559 lines
21 KiB
Rust
559 lines
21 KiB
Rust
// Copyright 2012-2014 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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//! ### Inferring borrow kinds for upvars
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//!
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//! Whenever there is a closure expression, we need to determine how each
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//! upvar is used. We do this by initially assigning each upvar an
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//! immutable "borrow kind" (see `ty::BorrowKind` for details) and then
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//! "escalating" the kind as needed. The borrow kind proceeds according to
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//! the following lattice:
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//!
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//! ty::ImmBorrow -> ty::UniqueImmBorrow -> ty::MutBorrow
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//!
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//! So, for example, if we see an assignment `x = 5` to an upvar `x`, we
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//! will promote its borrow kind to mutable borrow. If we see an `&mut x`
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//! we'll do the same. Naturally, this applies not just to the upvar, but
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//! to everything owned by `x`, so the result is the same for something
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//! like `x.f = 5` and so on (presuming `x` is not a borrowed pointer to a
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//! struct). These adjustments are performed in
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//! `adjust_upvar_borrow_kind()` (you can trace backwards through the code
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//! from there).
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//!
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//! The fact that we are inferring borrow kinds as we go results in a
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//! semi-hacky interaction with mem-categorization. In particular,
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//! mem-categorization will query the current borrow kind as it
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//! categorizes, and we'll return the *current* value, but this may get
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//! adjusted later. Therefore, in this module, we generally ignore the
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//! borrow kind (and derived mutabilities) that are returned from
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//! mem-categorization, since they may be inaccurate. (Another option
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//! would be to use a unification scheme, where instead of returning a
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//! concrete borrow kind like `ty::ImmBorrow`, we return a
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//! `ty::InferBorrow(upvar_id)` or something like that, but this would
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//! then mean that all later passes would have to check for these figments
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//! and report an error, and it just seems like more mess in the end.)
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use super::FnCtxt;
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use middle::expr_use_visitor as euv;
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use middle::mem_categorization as mc;
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use middle::ty::{self};
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use middle::infer::{InferCtxt, UpvarRegion};
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use std::collections::HashSet;
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use syntax::ast;
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use syntax::ast_util;
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use syntax::codemap::Span;
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use syntax::visit::{self, Visitor};
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use util::ppaux::Repr;
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///////////////////////////////////////////////////////////////////////////
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// PUBLIC ENTRY POINTS
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pub fn closure_analyze_fn(fcx: &FnCtxt,
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_id: ast::NodeId,
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_decl: &ast::FnDecl,
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body: &ast::Block)
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{
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let mut seed = SeedBorrowKind::new(fcx);
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seed.visit_block(body);
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let closures_with_inferred_kinds = seed.closures_with_inferred_kinds;
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let mut adjust = AdjustBorrowKind::new(fcx, &closures_with_inferred_kinds);
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adjust.visit_block(body);
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// it's our job to process these.
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assert!(fcx.inh.deferred_call_resolutions.borrow().is_empty());
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}
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///////////////////////////////////////////////////////////////////////////
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// SEED BORROW KIND
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struct SeedBorrowKind<'a,'tcx:'a> {
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fcx: &'a FnCtxt<'a,'tcx>,
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closures_with_inferred_kinds: HashSet<ast::NodeId>,
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}
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impl<'a, 'tcx, 'v> Visitor<'v> for SeedBorrowKind<'a, 'tcx> {
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fn visit_expr(&mut self, expr: &ast::Expr) {
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match expr.node {
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ast::ExprClosure(cc, _, ref body) => {
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self.check_closure(expr, cc, &**body);
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}
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_ => { }
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}
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visit::walk_expr(self, expr);
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}
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fn visit_fn(&mut self,
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fn_kind: visit::FnKind<'v>,
