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Auto merge of #89755 - jkugelman:must-use-conversions-that-move-self, r=joshtriplett

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Add #[must_use] to conversions that move self

Everything here got the same message. Is the wording okay?

```rust
#[must_use = "`self` will be dropped if the result is not used"]
```

I want to draw attention to these methods in particular:

```rust
alloc::sync::Arc<MaybeUninit<T>>     unsafe fn assume_init(self) -> Arc<T>;
alloc::sync::Arc<[MaybeUninit<T>]>   unsafe fn assume_init(self) -> Arc<[T]>;
core::pin::Pin<&'a mut T>            const fn into_ref(self) -> Pin<&'a T>;
core::pin::Pin<&'a mut T>            const fn get_mut(self) -> &'a mut T;
core::pin::Pin<&'a mut T>            const unsafe fn get_unchecked_mut(self) -> &'a mut T;
core::pin::Pin<&'a mut T>            unsafe fn map_unchecked_mut(self, func: F) -> Pin<&'a mut U>;
core::pin::Pin<&'a mut Pin<P>>       fn as_deref_mut(self) -> Pin<&'a mut P::Target>;
```

Parent issue: #89692

r? `@joshtriplett`
This commit is contained in:
bors 2021-10-11 07:27:44 +00:00
commit 86d6d2b738
19 changed files with 54 additions and 11 deletions
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2
library/alloc/src/collections/binary_heap.rs
View File

@ -848,6 +848,7 @@ impl<T> BinaryHeap<T> {
///
/// assert_eq!(heap.into_iter_sorted().take(2).collect::<Vec<_>>(), vec![5, 4]);
/// ```
#[must_use = "`self` will be dropped if the result is not used"]
#[unstable(feature = "binary_heap_into_iter_sorted", issue = "59278")]
pub fn into_iter_sorted(self) -> IntoIterSorted<T> {
IntoIterSorted { inner: self }
@ -1028,6 +1029,7 @@ impl<T> BinaryHeap<T> {
/// println!("{}", x);
/// }
/// ```
#[must_use = "`self` will be dropped if the result is not used"]
#[stable(feature = "binary_heap_extras_15", since = "1.5.0")]
pub fn into_vec(self) -> Vec<T> {
self.into()

2
library/alloc/src/collections/btree/map.rs
View File

@ -1264,6 +1264,7 @@ impl<K, V> BTreeMap<K, V> {
/// assert_eq!(keys, [1, 2]);
/// ```
#[inline]
#[must_use = "`self` will be dropped if the result is not used"]
#[stable(feature = "map_into_keys_values", since = "1.54.0")]
pub fn into_keys(self) -> IntoKeys<K, V> {
IntoKeys { inner: self.into_iter() }
@ -1286,6 +1287,7 @@ impl<K, V> BTreeMap<K, V> {
/// assert_eq!(values, ["hello", "goodbye"]);
/// ```
#[inline]
#[must_use = "`self` will be dropped if the result is not used"]
#[stable(feature = "map_into_keys_values", since = "1.54.0")]
pub fn into_values(self) -> IntoValues<K, V> {
IntoValues { inner: self.into_iter() }

1
library/alloc/src/collections/btree/map/entry.rs
View File

@ -448,6 +448,7 @@ impl<'a, K: Ord, V> OccupiedEntry<'a, K, V> {
/// }
/// assert_eq!(map["poneyland"], 22);
/// ```
#[must_use = "`self` will be dropped if the result is not used"]
#[stable(feature = "rust1", since = "1.0.0")]
pub fn into_mut(self) -> &'a mut V {
self.handle.into_val_mut()

20
library/alloc/src/collections/btree/map/tests.rs
View File

@ -1755,20 +1755,20 @@ fn test_send() {
#[test]
fn test_ord_absence() {
fn map<K>(mut map: BTreeMap<K, ()>) {
map.is_empty();
map.len();
let _ = map.is_empty();
let _ = map.len();
map.clear();
map.iter();
map.iter_mut();
map.keys();
map.values();
map.values_mut();
let _ = map.iter();
let _ = map.iter_mut();
let _ = map.keys();
let _ = map.values();
let _ = map.values_mut();
if true {
map.into_values();
let _ = map.into_values();
} else if true {
map.into_iter();
let _ = map.into_iter();
} else {
map.into_keys();
let _ = map.into_keys();
}
}

