9270a9217a
This avoids 4% of malloc calls when compiling rustc-benchmarks/issue-32278-big-array-of-strings, and 1--2% for other benchmarks. A small win, but an easy one.
407 lines
15 KiB
Rust
407 lines
15 KiB
Rust
// Copyright 2012 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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///////////////////////////////////////////////////////////////////////////
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// # Type combining
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//
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// There are four type combiners: equate, sub, lub, and glb. Each
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// implements the trait `Combine` and contains methods for combining
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// two instances of various things and yielding a new instance. These
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// combiner methods always yield a `Result<T>`. There is a lot of
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// common code for these operations, implemented as default methods on
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// the `Combine` trait.
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//
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// Each operation may have side-effects on the inference context,
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// though these can be unrolled using snapshots. On success, the
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// LUB/GLB operations return the appropriate bound. The Eq and Sub
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// operations generally return the first operand.
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//
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// ## Contravariance
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//
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// When you are relating two things which have a contravariant
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// relationship, you should use `contratys()` or `contraregions()`,
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// rather than inversing the order of arguments! This is necessary
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// because the order of arguments is not relevant for LUB and GLB. It
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// is also useful to track which value is the "expected" value in
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// terms of error reporting.
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use super::bivariate::Bivariate;
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use super::equate::Equate;
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use super::glb::Glb;
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use super::lub::Lub;
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use super::sub::Sub;
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use super::InferCtxt;
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use super::{MiscVariable, TypeTrace};
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use super::type_variable::{RelationDir, BiTo, EqTo, SubtypeOf, SupertypeOf};
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use ty::{IntType, UintType};
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use ty::{self, Ty, TyCtxt};
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use ty::error::TypeError;
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use ty::fold::TypeFoldable;
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use ty::relate::{RelateResult, TypeRelation};
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use traits::PredicateObligations;
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use syntax::ast;
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use syntax::util::small_vector::SmallVector;
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use syntax_pos::Span;
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#[derive(Clone)]
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pub struct CombineFields<'infcx, 'gcx: 'infcx+'tcx, 'tcx: 'infcx> {
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pub infcx: &'infcx InferCtxt<'infcx, 'gcx, 'tcx>,
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pub trace: TypeTrace<'tcx>,
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pub cause: Option<ty::relate::Cause>,
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pub obligations: PredicateObligations<'tcx>,
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}
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impl<'infcx, 'gcx, 'tcx> InferCtxt<'infcx, 'gcx, 'tcx> {
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pub fn super_combine_tys<R>(&self,
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relation: &mut R,
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a: Ty<'tcx>,
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b: Ty<'tcx>)
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-> RelateResult<'tcx, Ty<'tcx>>
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where R: TypeRelation<'infcx, 'gcx, 'tcx>
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{
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let a_is_expected = relation.a_is_expected();
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match (&a.sty, &b.sty) {
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// Relate integral variables to other types
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(&ty::TyInfer(ty::IntVar(a_id)), &ty::TyInfer(ty::IntVar(b_id))) => {
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self.int_unification_table
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.borrow_mut()
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.unify_var_var(a_id, b_id)
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.map_err(|e| int_unification_error(a_is_expected, e))?;
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Ok(a)
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}
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(&ty::TyInfer(ty::IntVar(v_id)), &ty::TyInt(v)) => {
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self.unify_integral_variable(a_is_expected, v_id, IntType(v))
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}
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(&ty::TyInt(v), &ty::TyInfer(ty::IntVar(v_id))) => {
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self.unify_integral_variable(!a_is_expected, v_id, IntType(v))
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}
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(&ty::TyInfer(ty::IntVar(v_id)), &ty::TyUint(v)) => {
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self.unify_integral_variable(a_is_expected, v_id, UintType(v))
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}
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(&ty::TyUint(v), &ty::TyInfer(ty::IntVar(v_id))) => {
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self.unify_integral_variable(!a_is_expected, v_id, UintType(v))
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}
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// Relate floating-point variables to other types
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(&ty::TyInfer(ty::FloatVar(a_id)), &ty::TyInfer(ty::FloatVar(b_id))) => {
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self.float_unification_table
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.borrow_mut()
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.unify_var_var(a_id, b_id)
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.map_err(|e| float_unification_error(relation.a_is_expected(), e))?;
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Ok(a)
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}
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(&ty::TyInfer(ty::FloatVar(v_id)), &ty::TyFloat(v)) => {
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self.unify_float_variable(a_is_expected, v_id, v)
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}
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(&ty::TyFloat(v), &ty::TyInfer(ty::FloatVar(v_id))) => {
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self.unify_float_variable(!a_is_expected, v_id, v)
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}
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// All other cases of inference are errors
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(&ty::TyInfer(_), _) |
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(_, &ty::TyInfer(_)) => {
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Err(TypeError::Sorts(ty::relate::expected_found(relation, &a, &b)))
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}
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_ => {
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ty::relate::super_relate_tys(relation, a, b)
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}
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}
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}
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fn unify_integral_variable(&self,
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vid_is_expected: bool,
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vid: ty::IntVid,
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val: ty::IntVarValue)
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-> RelateResult<'tcx, Ty<'tcx>>
