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|
//! Automatic migration of Rust 2021 patterns to a form valid in both Editions 2021 and 2024.
use rustc_data_structures::fx::FxIndexMap;
use rustc_errors::MultiSpan;
use rustc_hir::{BindingMode, ByRef, HirId, Mutability};
use rustc_lint as lint;
use rustc_middle::ty::{self, Rust2024IncompatiblePatInfo, TyCtxt};
use rustc_span::{Ident, Span};
use crate::errors::{Rust2024IncompatiblePat, Rust2024IncompatiblePatSugg};
use crate::fluent_generated as fluent;
/// For patterns flagged for migration during HIR typeck, this handles constructing and emitting
/// a diagnostic suggestion.
pub(super) struct PatMigration<'a> {
suggestion: Vec<(Span, String)>,
ref_pattern_count: usize,
binding_mode_count: usize,
/// Internal state: the ref-mutability of the default binding mode at the subpattern being
/// lowered, with the span where it was introduced. `None` for a by-value default mode.
default_mode_span: Option<(Span, ty::Mutability)>,
/// Labels for where incompatibility-causing by-ref default binding modes were introduced.
// FIXME(ref_pat_eat_one_layer_2024_structural): To track the default binding mode, we duplicate
// logic from HIR typeck (in order to avoid needing to store all changes to the dbm in
// TypeckResults). Since the default binding mode acts differently under this feature gate, the
// labels will be wrong.
default_mode_labels: FxIndexMap<Span, Mutability>,
/// Information collected from typeck, including spans for subpatterns invalid in Rust 2024.
info: &'a Rust2024IncompatiblePatInfo,
}
impl<'a> PatMigration<'a> {
pub(super) fn new(info: &'a Rust2024IncompatiblePatInfo) -> Self {
PatMigration {
suggestion: Vec::new(),
ref_pattern_count: 0,
binding_mode_count: 0,
default_mode_span: None,
default_mode_labels: Default::default(),
info,
}
}
/// On Rust 2024, this emits a hard error. On earlier Editions, this emits the
/// future-incompatibility lint `rust_2024_incompatible_pat`.
pub(super) fn emit<'tcx>(self, tcx: TyCtxt<'tcx>, pat_id: HirId) {
let mut spans =
MultiSpan::from_spans(self.info.primary_labels.iter().map(|(span, _)| *span).collect());
for (span, label) in self.info.primary_labels.iter() {
spans.push_span_label(*span, label.clone());
}
let sugg = Rust2024IncompatiblePatSugg {
suggest_eliding_modes: self.info.suggest_eliding_modes,
suggestion: self.suggestion,
ref_pattern_count: self.ref_pattern_count,
binding_mode_count: self.binding_mode_count,
default_mode_labels: self.default_mode_labels,
};
// If a relevant span is from at least edition 2024, this is a hard error.
let is_hard_error = spans.primary_spans().iter().any(|span| span.at_least_rust_2024());
if is_hard_error {
let mut err =
tcx.dcx().struct_span_err(spans, fluent::mir_build_rust_2024_incompatible_pat);
if let Some(info) = lint::builtin::RUST_2024_INCOMPATIBLE_PAT.future_incompatible {
// provide the same reference link as the lint
err.note(format!("for more information, see {}", info.reference));
}
err.arg("bad_modifiers", self.info.bad_modifiers);
err.arg("bad_ref_pats", self.info.bad_ref_pats);
err.arg("is_hard_error", true);
err.subdiagnostic(sugg);
err.emit();
} else {
tcx.emit_node_span_lint(
lint::builtin::RUST_2024_INCOMPATIBLE_PAT,
pat_id,
spans,
Rust2024IncompatiblePat {
sugg,
bad_modifiers: self.info.bad_modifiers,
bad_ref_pats: self.info.bad_ref_pats,
is_hard_error,
},
);
}
}
/// Tracks when we're lowering a pattern that implicitly dereferences the scrutinee.