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decl: &'v ast::FnDecl,
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block: &'v ast::Block,
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span: Span,
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_id: ast::NodeId)
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{
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match fn_kind {
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visit::FkItemFn(..) | visit::FkMethod(..) => {
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// ignore nested fn items
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}
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visit::FkFnBlock => {
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visit::walk_fn(self, fn_kind, decl, block, span);
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}
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}
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}
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}
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impl<'a,'tcx> SeedBorrowKind<'a,'tcx> {
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fn new(fcx: &'a FnCtxt<'a,'tcx>) -> SeedBorrowKind<'a,'tcx> {
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SeedBorrowKind { fcx: fcx, closures_with_inferred_kinds: HashSet::new() }
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}
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fn tcx(&self) -> &'a ty::ctxt<'tcx> {
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self.fcx.tcx()
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}
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fn infcx(&self) -> &'a InferCtxt<'a,'tcx> {
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self.fcx.infcx()
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}
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fn check_closure(&mut self,
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expr: &ast::Expr,
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capture_clause: ast::CaptureClause,
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_body: &ast::Block)
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{
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let closure_def_id = ast_util::local_def(expr.id);
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if !self.fcx.inh.closure_kinds.borrow().contains_key(&closure_def_id) {
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self.closures_with_inferred_kinds.insert(expr.id);
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self.fcx.inh.closure_kinds.borrow_mut().insert(closure_def_id, ty::FnClosureKind);
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debug!("check_closure: adding closure_id={} to closures_with_inferred_kinds",
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closure_def_id.repr(self.tcx()));
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}
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ty::with_freevars(self.tcx(), expr.id, |freevars| {
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for freevar in freevars {
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let var_node_id = freevar.def.local_node_id();
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let upvar_id = ty::UpvarId { var_id: var_node_id,
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closure_expr_id: expr.id };
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debug!("seed upvar_id {:?}", upvar_id);
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let capture_kind = match capture_clause {
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ast::CaptureByValue => {
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ty::UpvarCapture::ByValue
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}
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ast::CaptureByRef => {
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let origin = UpvarRegion(upvar_id, expr.span);
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let freevar_region = self.infcx().next_region_var(origin);
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let upvar_borrow = ty::UpvarBorrow { kind: ty::ImmBorrow,
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region: freevar_region };
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ty::UpvarCapture::ByRef(upvar_borrow)
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}
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};
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self.fcx.inh.upvar_capture_map.borrow_mut().insert(upvar_id, capture_kind);
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}
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});
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}
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}
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///////////////////////////////////////////////////////////////////////////
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// ADJUST BORROW KIND
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struct AdjustBorrowKind<'a,'tcx:'a> {
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fcx: &'a FnCtxt<'a,'tcx>,
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closures_with_inferred_kinds: &'a HashSet<ast::NodeId>,
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}
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impl<'a,'tcx> AdjustBorrowKind<'a,'tcx> {
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fn new(fcx: &'a FnCtxt<'a,'tcx>,
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closures_with_inferred_kinds: &'a HashSet<ast::NodeId>)
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-> AdjustBorrowKind<'a,'tcx> {
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AdjustBorrowKind { fcx: fcx, closures_with_inferred_kinds: closures_with_inferred_kinds }
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}
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fn tcx(&self) -> &'a ty::ctxt<'tcx> {
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self.fcx.tcx()
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}
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fn analyze_closure(&mut self, id: ast::NodeId, decl: &ast::FnDecl, body: &ast::Block) {
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/*!
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* Analysis starting point.
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*/
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self.visit_block(body);
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debug!("analyzing closure `{}` with fn body id `{}`", id, body.id);
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let mut euv = euv::ExprUseVisitor::new(self, self.fcx);
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euv.walk_fn(decl, body);
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// If we had not yet settled on a closure kind for this closure,
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// then we should have by now. Process and remove any deferred resolutions.
