1102 lines
42 KiB
Rust
1102 lines
42 KiB
Rust
// Copyright 2012-2016 The Rust Project Developers. See the COPYRIGHT
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// file at the top-level directory of this distribution and at
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// http://rust-lang.org/COPYRIGHT.
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//
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// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
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// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
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// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
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// option. This file may not be copied, modified, or distributed
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// except according to those terms.
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use self::Constructor::*;
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use self::Usefulness::*;
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use self::WitnessPreference::*;
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use rustc::middle::const_val::ConstVal;
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use eval::{compare_const_vals};
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use rustc_const_math::ConstInt;
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use rustc_data_structures::fx::FxHashMap;
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use rustc_data_structures::indexed_vec::Idx;
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use pattern::{FieldPattern, Pattern, PatternKind};
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use pattern::{PatternFoldable, PatternFolder};
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use rustc::hir::def_id::DefId;
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use rustc::hir::RangeEnd;
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use rustc::ty::{self, Ty, TyCtxt, TypeFoldable};
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use rustc::mir::Field;
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use rustc::util::common::ErrorReported;
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use syntax_pos::{Span, DUMMY_SP};
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use arena::TypedArena;
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use std::cmp::{self, Ordering};
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use std::fmt;
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use std::iter::{FromIterator, IntoIterator, repeat};
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pub fn expand_pattern<'a, 'tcx>(cx: &MatchCheckCtxt<'a, 'tcx>, pat: Pattern<'tcx>)
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-> &'a Pattern<'tcx>
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{
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cx.pattern_arena.alloc(LiteralExpander.fold_pattern(&pat))
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}
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struct LiteralExpander;
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impl<'tcx> PatternFolder<'tcx> for LiteralExpander {
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fn fold_pattern(&mut self, pat: &Pattern<'tcx>) -> Pattern<'tcx> {
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match (&pat.ty.sty, &*pat.kind) {
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(&ty::TyRef(_, mt), &PatternKind::Constant { ref value }) => {
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Pattern {
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ty: pat.ty,
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span: pat.span,
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kind: box PatternKind::Deref {
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subpattern: Pattern {
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ty: mt.ty,
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span: pat.span,
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kind: box PatternKind::Constant { value: value.clone() },
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}
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}
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}
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}
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(_, &PatternKind::Binding { subpattern: Some(ref s), .. }) => {
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s.fold_with(self)
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}
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_ => pat.super_fold_with(self)
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}
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}
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}
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impl<'tcx> Pattern<'tcx> {
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fn is_wildcard(&self) -> bool {
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match *self.kind {
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PatternKind::Binding { subpattern: None, .. } | PatternKind::Wild =>
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true,
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_ => false
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}
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}
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}
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pub struct Matrix<'a, 'tcx: 'a>(Vec<Vec<&'a Pattern<'tcx>>>);
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impl<'a, 'tcx> Matrix<'a, 'tcx> {
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pub fn empty() -> Self {
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Matrix(vec![])
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}
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pub fn push(&mut self, row: Vec<&'a Pattern<'tcx>>) {
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self.0.push(row)
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}
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}
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/// Pretty-printer for matrices of patterns, example:
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/// ++++++++++++++++++++++++++
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/// + _ + [] +
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/// ++++++++++++++++++++++++++
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/// + true + [First] +
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/// ++++++++++++++++++++++++++
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/// + true + [Second(true)] +
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/// ++++++++++++++++++++++++++
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/// + false + [_] +
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/// ++++++++++++++++++++++++++
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/// + _ + [_, _, ..tail] +
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/// ++++++++++++++++++++++++++
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impl<'a, 'tcx> fmt::Debug for Matrix<'a, 'tcx> {
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fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
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write!(f, "\n")?;
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let &Matrix(ref m) = self;
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let pretty_printed_matrix: Vec<Vec<String>> = m.iter().map(|row| {
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row.iter().map(|pat| format!("{:?}", pat)).collect()
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}).collect();
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let column_count = m.iter().map(|row| row.len()).max().unwrap_or(0);
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assert!(m.iter().all(|row| row.len() == column_count));
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let column_widths: Vec<usize> = (0..column_count).map(|col| {
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pretty_printed_matrix.iter().map(|row| row[col].len()).max().unwrap_or(0)
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}).collect();
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let total_width = column_widths.iter().cloned().sum::<usize>() + column_count * 3 + 1;
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let br = repeat('+').take(total_width).collect::<String>();
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write!(f, "{}\n", br)?;
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for row in pretty_printed_matrix {
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write!(f, "+")?;
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for (column, pat_str) in row.into_iter().enumerate() {
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write!(f, " ")?;
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write!(f, "{:1$}", pat_str, column_widths[column])?;
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write!(f, " +")?;
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}
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write!(f, "\n")?;
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write!(f, "{}\n", br)?;
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}
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Ok(())
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}
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}
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impl<'a, 'tcx> FromIterator<Vec<&'a Pattern<'tcx>>> for Matrix<'a, 'tcx> {
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fn from_iter<T: IntoIterator<Item=Vec<&'a Pattern<'tcx>>>>(iter: T) -> Self
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{
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Matrix(iter.into_iter().collect())
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}
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}
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//NOTE: appears to be the only place other then InferCtxt to contain a ParamEnv
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pub struct MatchCheckCtxt<'a, 'tcx: 'a> {
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pub tcx: TyCtxt<'a, 'tcx, 'tcx>,
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/// The module in which the match occurs. This is necessary for
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/// checking inhabited-ness of types because whether a type is (visibly)
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/// inhabited can depend on whether it was defined in the current module or
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/// not. eg. `struct Foo { _private: ! }` cannot be seen to be empty
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/// outside it's module and should not be matchable with an empty match
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/// statement.
