//! Validation of patterns/matches.

mod check_match;
mod const_to_pat;

use std::cmp::Ordering;

use rustc_abi::{FieldIdx, Integer};
use rustc_errors::MultiSpan;
use rustc_errors::codes::*;
use rustc_hir::def::{CtorOf, DefKind, Res};
use rustc_hir::pat_util::EnumerateAndAdjustIterator;
use rustc_hir::{self as hir, ByRef, Mutability, RangeEnd};
use rustc_index::Idx;
use rustc_lint as lint;
use rustc_middle::mir::interpret::LitToConstInput;
use rustc_middle::thir::{
    Ascription, FieldPat, LocalVarId, Pat, PatKind, PatRange, PatRangeBoundary,
};
use rustc_middle::ty::layout::IntegerExt;
use rustc_middle::ty::{self, CanonicalUserTypeAnnotation, Ty, TyCtxt, TypeVisitableExt};
use rustc_middle::{bug, span_bug};
use rustc_span::def_id::LocalDefId;
use rustc_span::{ErrorGuaranteed, Span};
use tracing::{debug, instrument};

pub(crate) use self::check_match::check_match;
use crate::errors::*;
use crate::fluent_generated as fluent;
use crate::thir::util::UserAnnotatedTyHelpers;

struct PatCtxt<'a, 'tcx> {
    tcx: TyCtxt<'tcx>,
    typing_env: ty::TypingEnv<'tcx>,
    typeck_results: &'a ty::TypeckResults<'tcx>,

    /// Used by the Rust 2024 migration lint.
    rust_2024_migration_suggestion: Option<Rust2024IncompatiblePatSugg<'a>>,
}

pub(super) fn pat_from_hir<'a, 'tcx>(
    tcx: TyCtxt<'tcx>,
    typing_env: ty::TypingEnv<'tcx>,
    typeck_results: &'a ty::TypeckResults<'tcx>,
    pat: &'tcx hir::Pat<'tcx>,
) -> Box<Pat<'tcx>> {
    let mut pcx = PatCtxt {
        tcx,
        typing_env,
        typeck_results,
        rust_2024_migration_suggestion: typeck_results
            .rust_2024_migration_desugared_pats()
            .get(pat.hir_id)
            .map(|labels| Rust2024IncompatiblePatSugg {
                suggestion: Vec::new(),
                ref_pattern_count: 0,
                binding_mode_count: 0,
                labels: labels.as_slice(),
            }),
    };
    let result = pcx.lower_pattern(pat);
    debug!("pat_from_hir({:?}) = {:?}", pat, result);
    if let Some(sugg) = pcx.rust_2024_migration_suggestion {
        let mut spans = MultiSpan::from_spans(sugg.labels.iter().map(|(span, _)| *span).collect());
        for (span, label) in sugg.labels {
            spans.push_span_label(*span, label.clone());
        }
        // 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.subdiagnostic(sugg);
            err.emit();
        } else {
            tcx.emit_node_span_lint(
                lint::builtin::RUST_2024_INCOMPATIBLE_PAT,
                pat.hir_id,
                spans,
                Rust2024IncompatiblePat { sugg },
            );
        }
    }
    result
}

impl<'a, 'tcx> PatCtxt<'a, 'tcx> {
    fn lower_pattern(&mut self, pat: &'tcx hir::Pat<'tcx>) -> Box<Pat<'tcx>> {
        // When implicit dereferences have been inserted in this pattern, the unadjusted lowered
        // pattern has the type that results *after* dereferencing. For example, in this code:
        //
        // ```
        // match &&Some(0i32) {
        //     Some(n) => { ... },
        //     _ => { ... },
        // }
        // ```
        //
        // the type assigned to `Some(n)` in `unadjusted_pat` would be `Option<i32>` (this is
        // determined in rustc_hir_analysis::check::match). The adjustments would be
        //
        // `vec![&&Option<i32>, &Option<i32>]`.
        //
        // Applying the adjustments, we want to instead output `&&Some(n)` (as a THIR pattern). So
        // we wrap the unadjusted pattern in `PatKind::Deref` repeatedly, consuming the
        // adjustments in *reverse order* (last-in-first-out, so that the last `Deref` inserted
        // gets the least-dereferenced type).
        let unadjusted_pat = match pat.kind {
            hir::PatKind::Ref(inner, _)
                if self.typeck_results.skipped_ref_pats().contains(pat.hir_id) =>
            {
                self.lower_pattern(inner)
            }
            _ => self.lower_pattern_unadjusted(pat),
        };