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//
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// Interesting fact: all calls to this closure must come
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// *after* its definition. Initially, I thought that some
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// kind of fixed-point iteration would be required, due to the
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// possibility of twisted examples like this one:
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//
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// ```rust
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// let mut closure0 = None;
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// let vec = vec!(1, 2, 3);
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//
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// loop {
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// {
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// let closure1 = || {
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// match closure0.take() {
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// Some(c) => {
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// return c(); // (*) call to `closure0` before it is defined
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// }
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// None => { }
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// }
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// };
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// closure1();
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// }
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//
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// closure0 = || vec;
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// }
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// ```
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//
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// However, this turns out to be wrong. Examples like this
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// fail to compile because the type of the variable `c` above
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// is an inference variable. And in fact since closure types
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// cannot be written, there is no way to make this example
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// work without a boxed closure. This implies that we can't
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// have two closures that recursively call one another without
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// some form of boxing (and hence explicit writing of a
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// closure kind) involved. Huzzah. -nmatsakis
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let closure_def_id = ast_util::local_def(id);
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if self.closures_with_inferred_kinds.contains(&id) {
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let mut deferred_call_resolutions =
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self.fcx.remove_deferred_call_resolutions(closure_def_id);
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for deferred_call_resolution in deferred_call_resolutions.iter_mut() {
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deferred_call_resolution.resolve(self.fcx);
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}
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}
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}
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fn adjust_upvar_borrow_kind_for_consume(&self,
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cmt: mc::cmt<'tcx>,
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mode: euv::ConsumeMode)
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{
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debug!("adjust_upvar_borrow_kind_for_consume(cmt={}, mode={:?})",
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cmt.repr(self.tcx()), mode);
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// we only care about moves
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match mode {
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euv::Copy => { return; }
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euv::Move(_) => { }
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}
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// watch out for a move of the deref of a borrowed pointer;
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// for that to be legal, the upvar would have to be borrowed
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// by value instead
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let guarantor = cmt.guarantor();
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debug!("adjust_upvar_borrow_kind_for_consume: guarantor={}",
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guarantor.repr(self.tcx()));
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match guarantor.cat {
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mc::cat_deref(_, _, mc::BorrowedPtr(..)) |
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mc::cat_deref(_, _, mc::Implicit(..)) => {
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match cmt.note {
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mc::NoteUpvarRef(upvar_id) => {
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debug!("adjust_upvar_borrow_kind_for_consume: \
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setting upvar_id={:?} to by value",
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upvar_id);
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// to move out of an upvar, this must be a FnOnce closure
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self.adjust_closure_kind(upvar_id.closure_expr_id, ty::FnOnceClosureKind);
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let mut upvar_capture_map = self.fcx.inh.upvar_capture_map.borrow_mut();
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upvar_capture_map.insert(upvar_id, ty::UpvarCapture::ByValue);
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}
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mc::NoteClosureEnv(upvar_id) => {
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// we get just a closureenv ref if this is a
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// `move` closure, or if the upvar has already
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// been inferred to by-value. In any case, we
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// must still adjust the kind of the closure
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// to be a FnOnce closure to permit moves out
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// of the environment.
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self.adjust_closure_kind(upvar_id.closure_expr_id, ty::FnOnceClosureKind);
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}
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mc::NoteNone => {
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}
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}
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}
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_ => { }
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}
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}
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/// Indicates that `cmt` is being directly mutated (e.g., assigned
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/// to). If cmt contains any by-ref upvars, this implies that
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/// those upvars must be borrowed using an `&mut` borow.
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fn adjust_upvar_borrow_kind_for_mut(&mut self, cmt: mc::cmt<'tcx>) {
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debug!("adjust_upvar_borrow_kind_for_mut(cmt={})",
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cmt.repr(self.tcx()));
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match cmt.cat.clone() {
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mc::cat_deref(base, _, mc::Unique) |
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mc::cat_interior(base, _) |
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mc::cat_downcast(base, _) => {
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// Interior or owned data is mutable if base is
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// mutable, so iterate to the base.
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self.adjust_upvar_borrow_kind_for_mut(base);
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}
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mc::cat_deref(base, _, mc::BorrowedPtr(..)) |
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mc::cat_deref(base, _, mc::Implicit(..)) => {
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if !self.try_adjust_upvar_deref(&cmt.note, ty::MutBorrow) {
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// assignment to deref of an `&mut`
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// borrowed pointer implies that the
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// pointer itself must be unique, but not
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// necessarily *mutable*
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self.adjust_upvar_borrow_kind_for_unique(base);
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}
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}
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mc::cat_deref(_, _, mc::UnsafePtr(..)) |
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mc::cat_static_item |
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mc::cat_rvalue(_) |
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mc::cat_local(_) |
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mc::cat_upvar(..) => {
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return;
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}
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}
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}
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fn adjust_upvar_borrow_kind_for_unique(&self, cmt: mc::cmt<'tcx>) {
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debug!("adjust_upvar_borrow_kind_for_unique(cmt={})",
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cmt.repr(self.tcx()));
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match cmt.cat.clone() {
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mc::cat_deref(base, _, mc::Unique) |
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mc::cat_interior(base, _) |
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mc::cat_downcast(base, _) => {
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// Interior or owned data is unique if base is
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// unique.