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pub module: DefId,
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pub pattern_arena: &'a TypedArena<Pattern<'tcx>>,
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pub byte_array_map: FxHashMap<*const Pattern<'tcx>, Vec<&'a Pattern<'tcx>>>,
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}
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impl<'a, 'tcx> MatchCheckCtxt<'a, 'tcx> {
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pub fn create_and_enter<F, R>(
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tcx: TyCtxt<'a, 'tcx, 'tcx>,
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module: DefId,
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f: F) -> R
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where F: for<'b> FnOnce(MatchCheckCtxt<'b, 'tcx>) -> R
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{
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let pattern_arena = TypedArena::new();
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f(MatchCheckCtxt {
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tcx,
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module,
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pattern_arena: &pattern_arena,
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byte_array_map: FxHashMap(),
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})
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}
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// convert a byte-string pattern to a list of u8 patterns.
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fn lower_byte_str_pattern<'p>(&mut self, pat: &'p Pattern<'tcx>) -> Vec<&'p Pattern<'tcx>>
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where 'a: 'p
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{
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let pattern_arena = &*self.pattern_arena;
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let tcx = self.tcx;
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self.byte_array_map.entry(pat).or_insert_with(|| {
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match pat.kind {
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box PatternKind::Constant {
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value: &ty::Const { val: ConstVal::ByteStr(b), .. }
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} => {
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b.data.iter().map(|&b| &*pattern_arena.alloc(Pattern {
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ty: tcx.types.u8,
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span: pat.span,
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kind: box PatternKind::Constant {
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value: tcx.mk_const(ty::Const {
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val: ConstVal::Integral(ConstInt::U8(b)),
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ty: tcx.types.u8
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})
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}
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})).collect()
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}
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_ => span_bug!(pat.span, "unexpected byte array pattern {:?}", pat)
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}
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}).clone()
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}
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fn is_uninhabited(&self, ty: Ty<'tcx>) -> bool {
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if self.tcx.sess.features.borrow().never_type {
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self.tcx.is_ty_uninhabited_from(self.module, ty)
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} else {
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false
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}
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}
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fn is_non_exhaustive_enum(&self, ty: Ty<'tcx>) -> bool {
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match ty.sty {
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ty::TyAdt(adt_def, ..) => adt_def.is_enum() && adt_def.is_non_exhaustive(),
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_ => false,
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}
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}
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fn is_local(&self, ty: Ty<'tcx>) -> bool {
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match ty.sty {
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ty::TyAdt(adt_def, ..) => adt_def.did.is_local(),
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_ => false,
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}
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}
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fn is_variant_uninhabited(&self,
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variant: &'tcx ty::VariantDef,
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substs: &'tcx ty::subst::Substs<'tcx>)
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-> bool
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{
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if self.tcx.sess.features.borrow().never_type {
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self.tcx.is_enum_variant_uninhabited_from(self.module, variant, substs)
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} else {
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false
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}
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}
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}
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#[derive(Clone, Debug, PartialEq)]
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pub enum Constructor<'tcx> {
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/// The constructor of all patterns that don't vary by constructor,
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/// e.g. struct patterns and fixed-length arrays.
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Single,
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/// Enum variants.
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Variant(DefId),
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/// Literal values.
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ConstantValue(&'tcx ty::Const<'tcx>),
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/// Ranges of literal values (`2...5` and `2..5`).
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ConstantRange(&'tcx ty::Const<'tcx>, &'tcx ty::Const<'tcx>, RangeEnd),
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/// Array patterns of length n.
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Slice(u64),
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}
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impl<'tcx> Constructor<'tcx> {
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fn variant_index_for_adt(&self, adt: &'tcx ty::AdtDef) -> usize {
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match self {
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&Variant(vid) => adt.variant_index_with_id(vid),
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&Single => {
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assert!(!adt.is_enum());
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0
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}
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_ => bug!("bad constructor {:?} for adt {:?}", self, adt)
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}
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}
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}
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#[derive(Clone)]
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pub enum Usefulness<'tcx> {
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Useful,
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UsefulWithWitness(Vec<Witness<'tcx>>),
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NotUseful
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}
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impl<'tcx> Usefulness<'tcx> {
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fn is_useful(&self) -> bool {
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match *self {
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NotUseful => false,
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_ => true
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}
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}
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}
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#[derive(Copy, Clone)]
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pub enum WitnessPreference {
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ConstructWitness,
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LeaveOutWitness
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}
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#[derive(Copy, Clone, Debug)]
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struct PatternContext<'tcx> {
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ty: Ty<'tcx>,
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max_slice_length: u64,
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}
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/// A stack of patterns in reverse order of construction
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#[derive(Clone)]
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pub struct Witness<'tcx>(Vec<Pattern<'tcx>>);
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impl<'tcx> Witness<'tcx> {
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pub fn single_pattern(&self) -> &Pattern<'tcx> {
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assert_eq!(self.0.len(), 1);
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&self.0[0]
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}
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fn push_wild_constructor<'a>(
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mut self,
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cx: &MatchCheckCtxt<'a, 'tcx>,
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ctor: &Constructor<'tcx>,
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ty: Ty<'tcx>)
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-> Self
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{
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let sub_pattern_tys = constructor_sub_pattern_tys(cx, ctor, ty);
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self.0.extend(sub_pattern_tys.into_iter().map(|ty| {
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Pattern {
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ty,
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span: DUMMY_SP,
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kind: box PatternKind::Wild,
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}
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}));
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self.apply_constructor(cx, ctor, ty)
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}
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/// Constructs a partial witness for a pattern given a list of
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/// patterns expanded by the specialization step.