        let adjustments: &[Ty<'tcx>] =
            self.typeck_results.pat_adjustments().get(pat.hir_id).map_or(&[], |v| &**v);
        let adjusted_pat = adjustments.iter().rev().fold(unadjusted_pat, |thir_pat, ref_ty| {
            debug!("{:?}: wrapping pattern with type {:?}", thir_pat, ref_ty);
            Box::new(Pat {
                span: thir_pat.span,
                ty: *ref_ty,
                kind: PatKind::Deref { subpattern: thir_pat },
            })
        });

        if let Some(s) = &mut self.rust_2024_migration_suggestion
            && !adjustments.is_empty()
        {
            let suggestion_str: String = adjustments
                .iter()
                .map(|ref_ty| {
                    let &ty::Ref(_, _, mutbl) = ref_ty.kind() else {
                        span_bug!(pat.span, "pattern implicitly dereferences a non-ref type");
                    };

                    match mutbl {
                        ty::Mutability::Not => "&",
                        ty::Mutability::Mut => "&mut ",
                    }
                })
                .collect();
            s.suggestion.push((pat.span.shrink_to_lo(), suggestion_str));
            s.ref_pattern_count += adjustments.len();
        };

        adjusted_pat
    }

    fn lower_pattern_range_endpoint(
        &mut self,
        expr: Option<&'tcx hir::PatExpr<'tcx>>,
    ) -> Result<
        (Option<PatRangeBoundary<'tcx>>, Option<Ascription<'tcx>>, Option<LocalDefId>),
        ErrorGuaranteed,
    > {
        match expr {
            None => Ok((None, None, None)),
            Some(expr) => {
                let (kind, ascr, inline_const) = match self.lower_lit(expr) {
                    PatKind::ExpandedConstant { subpattern, def_id, is_inline: true } => {
                        (subpattern.kind, None, def_id.as_local())
                    }
                    PatKind::ExpandedConstant { subpattern, is_inline: false, .. } => {
                        (subpattern.kind, None, None)
                    }
                    PatKind::AscribeUserType { ascription, subpattern: box Pat { kind, .. } } => {
                        (kind, Some(ascription), None)
                    }
                    kind => (kind, None, None),
                };
                let value = match kind {
                    PatKind::Constant { value } => value,
                    PatKind::ExpandedConstant { subpattern, .. }
                        if let PatKind::Constant { value } = subpattern.kind =>
                    {
                        value
                    }
                    _ => {
                        let msg = format!(
                            "found bad range pattern endpoint `{expr:?}` outside of error recovery"
                        );
                        return Err(self.tcx.dcx().span_delayed_bug(expr.span, msg));
                    }
                };
                Ok((Some(PatRangeBoundary::Finite(value)), ascr, inline_const))
            }
        }
    }

    /// Overflowing literals are linted against in a late pass. This is mostly fine, except when we
    /// encounter a range pattern like `-130i8..2`: if we believe `eval_bits`, this looks like a
    /// range where the endpoints are in the wrong order. To avoid a confusing error message, we
    /// check for overflow then.
    /// This is only called when the range is already known to be malformed.
    fn error_on_literal_overflow(
        &self,
        expr: Option<&'tcx hir::PatExpr<'tcx>>,
        ty: Ty<'tcx>,
    ) -> Result<(), ErrorGuaranteed> {
        use rustc_ast::ast::LitKind;

        let Some(expr) = expr else {
            return Ok(());
        };
        let span = expr.span;