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self.adjust_upvar_borrow_kind_for_unique(base);
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}
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mc::cat_deref(base, _, mc::BorrowedPtr(..)) |
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mc::cat_deref(base, _, mc::Implicit(..)) => {
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if !self.try_adjust_upvar_deref(&cmt.note, ty::UniqueImmBorrow) {
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// for a borrowed pointer to be unique, its
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// base must be unique
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self.adjust_upvar_borrow_kind_for_unique(base);
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}
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}
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mc::cat_deref(_, _, mc::UnsafePtr(..)) |
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mc::cat_static_item |
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mc::cat_rvalue(_) |
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mc::cat_local(_) |
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mc::cat_upvar(..) => {
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}
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}
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}
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fn try_adjust_upvar_deref(&self,
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note: &mc::Note,
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borrow_kind: ty::BorrowKind)
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-> bool
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{
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assert!(match borrow_kind {
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ty::MutBorrow => true,
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ty::UniqueImmBorrow => true,
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// imm borrows never require adjusting any kinds, so we don't wind up here
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ty::ImmBorrow => false,
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});
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match *note {
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mc::NoteUpvarRef(upvar_id) => {
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// if this is an implicit deref of an
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// upvar, then we need to modify the
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// borrow_kind of the upvar to make sure it
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// is inferred to mutable if necessary
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let mut upvar_capture_map = self.fcx.inh.upvar_capture_map.borrow_mut();
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let ub = &mut upvar_capture_map[upvar_id];
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self.adjust_upvar_borrow_kind(upvar_id, ub, borrow_kind);
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// also need to be in an FnMut closure since this is not an ImmBorrow
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self.adjust_closure_kind(upvar_id.closure_expr_id, ty::FnMutClosureKind);
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true
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}
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mc::NoteClosureEnv(upvar_id) => {
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// this kind of deref occurs in a `move` closure, or
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// for a by-value upvar; in either case, to mutate an
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// upvar, we need to be an FnMut closure
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self.adjust_closure_kind(upvar_id.closure_expr_id, ty::FnMutClosureKind);
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true
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}
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mc::NoteNone => {
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false
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}
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}
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}
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/// We infer the borrow_kind with which to borrow upvars in a stack closure. The borrow_kind
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/// basically follows a lattice of `imm < unique-imm < mut`, moving from left to right as needed
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/// (but never right to left). Here the argument `mutbl` is the borrow_kind that is required by
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/// some particular use.
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fn adjust_upvar_borrow_kind(&self,
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upvar_id: ty::UpvarId,
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upvar_capture: &mut ty::UpvarCapture,
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kind: ty::BorrowKind) {
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debug!("adjust_upvar_borrow_kind(upvar_id={:?}, upvar_capture={:?}, kind={:?})",
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upvar_id, upvar_capture, kind);
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match *upvar_capture {
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ty::UpvarCapture::ByValue => {
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// Upvar is already by-value, the strongest criteria.
