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use rustc_hir as hir;
use rustc_hir::def_id::DefId;
use rustc_index::Idx;
use rustc_infer::infer::{InferCtxt, TyCtxtInferExt};
use rustc_infer::traits::Obligation;
use rustc_middle::mir;
use rustc_middle::thir::{FieldPat, Pat, PatKind};
use rustc_middle::ty::{self, Ty, TyCtxt, ValTree};
use rustc_session::lint;
use rustc_span::Span;
use rustc_target::abi::{FieldIdx, VariantIdx};
use rustc_trait_selection::traits::query::evaluate_obligation::InferCtxtExt;
use rustc_trait_selection::traits::{self, ObligationCause};
use std::cell::Cell;
use super::PatCtxt;
use crate::errors::{
FloatPattern, IndirectStructuralMatch, InvalidPattern, NonPartialEqMatch,
NontrivialStructuralMatch, PointerPattern, TypeNotStructural, UnionPattern, UnsizedPattern,
};
impl<'a, 'tcx> PatCtxt<'a, 'tcx> {
/// Converts an evaluated constant to a pattern (if possible).
/// This means aggregate values (like structs and enums) are converted
/// to a pattern that matches the value (as if you'd compared via structural equality).
///
/// `cv` must be a valtree or a `mir::ConstValue`.
#[instrument(level = "debug", skip(self), ret)]
pub(super) fn const_to_pat(
&self,
cv: mir::Const<'tcx>,
id: hir::HirId,
span: Span,
check_body_for_struct_match_violation: Option<DefId>,
) -> Box<Pat<'tcx>> {
let infcx = self.tcx.infer_ctxt().build();
let mut convert = ConstToPat::new(self, id, span, infcx);
convert.to_pat(cv, check_body_for_struct_match_violation)
}
}
struct ConstToPat<'tcx> {
id: hir::HirId,
span: Span,
param_env: ty::ParamEnv<'tcx>,
// This tracks if we emitted some hard error for a given const value, so that
// we will not subsequently issue an irrelevant lint for the same const
// value.
saw_const_match_error: Cell<bool>,
// This tracks if we emitted some diagnostic for a given const value, so that
// we will not subsequently issue an irrelevant lint for the same const
// value.
saw_const_match_lint: Cell<bool>,
// For backcompat we need to keep allowing non-structurally-eq types behind references.
// See also all the `cant-hide-behind` tests.
behind_reference: Cell<bool>,
// inference context used for checking `T: Structural` bounds.
infcx: InferCtxt<'tcx>,
treat_byte_string_as_slice: bool,
}
/// This error type signals that we encountered a non-struct-eq situation.
/// We will fall back to calling `PartialEq::eq` on such patterns,
/// and exhaustiveness checking will consider them as matching nothing.
#[derive(Debug)]
struct FallbackToOpaqueConst;
impl<'tcx> ConstToPat<'tcx> {
fn new(
pat_ctxt: &PatCtxt<'_, 'tcx>,
id: hir::HirId,
span: Span,
infcx: InferCtxt<'tcx>,
) -> Self {
trace!(?pat_ctxt.typeck_results.hir_owner);
ConstToPat {
id,
span,
infcx,
param_env: pat_ctxt.param_env,
saw_const_match_error: Cell::new(false),
saw_const_match_lint: Cell::new(false),
behind_reference: Cell::new(false),
treat_byte_string_as_slice: pat_ctxt
.typeck_results
.treat_byte_string_as_slice
.contains(&id.local_id),
}
}
fn tcx(&self) -> TyCtxt<'tcx> {
self.infcx.tcx
}
fn type_marked_structural(&self, ty: Ty<'tcx>) -> bool {
ty.is_structural_eq_shallow(self.infcx.tcx)
}
fn to_pat(
&mut self,
cv: mir::Const<'tcx>,
check_body_for_struct_match_violation: Option<DefId>,
) -> Box<Pat<'tcx>> {
trace!(self.treat_byte_string_as_slice);
// This method is just a wrapper handling a validity check; the heavy lifting is
// performed by the recursive `recur` method, which is not meant to be
// invoked except by this method.
