2a14e084cf
These two containers are indeed collections, so their place is in libcollections, not in libstd. There will always be a hash map as part of the standard distribution of Rust, but by moving it out of the standard library it makes libstd that much more portable to more platforms and environments. This conveniently also removes the stuttering of 'std::hashmap::HashMap', although 'collections::HashMap' is only one character shorter.
716 lines
24 KiB
Rust
716 lines
24 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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# Moves Computation
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The goal of this file is to compute which
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expressions/patterns/captures correspond to *moves*. This is
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generally a function of the context in which the expression appears as
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well as the expression's type.
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## Examples
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We will use the following fragment of code to explain the various
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considerations. Note that in this code `x` is used after it has been
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moved here. This is not relevant to this pass, though the information
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we compute would later be used to detect this error (see the section
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Enforcement of Moves, below).
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struct Foo { a: int, b: ~int }
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let x: Foo = ...;
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let w = (x {Read}).a; // Read
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let y = (x {Move}).b; // Move
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let z = copy (x {Read}).b; // Read
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Let's look at these examples one by one. In the first case, `w`, the
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expression being assigned is `x.a`, which has `int` type. In that
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case, the value is read, and the container (`x`) is also read.
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In the second case, `y`, `x.b` is being assigned which has type
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`~int`. Because this type moves by default, that will be a move
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reference. Whenever we move from a compound expression like `x.b` (or
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`x[b]` or `*x` or `{x}[b].c`, etc), this invalidates all containing
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expressions since we do not currently permit "incomplete" variables
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where part of them has been moved and part has not. In this case,
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this means that the reference to `x` is also a move. We'll see later,
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though, that these kind of "partial moves", where part of the
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expression has been moved, are classified and stored somewhat
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differently.
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The final example (`z`) is `copy x.b`: in this case, although the
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expression being assigned has type `~int`, there are no moves
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involved.
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### Patterns
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For each binding in a match or let pattern, we also compute a read
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or move designation. A move binding means that the value will be
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moved from the value being matched. As a result, the expression
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being matched (aka, the 'discriminant') is either moved or read
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depending on whether the bindings move the value they bind to out of
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the discriminant.
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For examples, consider this match expression:
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match x {Move} {
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Foo { a: a {Read}, b: b {Move} } => {...}
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}
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Here, the binding `b` is value (not ref) mode, and `b` has type
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`~int`, and therefore the discriminant expression `x` would be
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incomplete so it also considered moved.
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In the following two examples, in contrast, the mode of `b` is either
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`copy` or `ref` and hence the overall result is a read:
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match x {Read} {
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Foo { a: a {Read}, b: copy b {Read} } => {...}
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}
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match x {Read} {
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Foo { a: a {Read}, b: ref b {Read} } => {...}
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}
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Similar reasoning can be applied to `let` expressions:
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let Foo { a: a {Read}, b: b {Move} } = x {Move};
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let Foo { a: a {Read}, b: copy b {Read} } = x {Read};
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let Foo { a: a {Read}, b: ref b {Read} } = x {Read};
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## Output
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The pass results in the struct `MoveMaps` which contains several
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maps:
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`moves_map` is a set containing the id of every *outermost expression* or
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*binding* that causes a move. Note that `moves_map` only contains the *outermost
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expressions* that are moved. Therefore, if you have a use of `x.b`,
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as in the example `y` above, the expression `x.b` would be in the
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`moves_map` but not `x`. The reason for this is that, for most
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purposes, it's only the outermost expression that is needed. The
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borrow checker and trans, for example, only care about the outermost
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expressions that are moved. It is more efficient therefore just to
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store those entries.
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Sometimes though we want to know the variables that are moved (in
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particular in the borrow checker). For these cases, the set
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`moved_variables_set` just collects the ids of variables that are
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moved.
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Finally, the `capture_map` maps from the node_id of a closure
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expression to an array of `CaptureVar` structs detailing which
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variables are captured and how (by ref, by copy, by move).