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{
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self.int_unification_table
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.borrow_mut()
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.unify_var_value(vid, val)
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.map_err(|e| int_unification_error(vid_is_expected, e))?;
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match val {
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IntType(v) => Ok(self.tcx.mk_mach_int(v)),
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UintType(v) => Ok(self.tcx.mk_mach_uint(v)),
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}
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}
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fn unify_float_variable(&self,
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vid_is_expected: bool,
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vid: ty::FloatVid,
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val: ast::FloatTy)
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-> RelateResult<'tcx, Ty<'tcx>>
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{
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self.float_unification_table
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.borrow_mut()
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.unify_var_value(vid, val)
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.map_err(|e| float_unification_error(vid_is_expected, e))?;
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Ok(self.tcx.mk_mach_float(val))
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}
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}
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impl<'infcx, 'gcx, 'tcx> CombineFields<'infcx, 'gcx, 'tcx> {
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pub fn tcx(&self) -> TyCtxt<'infcx, 'gcx, 'tcx> {
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self.infcx.tcx
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}
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pub fn equate<'a>(&'a mut self, a_is_expected: bool) -> Equate<'a, 'infcx, 'gcx, 'tcx> {
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Equate::new(self, a_is_expected)
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}
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pub fn bivariate<'a>(&'a mut self, a_is_expected: bool) -> Bivariate<'a, 'infcx, 'gcx, 'tcx> {
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Bivariate::new(self, a_is_expected)
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}
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pub fn sub<'a>(&'a mut self, a_is_expected: bool) -> Sub<'a, 'infcx, 'gcx, 'tcx> {
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Sub::new(self, a_is_expected)
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}
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pub fn lub<'a>(&'a mut self, a_is_expected: bool) -> Lub<'a, 'infcx, 'gcx, 'tcx> {
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Lub::new(self, a_is_expected)
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}
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pub fn glb<'a>(&'a mut self, a_is_expected: bool) -> Glb<'a, 'infcx, 'gcx, 'tcx> {
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Glb::new(self, a_is_expected)
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}
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pub fn instantiate(&mut self,
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a_ty: Ty<'tcx>,
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dir: RelationDir,
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b_vid: ty::TyVid,
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a_is_expected: bool)
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-> RelateResult<'tcx, ()>
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{
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// We use SmallVector here instead of Vec because this code is hot and
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// it's rare that the stack length exceeds 1.
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let mut stack = SmallVector::zero();
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stack.push((a_ty, dir, b_vid));
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loop {
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// For each turn of the loop, we extract a tuple
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//
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// (a_ty, dir, b_vid)
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//
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// to relate. Here dir is either SubtypeOf or
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// SupertypeOf. The idea is that we should ensure that
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// the type `a_ty` is a subtype or supertype (respectively) of the
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// type to which `b_vid` is bound.
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//
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// If `b_vid` has not yet been instantiated with a type
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// (which is always true on the first iteration, but not
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// necessarily true on later iterations), we will first
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// instantiate `b_vid` with a *generalized* version of
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// `a_ty`. Generalization introduces other inference
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// variables wherever subtyping could occur (at time of
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// this writing, this means replacing free regions with
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// region variables).
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let (a_ty, dir, b_vid) = match stack.pop() {
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None => break,
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Some(e) => e,
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};
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// Get the actual variable that b_vid has been inferred to
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let (b_vid, b_ty) = {
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let mut variables = self.infcx.type_variables.borrow_mut();
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let b_vid = variables.root_var(b_vid);
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(b_vid, variables.probe_root(b_vid))
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};
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debug!("instantiate(a_ty={:?} dir={:?} b_vid={:?})",
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a_ty,
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dir,
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b_vid);
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// Check whether `vid` has been instantiated yet. If not,
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// make a generalized form of `ty` and instantiate with
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// that.
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let b_ty = match b_ty {
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Some(t) => t, // ...already instantiated.
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None => { // ...not yet instantiated:
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// Generalize type if necessary.
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let generalized_ty = match dir {
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EqTo => self.generalize(a_ty, b_vid, false),
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BiTo | SupertypeOf | SubtypeOf => self.generalize(a_ty, b_vid, true),
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}?;
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debug!("instantiate(a_ty={:?}, dir={:?}, \
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b_vid={:?}, generalized_ty={:?})",
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a_ty, dir, b_vid,
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generalized_ty);
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self.infcx.type_variables
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.borrow_mut()
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.instantiate_and_push(
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b_vid, generalized_ty, &mut stack);
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generalized_ty
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}
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};
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// The original triple was `(a_ty, dir, b_vid)` -- now we have
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// resolved `b_vid` to `b_ty`, so apply `(a_ty, dir, b_ty)`:
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//
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// FIXME(#16847): This code is non-ideal because all these subtype
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// relations wind up attributed to the same spans. We need
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// to associate causes/spans with each of the relations in
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// the stack to get this right.
