rustc_mir_build/thir/pattern/const_to_pat.rs
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use rustc_abi::{FieldIdx, VariantIdx};
use rustc_apfloat::Float;
use rustc_hir as hir;
use rustc_index::Idx;
use rustc_infer::infer::TyCtxtInferExt;
use rustc_infer::traits::Obligation;
use rustc_middle::mir::interpret::ErrorHandled;
use rustc_middle::thir::{FieldPat, Pat, PatKind};
use rustc_middle::ty::{self, Ty, TyCtxt, TypeVisitableExt, ValTree};
use rustc_middle::{mir, span_bug};
use rustc_span::Span;
use rustc_trait_selection::traits::ObligationCause;
use rustc_trait_selection::traits::query::evaluate_obligation::InferCtxtExt;
use tracing::{debug, instrument, trace};
use super::PatCtxt;
use crate::errors::{
ConstPatternDependsOnGenericParameter, CouldNotEvalConstPattern, InvalidPattern, NaNPattern,
PointerPattern, TypeNotPartialEq, TypeNotStructural, UnionPattern, UnsizedPattern,
};
impl<'a, 'tcx> PatCtxt<'a, 'tcx> {
/// Converts a 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).
///
/// Only type system constants are supported, as we are using valtrees
/// as an intermediate step. Unfortunately those don't carry a type
/// so we have to carry one ourselves.
#[instrument(level = "debug", skip(self), ret)]
pub(super) fn const_to_pat(
&self,
c: ty::Const<'tcx>,
ty: Ty<'tcx>,
id: hir::HirId,
span: Span,
) -> Box<Pat<'tcx>> {
let mut convert = ConstToPat::new(self, id, span);
match c.kind() {
ty::ConstKind::Unevaluated(uv) => convert.unevaluated_to_pat(uv, ty),
ty::ConstKind::Value(_, val) => convert.valtree_to_pat(val, ty),
_ => span_bug!(span, "Invalid `ConstKind` for `const_to_pat`: {:?}", c),
}
}
}
struct ConstToPat<'tcx> {
tcx: TyCtxt<'tcx>,
typing_env: ty::TypingEnv<'tcx>,
span: Span,
treat_byte_string_as_slice: bool,
}
impl<'tcx> ConstToPat<'tcx> {
fn new(pat_ctxt: &PatCtxt<'_, 'tcx>, id: hir::HirId, span: Span) -> Self {
trace!(?pat_ctxt.typeck_results.hir_owner);
ConstToPat {
tcx: pat_ctxt.tcx,
typing_env: pat_ctxt.typing_env,
span,
treat_byte_string_as_slice: pat_ctxt
.typeck_results
.treat_byte_string_as_slice
.contains(&id.local_id),
}
}
fn type_marked_structural(&self, ty: Ty<'tcx>) -> bool {
ty.is_structural_eq_shallow(self.tcx)
}
fn unevaluated_to_pat(
&mut self,
uv: ty::UnevaluatedConst<'tcx>,
ty: Ty<'tcx>,
) -> Box<Pat<'tcx>> {
trace!(self.treat_byte_string_as_slice);
let pat_from_kind = |kind| Box::new(Pat { span: self.span, ty, kind });
// It's not *technically* correct to be revealing opaque types here as borrowcheck has
// not run yet. However, CTFE itself uses `Reveal::All` unconditionally even during
// typeck and not doing so has a lot of (undesirable) fallout (#101478, #119821). As a
// result we always use a revealed env when resolving the instance to evaluate.
//
// FIXME: `const_eval_resolve_for_typeck` should probably just set the env to `Reveal::All`
// instead of having this logic here
let typing_env =
self.tcx.erase_regions(self.typing_env).with_reveal_all_normalized(self.tcx);
let uv = self.tcx.erase_regions(uv);
// try to resolve e.g. associated constants to their definition on an impl, and then
// evaluate the const.
let valtree = match self.tcx.const_eval_resolve_for_typeck(typing_env, uv, self.span) {
Ok(Ok(c)) => c,
Err(ErrorHandled::Reported(_, _)) => {
// Let's tell the use where this failing const occurs.
let e = self.tcx.dcx().emit_err(CouldNotEvalConstPattern { span: self.span });
return pat_from_kind(PatKind::Error(e));
}
Err(ErrorHandled::TooGeneric(_)) => {
let e = self
.tcx
.dcx()
.emit_err(ConstPatternDependsOnGenericParameter { span: self.span });
return pat_from_kind(PatKind::Error(e));
}
Ok(Err(bad_ty)) => {
// The pattern cannot be turned into a valtree.
let e = match bad_ty.kind() {
ty::Adt(def, ..) => {
assert!(def.is_union());
self.tcx.dcx().emit_err(UnionPattern { span: self.span })
}
ty::FnPtr(..) | ty::RawPtr(..) => {
self.tcx.dcx().emit_err(PointerPattern { span: self.span })
}
_ => self
.tcx
.dcx()
.emit_err(InvalidPattern { span: self.span, non_sm_ty: bad_ty }),
};
return pat_from_kind(PatKind::Error(e));
}
};
// Convert the valtree to a const.