        // We need to inspect the original expression, because if we only inspect the output of
        // `eval_bits`, an overflowed value has already been wrapped around.
        // We mostly copy the logic from the `rustc_lint::OVERFLOWING_LITERALS` lint.
        let hir::PatExprKind::Lit { lit, negated } = expr.kind else {
            return Ok(());
        };
        let LitKind::Int(lit_val, _) = lit.node else {
            return Ok(());
        };
        let (min, max): (i128, u128) = match ty.kind() {
            ty::Int(ity) => {
                let size = Integer::from_int_ty(&self.tcx, *ity).size();
                (size.signed_int_min(), size.signed_int_max() as u128)
            }
            ty::Uint(uty) => {
                let size = Integer::from_uint_ty(&self.tcx, *uty).size();
                (0, size.unsigned_int_max())
            }
            _ => {
                return Ok(());
            }
        };
        // Detect literal value out of range `[min, max]` inclusive, avoiding use of `-min` to
        // prevent overflow/panic.
        if (negated && lit_val > max + 1) || (!negated && lit_val > max) {
            return Err(self.tcx.dcx().emit_err(LiteralOutOfRange { span, ty, min, max }));
        }
        Ok(())
    }

    fn lower_pattern_range(
        &mut self,
        lo_expr: Option<&'tcx hir::PatExpr<'tcx>>,
        hi_expr: Option<&'tcx hir::PatExpr<'tcx>>,
        end: RangeEnd,
        ty: Ty<'tcx>,
        span: Span,
    ) -> Result<PatKind<'tcx>, ErrorGuaranteed> {
        if lo_expr.is_none() && hi_expr.is_none() {
            let msg = "found twice-open range pattern (`..`) outside of error recovery";
            self.tcx.dcx().span_bug(span, msg);
        }

        let (lo, lo_ascr, lo_inline) = self.lower_pattern_range_endpoint(lo_expr)?;
        let (hi, hi_ascr, hi_inline) = self.lower_pattern_range_endpoint(hi_expr)?;

        let lo = lo.unwrap_or(PatRangeBoundary::NegInfinity);
        let hi = hi.unwrap_or(PatRangeBoundary::PosInfinity);

        let cmp = lo.compare_with(hi, ty, self.tcx, self.typing_env);
        let mut kind = PatKind::Range(Box::new(PatRange { lo, hi, end, ty }));
        match (end, cmp) {
            // `x..y` where `x < y`.
            (RangeEnd::Excluded, Some(Ordering::Less)) => {}
            // `x..=y` where `x < y`.
            (RangeEnd::Included, Some(Ordering::Less)) => {}
            // `x..=y` where `x == y` and `x` and `y` are finite.
            (RangeEnd::Included, Some(Ordering::Equal)) if lo.is_finite() && hi.is_finite() => {
                kind = PatKind::Constant { value: lo.as_finite().unwrap() };
            }
            // `..=x` where `x == ty::MIN`.
            (RangeEnd::Included, Some(Ordering::Equal)) if !lo.is_finite() => {}
            // `x..` where `x == ty::MAX` (yes, `x..` gives `RangeEnd::Included` since it is meant
            // to include `ty::MAX`).
            (RangeEnd::Included, Some(Ordering::Equal)) if !hi.is_finite() => {}
            // `x..y` where `x >= y`, or `x..=y` where `x > y`. The range is empty => error.
            _ => {
                // Emit a more appropriate message if there was overflow.
                self.error_on_literal_overflow(lo_expr, ty)?;
                self.error_on_literal_overflow(hi_expr, ty)?;
                let e = match end {
                    RangeEnd::Included => {
                        self.tcx.dcx().emit_err(LowerRangeBoundMustBeLessThanOrEqualToUpper {
                            span,
                            teach: self.tcx.sess.teach(E0030),
                        })
                    }
                    RangeEnd::Excluded => {
                        self.tcx.dcx().emit_err(LowerRangeBoundMustBeLessThanUpper { span })
                    }
                };
                return Err(e);
            }
        }