1
library/alloc/src/rc.rs
View File

@ -2130,6 +2130,7 @@ impl<T: ?Sized> Weak<T> {
///
/// [`from_raw`]: Weak::from_raw
/// [`as_ptr`]: Weak::as_ptr
#[must_use = "`self` will be dropped if the result is not used"]
#[stable(feature = "weak_into_raw", since = "1.45.0")]
pub fn into_raw(self) -> *const T {
let result = self.as_ptr();

4
library/alloc/src/string.rs
View File

@ -676,6 +676,7 @@ impl String {
/// let rebuilt = unsafe { String::from_raw_parts(ptr, len, cap) };
/// assert_eq!(rebuilt, "hello");
/// ```
#[must_use = "`self` will be dropped if the result is not used"]
#[unstable(feature = "vec_into_raw_parts", reason = "new API", issue = "65816")]
pub fn into_raw_parts(self) -> (*mut u8, usize, usize) {
self.vec.into_raw_parts()
@ -781,6 +782,7 @@ impl String {
/// assert_eq!(&[104, 101, 108, 108, 111][..], &bytes[..]);
/// ```
#[inline]
#[must_use = "`self` will be dropped if the result is not used"]
#[stable(feature = "rust1", since = "1.0.0")]
pub fn into_bytes(self) -> Vec<u8> {
self.vec
@ -1738,6 +1740,7 @@ impl String {
/// ```
#[cfg(not(no_global_oom_handling))]
#[stable(feature = "box_str", since = "1.4.0")]
#[must_use = "`self` will be dropped if the result is not used"]
#[inline]
pub fn into_boxed_str(self) -> Box<str> {
let slice = self.vec.into_boxed_slice();
@ -1783,6 +1786,7 @@ impl FromUtf8Error {
///
/// assert_eq!(vec![0, 159], value.unwrap_err().into_bytes());
/// ```
#[must_use = "`self` will be dropped if the result is not used"]
#[stable(feature = "rust1", since = "1.0.0")]
pub fn into_bytes(self) -> Vec<u8> {
self.bytes

3
library/alloc/src/sync.rs
View File

@ -735,6 +735,7 @@ impl<T> Arc<mem::MaybeUninit<T>> {
/// assert_eq!(*five, 5)
/// ```
#[unstable(feature = "new_uninit", issue = "63291")]
#[must_use = "`self` will be dropped if the result is not used"]
#[inline]
pub unsafe fn assume_init(self) -> Arc<T> {
Arc::from_inner(mem::ManuallyDrop::new(self).ptr.cast())
@ -776,6 +777,7 @@ impl<T> Arc<[mem::MaybeUninit<T>]> {
/// assert_eq!(*values, [1, 2, 3])
/// ```
#[unstable(feature = "new_uninit", issue = "63291")]
#[must_use = "`self` will be dropped if the result is not used"]
#[inline]
pub unsafe fn assume_init(self) -> Arc<[T]> {
unsafe { Arc::from_ptr(mem::ManuallyDrop::new(self).ptr.as_ptr() as _) }
@ -1759,6 +1761,7 @@ impl<T: ?Sized> Weak<T> {
///
/// [`from_raw`]: Weak::from_raw
/// [`as_ptr`]: Weak::as_ptr
#[must_use = "`self` will be dropped if the result is not used"]
#[stable(feature = "weak_into_raw", since = "1.45.0")]
pub fn into_raw(self) -> *const T {
let result = self.as_ptr();

2
library/core/src/option.rs
View File

@ -1473,6 +1473,7 @@ impl<T: Copy> Option<&mut T> {
/// let copied = opt_x.copied();
/// assert_eq!(copied, Some(12));
/// ```
#[must_use = "`self` will be dropped if the result is not used"]
#[stable(feature = "copied", since = "1.35.0")]
pub fn copied(self) -> Option<T> {
self.map(|&mut t| t)
@ -1492,6 +1493,7 @@ impl<T: Clone> Option<&T> {
/// let cloned = opt_x.cloned();
/// assert_eq!(cloned, Some(12));
/// ```
#[must_use = "`self` will be dropped if the result is not used"]
#[stable(feature = "rust1", since = "1.0.0")]
pub fn cloned(self) -> Option<T> {
self.map(|t| t.clone())

