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rust/src/test/compile-fail/borrowck-mutate-in-guard.rs

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librustc: Disallow mutation and assignment in pattern guards, and modify the CFG for match statements. There were two bugs in issue #14684. One was simply that the borrow check didn't know about the correct CFG for match statements: the pattern must be a predecessor of the guard. This disallows the bad behavior if there are bindings in the pattern. But it isn't enough to prevent the memory safety problem, because of wildcards; thus, this patch introduces a more restrictive rule, which disallows assignments and mutable borrows inside guards outright. I discussed this with Niko and we decided this was the best plan of action. This breaks code that performs mutable borrows in pattern guards. Most commonly, the code looks like this: impl Foo { fn f(&mut self, ...) {} fn g(&mut self, ...) { match bar { Baz if self.f(...) => { ... } _ => { ... } } } } Change this code to not use a guard. For example: impl Foo { fn f(&mut self, ...) {} fn g(&mut self, ...) { match bar { Baz => { if self.f(...) { ... } else { ... } } _ => { ... } } } } Sometimes this can result in code duplication, but often it illustrates a hidden memory safety problem. Closes #14684. [breaking-change]
2014-07-25 17:18:19 -05:00
// Copyright 2014 The Rust Project Developers. See the COPYRIGHT
// file at the top-level directory of this distribution and at
// http://rust-lang.org/COPYRIGHT.
//
// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
// option. This file may not be copied, modified, or distributed
// except according to those terms.
enum Enum<'a> {
A(&'a int),
B(bool),
}
fn foo() -> int {
let mut n = 42;
Switch to purely namespaced enums This breaks code that referred to variant names in the same namespace as their enum. Reexport the variants in the old location or alter code to refer to the new locations: ``` pub enum Foo { A, B } fn main() { let a = A; } ``` => ``` pub use self::Foo::{A, B}; pub enum Foo { A, B } fn main() { let a = A; } ``` or ``` pub enum Foo { A, B } fn main() { let a = Foo::A; } ``` [breaking-change]
2014-11-06 02:05:53 -06:00
let mut x = Enum::A(&mut n);
librustc: Disallow mutation and assignment in pattern guards, and modify the CFG for match statements. There were two bugs in issue #14684. One was simply that the borrow check didn't know about the correct CFG for match statements: the pattern must be a predecessor of the guard. This disallows the bad behavior if there are bindings in the pattern. But it isn't enough to prevent the memory safety problem, because of wildcards; thus, this patch introduces a more restrictive rule, which disallows assignments and mutable borrows inside guards outright. I discussed this with Niko and we decided this was the best plan of action. This breaks code that performs mutable borrows in pattern guards. Most commonly, the code looks like this: impl Foo { fn f(&mut self, ...) {} fn g(&mut self, ...) { match bar { Baz if self.f(...) => { ... } _ => { ... } } } } Change this code to not use a guard. For example: impl Foo { fn f(&mut self, ...) {} fn g(&mut self, ...) { match bar { Baz => { if self.f(...) { ... } else { ... } } _ => { ... } } } } Sometimes this can result in code duplication, but often it illustrates a hidden memory safety problem. Closes #14684. [breaking-change]
2014-07-25 17:18:19 -05:00
match x {
Switch to purely namespaced enums This breaks code that referred to variant names in the same namespace as their enum. Reexport the variants in the old location or alter code to refer to the new locations: ``` pub enum Foo { A, B } fn main() { let a = A; } ``` => ``` pub use self::Foo::{A, B}; pub enum Foo { A, B } fn main() { let a = A; } ``` or ``` pub enum Foo { A, B } fn main() { let a = Foo::A; } ``` [breaking-change]
2014-11-06 02:05:53 -06:00
Enum::A(_) if { x = Enum::B(false); false } => 1,
