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Rollup merge of #80834 - bugadani:vecdeque, r=oli-obk

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Remove unreachable panics from VecDeque::{front/back}[_mut]

`VecDeque`'s `front`, `front_mut`, `back` and `back_mut` methods are implemented in terms of the index operator, which causes these functions to contain [unreachable panic calls](https://rust.godbolt.org/z/MTnq1o).

This PR reimplements these methods in terms of `get[_mut]` instead.
This commit is contained in:
Yuki Okushi 2021-01-15 18:26:11 +09:00 • committed by GitHub
commit 1b8fd02daa
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2 changed files with 23 additions and 5 deletions
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9
library/alloc/src/collections/vec_deque/mod.rs
View file

@ -1292,7 +1292,7 @@ impl<T> VecDeque<T> {
/// ``` /// ```
#[stable(feature = "rust1", since = "1.0.0")] #[stable(feature = "rust1", since = "1.0.0")]
pub fn front(&self) -> Option<&T> { pub fn front(&self) -> Option<&T> {
if !self.is_empty() { Some(&self[0]) } else { None } self.get(0)
} }
/// Provides a mutable reference to the front element, or `None` if the /// Provides a mutable reference to the front element, or `None` if the
@ -1316,7 +1316,7 @@ impl<T> VecDeque<T> {
/// ``` /// ```
#[stable(feature = "rust1", since = "1.0.0")] #[stable(feature = "rust1", since = "1.0.0")]
pub fn front_mut(&mut self) -> Option<&mut T> { pub fn front_mut(&mut self) -> Option<&mut T> {
if !self.is_empty() { Some(&mut self[0]) } else { None } self.get_mut(0)
} }
/// Provides a reference to the back element, or `None` if the `VecDeque` is /// Provides a reference to the back element, or `None` if the `VecDeque` is
@ -1336,7 +1336,7 @@ impl<T> VecDeque<T> {
/// ``` /// ```
#[stable(feature = "rust1", since = "1.0.0")] #[stable(feature = "rust1", since = "1.0.0")]
pub fn back(&self) -> Option<&T> { pub fn back(&self) -> Option<&T> {
if !self.is_empty() { Some(&self[self.len() - 1]) } else { None } self.get(self.len().wrapping_sub(1))
} }
/// Provides a mutable reference to the back element, or `None` if the /// Provides a mutable reference to the back element, or `None` if the
@ -1360,8 +1360,7 @@ impl<T> VecDeque<T> {
/// ``` /// ```
#[stable(feature = "rust1", since = "1.0.0")] #[stable(feature = "rust1", since = "1.0.0")]
pub fn back_mut(&mut self) -> Option<&mut T> { pub fn back_mut(&mut self) -> Option<&mut T> {
let len = self.len(); self.get_mut(self.len().wrapping_sub(1))
if !self.is_empty() { Some(&mut self[len - 1]) } else { None }
} }
/// Removes the first element and returns it, or `None` if the `VecDeque` is /// Removes the first element and returns it, or `None` if the `VecDeque` is

19
src/test/codegen/vecdeque_no_panic.rs Normal file
View file

@ -0,0 +1,19 @@
// This test checks that `VecDeque::front[_mut]()` and `VecDeque::back[_mut]()` can't panic.
// compile-flags: -O
// ignore-debug: the debug assertions get in the way
#![crate_type = "lib"]
use std::collections::VecDeque;
// CHECK-LABEL: @dont_panic
#[no_mangle]
pub fn dont_panic(v: &mut VecDeque<usize>) {
// CHECK-NOT: expect
// CHECK-NOT: panic
v.front();
v.front_mut();
v.back();
v.back_mut();
}