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Auto merge of #119673 - petrochenkov:dialoc5, r=compiler-errors,cjgillot

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macro_rules: Preserve all metavariable spans in a global side table

This PR preserves spans of `tt` metavariables used to pass tokens to declarative macros.
Such metavariable spans can then be used in span combination operations like `Span::to` to improve all kinds of diagnostics.

Spans of non-`tt` metavariables are currently kept in nonterminal tokens, but the long term plan is remove all nonterminal tokens from rustc parser and rely on the proc macro model with invisible delimiters (#114647, #67062).
In particular, `NtIdent` nonterminal (corresponding to `ident` metavariables) becomes easy to remove when this PR lands (#119412 does it).

The metavariable spans are kept in a global side table keyed by `Span`s of original tokens.
The alternative to the side table is keeping them in `SpanData` instead, but the performance regressions would be large because any spans from tokens passed to declarative macros would stop being inline and would work through span interner instead, and the penalty would be paid even if we never use the metavar span for the given original span.
(But also see the comment on `fn maybe_use_metavar_location` describing the map collision issues with the side table approach.)

There are also other alternatives - keeping the metavar span in `Token` or `TokenTree`, but associating it with `Span` itsel is the most natural choice because metavar spans are used in span combining operations, and those operations are not necessarily tied to tokens.
This commit is contained in:
bors 2024-02-18 20:51:16 +00:00
commit 2bf78d12d3
31 changed files with 244 additions and 137 deletions
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75
compiler/rustc_span/src/lib.rs
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@ -72,6 +72,7 @@ pub mod fatal_error;
pub mod profiling;
use rustc_data_structures::fx::FxHashMap;
use rustc_data_structures::stable_hasher::{Hash128, Hash64, HashStable, StableHasher};
use rustc_data_structures::sync::{FreezeLock, FreezeWriteGuard, Lock, Lrc};
@ -98,6 +99,9 @@ mod tests;
pub struct SessionGlobals {
symbol_interner: symbol::Interner,
span_interner: Lock<span_encoding::SpanInterner>,
/// Maps a macro argument token into use of the corresponding metavariable in the macro body.
/// Collisions are possible and processed in `maybe_use_metavar_location` on best effort basis.
metavar_spans: Lock<FxHashMap<Span, Span>>,
hygiene_data: Lock<hygiene::HygieneData>,
/// A reference to the source map in the `Session`. It's an `Option`
@ -115,6 +119,7 @@ impl SessionGlobals {
SessionGlobals {
symbol_interner: symbol::Interner::fresh(),
span_interner: Lock::new(span_encoding::SpanInterner::default()),
metavar_spans: Default::default(),
hygiene_data: Lock::new(hygiene::HygieneData::new(edition)),
source_map: Lock::new(None),
}
@ -168,6 +173,11 @@ pub fn create_default_session_globals_then<R>(f: impl FnOnce() -> R) -> R {
// deserialization.
scoped_tls::scoped_thread_local!(static SESSION_GLOBALS: SessionGlobals);
#[inline]
pub fn with_metavar_spans<R>(f: impl FnOnce(&mut FxHashMap<Span, Span>) -> R) -> R {
with_session_globals(|session_globals| f(&mut session_globals.metavar_spans.lock()))
}
// FIXME: We should use this enum or something like it to get rid of the
// use of magic `/rust/1.x/...` paths across the board.
#[derive(Debug, Eq, PartialEq, Clone, Ord, PartialOrd, Decodable)]
@ -824,29 +834,64 @@ impl Span {
)
}
/// Check if you can select metavar spans for the given spans to get matching contexts.
fn try_metavars(a: SpanData, b: SpanData, a_orig: Span, b_orig: Span) -> (SpanData, SpanData) {
let get = |mspans: &FxHashMap<_, _>, s| mspans.get(&s).copied();
match with_metavar_spans(|mspans| (get(mspans, a_orig), get(mspans, b_orig))) {
(None, None) => {}
(Some(meta_a), None) => {
let meta_a = meta_a.data();
if meta_a.ctxt == b.ctxt {
return (meta_a, b);
}
}
(None, Some(meta_b)) => {
let meta_b = meta_b.data();
if a.ctxt == meta_b.ctxt {
return (a, meta_b);
}
}
(Some(meta_a), Some(meta_b)) => {
let meta_b = meta_b.data();
if a.ctxt == meta_b.ctxt {
return (a, meta_b);
}
let meta_a = meta_a.data();
if meta_a.ctxt == b.ctxt {
return (meta_a, b);
} else if meta_a.ctxt == meta_b.ctxt {
return (meta_a, meta_b);
}
}
}
(a, b)
}
/// Prepare two spans to a combine operation like `to` or `between`.
/// FIXME: consider using declarative macro metavariable spans for the given spans if they are
/// better suitable for combining (#119412).
fn prepare_to_combine(
a_orig: Span,
b_orig: Span,
) -> Result<(SpanData, SpanData, Option<LocalDefId>), Span> {
let (a, b) = (a_orig.data(), b_orig.data());
if a.ctxt != b.ctxt {
// Context mismatches usually happen when procedural macros combine spans copied from
// the macro input with spans produced by the macro (`Span::*_site`).
// In that case we consider the combined span to be produced by the macro and return
// the original macro-produced span as the result.
// Otherwise we just fall back to returning the first span.
// Combining locations typically doesn't make sense in case of context mismatches.
// `is_root` here is a fast path optimization.
let a_is_callsite = a.ctxt.is_root() || a.ctxt == b.span().source_callsite().ctxt();
return Err(if a_is_callsite { b_orig } else { a_orig });
if a.ctxt == b.ctxt {
return Ok((a, b, if a.parent == b.parent { a.parent } else { None }));
}
let parent = if a.parent == b.parent { a.parent } else { None };
Ok((a, b, parent))
let (a, b) = Span::try_metavars(a, b, a_orig, b_orig);
if a.ctxt == b.ctxt {
return Ok((a, b, if a.parent == b.parent { a.parent } else { None }));
}
// Context mismatches usually happen when procedural macros combine spans copied from
// the macro input with spans produced by the macro (`Span::*_site`).
// In that case we consider the combined span to be produced by the macro and return
// the original macro-produced span as the result.
// Otherwise we just fall back to returning the first span.
// Combining locations typically doesn't make sense in case of context mismatches.
// `is_root` here is a fast path optimization.
let a_is_callsite = a.ctxt.is_root() || a.ctxt == b.span().source_callsite().ctxt();
Err(if a_is_callsite { b_orig } else { a_orig })
}
/// This span, but in a larger context, may switch to the metavariable span if suitable.