        // If we are handling a range with associated constants (e.g.
        // `Foo::<'a>::A..=Foo::B`), we need to put the ascriptions for the associated
        // constants somewhere. Have them on the range pattern.
        for ascription in [lo_ascr, hi_ascr].into_iter().flatten() {
            kind = PatKind::AscribeUserType {
                ascription,
                subpattern: Box::new(Pat { span, ty, kind }),
            };
        }
        for def in [lo_inline, hi_inline].into_iter().flatten() {
            kind = PatKind::ExpandedConstant {
                def_id: def.to_def_id(),
                is_inline: true,
                subpattern: Box::new(Pat { span, ty, kind }),
            };
        }
        Ok(kind)
    }

    #[instrument(skip(self), level = "debug")]
    fn lower_pattern_unadjusted(&mut self, pat: &'tcx hir::Pat<'tcx>) -> Box<Pat<'tcx>> {
        let mut ty = self.typeck_results.node_type(pat.hir_id);
        let mut span = pat.span;

        let kind = match pat.kind {
            hir::PatKind::Wild => PatKind::Wild,

            hir::PatKind::Never => PatKind::Never,

            hir::PatKind::Expr(value) => self.lower_lit(value),

            hir::PatKind::Range(ref lo_expr, ref hi_expr, end) => {
                let (lo_expr, hi_expr) = (lo_expr.as_deref(), hi_expr.as_deref());
                self.lower_pattern_range(lo_expr, hi_expr, end, ty, span)
                    .unwrap_or_else(PatKind::Error)
            }

            hir::PatKind::Deref(subpattern) => {
                let mutable = self.typeck_results.pat_has_ref_mut_binding(subpattern);
                let mutability = if mutable { hir::Mutability::Mut } else { hir::Mutability::Not };
                PatKind::DerefPattern { subpattern: self.lower_pattern(subpattern), mutability }
            }
            hir::PatKind::Ref(subpattern, _) | hir::PatKind::Box(subpattern) => {
                PatKind::Deref { subpattern: self.lower_pattern(subpattern) }
            }

            hir::PatKind::Slice(prefix, slice, suffix) => {
                self.slice_or_array_pattern(pat.span, ty, prefix, slice, suffix)
            }

            hir::PatKind::Tuple(pats, ddpos) => {
                let ty::Tuple(tys) = ty.kind() else {
                    span_bug!(pat.span, "unexpected type for tuple pattern: {:?}", ty);
                };
                let subpatterns = self.lower_tuple_subpats(pats, tys.len(), ddpos);
                PatKind::Leaf { subpatterns }
            }

            hir::PatKind::Binding(explicit_ba, id, ident, sub) => {
                if let Some(ident_span) = ident.span.find_ancestor_inside(span) {
                    span = span.with_hi(ident_span.hi());
                }

                let mode = *self
                    .typeck_results
                    .pat_binding_modes()
                    .get(pat.hir_id)
                    .expect("missing binding mode");

                if let Some(s) = &mut self.rust_2024_migration_suggestion
                    && explicit_ba.0 == ByRef::No
                    && let ByRef::Yes(mutbl) = mode.0
                {
                    let sugg_str = match mutbl {
                        Mutability::Not => "ref ",
                        Mutability::Mut => "ref mut ",
                    };
                    s.suggestion.push((
                        pat.span.with_lo(ident.span.lo()).shrink_to_lo(),
                        sugg_str.to_owned(),
                    ));
                    s.binding_mode_count += 1;
                }