5
library/core/src/pin.rs
View File

@ -715,6 +715,7 @@ impl<'a, T: ?Sized> Pin<&'a T> {
impl<'a, T: ?Sized> Pin<&'a mut T> {
/// Converts this `Pin<&mut T>` into a `Pin<&T>` with the same lifetime.
#[inline(always)]
#[must_use = "`self` will be dropped if the result is not used"]
#[rustc_const_unstable(feature = "const_pin", issue = "76654")]
#[stable(feature = "pin", since = "1.33.0")]
pub const fn into_ref(self) -> Pin<&'a T> {
@ -731,6 +732,7 @@ impl<'a, T: ?Sized> Pin<&'a mut T> {
/// the `Pin` itself. This method allows turning the `Pin` into a reference
/// with the same lifetime as the original `Pin`.
#[inline(always)]
#[must_use = "`self` will be dropped if the result is not used"]
#[stable(feature = "pin", since = "1.33.0")]
#[rustc_const_unstable(feature = "const_pin", issue = "76654")]
pub const fn get_mut(self) -> &'a mut T
@ -751,6 +753,7 @@ impl<'a, T: ?Sized> Pin<&'a mut T> {
/// If the underlying data is `Unpin`, `Pin::get_mut` should be used
/// instead.
#[inline(always)]
#[must_use = "`self` will be dropped if the result is not used"]
#[stable(feature = "pin", since = "1.33.0")]
#[rustc_const_unstable(feature = "const_pin", issue = "76654")]
pub const unsafe fn get_unchecked_mut(self) -> &'a mut T {
@ -772,6 +775,7 @@ impl<'a, T: ?Sized> Pin<&'a mut T> {
/// not move out of the argument you receive to the interior function.
///
/// [`pin` module]: self#projections-and-structural-pinning
#[must_use = "`self` will be dropped if the result is not used"]
#[stable(feature = "pin", since = "1.33.0")]
pub unsafe fn map_unchecked_mut<U, F>(self, func: F) -> Pin<&'a mut U>
where
@ -811,6 +815,7 @@ impl<'a, P: DerefMut> Pin<&'a mut Pin<P>> {
/// implementations of `P::DerefMut` are likewise ruled out by the contract of
/// `Pin::new_unchecked`.
#[unstable(feature = "pin_deref_mut", issue = "86918")]
#[must_use = "`self` will be dropped if the result is not used"]
#[inline(always)]
pub fn as_deref_mut(self) -> Pin<&'a mut P::Target> {
// SAFETY: What we're asserting here is that going from

2
library/core/src/ptr/unique.rs
View File

@ -101,6 +101,7 @@ impl<T: ?Sized> Unique<T> {
}
/// Acquires the underlying `*mut` pointer.
#[must_use = "`self` will be dropped if the result is not used"]
#[inline]
pub const fn as_ptr(self) -> *mut T {
self.pointer as *mut T
@ -131,6 +132,7 @@ impl<T: ?Sized> Unique<T> {
}
/// Casts to a pointer of another type.
#[must_use = "`self` will be dropped if the result is not used"]
#[inline]
pub const fn cast<U>(self) -> Unique<U> {
// SAFETY: Unique::new_unchecked() creates a new unique and needs

4
library/core/src/slice/iter.rs
View File

@ -267,6 +267,7 @@ impl<'a, T> IterMut<'a, T> {
/// // Now slice is "[2, 2, 3]":
/// println!("{:?}", slice);
/// ```
#[must_use = "`self` will be dropped if the result is not used"]
#[stable(feature = "iter_to_slice", since = "1.4.0")]
pub fn into_slice(self) -> &'a mut [T] {
// SAFETY: the iterator was created from a mutable slice with pointer
@ -1869,6 +1870,7 @@ impl<'a, T> ChunksExactMut<'a, T> {
/// Returns the remainder of the original slice that is not going to be
/// returned by the iterator. The returned slice has at most `chunk_size-1`
/// elements.
#[must_use = "`self` will be dropped if the result is not used"]
#[stable(feature = "chunks_exact", since = "1.31.0")]
pub fn into_remainder(self) -> &'a mut [T] {
self.rem
@ -2264,6 +2266,7 @@ impl<'a, T, const N: usize> ArrayChunksMut<'a, T, N> {
/// Returns the remainder of the original slice that is not going to be
/// returned by the iterator. The returned slice has at most `N-1`
/// elements.
#[must_use = "`self` will be dropped if the result is not used"]
#[unstable(feature = "array_chunks", issue = "74985")]
pub fn into_remainder(self) -> &'a mut [T] {
self.rem
@ -2875,6 +2878,7 @@ impl<'a, T> RChunksExactMut<'a, T> {
/// Returns the remainder of the original slice that is not going to be
/// returned by the iterator. The returned slice has at most `chunk_size-1`
/// elements.
#[must_use = "`self` will be dropped if the result is not used"]
#[stable(feature = "rchunks", since = "1.31.0")]
pub fn into_remainder(self) -> &'a mut [T] {
self.rem