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## Enforcement of Moves
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The enforcement of moves is done by the borrow checker. Please see
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the section "Moves and initialization" in `middle/borrowck/doc.rs`.
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## Distributive property
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Copies are "distributive" over parenthesization, but blocks are
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considered rvalues. What this means is that, for example, neither
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`a.clone()` nor `(a).clone()` will move `a` (presuming that `a` has a
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linear type and `clone()` takes its self by reference), but
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`{a}.clone()` will move `a`, as would `(if cond {a} else {b}).clone()`
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and so on.
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*/
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use middle::pat_util::{pat_bindings};
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use middle::freevars;
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use middle::ty;
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use middle::typeck::method_map;
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use util::ppaux;
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use util::ppaux::Repr;
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use util::common::indenter;
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use util::ppaux::UserString;
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use std::cell::RefCell;
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use std::rc::Rc;
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use collections::{HashSet, HashMap};
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use syntax::ast::*;
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use syntax::ast_util;
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use syntax::visit;
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use syntax::visit::Visitor;
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use syntax::codemap::Span;
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#[deriving(Eq, Encodable, Decodable)]
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pub enum CaptureMode {
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CapCopy, // Copy the value into the closure.
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CapMove, // Move the value into the closure.
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CapRef, // Reference directly from parent stack frame (used by `||`).
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}
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#[deriving(Encodable, Decodable)]
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pub struct CaptureVar {
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def: Def, // Variable being accessed free
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span: Span, // Location of an access to this variable
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mode: CaptureMode // How variable is being accessed
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}
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pub type CaptureMap = @RefCell<HashMap<NodeId, Rc<~[CaptureVar]>>>;
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pub type MovesMap = @RefCell<HashSet<NodeId>>;
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/**
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* Set of variable node-ids that are moved.
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*
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* Note: The `VariableMovesMap` stores expression ids that
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* are moves, whereas this set stores the ids of the variables
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* that are moved at some point */
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pub type MovedVariablesSet = @RefCell<HashSet<NodeId>>;
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/** See the section Output on the module comment for explanation. */
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#[deriving(Clone)]
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pub struct MoveMaps {
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moves_map: MovesMap,
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moved_variables_set: MovedVariablesSet,
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capture_map: CaptureMap
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}
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#[deriving(Clone)]
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struct VisitContext {
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tcx: ty::ctxt,
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method_map: method_map,
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move_maps: MoveMaps
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}
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#[deriving(Eq)]
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enum UseMode {
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Move, // This value or something owned by it is moved.
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Read // Read no matter what the type.
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}
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impl visit::Visitor<()> for VisitContext {
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fn visit_fn(&mut self, fk: &visit::FnKind, fd: &FnDecl,
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b: &Block, s: Span, n: NodeId, _: ()) {
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compute_modes_for_fn(self, fk, fd, b, s, n);
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}
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fn visit_expr(&mut self, ex: &Expr, _: ()) {
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compute_modes_for_expr(self, ex);
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}
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fn visit_local(&mut self, l: &Local, _: ()) {
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compute_modes_for_local(self, l);
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}
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// FIXME(#10894) should continue recursing
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fn visit_ty(&mut self, _t: &Ty, _: ()) {}
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}
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pub fn compute_moves(tcx: ty::ctxt,
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method_map: method_map,
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krate: &Crate) -> MoveMaps
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{
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let mut visit_cx = VisitContext {
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tcx: tcx,
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method_map: method_map,
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move_maps: MoveMaps {
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moves_map: @RefCell::new(HashSet::new()),
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capture_map: @RefCell::new(HashMap::new()),
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moved_variables_set: @RefCell::new(HashSet::new())
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}
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};
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let visit_cx = &mut visit_cx;
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visit::walk_crate(visit_cx, krate, ());
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return visit_cx.move_maps;
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}
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pub fn moved_variable_node_id_from_def(def: Def) -> Option<NodeId> {
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match def {
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DefBinding(nid, _) |
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DefArg(nid, _) |
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DefLocal(nid, _) => Some(nid),
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_ => None
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}
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}
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///////////////////////////////////////////////////////////////////////////
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// Expressions
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fn compute_modes_for_local<'a>(cx: &mut VisitContext,
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local: &Local) {
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cx.use_pat(local.pat);
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for &init in local.init.iter() {
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cx.use_expr(init, Read);
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}
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}
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fn compute_modes_for_fn(cx: &mut VisitContext,
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fk: &visit::FnKind,
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decl: &FnDecl,
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body: &Block,
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span: Span,
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id: NodeId) {
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for a in decl.inputs.iter() {
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cx.use_pat(a.pat);
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}
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visit::walk_fn(cx, fk, decl, body, span, id, ());
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}
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fn compute_modes_for_expr(cx: &mut VisitContext,
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expr: &Expr)
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{
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cx.consume_expr(expr);
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}
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impl VisitContext {
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pub fn consume_exprs(&mut self, exprs: &[@Expr]) {
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for expr in exprs.iter() {
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self.consume_expr(*expr);
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}
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}
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pub fn consume_expr(&mut self, expr: &Expr) {
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/*!