                // A ref x pattern is the same node used for x, and as such it has
                // x's type, which is &T, where we want T (the type being matched).
                let var_ty = ty;
                if let hir::ByRef::Yes(_) = mode.0 {
                    if let ty::Ref(_, rty, _) = ty.kind() {
                        ty = *rty;
                    } else {
                        bug!("`ref {}` has wrong type {}", ident, ty);
                    }
                };

                PatKind::Binding {
                    mode,
                    name: ident.name,
                    var: LocalVarId(id),
                    ty: var_ty,
                    subpattern: self.lower_opt_pattern(sub),
                    is_primary: id == pat.hir_id,
                }
            }

            hir::PatKind::TupleStruct(ref qpath, pats, ddpos) => {
                let res = self.typeck_results.qpath_res(qpath, pat.hir_id);
                let ty::Adt(adt_def, _) = ty.kind() else {
                    span_bug!(pat.span, "tuple struct pattern not applied to an ADT {:?}", ty);
                };
                let variant_def = adt_def.variant_of_res(res);
                let subpatterns = self.lower_tuple_subpats(pats, variant_def.fields.len(), ddpos);
                self.lower_variant_or_leaf(res, pat.hir_id, pat.span, ty, subpatterns)
            }

            hir::PatKind::Struct(ref qpath, fields, _) => {
                let res = self.typeck_results.qpath_res(qpath, pat.hir_id);
                let subpatterns = fields
                    .iter()
                    .map(|field| FieldPat {
                        field: self.typeck_results.field_index(field.hir_id),
                        pattern: self.lower_pattern(field.pat),
                    })
                    .collect();

                self.lower_variant_or_leaf(res, pat.hir_id, pat.span, ty, subpatterns)
            }

            hir::PatKind::Or(pats) => PatKind::Or { pats: self.lower_patterns(pats) },

            // FIXME(guard_patterns): implement guard pattern lowering
            hir::PatKind::Guard(pat, _) => self.lower_pattern(pat).kind,

            hir::PatKind::Err(guar) => PatKind::Error(guar),
        };

        Box::new(Pat { span, ty, kind })
    }

    fn lower_tuple_subpats(
        &mut self,
        pats: &'tcx [hir::Pat<'tcx>],
        expected_len: usize,
        gap_pos: hir::DotDotPos,
    ) -> Vec<FieldPat<'tcx>> {
        pats.iter()
            .enumerate_and_adjust(expected_len, gap_pos)
            .map(|(i, subpattern)| FieldPat {
                field: FieldIdx::new(i),
                pattern: self.lower_pattern(subpattern),
            })
            .collect()
    }

    fn lower_patterns(&mut self, pats: &'tcx [hir::Pat<'tcx>]) -> Box<[Box<Pat<'tcx>>]> {
        pats.iter().map(|p| self.lower_pattern(p)).collect()
    }

    fn lower_opt_pattern(&mut self, pat: Option<&'tcx hir::Pat<'tcx>>) -> Option<Box<Pat<'tcx>>> {
        pat.map(|p| self.lower_pattern(p))
    }

    fn slice_or_array_pattern(
        &mut self,
        span: Span,
        ty: Ty<'tcx>,
        prefix: &'tcx [hir::Pat<'tcx>],
        slice: Option<&'tcx hir::Pat<'tcx>>,
        suffix: &'tcx [hir::Pat<'tcx>],
    ) -> PatKind<'tcx> {
        let prefix = self.lower_patterns(prefix);
        let slice = self.lower_opt_pattern(slice);
        let suffix = self.lower_patterns(suffix);
        match ty.kind() {
            // Matching a slice, `[T]`.
            ty::Slice(..) => PatKind::Slice { prefix, slice, suffix },
            // Fixed-length array, `[T; len]`.
            ty::Array(_, len) => {
                let len = len
                    .try_to_target_usize(self.tcx)
                    .expect("expected len of array pat to be definite");
                assert!(len >= prefix.len() as u64 + suffix.len() as u64);
                PatKind::Array { prefix, slice, suffix }
            }
            _ => span_bug!(span, "bad slice pattern type {:?}", ty),
        }
    }

