rust/src/librustc_const_eval/pattern.rs

// Copyright 2016 The Rust Project Developers. See the COPYRIGHT
// file at the top-level directory of this distribution and at
// http://rust-lang.org/COPYRIGHT.
//
// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
// option. This file may not be copied, modified, or distributed
// except according to those terms.

use eval;

use rustc::middle::const_val::ConstVal;
use rustc::mir::{Field, BorrowKind, Mutability};
use rustc::ty::{self, TyCtxt, AdtDef, Ty, Region};
use rustc::hir::{self, PatKind};
use rustc::hir::def::Def;
use rustc::hir::def_id::DefId;
use rustc::hir::pat_util::EnumerateAndAdjustIterator;

use rustc_data_structures::indexed_vec::Idx;

use syntax::ast;
use syntax::ptr::P;
use syntax_pos::Span;

#[derive(Clone, Debug)]
pub enum PatternError {
    StaticInPattern(Span),
    BadConstInPattern(Span, DefId),
    ConstEval(eval::ConstEvalErr),
}

#[derive(Copy, Clone, Debug)]
pub enum BindingMode<'tcx> {
    ByValue,
    ByRef(&'tcx Region, BorrowKind),
}

#[derive(Clone, Debug)]
pub struct FieldPattern<'tcx> {
    pub field: Field,
    pub pattern: Pattern<'tcx>,
}

#[derive(Clone, Debug)]
pub struct Pattern<'tcx> {
    pub ty: Ty<'tcx>,
    pub span: Span,
    pub kind: Box<PatternKind<'tcx>>,
}

#[derive(Clone, Debug)]
pub enum PatternKind<'tcx> {
    Wild,

    /// x, ref x, x @ P, etc
    Binding {
        mutability: Mutability,
        name: ast::Name,
        mode: BindingMode<'tcx>,
        var: ast::NodeId,
        ty: Ty<'tcx>,
        subpattern: Option<Pattern<'tcx>>,
    },

    /// Foo(...) or Foo{...} or Foo, where `Foo` is a variant name from an adt with >1 variants
    Variant {
        adt_def: AdtDef<'tcx>,
        variant_index: usize,
        subpatterns: Vec<FieldPattern<'tcx>>,
    },

    /// (...), Foo(...), Foo{...}, or Foo, where `Foo` is a variant name from an adt with 1 variant
    Leaf {
        subpatterns: Vec<FieldPattern<'tcx>>,
    },

    /// box P, &P, &mut P, etc
    Deref {
        subpattern: Pattern<'tcx>,
    },

    Constant {
        value: ConstVal,
    },

    Range {
        lo: ConstVal,
        hi: ConstVal,
    },

    /// matches against a slice, checking the length and extracting elements
    Slice {
        prefix: Vec<Pattern<'tcx>>,
        slice: Option<Pattern<'tcx>>,
        suffix: Vec<Pattern<'tcx>>,
    },

    /// fixed match against an array, irrefutable
    Array {
        prefix: Vec<Pattern<'tcx>>,
        slice: Option<Pattern<'tcx>>,
        suffix: Vec<Pattern<'tcx>>,
    },
}

pub struct PatternContext<'a, 'gcx: 'tcx, 'tcx: 'a> {
    pub tcx: TyCtxt<'a, 'gcx, 'tcx>,
    pub errors: Vec<PatternError>,
}

impl<'a, 'gcx, 'tcx> Pattern<'tcx> {
    pub fn from_hir(tcx: TyCtxt<'a, 'gcx, 'tcx>, pat: &hir::Pat) -> Self {
        let mut pcx = PatternContext::new(tcx);
        let result = pcx.lower_pattern(pat);
        if !pcx.errors.is_empty() {
            span_bug!(pat.span, "encountered errors lowering pattern: {:?}", pcx.errors)
        }
        debug!("Pattern::from_hir({:?}) = {:?}", pat, result);
        result
    }
}

impl<'a, 'gcx, 'tcx> PatternContext<'a, 'gcx, 'tcx> {
    pub fn new(tcx: TyCtxt<'a, 'gcx, 'tcx>) -> Self {
        PatternContext { tcx: tcx, errors: vec![] }
    }

    pub fn lower_pattern(&mut self, pat: &hir::Pat) -> Pattern<'tcx> {
        let mut ty = self.tcx.tables().node_id_to_type(pat.id);