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* Indicates that the value of `expr` will be consumed,
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* meaning either copied or moved depending on its type.
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*/
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debug!("consume_expr(expr={})",
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expr.repr(self.tcx));
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let expr_ty = ty::expr_ty_adjusted(self.tcx, expr);
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if ty::type_moves_by_default(self.tcx, expr_ty) {
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{
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let mut moves_map = self.move_maps.moves_map.borrow_mut();
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moves_map.get().insert(expr.id);
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}
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self.use_expr(expr, Move);
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} else {
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self.use_expr(expr, Read);
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};
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}
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pub fn consume_block(&mut self, blk: &Block) {
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/*!
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* Indicates that the value of `blk` will be consumed,
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* meaning either copied or moved depending on its type.
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*/
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debug!("consume_block(blk.id={:?})", blk.id);
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for stmt in blk.stmts.iter() {
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self.visit_stmt(*stmt, ());
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}
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for tail_expr in blk.expr.iter() {
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self.consume_expr(*tail_expr);
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}
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}
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pub fn use_expr(&mut self,
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expr: &Expr,
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expr_mode: UseMode) {
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/*!
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* Indicates that `expr` is used with a given mode. This will
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* in turn trigger calls to the subcomponents of `expr`.
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*/
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debug!("use_expr(expr={}, mode={:?})",
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expr.repr(self.tcx),
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expr_mode);
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// `expr_mode` refers to the post-adjustment value. If one of
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// those adjustments is to take a reference, then it's only
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// reading the underlying expression, not moving it.
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let comp_mode = {
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let adjustments = self.tcx.adjustments.borrow();
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match adjustments.get().find(&expr.id) {
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Some(adjustment) => {
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match **adjustment {
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ty::AutoDerefRef(ty::AutoDerefRef {
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autoref: Some(_),
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..
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}) => Read,
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_ => expr_mode,
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}
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}
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_ => expr_mode,
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}
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};
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debug!("comp_mode = {:?}", comp_mode);
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match expr.node {
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ExprPath(..) => {
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match comp_mode {
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Move => {
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let def_map = self.tcx.def_map.borrow();
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let def = def_map.get().get_copy(&expr.id);
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let r = moved_variable_node_id_from_def(def);
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for &id in r.iter() {
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let mut moved_variables_set =
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self.move_maps
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.moved_variables_set
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.borrow_mut();
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moved_variables_set.get().insert(id);
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}
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}
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Read => {}
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}
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}
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ExprUnary(_, UnDeref, base) => { // *base
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if !self.use_overloaded_operator(expr, base, [])
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{
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// Moving out of *base moves out of base.
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self.use_expr(base, comp_mode);
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}
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}
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ExprField(base, _, _) => { // base.f
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// Moving out of base.f moves out of base.
