, Copy, Debug)]
struct SyntaxContextData {
/// The last macro expansion in the chain.
/// (Here we say the most deeply nested macro expansion is the "outermost" expansion.)
outer_expn: ExpnId,
/// Transparency of the last macro expansion
outer_transparency: Transparency,
parent: SyntaxContext,
/// This context, but with all transparent and semi-opaque expansions filtered away.
Expand Down Expand Up @@ -450,11 +455,13 @@ impl HygieneData {
self.syntax_context_data[ctxt.0 as usize].opaque_and_semiopaque
}

/// See [`SyntaxContextData::outer_expn`]
#[inline]
fn outer_expn(&self, ctxt: SyntaxContext) -> ExpnId {
self.syntax_context_data[ctxt.0 as usize].outer_expn
}

/// The last macro expansion and its Transparency
#[inline]
fn outer_mark(&self, ctxt: SyntaxContext) -> (ExpnId, Transparency) {
let data = &self.syntax_context_data[ctxt.0 as usize];
Expand Down Expand Up @@ -900,6 +907,7 @@ impl SyntaxContext {
HygieneData::with(|data| data.normalize_to_macro_rules(self))
}

/// See [`SyntaxContextData::outer_expn`]
#[inline]
pub fn outer_expn(self) -> ExpnId {
HygieneData::with(|data| data.outer_expn(self))
Expand All @@ -912,6 +920,7 @@ impl SyntaxContext {
HygieneData::with(|data| data.expn_data(data.outer_expn(self)).clone())
}

/// See [`HygieneData::outer_mark`]
#[inline]
fn outer_mark(self) -> (ExpnId, Transparency) {
HygieneData::with(|data| data.outer_mark(self))
Expand Down Expand Up @@ -982,19 +991,20 @@ impl Span {
#[derive(Clone, Debug, Encodable, Decodable, HashStable_Generic)]
pub struct ExpnData {
// --- The part unique to each expansion.
/// The kind of this expansion - macro or compiler desugaring.
pub kind: ExpnKind,
/// The expansion that produced this expansion.
/// The expansion that contains the definition of the macro for this expansion.
pub parent: ExpnId,
/// The location of the actual macro invocation or syntax sugar , e.g.
/// `let x = foo!();` or `if let Some(y) = x {}`
/// The span of the macro call which produced this expansion.
///
/// This span will typically have a different `ExpnData` and `call_site`.
/// This recursively traces back through any macro calls which expanded into further
/// macro calls, until the "source call-site" is reached at the root SyntaxContext.
/// For example, if `food!()` expands to `fruit!()` which then expands to `grape`,
/// then the call-site of `grape` is `fruit!()` and the call-site of `fruit!()`
/// is `food!()`.
///
/// This may recursively refer to other macro invocations, e.g., if
/// `foo!()` invoked `bar!()` internally, and there was an
/// expression inside `bar!`; the call_site of the expression in
/// the expansion would point to the `bar!` invocation; that
/// call_site span would have its own ExpnData, with the call_site
/// pointing to the `foo!` invocation.
/// For a desugaring expansion, this is the span of the expression or node that was
/// desugared.
pub call_site: Span,
/// Used to force two `ExpnData`s to have different `Fingerprint`s.
/// Due to macro expansion, it's possible to end up with two `ExpnId`s
Expand Down
4 changes: 2 additions & 2 deletions compiler/rustc_span/src/lib.rs
View file Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -710,8 +710,8 @@ impl Span {
if !ctxt.is_root() { ctxt.outer_expn_data().call_site.source_callsite() } else { self }
}

/// The `Span` for the tokens in the previous macro expansion from which `self` was generated,
/// if any.
/// Returns the call-site span of the last macro expansion which produced this `Span`.
/// (see [`ExpnData::call_site`]). Returns `None` if this is not an expansion.
pub fn parent_callsite(self) -> Option<Span> {
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Contributor Author

@camsteffen camsteffen Sep 6, 2025

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This name is a bit unfortunate since it does not use ExpnData::parent.

let ctxt = self.ctxt();
(!ctxt.is_root()).then(|| ctxt.outer_expn_data().call_site)
Expand Down
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