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///
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/// When a pattern P is discovered to be useful, this function is used bottom-up
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/// to reconstruct a complete witness, e.g. a pattern P' that covers a subset
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/// of values, V, where each value in that set is not covered by any previously
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/// used patterns and is covered by the pattern P'. Examples:
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///
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/// left_ty: tuple of 3 elements
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/// pats: [10, 20, _] => (10, 20, _)
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///
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/// left_ty: struct X { a: (bool, &'static str), b: usize}
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/// pats: [(false, "foo"), 42] => X { a: (false, "foo"), b: 42 }
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fn apply_constructor<'a>(
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mut self,
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cx: &MatchCheckCtxt<'a,'tcx>,
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ctor: &Constructor<'tcx>,
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ty: Ty<'tcx>)
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-> Self
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{
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let arity = constructor_arity(cx, ctor, ty);
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let pat = {
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let len = self.0.len() as u64;
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let mut pats = self.0.drain((len-arity) as usize..).rev();
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match ty.sty {
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ty::TyAdt(..) |
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ty::TyTuple(..) => {
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let pats = pats.enumerate().map(|(i, p)| {
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FieldPattern {
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field: Field::new(i),
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pattern: p
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}
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}).collect();
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if let ty::TyAdt(adt, substs) = ty.sty {
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if adt.is_enum() {
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PatternKind::Variant {
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adt_def: adt,
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substs,
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variant_index: ctor.variant_index_for_adt(adt),
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subpatterns: pats
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}
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} else {
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PatternKind::Leaf { subpatterns: pats }
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}
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} else {
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PatternKind::Leaf { subpatterns: pats }
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}
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}
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ty::TyRef(..) => {
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PatternKind::Deref { subpattern: pats.nth(0).unwrap() }
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}
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ty::TySlice(_) | ty::TyArray(..) => {
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PatternKind::Slice {
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prefix: pats.collect(),
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slice: None,
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suffix: vec![]
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}
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}
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_ => {
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match *ctor {
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ConstantValue(value) => PatternKind::Constant { value },
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_ => PatternKind::Wild,
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}
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}
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}
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};
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self.0.push(Pattern {
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ty,
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span: DUMMY_SP,
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kind: Box::new(pat),
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});
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self
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}
|
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}
|
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|
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/// This determines the set of all possible constructors of a pattern matching
|
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/// values of type `left_ty`. For vectors, this would normally be an infinite set
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/// but is instead bounded by the maximum fixed length of slice patterns in
|
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/// the column of patterns being analyzed.
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///
|
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/// This intentionally does not list ConstantValue specializations for
|
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/// non-booleans, because we currently assume that there is always a
|
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/// "non-standard constant" that matches. See issue #12483.
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///
|
||
/// We make sure to omit constructors that are statically impossible. eg for
|
||
/// Option<!> we do not include Some(_) in the returned list of constructors.
|
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fn all_constructors<'a, 'tcx: 'a>(cx: &mut MatchCheckCtxt<'a, 'tcx>,
|
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pcx: PatternContext<'tcx>)
|
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-> Vec<Constructor<'tcx>>
|
||
{
|
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debug!("all_constructors({:?})", pcx.ty);
|
||
match pcx.ty.sty {
|
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ty::TyBool => {
|
||
[true, false].iter().map(|&b| {
|
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ConstantValue(cx.tcx.mk_const(ty::Const {
|
||
val: ConstVal::Bool(b),
|
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ty: cx.tcx.types.bool
|
||
}))
|
||
}).collect()
|
||
}
|
||
ty::TyArray(ref sub_ty, len) if len.val.to_const_int().is_some() => {
|
||
let len = len.val.to_const_int().unwrap().to_u64().unwrap();
|
||
if len != 0 && cx.is_uninhabited(sub_ty) {
|
||
vec![]
|
||
} else {
|
||
vec![Slice(len)]
|
||
}
|
||
}
|
||
// Treat arrays of a constant but unknown length like slices.
|
||
ty::TyArray(ref sub_ty, _) |
|
||
ty::TySlice(ref sub_ty) => {
|
||
if cx.is_uninhabited(sub_ty) {
|
||
vec![Slice(0)]
|
||
} else {
|
||
(0..pcx.max_slice_length+1).map(|length| Slice(length)).collect()
|
||
}
|
||
}
|
||
ty::TyAdt(def, substs) if def.is_enum() => {
|
||
def.variants.iter()
|
||
.filter(|v| !cx.is_variant_uninhabited(v, substs))
|
||
.map(|v| Variant(v.did))
|
||
.collect()
|
||
}
|
||
_ => {
|
||
if cx.is_uninhabited(pcx.ty) {
|
||
vec![]
|
||
} else {
|
||
vec![Single]
|
||
}
|
||
}
|
||
}
|
||
}
|
||
|
||
fn max_slice_length<'p, 'a: 'p, 'tcx: 'a, I>(
|
||
_cx: &mut MatchCheckCtxt<'a, 'tcx>,
|
||
patterns: I) -> u64
|
||
where I: Iterator<Item=&'p Pattern<'tcx>>
|
||
{
|
||
// The exhaustiveness-checking paper does not include any details on
|
||
// checking variable-length slice patterns. However, they are matched
|
||
// by an infinite collection of fixed-length array patterns.
|
||
//
|
||
// Checking the infinite set directly would take an infinite amount
|
||
// of time. However, it turns out that for each finite set of
|
||
// patterns `P`, all sufficiently large array lengths are equivalent:
|
||
//
|
||
// Each slice `s` with a "sufficiently-large" length `l ≥ L` that applies
|
||
// to exactly the subset `Pₜ` of `P` can be transformed to a slice
|
||
// `sₘ` for each sufficiently-large length `m` that applies to exactly
|
||
// the same subset of `P`.
|
||
//
|
||
// Because of that, each witness for reachability-checking from one
|
||
// of the sufficiently-large lengths can be transformed to an
|
||
// equally-valid witness from any other length, so we only have
|
||
// to check slice lengths from the "minimal sufficiently-large length"
|
||
// and below.