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}
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ty::UpvarCapture::ByRef(ref mut upvar_borrow) => {
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match (upvar_borrow.kind, kind) {
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// Take RHS:
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(ty::ImmBorrow, ty::UniqueImmBorrow) |
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(ty::ImmBorrow, ty::MutBorrow) |
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(ty::UniqueImmBorrow, ty::MutBorrow) => {
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upvar_borrow.kind = kind;
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}
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// Take LHS:
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(ty::ImmBorrow, ty::ImmBorrow) |
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(ty::UniqueImmBorrow, ty::ImmBorrow) |
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(ty::UniqueImmBorrow, ty::UniqueImmBorrow) |
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(ty::MutBorrow, _) => {
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}
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}
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}
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}
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}
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fn adjust_closure_kind(&self,
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closure_id: ast::NodeId,
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new_kind: ty::ClosureKind) {
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debug!("adjust_closure_kind(closure_id={}, new_kind={:?})",
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closure_id, new_kind);
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if !self.closures_with_inferred_kinds.contains(&closure_id) {
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return;
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}
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let closure_def_id = ast_util::local_def(closure_id);
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let mut closure_kinds = self.fcx.inh.closure_kinds.borrow_mut();
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let existing_kind = closure_kinds[closure_def_id];
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debug!("adjust_closure_kind: closure_id={}, existing_kind={:?}, new_kind={:?}",
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closure_id, existing_kind, new_kind);
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match (existing_kind, new_kind) {
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(ty::FnClosureKind, ty::FnClosureKind) |
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(ty::FnMutClosureKind, ty::FnClosureKind) |
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(ty::FnMutClosureKind, ty::FnMutClosureKind) |
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(ty::FnOnceClosureKind, _) => {
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// no change needed
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}
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(ty::FnClosureKind, ty::FnMutClosureKind) |
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(ty::FnClosureKind, ty::FnOnceClosureKind) |
|
|
(ty::FnMutClosureKind, ty::FnOnceClosureKind) => {
|
|
// new kind is stronger than the old kind
|
|
closure_kinds.insert(closure_def_id, new_kind);
|
|
}
|
|
}
|
|
}
|
|
}
|
|
|
|
impl<'a, 'tcx, 'v> Visitor<'v> for AdjustBorrowKind<'a, 'tcx> {
|
|
fn visit_fn(&mut self,
|
|
fn_kind: visit::FnKind<'v>,
|
|
decl: &'v ast::FnDecl,
|
|
body: &'v ast::Block,
|
|
span: Span,
|
|
id: ast::NodeId)
|
|
{
|
|
match fn_kind {
|
|
visit::FkItemFn(..) | visit::FkMethod(..) => {
|
|
// ignore nested fn items
|
|
}
|
|
visit::FkFnBlock => {
|
|
self.analyze_closure(id, decl, body);
|
|
visit::walk_fn(self, fn_kind, decl, body, span);
|
|
}
|
|
}
|
|
}
|
|
}
|
|
|
|
impl<'a,'tcx> euv::Delegate<'tcx> for AdjustBorrowKind<'a,'tcx> {
|
|
fn consume(&mut self,
|
|
_consume_id: ast::NodeId,
|
|
_consume_span: Span,
|
|
cmt: mc::cmt<'tcx>,
|
|
mode: euv::ConsumeMode)
|
|
{
|
|
debug!("consume(cmt={},mode={:?})", cmt.repr(self.tcx()), mode);
|
|
self.adjust_upvar_borrow_kind_for_consume(cmt, mode);
|
|
}
|
|
|
|
fn matched_pat(&mut self,
|
|
_matched_pat: &ast::Pat,
|
|
_cmt: mc::cmt<'tcx>,
|
|
_mode: euv::MatchMode)
|
|
{}
|
|
|
|
fn consume_pat(&mut self,
|
|
_consume_pat: &ast::Pat,
|
|
cmt: mc::cmt<'tcx>,
|
|
mode: euv::ConsumeMode)
|
|
{
|
|
debug!("consume_pat(cmt={},mode={:?})", cmt.repr(self.tcx()), mode);
|
|
self.adjust_upvar_borrow_kind_for_consume(cmt, mode);
|
|
}
|
|
|
|
fn borrow(&mut self,
|
|
borrow_id: ast::NodeId,
|
|
_borrow_span: Span,
|
|
cmt: mc::cmt<'tcx>,
|
|
_loan_region: ty::Region,
|
|
bk: ty::BorrowKind,
|
|
_loan_cause: euv::LoanCause)
|
|
{
|
|
debug!("borrow(borrow_id={}, cmt={}, bk={:?})",
|
|
borrow_id, cmt.repr(self.tcx()), bk);
|
|
|
|
match bk {
|
|
ty::ImmBorrow => { }
|
|
ty::UniqueImmBorrow => {
|
|
self.adjust_upvar_borrow_kind_for_unique(cmt);
|
|
}
|
|
ty::MutBorrow => {
|
|
self.adjust_upvar_borrow_kind_for_mut(cmt);
|
|
}
|
|
}
|
|
}
|
|
|
|
fn decl_without_init(&mut self,
|
|
_id: ast::NodeId,
|
|
_span: Span)
|
|
{}
|
|
|
|
fn mutate(&mut self,
|
|
_assignment_id: ast::NodeId,
|
|
_assignment_span: Span,
|
|
assignee_cmt: mc::cmt<'tcx>,
|
|
_mode: euv::MutateMode)
|
|
{
|
|
debug!("mutate(assignee_cmt={})",
|
|
assignee_cmt.repr(self.tcx()));
|
|
|
|
self.adjust_upvar_borrow_kind_for_mut(assignee_cmt);
|
|
}
|
|
}
|