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self.use_expr(base, comp_mode);
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}
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ExprIndex(_, lhs, rhs) => { // lhs[rhs]
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if !self.use_overloaded_operator(expr, lhs, [rhs])
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{
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self.use_expr(lhs, comp_mode);
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self.consume_expr(rhs);
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}
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}
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ExprCall(callee, ref args) => { // callee(args)
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// Figure out whether the called function is consumed.
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let mode = match ty::get(ty::expr_ty(self.tcx, callee)).sty {
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ty::ty_closure(ref cty) => {
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match cty.onceness {
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Once => Move,
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Many => Read,
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}
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},
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ty::ty_bare_fn(..) => Read,
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ref x =>
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self.tcx.sess.span_bug(callee.span,
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format!("non-function type in moves for expr_call: {:?}", x)),
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};
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// Note we're not using consume_expr, which uses type_moves_by_default
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// to determine the mode, for this. The reason is that while stack
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// closures should be noncopyable, they shouldn't move by default;
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// calling a closure should only consume it if it's once.
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if mode == Move {
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{
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let mut moves_map = self.move_maps
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.moves_map
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.borrow_mut();
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moves_map.get().insert(callee.id);
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}
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}
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self.use_expr(callee, mode);
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self.use_fn_args(callee.id, *args);
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}
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ExprMethodCall(callee_id, _, _, ref args) => { // callee.m(args)
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self.use_fn_args(callee_id, *args);
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}
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ExprStruct(_, ref fields, opt_with) => {
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for field in fields.iter() {
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self.consume_expr(field.expr);
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}
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for with_expr in opt_with.iter() {
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// If there are any fields whose type is move-by-default,
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// then `with` is consumed, otherwise it is only read
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let with_ty = ty::expr_ty(self.tcx, *with_expr);
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let with_fields = match ty::get(with_ty).sty {
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ty::ty_struct(did, ref substs) => {
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ty::struct_fields(self.tcx, did, substs)
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}
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ref r => {
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self.tcx.sess.span_bug(
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with_expr.span,
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format!("bad base expr type in record: {:?}", r))
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}
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};
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// The `with` expr must be consumed if it contains
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// any fields which (1) were not explicitly
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// specified and (2) have a type that
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// moves-by-default:
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let consume_with = with_fields.iter().any(|tf| {
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!fields.iter().any(|f| f.ident.node.name == tf.ident.name) &&
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ty::type_moves_by_default(self.tcx, tf.mt.ty)
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});
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fn has_dtor(tcx: ty::ctxt, ty: ty::t) -> bool {
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use middle::ty::{get,ty_struct,ty_enum};
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match get(ty).sty {
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ty_struct(did, _) | ty_enum(did, _) => ty::has_dtor(tcx, did),
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_ => false,
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}
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}
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if consume_with {
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if has_dtor(self.tcx, with_ty) {
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self.tcx.sess.span_err(with_expr.span,
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format!("cannot move out of type `{}`, \
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which defines the `Drop` trait",
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with_ty.user_string(self.tcx)));
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}
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self.consume_expr(*with_expr);
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} else {
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self.use_expr(*with_expr, Read);
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}
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}
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}
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ExprTup(ref exprs) => {
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self.consume_exprs(*exprs);
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}
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ExprIf(cond_expr, then_blk, opt_else_expr) => {
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self.consume_expr(cond_expr);
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self.consume_block(then_blk);
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for else_expr in opt_else_expr.iter() {
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self.consume_expr(*else_expr);
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}
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}
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ExprMatch(discr, ref arms) => {
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for arm in arms.iter() {
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self.consume_arm(arm);
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}
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// The discriminant may, in fact, be partially moved
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// if there are by-move bindings, but borrowck deals
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// with that itself.
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self.use_expr(discr, Read);
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}
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ExprParen(base) => {
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// Note: base is not considered a *component* here, so
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// use `expr_mode` not `comp_mode`.