let inlined_const_as_pat = self.valtree_to_pat(valtree, ty);
if !inlined_const_as_pat.references_error() {
// Always check for `PartialEq` if we had no other errors yet.
if !self.type_has_partial_eq_impl(ty) {
let err = TypeNotPartialEq { span: self.span, non_peq_ty: ty };
let e = self.tcx.dcx().emit_err(err);
return pat_from_kind(PatKind::Error(e));
}
}
inlined_const_as_pat
}
#[instrument(level = "trace", skip(self), ret)]
fn type_has_partial_eq_impl(&self, ty: Ty<'tcx>) -> bool {
let (infcx, param_env) = self.tcx.infer_ctxt().build_with_typing_env(self.typing_env);
// 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(),
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`.
infcx.predicate_must_hold_modulo_regions(&partial_eq_obligation)
}
fn field_pats(
&self,
vals: impl Iterator<Item = (ValTree<'tcx>, Ty<'tcx>)>,
) -> Vec<FieldPat<'tcx>> {
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.typing_env, ty);
FieldPat { field, pattern: self.valtree_to_pat(val, ty) }
})
.collect()
}
// Recursive helper for `to_pat`; invoke that (instead of calling this directly).
#[instrument(skip(self), level = "debug")]
fn valtree_to_pat(&self, cv: ValTree<'tcx>, ty: Ty<'tcx>) -> Box<Pat<'tcx>> {
let span = self.span;
let tcx = self.tcx;
let kind = match ty.kind() {
ty::Adt(adt_def, _) if !self.type_marked_structural(ty) => {
// Extremely important check for all ADTs! Make sure they opted-in to be used in
// patterns.
debug!("adt_def {:?} has !type_marked_structural for cv.ty: {:?}", adt_def, ty);
let err = TypeNotStructural { span, non_sm_ty: ty };
let e = tcx.dcx().emit_err(err);
// We errored. Signal that in the pattern, so that follow up errors can be silenced.
PatKind::Error(e)
}
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().to_u32());
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::Adt(def, args) => {
assert!(!def.is_union()); // Valtree construction would never succeed for unions.
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::Tuple(fields) => PatKind::Leaf {
subpatterns: self.field_pats(cv.unwrap_branch().iter().copied().zip(fields.iter())),
},
ty::Slice(elem_ty) => PatKind::Slice {
prefix: cv
.unwrap_branch()
.iter()
.map(|val| self.valtree_to_pat(*val, *elem_ty))
.collect(),
slice: None,
suffix: Box::new([]),
},
ty::Array(elem_ty, _) => PatKind::Array {
prefix: cv
.unwrap_branch()
.iter()
.map(|val| self.valtree_to_pat(*val, *elem_ty))
.collect(),
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, ty::Const::new_value(tcx, cv, ty)),
},
// 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, self.typing_env) && !pointee_ty.is_slice() {
let err = UnsizedPattern { span, non_sm_ty: *pointee_ty };
let e = tcx.dcx().emit_err(err);
// We errored. Signal that in the pattern, so that follow up errors can be silenced.
PatKind::Error(e)
} else {
// `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.valtree_to_pat(cv, pointee_ty);
PatKind::Deref { subpattern }
}
}
},
ty::Float(flt) => {
let v = cv.unwrap_leaf();
let is_nan = match flt {
ty::FloatTy::F16 => v.to_f16().is_nan(),
ty::FloatTy::F32 => v.to_f32().is_nan(),
ty::FloatTy::F64 => v.to_f64().is_nan(),
ty::FloatTy::F128 => v.to_f128().is_nan(),
};
if is_nan {
// NaNs are not ever equal to anything so they make no sense as patterns.
// Also see <https://github.com/rust-lang/rfcs/pull/3535>.
let e = tcx.dcx().emit_err(NaNPattern { span });
PatKind::Error(e)
} else {
PatKind::Constant {
value: mir::Const::Ty(ty, ty::Const::new_value(tcx, cv, ty)),
}
}
}
ty::Pat(..) | ty::Bool | ty::Char | ty::Int(_) | ty::Uint(_) | ty::RawPtr(..) => {
// The raw pointers we see here have been "vetted" by valtree construction to be
// just integers, so we simply allow them.
PatKind::Constant { value: mir::Const::Ty(ty, ty::Const::new_value(tcx, cv, ty)) }
}
ty::FnPtr(..) => {
unreachable!(
"Valtree construction would never succeed for FnPtr, so this is unreachable."
)
}
_ => {
let err = InvalidPattern { span, non_sm_ty: ty };
let e = tcx.dcx().emit_err(err);
// We errored. Signal that in the pattern, so that follow up errors can be silenced.
PatKind::Error(e)
}
};
Box::new(Pat { span, ty, kind })
}
}