|
||
//
|
||
// Note that the fact that there is a *single* `sₘ` for each `m`
|
||
// not depending on the specific pattern in `P` is important: if
|
||
// you look at the pair of patterns
|
||
// `[true, ..]`
|
||
// `[.., false]`
|
||
// Then any slice of length ≥1 that matches one of these two
|
||
// patterns can be be trivially turned to a slice of any
|
||
// other length ≥1 that matches them and vice-versa - for
|
||
// but the slice from length 2 `[false, true]` that matches neither
|
||
// of these patterns can't be turned to a slice from length 1 that
|
||
// matches neither of these patterns, so we have to consider
|
||
// slices from length 2 there.
|
||
//
|
||
// Now, to see that that length exists and find it, observe that slice
|
||
// patterns are either "fixed-length" patterns (`[_, _, _]`) or
|
||
// "variable-length" patterns (`[_, .., _]`).
|
||
//
|
||
// For fixed-length patterns, all slices with lengths *longer* than
|
||
// the pattern's length have the same outcome (of not matching), so
|
||
// as long as `L` is greater than the pattern's length we can pick
|
||
// any `sₘ` from that length and get the same result.
|
||
//
|
||
// For variable-length patterns, the situation is more complicated,
|
||
// because as seen above the precise value of `sₘ` matters.
|
||
//
|
||
// However, for each variable-length pattern `p` with a prefix of length
|
||
// `plₚ` and suffix of length `slₚ`, only the first `plₚ` and the last
|
||
// `slₚ` elements are examined.
|
||
//
|
||
// Therefore, as long as `L` is positive (to avoid concerns about empty
|
||
// types), all elements after the maximum prefix length and before
|
||
// the maximum suffix length are not examined by any variable-length
|
||
// pattern, and therefore can be added/removed without affecting
|
||
// them - creating equivalent patterns from any sufficiently-large
|
||
// length.
|
||
//
|
||
// Of course, if fixed-length patterns exist, we must be sure
|
||
// that our length is large enough to miss them all, so
|
||
// we can pick `L = max(FIXED_LEN+1 ∪ {max(PREFIX_LEN) + max(SUFFIX_LEN)})`
|
||
//
|
||
// for example, with the above pair of patterns, all elements
|
||
// but the first and last can be added/removed, so any
|
||
// witness of length ≥2 (say, `[false, false, true]`) can be
|
||
// turned to a witness from any other length ≥2.
|
||
|
||
let mut max_prefix_len = 0;
|
||
let mut max_suffix_len = 0;
|
||
let mut max_fixed_len = 0;
|
||
|
||
for row in patterns {
|
||
match *row.kind {
|
||
PatternKind::Constant { value: &ty::Const { val: ConstVal::ByteStr(b), .. } } => {
|
||
max_fixed_len = cmp::max(max_fixed_len, b.data.len() as u64);
|
||
}
|
||
PatternKind::Slice { ref prefix, slice: None, ref suffix } => {
|
||
let fixed_len = prefix.len() as u64 + suffix.len() as u64;
|
||
max_fixed_len = cmp::max(max_fixed_len, fixed_len);
|
||
}
|
||
PatternKind::Slice { ref prefix, slice: Some(_), ref suffix } => {
|
||
max_prefix_len = cmp::max(max_prefix_len, prefix.len() as u64);
|
||
max_suffix_len = cmp::max(max_suffix_len, suffix.len() as u64);
|
||
}
|
||
_ => {}
|
||
}
|
||
}
|
||
|
||
cmp::max(max_fixed_len + 1, max_prefix_len + max_suffix_len)
|
||
}
|
||
|
||
/// Algorithm from http://moscova.inria.fr/~maranget/papers/warn/index.html
|
||
/// The algorithm from the paper has been modified to correctly handle empty
|
||
/// types. The changes are:
|
||
/// (0) We don't exit early if the pattern matrix has zero rows. We just
|
||
/// continue to recurse over columns.
|
||
/// (1) all_constructors will only return constructors that are statically
|
||
/// possible. eg. it will only return Ok for Result<T, !>
|
||
///
|
||
/// This finds whether a (row) vector `v` of patterns is 'useful' in relation
|
||
/// to a set of such vectors `m` - this is defined as there being a set of
|
||
/// inputs that will match `v` but not any of the sets in `m`.
|
||
///
|
||
/// All the patterns at each column of the `matrix ++ v` matrix must
|
||
/// have the same type, except that wildcard (PatternKind::Wild) patterns
|
||
/// with type TyErr are also allowed, even if the "type of the column"
|
||
/// is not TyErr. That is used to represent private fields, as using their
|
||
/// real type would assert that they are inhabited.
|
||
///
|
||
/// This is used both for reachability checking (if a pattern isn't useful in
|
||
/// relation to preceding patterns, it is not reachable) and exhaustiveness
|
||
/// checking (if a wildcard pattern is useful in relation to a matrix, the
|
||
/// matrix isn't exhaustive).
|
||
pub fn is_useful<'p, 'a: 'p, 'tcx: 'a>(cx: &mut MatchCheckCtxt<'a, 'tcx>,
|
||
matrix: &Matrix<'p, 'tcx>,
|
||
v: &[&'p Pattern<'tcx>],
|
||
witness: WitnessPreference)
|
||
-> Usefulness<'tcx> {
|
||
let &Matrix(ref rows) = matrix;
|
||
debug!("is_useful({:?}, {:?})", matrix, v);
|
||
|
||
// The base case. We are pattern-matching on () and the return value is
|
||
// based on whether our matrix has a row or not.
|
||
// NOTE: This could potentially be optimized by checking rows.is_empty()
|
||
// first and then, if v is non-empty, the return value is based on whether
|
||
// the type of the tuple we're checking is inhabited or not.