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self.use_expr(base, expr_mode);
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}
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ExprVec(ref exprs, _) => {
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self.consume_exprs(*exprs);
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}
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ExprAddrOf(_, base) => { // &base
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self.use_expr(base, Read);
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}
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|
|
ExprLogLevel |
|
|
ExprInlineAsm(..) |
|
|
ExprBreak(..) |
|
|
ExprAgain(..) |
|
|
ExprLit(..) => {}
|
|
|
|
ExprLoop(blk, _) => {
|
|
self.consume_block(blk);
|
|
}
|
|
|
|
ExprWhile(cond_expr, blk) => {
|
|
self.consume_expr(cond_expr);
|
|
self.consume_block(blk);
|
|
}
|
|
|
|
ExprForLoop(..) => fail!("non-desugared expr_for_loop"),
|
|
|
|
ExprUnary(_, _, lhs) => {
|
|
if !self.use_overloaded_operator(expr, lhs, [])
|
|
{
|
|
self.consume_expr(lhs);
|
|
}
|
|
}
|
|
|
|
ExprBinary(_, _, lhs, rhs) => {
|
|
if !self.use_overloaded_operator(expr, lhs, [rhs])
|
|
{
|
|
self.consume_expr(lhs);
|
|
self.consume_expr(rhs);
|
|
}
|
|
}
|
|
|
|
ExprBlock(blk) => {
|
|
self.consume_block(blk);
|
|
}
|
|
|
|
ExprRet(ref opt_expr) => {
|
|
for expr in opt_expr.iter() {
|
|
self.consume_expr(*expr);
|
|
}
|
|
}
|
|
|
|
ExprAssign(lhs, rhs) => {
|
|
self.use_expr(lhs, Read);
|
|
self.consume_expr(rhs);
|
|
}
|
|
|
|
ExprCast(base, _) => {
|
|
self.consume_expr(base);
|
|
}
|
|
|
|
ExprAssignOp(_, _, lhs, rhs) => {
|
|
// FIXME(#4712) --- Overloaded operators?
|
|
//
|
|
// if !self.use_overloaded_operator(expr, DoDerefArgs, lhs, [rhs])
|
|
// {
|
|
self.consume_expr(lhs);
|
|
self.consume_expr(rhs);
|
|
// }
|
|
}
|
|
|
|
ExprRepeat(base, count, _) => {
|
|
self.consume_expr(base);
|
|
self.consume_expr(count);
|
|
}
|
|
|
|
ExprFnBlock(ref decl, body) |
|
|
ExprProc(ref decl, body) => {
|
|
for a in decl.inputs.iter() {
|
|
self.use_pat(a.pat);
|
|
}
|
|
let cap_vars = self.compute_captures(expr.id);
|
|
{
|
|
let mut capture_map = self.move_maps
|
|
.capture_map
|
|
.borrow_mut();
|
|
capture_map.get().insert(expr.id, cap_vars);
|
|
}
|
|
self.consume_block(body);
|
|
}
|
|
|
|
ExprVstore(base, _) => {
|
|
self.use_expr(base, comp_mode);
|
|
}
|
|
|
|
ExprBox(place, base) => {
|
|
self.use_expr(place, comp_mode);
|
|
self.use_expr(base, comp_mode);
|
|
}
|
|
|
|
ExprMac(..) => {
|
|
self.tcx.sess.span_bug(
|
|
expr.span,
|
|
"macro expression remains after expansion");
|
|
}
|
|
}
|
|
}
|
|
|
|
pub fn use_overloaded_operator(&mut self,
|
|
expr: &Expr,
|
|
receiver_expr: @Expr,
|
|
arg_exprs: &[@Expr])
|
|
-> bool {
|
|
let method_map = self.method_map.borrow();
|
|
if !method_map.get().contains_key(&expr.id) {
|
|
return false;
|
|
}
|
|
|
|
self.use_fn_arg(receiver_expr);
|
|
|
|
// for overloaded operatrs, we are always passing in a
|
|
// reference, so it's always read mode:
|
|
for arg_expr in arg_exprs.iter() {
|
|
self.use_expr(*arg_expr, Read);
|
|
}
|
|
|
|
return true;
|
|
}
|
|
|
|
pub fn consume_arm(&mut self, arm: &Arm) {
|
|
for pat in arm.pats.iter() {
|
|
self.use_pat(*pat);
|
|
}
|
|
|
|
for guard in arm.guard.iter() {
|
|
self.consume_expr(*guard);
|
|
}
|
|
|
|
self.consume_block(arm.body);
|
|
}
|
|
|
|
pub fn use_pat(&mut self, pat: @Pat) {
|
|
/*!