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

            PatKind::Lit(ref value) => {
                match eval::eval_const_expr_checked(self.tcx.global_tcx(), value) {
                    Ok(value) => {
                        PatternKind::Constant { value: value }
                    }
                    Err(e) => {
                        self.errors.push(PatternError::ConstEval(e));
                        PatternKind::Wild
                    }
                }
            }

            PatKind::Range(ref lo, ref hi) => {
                let r_lo = eval::eval_const_expr_checked(self.tcx.global_tcx(), lo);
                if let Err(ref e_lo) = r_lo {
                    self.errors.push(PatternError::ConstEval(e_lo.clone()));
                }

                let r_hi = eval::eval_const_expr_checked(self.tcx.global_tcx(), hi);
                if let Err(ref e_hi) = r_hi {
                    self.errors.push(PatternError::ConstEval(e_hi.clone()));
                }

                if let (Ok(lo), Ok(hi)) = (r_lo, r_hi) {
                    PatternKind::Range { lo: lo, hi: hi }
                } else {
                    PatternKind::Wild
                }
            }

            PatKind::Path(ref qpath) => {
                let def = self.tcx.tables().qpath_def(qpath, pat.id);
                match def {
                    Def::Const(def_id) | Def::AssociatedConst(def_id) => {
                        let tcx = self.tcx.global_tcx();
                        let substs = tcx.tables().node_id_item_substs(pat.id)
                            .unwrap_or_else(|| tcx.intern_substs(&[]));
                        match eval::lookup_const_by_id(tcx, def_id, Some(substs)) {
                            Some((const_expr, _const_ty)) => {
                                match eval::const_expr_to_pat(
                                    tcx, const_expr, pat.id, pat.span)
                                {
                                    Ok(pat) => return self.lower_pattern(&pat),
                                    Err(_) => {
                                        self.errors.push(PatternError::BadConstInPattern(
                                            pat.span, def_id));
                                        PatternKind::Wild
                                    }
                                }
                            }
                            None => {
                                self.errors.push(PatternError::StaticInPattern(pat.span));
                                PatternKind::Wild
                            }
                        }
                    }
                    _ => self.lower_variant_or_leaf(def, vec![])
                }
            }

            PatKind::Ref(ref subpattern, _) |
            PatKind::Box(ref subpattern) => {
                PatternKind::Deref { subpattern: self.lower_pattern(subpattern) }
            }

            PatKind::Slice(ref prefix, ref slice, ref suffix) => {
                let ty = self.tcx.tables().node_id_to_type(pat.id);
                match ty.sty {
                    ty::TyRef(_, mt) =>
                        PatternKind::Deref {
                            subpattern: Pattern {
                                ty: mt.ty,
                                span: pat.span,
                                kind: Box::new(self.slice_or_array_pattern(
                                    pat.span, mt.ty, prefix, slice, suffix))
                            },
                        },

                    ty::TySlice(..) |
                    ty::TyArray(..) =>
                        self.slice_or_array_pattern(pat.span, ty, prefix, slice, suffix),

                    ref sty =>
                        span_bug!(
                            pat.span,
                            "unexpanded type for vector pattern: {:?}",
                            sty),
                }
            }

            PatKind::Tuple(ref subpatterns, ddpos) => {
                let ty = self.tcx.tables().node_id_to_type(pat.id);
                match ty.sty {
                    ty::TyTuple(ref tys) => {
                        let subpatterns =
                            subpatterns.iter()
                                       .enumerate_and_adjust(tys.len(), ddpos)
                                       .map(|(i, subpattern)| FieldPattern {
                                            field: Field::new(i),
                                            pattern: self.lower_pattern(subpattern)
                                       })
                                       .collect();

                        PatternKind::Leaf { subpatterns: subpatterns }
                    }

                    ref sty => span_bug!(pat.span, "unexpected type for tuple pattern: {:?}", sty),
                }
            }