|
||
if v.is_empty() {
|
||
return if rows.is_empty() {
|
||
match witness {
|
||
ConstructWitness => UsefulWithWitness(vec![Witness(vec![])]),
|
||
LeaveOutWitness => Useful,
|
||
}
|
||
} else {
|
||
NotUseful
|
||
}
|
||
};
|
||
|
||
assert!(rows.iter().all(|r| r.len() == v.len()));
|
||
|
||
let pcx = PatternContext {
|
||
// TyErr is used to represent the type of wildcard patterns matching
|
||
// against inaccessible (private) fields of structs, so that we won't
|
||
// be able to observe whether the types of the struct's fields are
|
||
// inhabited.
|
||
//
|
||
// If the field is truely inaccessible, then all the patterns
|
||
// matching against it must be wildcard patterns, so its type
|
||
// does not matter.
|
||
//
|
||
// However, if we are matching against non-wildcard patterns, we
|
||
// need to know the real type of the field so we can specialize
|
||
// against it. This primarily occurs through constants - they
|
||
// can include contents for fields that are inaccessible at the
|
||
// location of the match. In that case, the field's type is
|
||
// inhabited - by the constant - so we can just use it.
|
||
//
|
||
// FIXME: this might lead to "unstable" behavior with macro hygiene
|
||
// introducing uninhabited patterns for inaccessible fields. We
|
||
// need to figure out how to model that.
|
||
ty: rows.iter().map(|r| r[0].ty).find(|ty| !ty.references_error())
|
||
.unwrap_or(v[0].ty),
|
||
max_slice_length: max_slice_length(cx, rows.iter().map(|r| r[0]).chain(Some(v[0])))
|
||
};
|
||
|
||
debug!("is_useful_expand_first_col: pcx={:?}, expanding {:?}", pcx, v[0]);
|
||
|
||
if let Some(constructors) = pat_constructors(cx, v[0], pcx) {
|
||
debug!("is_useful - expanding constructors: {:?}", constructors);
|
||
constructors.into_iter().map(|c|
|
||
is_useful_specialized(cx, matrix, v, c.clone(), pcx.ty, witness)
|
||
).find(|result| result.is_useful()).unwrap_or(NotUseful)
|
||
} else {
|
||
debug!("is_useful - expanding wildcard");
|
||
|
||
let used_ctors: Vec<Constructor> = rows.iter().flat_map(|row| {
|
||
pat_constructors(cx, row[0], pcx).unwrap_or(vec![])
|
||
}).collect();
|
||
debug!("used_ctors = {:?}", used_ctors);
|
||
let all_ctors = all_constructors(cx, pcx);
|
||
debug!("all_ctors = {:?}", all_ctors);
|
||
let missing_ctors: Vec<Constructor> = all_ctors.iter().filter(|c| {
|
||
!used_ctors.contains(*c)
|
||
}).cloned().collect();
|
||
|
||
// `missing_ctors` is the set of constructors from the same type as the
|
||
// first column of `matrix` that are matched only by wildcard patterns
|
||
// from the first column.
|
||
//
|
||
// Therefore, if there is some pattern that is unmatched by `matrix`,
|
||
// it will still be unmatched if the first constructor is replaced by
|
||
// any of the constructors in `missing_ctors`
|
||
//
|
||
// However, if our scrutinee is *privately* an empty enum, we
|
||
// must treat it as though it had an "unknown" constructor (in
|
||
// that case, all other patterns obviously can't be variants)
|
||
// to avoid exposing its emptyness. See the `match_privately_empty`
|
||
// test for details.
|
||
//
|
||
// FIXME: currently the only way I know of something can
|
||
// be a privately-empty enum is when the never_type
|
||
// feature flag is not present, so this is only
|
||
// needed for that case.
|
||
|
||
let is_privately_empty =
|
||
all_ctors.is_empty() && !cx.is_uninhabited(pcx.ty);
|
||
let is_declared_nonexhaustive =
|
||
cx.is_non_exhaustive_enum(pcx.ty) && !cx.is_local(pcx.ty);
|
||
debug!("missing_ctors={:?} is_privately_empty={:?} is_declared_nonexhaustive={:?}",
|
||
missing_ctors, is_privately_empty, is_declared_nonexhaustive);
|
||
|
||
// For privately empty and non-exhaustive enums, we work as if there were an "extra"
|
||
// `_` constructor for the type, so we can never match over all constructors.
|
||
let is_non_exhaustive = is_privately_empty || is_declared_nonexhaustive;
|
||
|
||
if missing_ctors.is_empty() && !is_non_exhaustive {
|
||
all_ctors.into_iter().map(|c| {
|
||
is_useful_specialized(cx, matrix, v, c.clone(), pcx.ty, witness)
|
||
}).find(|result| result.is_useful()).unwrap_or(NotUseful)
|
||
} else {
|
||
let matrix = rows.iter().filter_map(|r| {
|
||
if r[0].is_wildcard() {
|
||
Some(r[1..].to_vec())
|
||
} else {
|
||
None
|
||
}
|
||
}).collect();
|
||
match is_useful(cx, &matrix, &v[1..], witness) {
|
||
UsefulWithWitness(pats) => {
|
||
let cx = &*cx;
|
||
// In this case, there's at least one "free"
|
||
// constructor that is only matched against by
|
||
// wildcard patterns.
|
||
//
|
||
// There are 2 ways we can report a witness here.
|
||
// Commonly, we can report all the "free"
|
||
// constructors as witnesses, e.g. if we have:
|
||
//
|
||
// ```
|
||
// enum Direction { N, S, E, W }
|
||
// let Direction::N = ...;
|
||
// ```
|
||
//
|
||
// we can report 3 witnesses: `S`, `E`, and `W`.
