diff --git a/library/alloc/src/str.rs b/library/alloc/src/str.rs
index 2900d01d9bdae..ac7f230445656 100644
--- a/library/alloc/src/str.rs
+++ b/library/alloc/src/str.rs
@@ -595,6 +595,7 @@ impl str {
/// assert_eq!("☺", &*smile);
/// ```
#[stable(feature = "str_box_extras", since = "1.20.0")]
+#[must_use]
#[inline]
pub unsafe fn from_boxed_utf8_unchecked(v: Box<[u8]>) -> Box<str> {
unsafe { Box::from_raw(Box::into_raw(v) as *mut str) }
diff --git a/library/alloc/src/string.rs b/library/alloc/src/string.rs
index d88b8e398985a..0c383b8bdb6c6 100644
--- a/library/alloc/src/string.rs
+++ b/library/alloc/src/string.rs
@@ -761,6 +761,7 @@ impl String {
/// assert_eq!("💖", sparkle_heart);
/// ```
#[inline]
+ #[must_use]
#[stable(feature = "rust1", since = "1.0.0")]
pub unsafe fn from_utf8_unchecked(bytes: Vec<u8>) -> String {
String { vec: bytes }
diff --git a/library/core/src/alloc/layout.rs b/library/core/src/alloc/layout.rs
index ccf6e420de7a9..8086dd357306e 100644
--- a/library/core/src/alloc/layout.rs
+++ b/library/core/src/alloc/layout.rs
@@ -94,6 +94,7 @@ impl Layout {
/// [`Layout::from_size_align`].
#[stable(feature = "alloc_layout", since = "1.28.0")]
#[rustc_const_stable(feature = "alloc_layout", since = "1.36.0")]
+ #[must_use]
#[inline]
pub const unsafe fn from_size_align_unchecked(size: usize, align: usize) -> Self {
// SAFETY: the caller must ensure that `align` is greater than zero.
diff --git a/library/core/src/char/convert.rs b/library/core/src/char/convert.rs
index 7a0ec32cc61a9..72921414fb3f2 100644
--- a/library/core/src/char/convert.rs
+++ b/library/core/src/char/convert.rs
@@ -48,6 +48,7 @@ use super::MAX;
/// assert_eq!(None, c);
/// ```
#[doc(alias = "chr")]
+#[must_use]
#[inline]
#[stable(feature = "rust1", since = "1.0.0")]
pub fn from_u32(i: u32) -> Option<char> {
@@ -88,6 +89,7 @@ pub fn from_u32(i: u32) -> Option<char> {
/// assert_eq!('❤', c);
/// ```
#[inline]
+#[must_use]
#[stable(feature = "char_from_unchecked", since = "1.5.0")]
pub unsafe fn from_u32_unchecked(i: u32) -> char {
// SAFETY: the caller must guarantee that `i` is a valid char value.
@@ -319,6 +321,7 @@ impl fmt::Display for CharTryFromError {
/// let c = char::from_digit(1, 37);
/// ```
#[inline]
+#[must_use]
#[stable(feature = "rust1", since = "1.0.0")]
pub fn from_digit(num: u32, radix: u32) -> Option<char> {
if radix > 36 {
diff --git a/library/core/src/char/methods.rs b/library/core/src/char/methods.rs
index b3af1f1ffb592..07ac08f45c79f 100644
--- a/library/core/src/char/methods.rs
+++ b/library/core/src/char/methods.rs
@@ -136,6 +136,7 @@ impl char {
/// assert_eq!(None, c);
/// ```
#[stable(feature = "assoc_char_funcs", since = "1.52.0")]
+ #[must_use]
#[inline]
pub fn from_u32(i: u32) -> Option<char> {
super::convert::from_u32(i)
@@ -177,6 +178,7 @@ impl char {
/// assert_eq!('❤', c);
/// ```
#[stable(feature = "assoc_char_funcs", since = "1.52.0")]
+ #[must_use]
#[inline]
pub unsafe fn from_u32_unchecked(i: u32) -> char {
// SAFETY: the safety contract must be upheld by the caller.