            PatKind::Binding(bm, def_id, ref ident, ref sub) => {
                let id = self.tcx.map.as_local_node_id(def_id).unwrap();
                let var_ty = self.tcx.tables().node_id_to_type(pat.id);
                let region = match var_ty.sty {
                    ty::TyRef(r, _) => Some(r),
                    _ => None,
                };
                let (mutability, mode) = match bm {
                    hir::BindByValue(hir::MutMutable) =>
                        (Mutability::Mut, BindingMode::ByValue),
                    hir::BindByValue(hir::MutImmutable) =>
                        (Mutability::Not, BindingMode::ByValue),
                    hir::BindByRef(hir::MutMutable) =>
                        (Mutability::Not, BindingMode::ByRef(region.unwrap(), BorrowKind::Mut)),
                    hir::BindByRef(hir::MutImmutable) =>
                        (Mutability::Not, BindingMode::ByRef(region.unwrap(), BorrowKind::Shared)),
                };

                // 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).
                if let hir::BindByRef(_) = bm {
                    if let ty::TyRef(_, mt) = ty.sty {
                        ty = mt.ty;
                    } else {
                        bug!("`ref {}` has wrong type {}", ident.node, ty);
                    }
                }

                PatternKind::Binding {
                    mutability: mutability,
                    mode: mode,
                    name: ident.node,
                    var: id,
                    ty: var_ty,
                    subpattern: self.lower_opt_pattern(sub),
                }
            }

            PatKind::TupleStruct(ref qpath, ref subpatterns, ddpos) => {
                let def = self.tcx.tables().qpath_def(qpath, pat.id);
                let pat_ty = self.tcx.tables().node_id_to_type(pat.id);
                let adt_def = match pat_ty.sty {
                    ty::TyAdt(adt_def, _) => adt_def,
                    _ => span_bug!(pat.span, "tuple struct pattern not applied to an ADT"),
                };
                let variant_def = adt_def.variant_of_def(def);

                let subpatterns =
                        subpatterns.iter()
                                   .enumerate_and_adjust(variant_def.fields.len(), ddpos)
                                   .map(|(i, field)| FieldPattern {
                                       field: Field::new(i),
                                       pattern: self.lower_pattern(field),
                                   })
                                   .collect();
                self.lower_variant_or_leaf(def, subpatterns)
            }

            PatKind::Struct(ref qpath, ref fields, _) => {
                let def = self.tcx.tables().qpath_def(qpath, pat.id);
                let pat_ty = self.tcx.tables().node_id_to_type(pat.id);
                let adt_def = match pat_ty.sty {
                    ty::TyAdt(adt_def, _) => adt_def,
                    _ => {
                        span_bug!(
                            pat.span,
                            "struct pattern not applied to an ADT");
                    }
                };
                let variant_def = adt_def.variant_of_def(def);

                let subpatterns =
                    fields.iter()
                          .map(|field| {
                              let index = variant_def.index_of_field_named(field.node.name);
                              let index = index.unwrap_or_else(|| {
                                  span_bug!(
                                      pat.span,
                                      "no field with name {:?}",
                                      field.node.name);
                              });
                              FieldPattern {
                                  field: Field::new(index),
                                  pattern: self.lower_pattern(&field.node.pat),
                              }
                          })
                          .collect();

                self.lower_variant_or_leaf(def, subpatterns)
            }
        };

        Pattern {
            span: pat.span,
            ty: ty,
            kind: Box::new(kind),
        }
    }

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

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

    fn flatten_nested_slice_patterns(
        &mut self,
        prefix: Vec<Pattern<'tcx>>,
        slice: Option<Pattern<'tcx>>,
        suffix: Vec<Pattern<'tcx>>)
        -> (Vec<Pattern<'tcx>>, Option<Pattern<'tcx>>, Vec<Pattern<'tcx>>)
    {
        let orig_slice = match slice {
            Some(orig_slice) => orig_slice,
            None => return (prefix, slice, suffix)
        };
        let orig_prefix = prefix;
        let orig_suffix = suffix;