|
||
//
|
||
// However, there are 2 cases where we don't want
|
||
// to do this and instead report a single `_` witness:
|
||
//
|
||
// 1) If the user is matching against a non-exhaustive
|
||
// enum, there is no point in enumerating all possible
|
||
// variants, because the user can't actually match
|
||
// against them himself, e.g. in an example like:
|
||
// ```
|
||
// let err: io::ErrorKind = ...;
|
||
// match err {
|
||
// io::ErrorKind::NotFound => {},
|
||
// }
|
||
// ```
|
||
// we don't want to show every possible IO error,
|
||
// but instead have `_` as the witness (this is
|
||
// actually *required* if the user specified *all*
|
||
// IO errors, but is probably what we want in every
|
||
// case).
|
||
//
|
||
// 2) If the user didn't actually specify a constructor
|
||
// in this arm, e.g. in
|
||
// ```
|
||
// let x: (Direction, Direction, bool) = ...;
|
||
// let (_, _, false) = x;
|
||
// ```
|
||
// we don't want to show all 16 possible witnesses
|
||
// `(<direction-1>, <direction-2>, true)` - we are
|
||
// satisfied with `(_, _, true)`. In this case,
|
||
// `used_ctors` is empty.
|
||
let new_witnesses = if is_non_exhaustive || used_ctors.is_empty() {
|
||
// All constructors are unused. Add wild patterns
|
||
// rather than each individual constructor
|
||
pats.into_iter().map(|mut witness| {
|
||
witness.0.push(Pattern {
|
||
ty: pcx.ty,
|
||
span: DUMMY_SP,
|
||
kind: box PatternKind::Wild,
|
||
});
|
||
witness
|
||
}).collect()
|
||
} else {
|
||
pats.into_iter().flat_map(|witness| {
|
||
missing_ctors.iter().map(move |ctor| {
|
||
witness.clone().push_wild_constructor(cx, ctor, pcx.ty)
|
||
})
|
||
}).collect()
|
||
};
|
||
UsefulWithWitness(new_witnesses)
|
||
}
|
||
result => result
|
||
}
|
||
}
|
||
}
|
||
}
|
||
|
||
fn is_useful_specialized<'p, 'a:'p, 'tcx: 'a>(
|
||
cx: &mut MatchCheckCtxt<'a, 'tcx>,
|
||
&Matrix(ref m): &Matrix<'p, 'tcx>,
|
||
v: &[&'p Pattern<'tcx>],
|
||
ctor: Constructor<'tcx>,
|
||
lty: Ty<'tcx>,
|
||
witness: WitnessPreference) -> Usefulness<'tcx>
|
||
{
|
||
debug!("is_useful_specialized({:?}, {:?}, {:?})", v, ctor, lty);
|
||
let sub_pat_tys = constructor_sub_pattern_tys(cx, &ctor, lty);
|
||
let wild_patterns_owned: Vec<_> = sub_pat_tys.iter().map(|ty| {
|
||
Pattern {
|
||
ty,
|
||
span: DUMMY_SP,
|
||
kind: box PatternKind::Wild,
|
||
}
|
||
}).collect();
|
||
let wild_patterns: Vec<_> = wild_patterns_owned.iter().collect();
|
||
let matrix = Matrix(m.iter().flat_map(|r| {
|
||
specialize(cx, &r, &ctor, &wild_patterns)
|
||
}).collect());
|
||
match specialize(cx, v, &ctor, &wild_patterns) {
|
||
Some(v) => match is_useful(cx, &matrix, &v, witness) {
|
||
UsefulWithWitness(witnesses) => UsefulWithWitness(
|
||
witnesses.into_iter()
|
||
.map(|witness| witness.apply_constructor(cx, &ctor, lty))
|
||
.collect()
|
||
),
|
||
result => result
|
||
},
|
||
None => NotUseful
|
||
}
|
||
}
|
||
|
||
/// Determines the constructors that the given pattern can be specialized to.
|
||
///
|
||
/// In most cases, there's only one constructor that a specific pattern
|
||
/// represents, such as a specific enum variant or a specific literal value.
|
||
/// Slice patterns, however, can match slices of different lengths. For instance,
|
||
/// `[a, b, ..tail]` can match a slice of length 2, 3, 4 and so on.
|
||
///
|
||
/// Returns None in case of a catch-all, which can't be specialized.
|
||
fn pat_constructors<'tcx>(_cx: &mut MatchCheckCtxt,
|
||
pat: &Pattern<'tcx>,
|
||
pcx: PatternContext)
|
||
-> Option<Vec<Constructor<'tcx>>>
|
||
{
|
||
match *pat.kind {
|
||
PatternKind::Binding { .. } | PatternKind::Wild =>
|
||
None,
|
||
PatternKind::Leaf { .. } | PatternKind::Deref { .. } =>
|
||
Some(vec![Single]),
|
||
PatternKind::Variant { adt_def, variant_index, .. } =>
|
||
Some(vec![Variant(adt_def.variants[variant_index].did)]),
|
||
PatternKind::Constant { value } =>
|
||
Some(vec![ConstantValue(value)]),
|
||
PatternKind::Range { lo, hi, end } =>
|
||
Some(vec![ConstantRange(lo, hi, end)]),
|
||
PatternKind::Array { .. } => match pcx.ty.sty {
|
||
ty::TyArray(_, length) => Some(vec![
|
||
Slice(length.val.to_const_int().unwrap().to_u64().unwrap())
|
||
]),
|
||
_ => span_bug!(pat.span, "bad ty {:?} for array pattern", pcx.ty)
|
||
},
|
||
PatternKind::Slice { ref prefix, ref slice, ref suffix } => {
|
||
let pat_len = prefix.len() as u64 + suffix.len() as u64;
|
||
if slice.is_some() {
|
||
Some((pat_len..pcx.max_slice_length+1).map(Slice).collect())
|
||
} else {
|
||
Some(vec![Slice(pat_len)])
|
||
}
|
||
}
|
||
}
|
||
}
|
||
|
||
/// This computes the arity of a constructor. The arity of a constructor
|
||
/// is how many subpattern patterns of that constructor should be expanded to.