@@ -230,9 +232,10 @@ impl char {
/// use std::char;
///
/// // this panics
- /// char::from_digit(1, 37);
+ /// let _c = char::from_digit(1, 37);
/// ```
#[stable(feature = "assoc_char_funcs", since = "1.52.0")]
+ #[must_use]
#[inline]
pub fn from_digit(num: u32, radix: u32) -> Option<char> {
super::convert::from_digit(num, radix)
diff --git a/library/core/src/num/f32.rs b/library/core/src/num/f32.rs
index c47a2e8b05c4b..fd82be33d1abd 100644
--- a/library/core/src/num/f32.rs
+++ b/library/core/src/num/f32.rs
@@ -786,6 +786,7 @@ impl f32 {
/// ```
#[stable(feature = "float_bits_conv", since = "1.20.0")]
#[rustc_const_unstable(feature = "const_float_bits_conv", issue = "72447")]
+ #[must_use]
#[inline]
pub const fn from_bits(v: u32) -> Self {
// SAFETY: `u32` is a plain old datatype so we can always transmute from it
@@ -864,6 +865,7 @@ impl f32 {
/// ```
#[stable(feature = "float_to_from_bytes", since = "1.40.0")]
#[rustc_const_unstable(feature = "const_float_bits_conv", issue = "72447")]
+ #[must_use]
#[inline]
pub const fn from_be_bytes(bytes: [u8; 4]) -> Self {
Self::from_bits(u32::from_be_bytes(bytes))
@@ -879,6 +881,7 @@ impl f32 {
/// ```
#[stable(feature = "float_to_from_bytes", since = "1.40.0")]
#[rustc_const_unstable(feature = "const_float_bits_conv", issue = "72447")]
+ #[must_use]
#[inline]
pub const fn from_le_bytes(bytes: [u8; 4]) -> Self {
Self::from_bits(u32::from_le_bytes(bytes))
@@ -905,6 +908,7 @@ impl f32 {
/// ```
#[stable(feature = "float_to_from_bytes", since = "1.40.0")]
#[rustc_const_unstable(feature = "const_float_bits_conv", issue = "72447")]
+ #[must_use]
#[inline]
pub const fn from_ne_bytes(bytes: [u8; 4]) -> Self {
Self::from_bits(u32::from_ne_bytes(bytes))
diff --git a/library/core/src/num/f64.rs b/library/core/src/num/f64.rs
index cfcc08b9addeb..e7dec62c04ead 100644
--- a/library/core/src/num/f64.rs
+++ b/library/core/src/num/f64.rs
@@ -800,6 +800,7 @@ impl f64 {
/// ```
#[stable(feature = "float_bits_conv", since = "1.20.0")]
#[rustc_const_unstable(feature = "const_float_bits_conv", issue = "72447")]
+ #[must_use]
#[inline]
pub const fn from_bits(v: u64) -> Self {
// SAFETY: `u64` is a plain old datatype so we can always transmute from it
@@ -878,6 +879,7 @@ impl f64 {
/// ```
#[stable(feature = "float_to_from_bytes", since = "1.40.0")]
#[rustc_const_unstable(feature = "const_float_bits_conv", issue = "72447")]
+ #[must_use]
#[inline]
pub const fn from_be_bytes(bytes: [u8; 8]) -> Self {
Self::from_bits(u64::from_be_bytes(bytes))
@@ -893,6 +895,7 @@ impl f64 {
/// ```
#[stable(feature = "float_to_from_bytes", since = "1.40.0")]
#[rustc_const_unstable(feature = "const_float_bits_conv", issue = "72447")]
+ #[must_use]
#[inline]
pub const fn from_le_bytes(bytes: [u8; 8]) -> Self {
Self::from_bits(u64::from_le_bytes(bytes))
@@ -919,6 +922,7 @@ impl f64 {
/// ```
#[stable(feature = "float_to_from_bytes", since = "1.40.0")]
#[rustc_const_unstable(feature = "const_float_bits_conv", issue = "72447")]
+ #[must_use]
#[inline]
pub const fn from_ne_bytes(bytes: [u8; 8]) -> Self {
Self::from_bits(u64::from_ne_bytes(bytes))
diff --git a/library/core/src/num/int_macros.rs b/library/core/src/num/int_macros.rs
index 12dda61400f2a..7ef2d5c40034d 100644
--- a/library/core/src/num/int_macros.rs
+++ b/library/core/src/num/int_macros.rs
@@ -282,6 +282,7 @@ macro_rules! int_impl {
/// ```
#[stable(feature = "rust1", since = "1.0.0")]
#[rustc_const_stable(feature = "const_int_conversions", since = "1.32.0")]
+ #[must_use]
#[inline]
pub const fn from_be(x: Self) -> Self {
#[cfg(target_endian = "big")]
@@ -313,6 +314,7 @@ macro_rules! int_impl {
/// ```
#[stable(feature = "rust1", since = "1.0.0")]