    fn lower_variant_or_leaf(
        &mut self,
        res: Res,
        hir_id: hir::HirId,
        span: Span,
        ty: Ty<'tcx>,
        subpatterns: Vec<FieldPat<'tcx>>,
    ) -> PatKind<'tcx> {
        let res = match res {
            Res::Def(DefKind::Ctor(CtorOf::Variant, ..), variant_ctor_id) => {
                let variant_id = self.tcx.parent(variant_ctor_id);
                Res::Def(DefKind::Variant, variant_id)
            }
            res => res,
        };

        let mut kind = match res {
            Res::Def(DefKind::Variant, variant_id) => {
                let enum_id = self.tcx.parent(variant_id);
                let adt_def = self.tcx.adt_def(enum_id);
                if adt_def.is_enum() {
                    let args = match ty.kind() {
                        ty::Adt(_, args) | ty::FnDef(_, args) => args,
                        ty::Error(e) => {
                            // Avoid ICE (#50585)
                            return PatKind::Error(*e);
                        }
                        _ => bug!("inappropriate type for def: {:?}", ty),
                    };
                    PatKind::Variant {
                        adt_def,
                        args,
                        variant_index: adt_def.variant_index_with_id(variant_id),
                        subpatterns,
                    }
                } else {
                    PatKind::Leaf { subpatterns }
                }
            }

            Res::Def(
                DefKind::Struct
                | DefKind::Ctor(CtorOf::Struct, ..)
                | DefKind::Union
                | DefKind::TyAlias
                | DefKind::AssocTy,
                _,
            )
            | Res::SelfTyParam { .. }
            | Res::SelfTyAlias { .. }
            | Res::SelfCtor(..) => PatKind::Leaf { subpatterns },
            _ => {
                let e = match res {
                    Res::Def(DefKind::ConstParam, def_id) => {
                        self.tcx.dcx().emit_err(ConstParamInPattern {
                            span,
                            const_span: self.tcx().def_span(def_id),
                        })
                    }
                    Res::Def(DefKind::Static { .. }, def_id) => {
                        self.tcx.dcx().emit_err(StaticInPattern {
                            span,
                            static_span: self.tcx().def_span(def_id),
                        })
                    }
                    _ => self.tcx.dcx().emit_err(NonConstPath { span }),
                };
                PatKind::Error(e)
            }
        };

        if let Some(user_ty) = self.user_args_applied_to_ty_of_hir_id(hir_id) {
            debug!("lower_variant_or_leaf: kind={:?} user_ty={:?} span={:?}", kind, user_ty, span);
            let annotation = CanonicalUserTypeAnnotation {
                user_ty: Box::new(user_ty),
                span,
                inferred_ty: self.typeck_results.node_type(hir_id),
            };
            kind = PatKind::AscribeUserType {
                subpattern: Box::new(Pat { span, ty, kind }),
                ascription: Ascription { annotation, variance: ty::Covariant },
            };
        }

        kind
    }

    /// Takes a HIR Path. If the path is a constant, evaluates it and feeds
    /// it to `const_to_pat`. Any other path (like enum variants without fields)
    /// is converted to the corresponding pattern via `lower_variant_or_leaf`.
    #[instrument(skip(self), level = "debug")]
    fn lower_path(&mut self, qpath: &hir::QPath<'_>, id: hir::HirId, span: Span) -> Box<Pat<'tcx>> {
        let ty = self.typeck_results.node_type(id);
        let res = self.typeck_results.qpath_res(qpath, id);

        let pat_from_kind = |kind| Box::new(Pat { span, ty, kind });

        let (def_id, is_associated_const) = match res {
            Res::Def(DefKind::Const, def_id) => (def_id, false),
            Res::Def(DefKind::AssocConst, def_id) => (def_id, true),