3
library/std/src/collections/hash/map.rs
View File

@ -1720,6 +1720,7 @@ impl<'a, K, V, S> RawOccupiedEntryMut<'a, K, V, S> {
/// Converts the entry into a mutable reference to the key in the entry
/// with a lifetime bound to the map itself.
#[inline]
#[must_use = "`self` will be dropped if the result is not used"]
#[unstable(feature = "hash_raw_entry", issue = "56167")]
pub fn into_key(self) -> &'a mut K {
self.base.into_key()
@ -1735,6 +1736,7 @@ impl<'a, K, V, S> RawOccupiedEntryMut<'a, K, V, S> {
/// Converts the `OccupiedEntry` into a mutable reference to the value in the entry
/// with a lifetime bound to the map itself.
#[inline]
#[must_use = "`self` will be dropped if the result is not used"]
#[unstable(feature = "hash_raw_entry", issue = "56167")]
pub fn into_mut(self) -> &'a mut V {
self.base.into_mut()
@ -1764,6 +1766,7 @@ impl<'a, K, V, S> RawOccupiedEntryMut<'a, K, V, S> {
/// Converts the `OccupiedEntry` into a mutable reference to the key and value in the entry
/// with a lifetime bound to the map itself.
#[inline]
#[must_use = "`self` will be dropped if the result is not used"]
#[unstable(feature = "hash_raw_entry", issue = "56167")]
pub fn into_key_value(self) -> (&'a mut K, &'a mut V) {
self.base.into_key_value()

8
library/std/src/ffi/c_str.rs
View File

@ -322,6 +322,7 @@ impl FromVecWithNulError {
///
/// assert_eq!(bytes, value.unwrap_err().into_bytes());
/// ```
#[must_use = "`self` will be dropped if the result is not used"]
pub fn into_bytes(self) -> Vec<u8> {
self.bytes
}
@ -524,6 +525,7 @@ impl CString {
/// }
/// ```
#[inline]
#[must_use = "`self` will be dropped if the result is not used"]
#[stable(feature = "cstr_memory", since = "1.4.0")]
pub fn into_raw(self) -> *mut c_char {
Box::into_raw(self.into_inner()) as *mut c_char
@ -547,7 +549,6 @@ impl CString {
/// let err = cstring.into_string().err().expect("into_string().err() failed");
/// assert_eq!(err.utf8_error().valid_up_to(), 1);
/// ```
#[stable(feature = "cstring_into", since = "1.7.0")]
pub fn into_string(self) -> Result<String, IntoStringError> {
String::from_utf8(self.into_bytes()).map_err(|e| IntoStringError {
@ -571,6 +572,7 @@ impl CString {
/// let bytes = c_string.into_bytes();
/// assert_eq!(bytes, vec![b'f', b'o', b'o']);
/// ```
#[must_use = "`self` will be dropped if the result is not used"]
#[stable(feature = "cstring_into", since = "1.7.0")]
pub fn into_bytes(self) -> Vec<u8> {
let mut vec = self.into_inner().into_vec();
@ -591,6 +593,7 @@ impl CString {
/// let bytes = c_string.into_bytes_with_nul();
/// assert_eq!(bytes, vec![b'f', b'o', b'o', b'\0']);
/// ```
#[must_use = "`self` will be dropped if the result is not used"]
#[stable(feature = "cstring_into", since = "1.7.0")]
pub fn into_bytes_with_nul(self) -> Vec<u8> {
self.into_inner().into_vec()
@ -667,6 +670,7 @@ impl CString {
/// assert_eq!(&*boxed,
/// CStr::from_bytes_with_nul(b"foo\0").expect("CStr::from_bytes_with_nul failed"));
/// ```
#[must_use = "`self` will be dropped if the result is not used"]
#[stable(feature = "into_boxed_c_str", since = "1.20.0")]
pub fn into_boxed_c_str(self) -> Box<CStr> {
unsafe { Box::from_raw(Box::into_raw(self.into_inner()) as *mut CStr) }
@ -1018,6 +1022,7 @@ impl NulError {
/// let nul_error = CString::new("foo\0bar").unwrap_err();
/// assert_eq!(nul_error.into_vec(), b"foo\0bar");
/// ```
#[must_use = "`self` will be dropped if the result is not used"]
#[stable(feature = "rust1", since = "1.0.0")]
pub fn into_vec(self) -> Vec<u8> {
self.1
@ -1092,6 +1097,7 @@ impl fmt::Display for FromVecWithNulError {
impl IntoStringError {
/// Consumes this error, returning original [`CString`] which generated the
/// error.
#[must_use = "`self` will be dropped if the result is not used"]
#[stable(feature = "cstring_into", since = "1.7.0")]
pub fn into_cstring(self) -> CString {
self.inner