librustc: Disallow mutation and assignment in pattern guards, and modify the CFG for match statements. There were two bugs in issue #14684. One was simply that the borrow check didn't know about the correct CFG for match statements: the pattern must be a predecessor of the guard. This disallows the bad behavior if there are bindings in the pattern. But it isn't enough to prevent the memory safety problem, because of wildcards; thus, this patch introduces a more restrictive rule, which disallows assignments and mutable borrows inside guards outright. I discussed this with Niko and we decided this was the best plan of action. This breaks code that performs mutable borrows in pattern guards. Most commonly, the code looks like this: impl Foo { fn f(&mut self, ...) {} fn g(&mut self, ...) { match bar { Baz if self.f(...) => { ... } _ => { ... } } } } Change this code to not use a guard. For example: impl Foo { fn f(&mut self, ...) {} fn g(&mut self, ...) { match bar { Baz => { if self.f(...) { ... } else { ... } } _ => { ... } } } } Sometimes this can result in code duplication, but often it illustrates a hidden memory safety problem. Closes #14684. [breaking-change]
2014-07-25 17:18:19 -05:00
//~^ ERROR cannot assign in a pattern guard
Switch to purely namespaced enums This breaks code that referred to variant names in the same namespace as their enum. Reexport the variants in the old location or alter code to refer to the new locations: ``` pub enum Foo { A, B } fn main() { let a = A; } ``` => ``` pub use self::Foo::{A, B}; pub enum Foo { A, B } fn main() { let a = A; } ``` or ``` pub enum Foo { A, B } fn main() { let a = Foo::A; } ``` [breaking-change]
2014-11-06 02:05:53 -06:00
Enum::A(_) if { let y = &mut x; *y = Enum::B(false); false } => 1,
librustc: Disallow mutation and assignment in pattern guards, and modify the CFG for match statements. There were two bugs in issue #14684. One was simply that the borrow check didn't know about the correct CFG for match statements: the pattern must be a predecessor of the guard. This disallows the bad behavior if there are bindings in the pattern. But it isn't enough to prevent the memory safety problem, because of wildcards; thus, this patch introduces a more restrictive rule, which disallows assignments and mutable borrows inside guards outright. I discussed this with Niko and we decided this was the best plan of action. This breaks code that performs mutable borrows in pattern guards. Most commonly, the code looks like this: impl Foo { fn f(&mut self, ...) {} fn g(&mut self, ...) { match bar { Baz if self.f(...) => { ... } _ => { ... } } } } Change this code to not use a guard. For example: impl Foo { fn f(&mut self, ...) {} fn g(&mut self, ...) { match bar { Baz => { if self.f(...) { ... } else { ... } } _ => { ... } } } } Sometimes this can result in code duplication, but often it illustrates a hidden memory safety problem. Closes #14684. [breaking-change]
2014-07-25 17:18:19 -05:00
//~^ ERROR cannot mutably borrow in a pattern guard
//~^^ ERROR cannot assign in a pattern guard
Switch to purely namespaced enums This breaks code that referred to variant names in the same namespace as their enum. Reexport the variants in the old location or alter code to refer to the new locations: ``` pub enum Foo { A, B } fn main() { let a = A; } ``` => ``` pub use self::Foo::{A, B}; pub enum Foo { A, B } fn main() { let a = A; } ``` or ``` pub enum Foo { A, B } fn main() { let a = Foo::A; } ``` [breaking-change]
2014-11-06 02:05:53 -06:00
Enum::A(p) => *p,
Enum::B(_) => 2,
librustc: Disallow mutation and assignment in pattern guards, and modify the CFG for match statements. There were two bugs in issue #14684. One was simply that the borrow check didn't know about the correct CFG for match statements: the pattern must be a predecessor of the guard. This disallows the bad behavior if there are bindings in the pattern. But it isn't enough to prevent the memory safety problem, because of wildcards; thus, this patch introduces a more restrictive rule, which disallows assignments and mutable borrows inside guards outright. I discussed this with Niko and we decided this was the best plan of action. This breaks code that performs mutable borrows in pattern guards. Most commonly, the code looks like this: impl Foo { fn f(&mut self, ...) {} fn g(&mut self, ...) { match bar { Baz if self.f(...) => { ... } _ => { ... } } } } Change this code to not use a guard. For example: impl Foo { fn f(&mut self, ...) {} fn g(&mut self, ...) { match bar { Baz => { if self.f(...) { ... } else { ... } } _ => { ... } } } } Sometimes this can result in code duplication, but often it illustrates a hidden memory safety problem. Closes #14684. [breaking-change]
2014-07-25 17:18:19 -05:00
}
}
fn main() {
foo();
}
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