//
// once indirect_structural_match is a full fledged error, this
// level of indirection can be eliminated
let mir_structural_match_violation = check_body_for_struct_match_violation.map(|def_id| {
// `mir_const_qualif` must be called with the `DefId` of the item where the const is
// defined, not where it is declared. The difference is significant for associated
// constants.
self.tcx().mir_const_qualif(def_id).custom_eq
});
debug!(?check_body_for_struct_match_violation, ?mir_structural_match_violation);
let inlined_const_as_pat = match cv {
mir::Const::Ty(c) => match c.kind() {
ty::ConstKind::Param(_)
| ty::ConstKind::Infer(_)
| ty::ConstKind::Bound(_, _)
| ty::ConstKind::Placeholder(_)
| ty::ConstKind::Unevaluated(_)
| ty::ConstKind::Error(_)
| ty::ConstKind::Expr(_) => {
span_bug!(self.span, "unexpected const in `to_pat`: {:?}", c.kind())
}
ty::ConstKind::Value(valtree) => self
.recur(valtree, cv.ty(), mir_structural_match_violation.unwrap_or(false))
.unwrap_or_else(|_: FallbackToOpaqueConst| {
Box::new(Pat {
span: self.span,
ty: cv.ty(),
kind: PatKind::Constant { value: cv },
})
}),
},
mir::Const::Unevaluated(_, _) => {
span_bug!(self.span, "unevaluated const in `to_pat`: {cv:?}")
}
mir::Const::Val(_, _) => Box::new(Pat {
span: self.span,
ty: cv.ty(),
kind: PatKind::Constant { value: cv },
}),
};
if !self.saw_const_match_error.get() {
// If we were able to successfully convert the const to some pat (possibly with some
// lints, but no errors), double-check that all types in the const implement
// `Structural` and `PartialEq`.
let structural =
traits::search_for_structural_match_violation(self.span, self.tcx(), cv.ty());
debug!(
"search_for_structural_match_violation cv.ty: {:?} returned: {:?}",
cv.ty(),
structural
);
// This can occur because const qualification treats all associated constants as
// opaque, whereas `search_for_structural_match_violation` tries to monomorphize them
// before it runs.
//
// FIXME(#73448): Find a way to bring const qualification into parity with
// `search_for_structural_match_violation`.
if structural.is_none() && mir_structural_match_violation.unwrap_or(false) {
warn!("MIR const-checker found novel structural match violation. See #73448.");
return inlined_const_as_pat;
}
if let Some(non_sm_ty) = structural {
if !self.type_has_partial_eq_impl(cv.ty()) {
if let ty::Adt(def, ..) = non_sm_ty.kind() {
if def.is_union() {
let err = UnionPattern { span: self.span };
self.tcx().sess.emit_err(err);
} else {
// fatal avoids ICE from resolution of nonexistent method (rare case).
self.tcx()
.sess
.emit_fatal(TypeNotStructural { span: self.span, non_sm_ty });
}
} else {
let err = InvalidPattern { span: self.span, non_sm_ty };
self.tcx().sess.emit_err(err);
}
// All branches above emitted an error. Don't print any more lints.
// The pattern we return is irrelevant since we errored.
return Box::new(Pat { span: self.span, ty: cv.ty(), kind: PatKind::Wild });
} else if !self.saw_const_match_lint.get() {
if let Some(mir_structural_match_violation) = mir_structural_match_violation {
match non_sm_ty.kind() {
ty::RawPtr(pointee)
if pointee.ty.is_sized(self.tcx(), self.param_env) => {}
ty::FnPtr(..) | ty::RawPtr(..) => {
self.tcx().emit_spanned_lint(
lint::builtin::POINTER_STRUCTURAL_MATCH,
self.id,
self.span,
PointerPattern,
);
}
ty::Adt(..) if mir_structural_match_violation => {
self.tcx().emit_spanned_lint(
lint::builtin::INDIRECT_STRUCTURAL_MATCH,
self.id,
self.span,
IndirectStructuralMatch { non_sm_ty },
);
}
_ => {
debug!(
"`search_for_structural_match_violation` found one, but `CustomEq` was \
not in the qualifs for that `const`"
);
}
}
}
}
} else if !self.saw_const_match_lint.get() {
match cv.ty().kind() {
ty::RawPtr(pointee) if pointee.ty.is_sized(self.tcx(), self.param_env) => {}
ty::FnPtr(..) | ty::RawPtr(..) => {
self.tcx().emit_spanned_lint(
lint::builtin::POINTER_STRUCTURAL_MATCH,
self.id,
self.span,
PointerPattern,
);
}
_ => {}
}
}
// Always check for `PartialEq`, even if we emitted other lints. (But not if there were
// any errors.) This ensures it shows up in cargo's future-compat reports as well.
if !self.type_has_partial_eq_impl(cv.ty()) {
self.tcx().emit_spanned_lint(
lint::builtin::CONST_PATTERNS_WITHOUT_PARTIAL_EQ,
self.id,
self.span,
NonPartialEqMatch { non_peq_ty: cv.ty() },
);
}
}
inlined_const_as_pat
}
#[instrument(level = "trace", skip(self), ret)]
fn type_has_partial_eq_impl(&self, ty: Ty<'tcx>) -> bool {
// double-check there even *is* a semantic `PartialEq` to dispatch to.