        // dance because of intentional borrow-checker stupidity.
        let kind = *orig_slice.kind;
        match kind {
            PatternKind::Slice { prefix, slice, mut suffix } |
            PatternKind::Array { prefix, slice, mut suffix } => {
                let mut orig_prefix = orig_prefix;

                orig_prefix.extend(prefix);
                suffix.extend(orig_suffix);

                (orig_prefix, slice, suffix)
            }
            _ => {
                (orig_prefix, Some(Pattern {
                    kind: box kind, ..orig_slice
                }), orig_suffix)
            }
        }
    }

    fn slice_or_array_pattern(
        &mut self,
        span: Span,
        ty: Ty<'tcx>,
        prefix: &[P<hir::Pat>],
        slice: &Option<P<hir::Pat>>,
        suffix: &[P<hir::Pat>])
        -> PatternKind<'tcx>
    {
        let prefix = self.lower_patterns(prefix);
        let slice = self.lower_opt_pattern(slice);
        let suffix = self.lower_patterns(suffix);
        let (prefix, slice, suffix) =
            self.flatten_nested_slice_patterns(prefix, slice, suffix);

        match ty.sty {
            ty::TySlice(..) => {
                // matching a slice or fixed-length array
                PatternKind::Slice { prefix: prefix, slice: slice, suffix: suffix }
            }

            ty::TyArray(_, len) => {
                // fixed-length array
                assert!(len >= prefix.len() + suffix.len());
                PatternKind::Array { prefix: prefix, slice: slice, suffix: suffix }
            }

            _ => {
                span_bug!(span, "bad slice pattern type {:?}", ty);
            }
        }
    }

    fn lower_variant_or_leaf(
        &mut self,
        def: Def,
        subpatterns: Vec<FieldPattern<'tcx>>)
        -> PatternKind<'tcx>
    {
        match def {
            Def::Variant(variant_id) | Def::VariantCtor(variant_id, ..) => {
                let enum_id = self.tcx.parent_def_id(variant_id).unwrap();
                let adt_def = self.tcx.lookup_adt_def(enum_id);
                if adt_def.variants.len() > 1 {
                    PatternKind::Variant {
                        adt_def: adt_def,
                        variant_index: adt_def.variant_index_with_id(variant_id),
                        subpatterns: subpatterns,
                    }
                } else {
                    PatternKind::Leaf { subpatterns: subpatterns }
                }
            }

            Def::Struct(..) | Def::StructCtor(..) | Def::Union(..) |
            Def::TyAlias(..) | Def::AssociatedTy(..) | Def::SelfTy(..) => {
                PatternKind::Leaf { subpatterns: subpatterns }
            }

            _ => bug!()
        }
    }
}

pub trait PatternFoldable<'tcx> : Sized {
    fn fold_with<F: PatternFolder<'tcx>>(&self, folder: &mut F) -> Self {
        self.super_fold_with(folder)
    }

    fn super_fold_with<F: PatternFolder<'tcx>>(&self, folder: &mut F) -> Self;
}

pub trait PatternFolder<'tcx> : Sized {
    fn fold_pattern(&mut self, pattern: &Pattern<'tcx>) -> Pattern<'tcx> {
        pattern.super_fold_with(self)
    }

    fn fold_pattern_kind(&mut self, kind: &PatternKind<'tcx>) -> PatternKind<'tcx> {
        kind.super_fold_with(self)
    }
}


impl<'tcx, T: PatternFoldable<'tcx>> PatternFoldable<'tcx> for Box<T> {
    fn super_fold_with<F: PatternFolder<'tcx>>(&self, folder: &mut F) -> Self {
        let content: T = (**self).fold_with(folder);
        box content
    }
}

impl<'tcx, T: PatternFoldable<'tcx>> PatternFoldable<'tcx> for Vec<T> {
    fn super_fold_with<F: PatternFolder<'tcx>>(&self, folder: &mut F) -> Self {
        self.iter().map(|t| t.fold_with(folder)).collect()
    }
}