            _ => return pat_from_kind(self.lower_variant_or_leaf(res, id, span, ty, vec![])),
        };

        let args = self.typeck_results.node_args(id);
        let c = ty::Const::new_unevaluated(self.tcx, ty::UnevaluatedConst { def: def_id, args });
        let subpattern = self.const_to_pat(c, ty, id, span);
        let pattern = Box::new(Pat {
            span,
            ty,
            kind: PatKind::ExpandedConstant { subpattern, def_id, is_inline: false },
        });

        if !is_associated_const {
            return pattern;
        }

        let user_provided_types = self.typeck_results().user_provided_types();
        if let Some(&user_ty) = user_provided_types.get(id) {
            let annotation = CanonicalUserTypeAnnotation {
                user_ty: Box::new(user_ty),
                span,
                inferred_ty: self.typeck_results().node_type(id),
            };
            Box::new(Pat {
                span,
                kind: PatKind::AscribeUserType {
                    subpattern: pattern,
                    ascription: Ascription {
                        annotation,
                        // Note that use `Contravariant` here. See the
                        // `variance` field documentation for details.
                        variance: ty::Contravariant,
                    },
                },
                ty,
            })
        } else {
            pattern
        }
    }

    /// Converts inline const patterns.
    fn lower_inline_const(
        &mut self,
        block: &'tcx hir::ConstBlock,
        id: hir::HirId,
        span: Span,
    ) -> PatKind<'tcx> {
        let tcx = self.tcx;
        let def_id = block.def_id;
        let ty = tcx.typeck(def_id).node_type(block.hir_id);

        let typeck_root_def_id = tcx.typeck_root_def_id(def_id.to_def_id());
        let parent_args =
            tcx.erase_regions(ty::GenericArgs::identity_for_item(tcx, typeck_root_def_id));
        let args = ty::InlineConstArgs::new(tcx, ty::InlineConstArgsParts { parent_args, ty }).args;

        debug_assert!(!args.has_free_regions());

        let ct = ty::UnevaluatedConst { def: def_id.to_def_id(), args };
        let subpattern = self.const_to_pat(ty::Const::new_unevaluated(self.tcx, ct), ty, id, span);
        PatKind::ExpandedConstant { subpattern, def_id: def_id.to_def_id(), is_inline: true }
    }

    /// Converts literals, paths and negation of literals to patterns.
    /// The special case for negation exists to allow things like `-128_i8`
    /// which would overflow if we tried to evaluate `128_i8` and then negate
    /// afterwards.
    fn lower_lit(&mut self, expr: &'tcx hir::PatExpr<'tcx>) -> PatKind<'tcx> {
        let (lit, neg) = match &expr.kind {
            hir::PatExprKind::Path(qpath) => {
                return self.lower_path(qpath, expr.hir_id, expr.span).kind;
            }
            hir::PatExprKind::ConstBlock(anon_const) => {
                return self.lower_inline_const(anon_const, expr.hir_id, expr.span);
            }
            hir::PatExprKind::Lit { lit, negated } => (lit, *negated),
        };

        let ct_ty = self.typeck_results.node_type(expr.hir_id);
        let lit_input = LitToConstInput { lit: &lit.node, ty: ct_ty, neg };
        let constant = self.tcx.at(expr.span).lit_to_const(lit_input);
        self.const_to_pat(constant, ct_ty, expr.hir_id, lit.span).kind
    }
}

impl<'tcx> UserAnnotatedTyHelpers<'tcx> for PatCtxt<'_, 'tcx> {
    fn tcx(&self) -> TyCtxt<'tcx> {
        self.tcx
    }

    fn typeck_results(&self) -> &ty::TypeckResults<'tcx> {
        self.typeck_results
    }
}