//
// (If there isn't, then we can safely issue a hard
// error, because that's never worked, due to compiler
// using `PartialEq::eq` in this scenario in the past.)
let partial_eq_trait_id =
self.tcx().require_lang_item(hir::LangItem::PartialEq, Some(self.span));
let partial_eq_obligation = Obligation::new(
self.tcx(),
ObligationCause::dummy(),
self.param_env,
ty::TraitRef::new(self.tcx(), partial_eq_trait_id, [ty, ty]),
);
// This *could* accept a type that isn't actually `PartialEq`, because region bounds get
// ignored. However that should be pretty much impossible since consts that do not depend on
// generics can only mention the `'static` lifetime, and how would one have a type that's
// `PartialEq` for some lifetime but *not* for `'static`? If this ever becomes a problem
// we'll need to leave some sort of trace of this requirement in the MIR so that borrowck
// can ensure that the type really implements `PartialEq`.
self.infcx.predicate_must_hold_modulo_regions(&partial_eq_obligation)
}
fn field_pats(
&self,
vals: impl Iterator<Item = (ValTree<'tcx>, Ty<'tcx>)>,
) -> Result<Vec<FieldPat<'tcx>>, FallbackToOpaqueConst> {
vals.enumerate()
.map(|(idx, (val, ty))| {
let field = FieldIdx::new(idx);
// Patterns can only use monomorphic types.
let ty = self.tcx().normalize_erasing_regions(self.param_env, ty);
Ok(FieldPat { field, pattern: self.recur(val, ty, false)? })
})
.collect()
}
// Recursive helper for `to_pat`; invoke that (instead of calling this directly).
#[instrument(skip(self), level = "debug")]
fn recur(
&self,
cv: ValTree<'tcx>,
ty: Ty<'tcx>,
mir_structural_match_violation: bool,
) -> Result<Box<Pat<'tcx>>, FallbackToOpaqueConst> {
let id = self.id;
let span = self.span;
let tcx = self.tcx();
let param_env = self.param_env;
let kind = match ty.kind() {
ty::Float(_) => {
self.saw_const_match_lint.set(true);
tcx.emit_spanned_lint(
lint::builtin::ILLEGAL_FLOATING_POINT_LITERAL_PATTERN,
id,
span,
FloatPattern,
);
return Err(FallbackToOpaqueConst);
}
// If the type is not structurally comparable, just emit the constant directly,
// causing the pattern match code to treat it opaquely.
// FIXME: This code doesn't emit errors itself, the caller emits the errors.
// So instead of specific errors, you just get blanket errors about the whole
// const type. See
// https://github.com/rust-lang/rust/pull/70743#discussion_r404701963 for
// details.
// Backwards compatibility hack because we can't cause hard errors on these
// types, so we compare them via `PartialEq::eq` at runtime.
ty::Adt(..) if !self.type_marked_structural(ty) && self.behind_reference.get() => {
if !self.saw_const_match_error.get() && !self.saw_const_match_lint.get() {
self.saw_const_match_lint.set(true);
tcx.emit_spanned_lint(
lint::builtin::INDIRECT_STRUCTURAL_MATCH,
id,
span,
IndirectStructuralMatch { non_sm_ty: ty },
);
}
// Since we are behind a reference, we can just bubble the error up so we get a
// constant at reference type, making it easy to let the fallback call
// `PartialEq::eq` on it.
return Err(FallbackToOpaqueConst);
}
ty::FnDef(..) => {
self.saw_const_match_error.set(true);
tcx.sess.emit_err(InvalidPattern { span, non_sm_ty: ty });
// We errored, so the pattern we generate is irrelevant.
PatKind::Wild
}
ty::Adt(adt_def, _) if !self.type_marked_structural(ty) => {
debug!("adt_def {:?} has !type_marked_structural for cv.ty: {:?}", adt_def, ty,);
self.saw_const_match_error.set(true);
let err = TypeNotStructural { span, non_sm_ty: ty };
tcx.sess.emit_err(err);
// We errored, so the pattern we generate is irrelevant.
PatKind::Wild
}
ty::Adt(adt_def, args) if adt_def.is_enum() => {
let (&variant_index, fields) = cv.unwrap_branch().split_first().unwrap();
let variant_index =
VariantIdx::from_u32(variant_index.unwrap_leaf().try_to_u32().ok().unwrap());
PatKind::Variant {
adt_def: *adt_def,
args,
variant_index,
subpatterns: self.field_pats(
fields.iter().copied().zip(
adt_def.variants()[variant_index]
.fields
.iter()
.map(|field| field.ty(self.tcx(), args)),
),
)?,
}
}
ty::Tuple(fields) => PatKind::Leaf {
subpatterns: self
.field_pats(cv.unwrap_branch().iter().copied().zip(fields.iter()))?,
},
ty::Adt(def, args) => PatKind::Leaf {
subpatterns: self.field_pats(cv.unwrap_branch().iter().copied().zip(
def.non_enum_variant().fields.iter().map(|field| field.ty(self.tcx(), args)),
))?,
},
ty::Slice(elem_ty) => PatKind::Slice {
prefix: cv
.unwrap_branch()
.iter()
.map(|val| self.recur(*val, *elem_ty, false))
.collect::<Result<_, _>>()?,
slice: None,
suffix: Box::new([]),
},
ty::Array(elem_ty, _) => PatKind::Array {
prefix: cv
.unwrap_branch()
.iter()
.map(|val| self.recur(*val, *elem_ty, false))
.collect::<Result<_, _>>()?,
slice: None,
suffix: Box::new([]),
},
ty::Ref(_, pointee_ty, ..) => match *pointee_ty.kind() {
// `&str` is represented as a valtree, let's keep using this
// optimization for now.