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match dir {
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BiTo => self.bivariate(a_is_expected).relate(&a_ty, &b_ty),
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EqTo => self.equate(a_is_expected).relate(&a_ty, &b_ty),
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SubtypeOf => self.sub(a_is_expected).relate(&a_ty, &b_ty),
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SupertypeOf => self.sub(a_is_expected).relate_with_variance(
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ty::Contravariant, &a_ty, &b_ty),
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}?;
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}
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Ok(())
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}
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/// Attempts to generalize `ty` for the type variable `for_vid`. This checks for cycle -- that
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/// is, whether the type `ty` references `for_vid`. If `make_region_vars` is true, it will also
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/// replace all regions with fresh variables. Returns `TyError` in the case of a cycle, `Ok`
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/// otherwise.
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fn generalize(&self,
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ty: Ty<'tcx>,
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for_vid: ty::TyVid,
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make_region_vars: bool)
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-> RelateResult<'tcx, Ty<'tcx>>
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{
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let mut generalize = Generalizer {
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infcx: self.infcx,
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span: self.trace.origin.span(),
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for_vid: for_vid,
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make_region_vars: make_region_vars,
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cycle_detected: false
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};
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let u = ty.fold_with(&mut generalize);
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if generalize.cycle_detected {
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Err(TypeError::CyclicTy)
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} else {
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Ok(u)
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}
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}
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}
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struct Generalizer<'cx, 'gcx: 'cx+'tcx, 'tcx: 'cx> {
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infcx: &'cx InferCtxt<'cx, 'gcx, 'tcx>,
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span: Span,
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for_vid: ty::TyVid,
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make_region_vars: bool,
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cycle_detected: bool,
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}
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impl<'cx, 'gcx, 'tcx> ty::fold::TypeFolder<'gcx, 'tcx> for Generalizer<'cx, 'gcx, 'tcx> {
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fn tcx<'a>(&'a self) -> TyCtxt<'a, 'gcx, 'tcx> {
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self.infcx.tcx
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}
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fn fold_ty(&mut self, t: Ty<'tcx>) -> Ty<'tcx> {
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// Check to see whether the type we are genealizing references
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// `vid`. At the same time, also update any type variables to
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// the values that they are bound to. This is needed to truly
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// check for cycles, but also just makes things readable.
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//
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// (In particular, you could have something like `$0 = Box<$1>`
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// where `$1` has already been instantiated with `Box<$0>`)
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match t.sty {
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ty::TyInfer(ty::TyVar(vid)) => {
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let mut variables = self.infcx.type_variables.borrow_mut();
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let vid = variables.root_var(vid);
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if vid == self.for_vid {
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self.cycle_detected = true;
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self.tcx().types.err
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} else {
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match variables.probe_root(vid) {
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Some(u) => {
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drop(variables);
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self.fold_ty(u)
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}
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None => t,
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}
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}
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}
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_ => {
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t.super_fold_with(self)
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}
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}
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}
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fn fold_region(&mut self, r: &'tcx ty::Region) -> &'tcx ty::Region {
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match *r {
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// Never make variables for regions bound within the type itself,
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// nor for erased regions.
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ty::ReLateBound(..) |
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ty::ReErased => { return r; }
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// Early-bound regions should really have been substituted away before
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// we get to this point.
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ty::ReEarlyBound(..) => {
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span_bug!(
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self.span,
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"Encountered early bound region when generalizing: {:?}",
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r);
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}
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// Always make a fresh region variable for skolemized regions;
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// the higher-ranked decision procedures rely on this.
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ty::ReSkolemized(..) => { }
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// For anything else, we make a region variable, unless we
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// are *equating*, in which case it's just wasteful.
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ty::ReEmpty |
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ty::ReStatic |
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ty::ReScope(..) |
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ty::ReVar(..) |
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ty::ReFree(..) => {
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if !self.make_region_vars {
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return r;
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}
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}
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}
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// FIXME: This is non-ideal because we don't give a
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// very descriptive origin for this region variable.
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self.infcx.next_region_var(MiscVariable(self.span))
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}
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}
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pub trait RelateResultCompare<'tcx, T> {
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fn compare<F>(&self, t: T, f: F) -> RelateResult<'tcx, T> where
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F: FnOnce() -> TypeError<'tcx>;
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}
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impl<'tcx, T:Clone + PartialEq> RelateResultCompare<'tcx, T> for RelateResult<'tcx, T> {
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fn compare<F>(&self, t: T, f: F) -> RelateResult<'tcx, T> where
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F: FnOnce() -> TypeError<'tcx>,
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{
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self.clone().and_then(|s| {
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if s == t {
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self.clone()
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} else {
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Err(f())
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}
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})
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}
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}
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fn int_unification_error<'tcx>(a_is_expected: bool, v: (ty::IntVarValue, ty::IntVarValue))
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-> TypeError<'tcx>
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{
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let (a, b) = v;
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TypeError::IntMismatch(ty::relate::expected_found_bool(a_is_expected, &a, &b))
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}
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fn float_unification_error<'tcx>(a_is_expected: bool,
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v: (ast::FloatTy, ast::FloatTy))
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-> TypeError<'tcx>
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{
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let (a, b) = v;
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TypeError::FloatMismatch(ty::relate::expected_found_bool(a_is_expected, &a, &b))
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}
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