impl<'tcx, T: PatternFoldable<'tcx>> PatternFoldable<'tcx> for Option<T> {
    fn super_fold_with<F: PatternFolder<'tcx>>(&self, folder: &mut F) -> Self{
        self.as_ref().map(|t| t.fold_with(folder))
    }
}

macro_rules! CopyImpls {
    ($($ty:ty),+) => {
        $(
            impl<'tcx> PatternFoldable<'tcx> for $ty {
                fn super_fold_with<F: PatternFolder<'tcx>>(&self, _: &mut F) -> Self {
                    self.clone()
                }
            }
            )+
    }
}

macro_rules! TcxCopyImpls {
    ($($ty:ident),+) => {
        $(
            impl<'tcx> PatternFoldable<'tcx> for $ty<'tcx> {
                fn super_fold_with<F: PatternFolder<'tcx>>(&self, _: &mut F) -> Self {
                    *self
                }
            }
        )+
    }
}

CopyImpls!{ Span, Field, Mutability, ast::Name, ast::NodeId, usize, ConstVal }
TcxCopyImpls!{ Ty, BindingMode, AdtDef }

impl<'tcx> PatternFoldable<'tcx> for FieldPattern<'tcx> {
    fn super_fold_with<F: PatternFolder<'tcx>>(&self, folder: &mut F) -> Self {
        FieldPattern {
            field: self.field.fold_with(folder),
            pattern: self.pattern.fold_with(folder)
        }
    }
}

impl<'tcx> PatternFoldable<'tcx> for Pattern<'tcx> {
    fn fold_with<F: PatternFolder<'tcx>>(&self, folder: &mut F) -> Self {
        folder.fold_pattern(self)
    }

    fn super_fold_with<F: PatternFolder<'tcx>>(&self, folder: &mut F) -> Self {
        Pattern {
            ty: self.ty.fold_with(folder),
            span: self.span.fold_with(folder),
            kind: self.kind.fold_with(folder)
        }
    }
}

impl<'tcx> PatternFoldable<'tcx> for PatternKind<'tcx> {
    fn fold_with<F: PatternFolder<'tcx>>(&self, folder: &mut F) -> Self {
        folder.fold_pattern_kind(self)
    }

    fn super_fold_with<F: PatternFolder<'tcx>>(&self, folder: &mut F) -> Self {
        match *self {
            PatternKind::Wild => PatternKind::Wild,
            PatternKind::Binding {
                mutability,
                name,
                mode,
                var,
                ty,
                ref subpattern,
            } => PatternKind::Binding {
                mutability: mutability.fold_with(folder),
                name: name.fold_with(folder),
                mode: mode.fold_with(folder),
                var: var.fold_with(folder),
                ty: ty.fold_with(folder),
                subpattern: subpattern.fold_with(folder),
            },
            PatternKind::Variant {
                adt_def,
                variant_index,
                ref subpatterns,
            } => PatternKind::Variant {
                adt_def: adt_def.fold_with(folder),
                variant_index: variant_index.fold_with(folder),
                subpatterns: subpatterns.fold_with(folder)
            },
            PatternKind::Leaf {
                ref subpatterns,
            } => PatternKind::Leaf {
                subpatterns: subpatterns.fold_with(folder),
            },
            PatternKind::Deref {
                ref subpattern,
            } => PatternKind::Deref {
                subpattern: subpattern.fold_with(folder),
            },
            PatternKind::Constant {
                ref value
            } => PatternKind::Constant {
                value: value.fold_with(folder)
            },
            PatternKind::Range {
                ref lo,
                ref hi
            } => PatternKind::Range {
                lo: lo.fold_with(folder),
                hi: hi.fold_with(folder)
            },
            PatternKind::Slice {
                ref prefix,
                ref slice,
                ref suffix,
            } => PatternKind::Slice {
                prefix: prefix.fold_with(folder),
                slice: slice.fold_with(folder),
                suffix: suffix.fold_with(folder)
            },
            PatternKind::Array {
                ref prefix,
                ref slice,
                ref suffix
            } => PatternKind::Array {
                prefix: prefix.fold_with(folder),
                slice: slice.fold_with(folder),
                suffix: suffix.fold_with(folder)
            },
        }
    }
}