159a10da4c
This alters the borrow checker's requirements on invoking closures from
requiring an immutable borrow to requiring a unique immutable borrow. This means
that it is illegal to invoke a closure through a `&` pointer because there is no
guarantee that is not aliased. This does not mean that a closure is required to
be in a mutable location, but rather a location which can be proven to be
unique (often through a mutable pointer).
For example, the following code is unsound and is no longer allowed:
type Fn<'a> = ||:'a;
fn call(f: |Fn|) {
f(|| {
f(|| {})
});
}
fn main() {
call(|a| {
a();
});
}
There is no replacement for this pattern. For all closures which are stored in
structures, it was previously allowed to invoke the closure through `&self` but
it now requires invocation through `&mut self`.
The standard library has a good number of violations of this new rule, but the
fixes will be separated into multiple breaking change commits.
Closes #12224
[breaking-change]
65 lines
1.3 KiB
Rust
65 lines
1.3 KiB
Rust
// Copyright 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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// Ensure that invoking a closure counts as a unique immutable borrow
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type Fn<'a> = ||:'a;
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struct Test<'a> {
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f: ||: 'a
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}
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fn call(f: |Fn|) {
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f(|| {
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//~^ ERROR: closure requires unique access to `f` but it is already borrowed
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f(|| {})
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});
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}
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fn test1() {
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call(|a| {
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a();
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});
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}
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fn test2(f: &||) {
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(*f)(); //~ ERROR: closure invocation in a `&` reference
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}
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fn test3(f: &mut ||) {
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(*f)();
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}
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fn test4(f: &Test) {
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(f.f)() //~ ERROR: closure invocation in a `&` reference
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}
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fn test5(f: &mut Test) {
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(f.f)()
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}
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fn test6() {
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let f = || {};
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(|| {
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f();
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})();
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}
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fn test7() {
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fn foo(_: |g: |int|, b: int|) {}
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let f = |g: |int|, b: int| {};
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f(|a| { //~ ERROR: cannot borrow `f` as immutable because previous closure
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foo(f); //~ ERROR: cannot move out of captured outer variable
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}, 3);
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}
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fn main() {}
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