|
||
///
|
||
/// For instance, a tuple pattern (_, 42, Some([])) has the arity of 3.
|
||
/// A struct pattern's arity is the number of fields it contains, etc.
|
||
fn constructor_arity(_cx: &MatchCheckCtxt, ctor: &Constructor, ty: Ty) -> u64 {
|
||
debug!("constructor_arity({:?}, {:?})", ctor, ty);
|
||
match ty.sty {
|
||
ty::TyTuple(ref fs, _) => fs.len() as u64,
|
||
ty::TySlice(..) | ty::TyArray(..) => match *ctor {
|
||
Slice(length) => length,
|
||
ConstantValue(_) => 0,
|
||
_ => bug!("bad slice pattern {:?} {:?}", ctor, ty)
|
||
},
|
||
ty::TyRef(..) => 1,
|
||
ty::TyAdt(adt, _) => {
|
||
adt.variants[ctor.variant_index_for_adt(adt)].fields.len() as u64
|
||
}
|
||
_ => 0
|
||
}
|
||
}
|
||
|
||
/// This computes the types of the sub patterns that a constructor should be
|
||
/// expanded to.
|
||
///
|
||
/// For instance, a tuple pattern (43u32, 'a') has sub pattern types [u32, char].
|
||
fn constructor_sub_pattern_tys<'a, 'tcx: 'a>(cx: &MatchCheckCtxt<'a, 'tcx>,
|
||
ctor: &Constructor,
|
||
ty: Ty<'tcx>) -> Vec<Ty<'tcx>>
|
||
{
|
||
debug!("constructor_sub_pattern_tys({:?}, {:?})", ctor, ty);
|
||
match ty.sty {
|
||
ty::TyTuple(ref fs, _) => fs.into_iter().map(|t| *t).collect(),
|
||
ty::TySlice(ty) | ty::TyArray(ty, _) => match *ctor {
|
||
Slice(length) => (0..length).map(|_| ty).collect(),
|
||
ConstantValue(_) => vec![],
|
||
_ => bug!("bad slice pattern {:?} {:?}", ctor, ty)
|
||
},
|
||
ty::TyRef(_, ref ty_and_mut) => vec![ty_and_mut.ty],
|
||
ty::TyAdt(adt, substs) => {
|
||
if adt.is_box() {
|
||
// Use T as the sub pattern type of Box<T>.
|
||
vec![substs[0].as_type().unwrap()]
|
||
} else {
|
||
adt.variants[ctor.variant_index_for_adt(adt)].fields.iter().map(|field| {
|
||
let is_visible = adt.is_enum()
|
||
|| field.vis.is_accessible_from(cx.module, cx.tcx);
|
||
if is_visible {
|
||
field.ty(cx.tcx, substs)
|
||
} else {
|
||
// Treat all non-visible fields as TyErr. They
|
||
// can't appear in any other pattern from
|
||
// this match (because they are private),
|
||
// so their type does not matter - but
|
||
// we don't want to know they are
|
||
// uninhabited.
|
||
cx.tcx.types.err
|
||
}
|
||
}).collect()
|
||
}
|
||
}
|
||
_ => vec![],
|
||
}
|
||
}
|
||
|
||
fn slice_pat_covered_by_constructor(_tcx: TyCtxt, _span: Span,
|
||
ctor: &Constructor,
|
||
prefix: &[Pattern],
|
||
slice: &Option<Pattern>,
|
||
suffix: &[Pattern])
|
||
-> Result<bool, ErrorReported> {
|
||
let data = match *ctor {
|
||
ConstantValue(&ty::Const { val: ConstVal::ByteStr(b), .. }) => b.data,
|
||
_ => bug!()
|
||
};
|
||
|
||
let pat_len = prefix.len() + suffix.len();
|
||
if data.len() < pat_len || (slice.is_none() && data.len() > pat_len) {
|
||
return Ok(false);
|
||
}
|
||
|
||
for (ch, pat) in
|
||
data[..prefix.len()].iter().zip(prefix).chain(
|
||
data[data.len()-suffix.len()..].iter().zip(suffix))
|
||
{
|
||
match pat.kind {
|
||
box PatternKind::Constant { value } => match value.val {
|
||
ConstVal::Integral(ConstInt::U8(u)) => {
|
||
if u != *ch {
|
||
return Ok(false);
|
||
}
|
||
},
|
||
_ => span_bug!(pat.span, "bad const u8 {:?}", value)
|
||
},
|
||
_ => {}
|
||
}
|
||
}
|
||
|
||
Ok(true)
|
||
}
|
||
|
||
fn constructor_covered_by_range(tcx: TyCtxt, span: Span,
|
||
ctor: &Constructor,
|
||
from: &ConstVal, to: &ConstVal,
|
||
end: RangeEnd)
|
||
-> Result<bool, ErrorReported> {
|
||
let cmp_from = |c_from| Ok(compare_const_vals(tcx, span, c_from, from)? != Ordering::Less);
|
||
let cmp_to = |c_to| compare_const_vals(tcx, span, c_to, to);
|
||
match *ctor {
|
||
ConstantValue(value) => {
|
||
let to = cmp_to(&value.val)?;
|
||
let end = (to == Ordering::Less) ||
|
||
(end == RangeEnd::Included && to == Ordering::Equal);
|
||
Ok(cmp_from(&value.val)? && end)
|
||
},
|
||
ConstantRange(from, to, RangeEnd::Included) => {
|
||
let to = cmp_to(&to.val)?;
|
||
let end = (to == Ordering::Less) ||
|
||
(end == RangeEnd::Included && to == Ordering::Equal);
|
||
Ok(cmp_from(&from.val)? && end)
|
||
},
|
||
ConstantRange(from, to, RangeEnd::Excluded) => {
|
||
let to = cmp_to(&to.val)?;
|
||
let end = (to == Ordering::Less) ||
|
||
(end == RangeEnd::Excluded && to == Ordering::Equal);
|
||
Ok(cmp_from(&from.val)? && end)
|
||
}
|
||
Single => Ok(true),
|
||
_ => bug!(),
|
||
}
|
||
}
|
||
|
||
fn patterns_for_variant<'p, 'a: 'p, 'tcx: 'a>(
|
||
subpatterns: &'p [FieldPattern<'tcx>],
|
||
wild_patterns: &[&'p Pattern<'tcx>])
|
||
-> Vec<&'p Pattern<'tcx>>
|
||
{
|
||
let mut result = wild_patterns.to_owned();
|
||
|
||
for subpat in subpatterns {
|
||
result[subpat.field.index()] = &subpat.pattern;
|
||
}
|
||
|
||
debug!("patterns_for_variant({:?}, {:?}) = {:?}", subpatterns, wild_patterns, result);
|
||
result
|
||
}
|
||
|
||
/// This is the main specialization step. It expands the first pattern in the given row
|
||
/// into `arity` patterns based on the constructor. For most patterns, the step is trivial,
|
||
/// for instance tuple patterns are flattened and box patterns expand into their inner pattern.