ty::Str => {
PatKind::Constant { value: mir::Const::Ty(ty::Const::new_value(tcx, cv, ty)) }
}
// Backwards compatibility hack: support references to non-structural types,
// but hard error if we aren't behind a double reference. We could just use
// the fallback code path below, but that would allow *more* of this fishy
// code to compile, as then it only goes through the future incompat lint
// instead of a hard error.
ty::Adt(_, _) if !self.type_marked_structural(*pointee_ty) => {
if self.behind_reference.get() {
if !self.saw_const_match_error.get() && !self.saw_const_match_lint.get() {
self.saw_const_match_lint.set(true);
tcx.emit_spanned_lint(
lint::builtin::INDIRECT_STRUCTURAL_MATCH,
self.id,
span,
IndirectStructuralMatch { non_sm_ty: *pointee_ty },
);
}
return Err(FallbackToOpaqueConst);
} else {
if !self.saw_const_match_error.get() {
self.saw_const_match_error.set(true);
let err = TypeNotStructural { span, non_sm_ty: *pointee_ty };
tcx.sess.emit_err(err);
}
tcx.sess.delay_span_bug(span, "`saw_const_match_error` set but no error?");
// We errored, so the pattern we generate is irrelevant.
PatKind::Wild
}
}
// All other references are converted into deref patterns and then recursively
// convert the dereferenced constant to a pattern that is the sub-pattern of the
// deref pattern.
_ => {
if !pointee_ty.is_sized(tcx, param_env) && !pointee_ty.is_slice() {
let err = UnsizedPattern { span, non_sm_ty: *pointee_ty };
tcx.sess.emit_err(err);
// FIXME: introduce PatKind::Error to silence follow up diagnostics due to unreachable patterns.
// We errored, so the pattern we generate is irrelevant.
PatKind::Wild
} else {
let old = self.behind_reference.replace(true);
// `b"foo"` produces a `&[u8; 3]`, but you can't use constants of array type when
// matching against references, you can only use byte string literals.
// The typechecker has a special case for byte string literals, by treating them
// as slices. This means we turn `&[T; N]` constants into slice patterns, which
// has no negative effects on pattern matching, even if we're actually matching on
// arrays.
let pointee_ty = match *pointee_ty.kind() {
ty::Array(elem_ty, _) if self.treat_byte_string_as_slice => {
Ty::new_slice(tcx, elem_ty)
}
_ => *pointee_ty,
};
// References have the same valtree representation as their pointee.
let subpattern = self.recur(cv, pointee_ty, false)?;
self.behind_reference.set(old);
PatKind::Deref { subpattern }
}
}
},
ty::Bool | ty::Char | ty::Int(_) | ty::Uint(_) => {
PatKind::Constant { value: mir::Const::Ty(ty::Const::new_value(tcx, cv, ty)) }
}
ty::FnPtr(..) | ty::RawPtr(..) => unreachable!(),
_ => {
self.saw_const_match_error.set(true);
let err = InvalidPattern { span, non_sm_ty: ty };
tcx.sess.emit_err(err);
// We errored, so the pattern we generate is irrelevant.
PatKind::Wild
}
};
if !self.saw_const_match_error.get()
&& !self.saw_const_match_lint.get()
&& mir_structural_match_violation
// FIXME(#73448): Find a way to bring const qualification into parity with
// `search_for_structural_match_violation` and then remove this condition.
// Obtain the actual type that isn't annotated. If we just looked at `cv.ty` we
// could get `Option<NonStructEq>`, even though `Option` is annotated with derive.
&& let Some(non_sm_ty) = traits::search_for_structural_match_violation(span, tcx, ty)
{
self.saw_const_match_lint.set(true);
tcx.emit_spanned_lint(
lint::builtin::NONTRIVIAL_STRUCTURAL_MATCH,
id,
span,
NontrivialStructuralMatch {non_sm_ty}
);
}
Ok(Box::new(Pat { span, ty, kind }))
}
}