|
|
*
|
|
* Decides whether each binding in a pattern moves the value
|
|
* into itself or not based on its type and annotation.
|
|
*/
|
|
|
|
pat_bindings(self.tcx.def_map, pat, |bm, id, _span, path| {
|
|
let binding_moves = match bm {
|
|
BindByRef(_) => false,
|
|
BindByValue(_) => {
|
|
let pat_ty = ty::node_id_to_type(self.tcx, id);
|
|
debug!("pattern {:?} {} type is {}",
|
|
id,
|
|
ast_util::path_to_ident(path).repr(self.tcx),
|
|
pat_ty.repr(self.tcx));
|
|
ty::type_moves_by_default(self.tcx, pat_ty)
|
|
}
|
|
};
|
|
|
|
debug!("pattern binding {:?}: bm={:?}, binding_moves={}",
|
|
id, bm, binding_moves);
|
|
|
|
if binding_moves {
|
|
{
|
|
let mut moves_map = self.move_maps.moves_map.borrow_mut();
|
|
moves_map.get().insert(id);
|
|
}
|
|
}
|
|
})
|
|
}
|
|
|
|
pub fn use_fn_args(&mut self,
|
|
_: NodeId,
|
|
arg_exprs: &[@Expr]) {
|
|
//! Uses the argument expressions.
|
|
for arg_expr in arg_exprs.iter() {
|
|
self.use_fn_arg(*arg_expr);
|
|
}
|
|
}
|
|
|
|
pub fn use_fn_arg(&mut self, arg_expr: @Expr) {
|
|
//! Uses the argument.
|
|
self.consume_expr(arg_expr)
|
|
}
|
|
|
|
pub fn compute_captures(&mut self, fn_expr_id: NodeId) -> Rc<~[CaptureVar]> {
|
|
debug!("compute_capture_vars(fn_expr_id={:?})", fn_expr_id);
|
|
let _indenter = indenter();
|
|
|
|
let fn_ty = ty::node_id_to_type(self.tcx, fn_expr_id);
|
|
let sigil = ty::ty_closure_sigil(fn_ty);
|
|
let freevars = freevars::get_freevars(self.tcx, fn_expr_id);
|
|
let v = if sigil == BorrowedSigil {
|
|
// || captures everything by ref
|
|
freevars.iter()
|
|
.map(|fvar| CaptureVar {def: fvar.def, span: fvar.span, mode: CapRef})
|
|
.collect()
|
|
} else {
|
|
// @fn() and ~fn() capture by copy or by move depending on type
|
|
freevars.iter()
|
|
.map(|fvar| {
|
|
let fvar_def_id = ast_util::def_id_of_def(fvar.def).node;
|
|
let fvar_ty = ty::node_id_to_type(self.tcx, fvar_def_id);
|
|
debug!("fvar_def_id={:?} fvar_ty={}",
|
|
fvar_def_id, ppaux::ty_to_str(self.tcx, fvar_ty));
|
|
let mode = if ty::type_moves_by_default(self.tcx, fvar_ty) {
|
|
CapMove
|
|
} else {
|
|
CapCopy
|
|
};
|
|
CaptureVar {def: fvar.def, span: fvar.span, mode:mode}
|
|
|
|
}).collect()
|
|
};
|
|
Rc::new(v)
|
|
}
|
|
}
|