|
||
///
|
||
/// OTOH, slice patterns with a subslice pattern (..tail) can be expanded into multiple
|
||
/// different patterns.
|
||
/// Structure patterns with a partial wild pattern (Foo { a: 42, .. }) have their missing
|
||
/// fields filled with wild patterns.
|
||
fn specialize<'p, 'a: 'p, 'tcx: 'a>(
|
||
cx: &mut MatchCheckCtxt<'a, 'tcx>,
|
||
r: &[&'p Pattern<'tcx>],
|
||
constructor: &Constructor,
|
||
wild_patterns: &[&'p Pattern<'tcx>])
|
||
-> Option<Vec<&'p Pattern<'tcx>>>
|
||
{
|
||
let pat = &r[0];
|
||
|
||
let head: Option<Vec<&Pattern>> = match *pat.kind {
|
||
PatternKind::Binding { .. } | PatternKind::Wild => {
|
||
Some(wild_patterns.to_owned())
|
||
},
|
||
|
||
PatternKind::Variant { adt_def, variant_index, ref subpatterns, .. } => {
|
||
let ref variant = adt_def.variants[variant_index];
|
||
if *constructor == Variant(variant.did) {
|
||
Some(patterns_for_variant(subpatterns, wild_patterns))
|
||
} else {
|
||
None
|
||
}
|
||
}
|
||
|
||
PatternKind::Leaf { ref subpatterns } => {
|
||
Some(patterns_for_variant(subpatterns, wild_patterns))
|
||
}
|
||
PatternKind::Deref { ref subpattern } => {
|
||
Some(vec![subpattern])
|
||
}
|
||
|
||
PatternKind::Constant { value } => {
|
||
match *constructor {
|
||
Slice(..) => match value.val {
|
||
ConstVal::ByteStr(b) => {
|
||
if wild_patterns.len() == b.data.len() {
|
||
Some(cx.lower_byte_str_pattern(pat))
|
||
} else {
|
||
None
|
||
}
|
||
}
|
||
_ => span_bug!(pat.span,
|
||
"unexpected const-val {:?} with ctor {:?}", value, constructor)
|
||
},
|
||
_ => {
|
||
match constructor_covered_by_range(
|
||
cx.tcx, pat.span, constructor, &value.val, &value.val, RangeEnd::Included
|
||
) {
|
||
Ok(true) => Some(vec![]),
|
||
Ok(false) => None,
|
||
Err(ErrorReported) => None,
|
||
}
|
||
}
|
||
}
|
||
}
|
||
|
||
PatternKind::Range { lo, hi, ref end } => {
|
||
match constructor_covered_by_range(
|
||
cx.tcx, pat.span, constructor, &lo.val, &hi.val, end.clone()
|
||
) {
|
||
Ok(true) => Some(vec![]),
|
||
Ok(false) => None,
|
||
Err(ErrorReported) => None,
|
||
}
|
||
}
|
||
|
||
PatternKind::Array { ref prefix, ref slice, ref suffix } |
|
||
PatternKind::Slice { ref prefix, ref slice, ref suffix } => {
|
||
match *constructor {
|
||
Slice(..) => {
|
||
let pat_len = prefix.len() + suffix.len();
|
||
if let Some(slice_count) = wild_patterns.len().checked_sub(pat_len) {
|
||
if slice_count == 0 || slice.is_some() {
|
||
Some(
|
||
prefix.iter().chain(
|
||
wild_patterns.iter().map(|p| *p)
|
||
.skip(prefix.len())
|
||
.take(slice_count)
|
||
.chain(
|
||
suffix.iter()
|
||
)).collect())
|
||
} else {
|
||
None
|
||
}
|
||
} else {
|
||
None
|
||
}
|
||
}
|
||
ConstantValue(..) => {
|
||
match slice_pat_covered_by_constructor(
|
||
cx.tcx, pat.span, constructor, prefix, slice, suffix
|
||
) {
|
||
Ok(true) => Some(vec![]),
|
||
Ok(false) => None,
|
||
Err(ErrorReported) => None
|
||
}
|
||
}
|
||
_ => span_bug!(pat.span,
|
||
"unexpected ctor {:?} for slice pat", constructor)
|
||
}
|
||
}
|
||
};
|
||
debug!("specialize({:?}, {:?}) = {:?}", r[0], wild_patterns, head);
|
||
|
||
head.map(|mut head| {
|
||
head.extend_from_slice(&r[1 ..]);
|
||
head
|
||
})
|
||
}
|