1
library/std/src/ffi/os_str.rs
View File

@ -346,6 +346,7 @@ impl OsString {
///
/// let b: Box<OsStr> = s.into_boxed_os_str();
/// ```
#[must_use = "`self` will be dropped if the result is not used"]
#[stable(feature = "into_boxed_os_str", since = "1.20.0")]
pub fn into_boxed_os_str(self) -> Box<OsStr> {
let rw = Box::into_raw(self.inner.into_box()) as *mut OsStr;

1
library/std/src/io/buffered/bufwriter.rs
View File

@ -476,6 +476,7 @@ pub struct WriterPanicked {
impl WriterPanicked {
/// Returns the perhaps-unwritten data. Some of this data may have been written by the
/// panicking call(s) to the underlying writer, so simply writing it again is not a good idea.
#[must_use = "`self` will be dropped if the result is not used"]
#[stable(feature = "bufwriter_into_parts", since = "1.56.0")]
pub fn into_inner(self) -> Vec<u8> {
self.buf

1
library/std/src/io/error.rs
View File

@ -657,6 +657,7 @@ impl Error {
/// }
/// ```
#[stable(feature = "io_error_inner", since = "1.3.0")]
#[must_use = "`self` will be dropped if the result is not used"]
#[inline]
pub fn into_inner(self) -> Option<Box<dyn error::Error + Send + Sync>> {
match self.repr {

1
library/std/src/io/stdio.rs
View File

@ -464,6 +464,7 @@ impl Stdin {
/// println!("got a line: {}", line.unwrap());
/// }
/// ```
#[must_use = "`self` will be dropped if the result is not used"]
#[unstable(feature = "stdin_forwarders", issue = "87096")]
pub fn lines(self) -> Lines<StdinLock<'static>> {
self.into_locked().lines()

1
library/std/src/net/tcp.rs
View File

@ -883,6 +883,7 @@ impl TcpListener {
/// Ok(())
/// }
/// ```
#[must_use = "`self` will be dropped if the result is not used"]
#[unstable(feature = "tcplistener_into_incoming", issue = "88339")]
pub fn into_incoming(self) -> IntoIncoming {
IntoIncoming { listener: self }

3
library/std/src/path.rs
View File

@ -532,6 +532,7 @@ impl<'a> Component<'a> {
/// let components: Vec<_> = path.components().map(|comp| comp.as_os_str()).collect();
/// assert_eq!(&components, &[".", "tmp", "foo", "bar.txt"]);
/// ```
#[must_use = "`self` will be dropped if the result is not used"]
#[stable(feature = "rust1", since = "1.0.0")]
pub fn as_os_str(self) -> &'a OsStr {
match self {
@ -1428,6 +1429,7 @@ impl PathBuf {
/// let os_str = p.into_os_string();
/// ```
#[stable(feature = "rust1", since = "1.0.0")]
#[must_use = "`self` will be dropped if the result is not used"]
#[inline]
pub fn into_os_string(self) -> OsString {
self.inner
@ -1435,6 +1437,7 @@ impl PathBuf {
/// Converts this `PathBuf` into a [boxed](Box) [`Path`].
#[stable(feature = "into_boxed_path", since = "1.20.0")]
#[must_use = "`self` will be dropped if the result is not used"]
#[inline]
pub fn into_boxed_path(self) -> Box<Path> {
let rw = Box::into_raw(self.inner.into_boxed_os_str()) as *mut Path;