/// This should only be called when the pattern type adjustments list `adjustments` contains an
/// implicit deref of a reference type. Returns the prior default binding mode; this should be
/// followed by a call to [`PatMigration::leave_ref`] to restore it when we leave the pattern.
pub(super) fn visit_implicit_derefs<'tcx>(
&mut self,
pat_span: Span,
adjustments: &[ty::adjustment::PatAdjustment<'tcx>],
) -> Option<(Span, Mutability)> {
// Implicitly dereferencing references changes the default binding mode, but implicit derefs
// of smart pointers do not. Thus, we only consider implicit derefs of reference types.
let implicit_deref_mutbls = adjustments.iter().filter_map(|adjust| {
if let &ty::Ref(_, _, mutbl) = adjust.source.kind() { Some(mutbl) } else { None }
});
if !self.info.suggest_eliding_modes {
// If we can't fix the pattern by eliding modifiers, we'll need to make the pattern
// fully explicit. i.e. we'll need to suggest reference patterns for this.
let suggestion_str: String =
implicit_deref_mutbls.clone().map(|mutbl| mutbl.ref_prefix_str()).collect();
self.suggestion.push((pat_span.shrink_to_lo(), suggestion_str));
self.ref_pattern_count += adjustments.len();
}
// Remember if this changed the default binding mode, in case we want to label it.
let min_mutbl = implicit_deref_mutbls.min().unwrap();
if self.default_mode_span.is_none_or(|(_, old_mutbl)| min_mutbl < old_mutbl) {
// This changes the default binding mode to `ref` or `ref mut`. Return the old mode so
// it can be reinstated when we leave the pattern.
self.default_mode_span.replace((pat_span, min_mutbl))
} else {
// This does not change the default binding mode; it was already `ref` or `ref mut`.
self.default_mode_span
}
}
/// Tracks the default binding mode when we're lowering a `&` or `&mut` pattern.
/// Returns the prior default binding mode; this should be followed by a call to
/// [`PatMigration::leave_ref`] to restore it when we leave the pattern.
pub(super) fn visit_explicit_deref(&mut self) -> Option<(Span, Mutability)> {
if let Some((default_mode_span, default_ref_mutbl)) = self.default_mode_span {
// If this eats a by-ref default binding mode, label the binding mode.
self.default_mode_labels.insert(default_mode_span, default_ref_mutbl);
}
// Set the default binding mode to by-value and return the old default binding mode so it
// can be reinstated when we leave the pattern.
self.default_mode_span.take()
}
/// Restores the default binding mode after lowering a pattern that could change it.
/// This should follow a call to either [`PatMigration::visit_explicit_deref`] or
/// [`PatMigration::visit_implicit_derefs`].
pub(super) fn leave_ref(&mut self, old_mode_span: Option<(Span, Mutability)>) {
self.default_mode_span = old_mode_span
}
/// Determines if a binding is relevant to the diagnostic and adjusts the notes/suggestion if
/// so. Bindings are relevant if they have a modifier under a by-ref default mode (invalid in
/// Rust 2024) or if we need to suggest a binding modifier for them.
pub(super) fn visit_binding(
&mut self,
pat_span: Span,
mode: BindingMode,
explicit_ba: BindingMode,
ident: Ident,
) {
if explicit_ba != BindingMode::NONE
&& let Some((default_mode_span, default_ref_mutbl)) = self.default_mode_span
{
// If this overrides a by-ref default binding mode, label the binding mode.
self.default_mode_labels.insert(default_mode_span, default_ref_mutbl);
// If our suggestion is to elide redundnt modes, this will be one of them.
if self.info.suggest_eliding_modes {
self.suggestion.push((pat_span.with_hi(ident.span.lo()), String::new()));
self.binding_mode_count += 1;
}
}
if !self.info.suggest_eliding_modes
&& explicit_ba.0 == ByRef::No
&& let ByRef::Yes(mutbl) = mode.0
{
// If we can't fix the pattern by eliding modifiers, we'll need to make the pattern
// fully explicit. i.e. we'll need to suggest reference patterns for this.
let sugg_str = match mutbl {
Mutability::Not => "ref ",
Mutability::Mut => "ref mut ",
};
self.suggestion
.push((pat_span.with_lo(ident.span.lo()).shrink_to_lo(), sugg_str.to_owned()));
self.binding_mode_count += 1;
}
}
}
|