#[rustc_const_stable(feature = "const_int_conversions", since = "1.32.0")]
+ #[must_use]
#[inline]
pub const fn from_le(x: Self) -> Self {
#[cfg(target_endian = "little")]
@@ -2620,6 +2622,7 @@ macro_rules! int_impl {
/// ```
#[stable(feature = "int_to_from_bytes", since = "1.32.0")]
#[rustc_const_stable(feature = "const_int_conversion", since = "1.44.0")]
+ #[must_use]
#[inline]
pub const fn from_be_bytes(bytes: [u8; mem::size_of::<Self>()]) -> Self {
Self::from_be(Self::from_ne_bytes(bytes))
@@ -2650,6 +2653,7 @@ macro_rules! int_impl {
/// ```
#[stable(feature = "int_to_from_bytes", since = "1.32.0")]
#[rustc_const_stable(feature = "const_int_conversion", since = "1.44.0")]
+ #[must_use]
#[inline]
pub const fn from_le_bytes(bytes: [u8; mem::size_of::<Self>()]) -> Self {
Self::from_le(Self::from_ne_bytes(bytes))
@@ -2691,6 +2695,7 @@ macro_rules! int_impl {
/// ```
#[stable(feature = "int_to_from_bytes", since = "1.32.0")]
#[rustc_const_stable(feature = "const_int_conversion", since = "1.44.0")]
+ #[must_use]
// SAFETY: const sound because integers are plain old datatypes so we can always
// transmute to them
#[inline]
diff --git a/library/core/src/num/saturating.rs b/library/core/src/num/saturating.rs
index f6dd3603c4914..cf8cf79fe46e0 100644
--- a/library/core/src/num/saturating.rs
+++ b/library/core/src/num/saturating.rs
@@ -644,6 +644,7 @@ macro_rules! saturating_int_impl {
/// }
/// ```
#[inline]
+ #[must_use]
#[unstable(feature = "saturating_int_impl", issue = "87920")]
pub const fn from_be(x: Self) -> Self {
Saturating(<$t>::from_be(x.0))
@@ -671,6 +672,7 @@ macro_rules! saturating_int_impl {
/// }
/// ```
#[inline]
+ #[must_use]
#[unstable(feature = "saturating_int_impl", issue = "87920")]
pub const fn from_le(x: Self) -> Self {
Saturating(<$t>::from_le(x.0))
diff --git a/library/core/src/num/uint_macros.rs b/library/core/src/num/uint_macros.rs
index 25cd582bb67d7..eb03be2a62ae9 100644
--- a/library/core/src/num/uint_macros.rs
+++ b/library/core/src/num/uint_macros.rs
@@ -285,6 +285,7 @@ macro_rules! uint_impl {
/// ```
#[stable(feature = "rust1", since = "1.0.0")]
#[rustc_const_stable(feature = "const_math", since = "1.32.0")]
+ #[must_use]
#[inline(always)]
pub const fn from_be(x: Self) -> Self {
#[cfg(target_endian = "big")]
@@ -317,6 +318,7 @@ macro_rules! uint_impl {
/// ```
#[stable(feature = "rust1", since = "1.0.0")]
#[rustc_const_stable(feature = "const_math", since = "1.32.0")]
+ #[must_use]
#[inline(always)]
pub const fn from_le(x: Self) -> Self {
#[cfg(target_endian = "little")]
@@ -2278,6 +2280,7 @@ macro_rules! uint_impl {
/// ```
#[stable(feature = "int_to_from_bytes", since = "1.32.0")]
#[rustc_const_stable(feature = "const_int_conversion", since = "1.44.0")]
+ #[must_use]
#[inline]
pub const fn from_be_bytes(bytes: [u8; mem::size_of::<Self>()]) -> Self {
Self::from_be(Self::from_ne_bytes(bytes))
@@ -2308,6 +2311,7 @@ macro_rules! uint_impl {
/// ```
#[stable(feature = "int_to_from_bytes", since = "1.32.0")]
#[rustc_const_stable(feature = "const_int_conversion", since = "1.44.0")]
+ #[must_use]
#[inline]
pub const fn from_le_bytes(bytes: [u8; mem::size_of::<Self>()]) -> Self {
Self::from_le(Self::from_ne_bytes(bytes))
@@ -2349,6 +2353,7 @@ macro_rules! uint_impl {
/// ```
#[stable(feature = "int_to_from_bytes", since = "1.32.0")]
#[rustc_const_stable(feature = "const_int_conversion", since = "1.44.0")]
+ #[must_use]
// SAFETY: const sound because integers are plain old datatypes so we can always
// transmute to them
#[inline]
diff --git a/library/core/src/num/wrapping.rs b/library/core/src/num/wrapping.rs
index b078cdf5479d7..cca83661b7ea6 100644
--- a/library/core/src/num/wrapping.rs
+++ b/library/core/src/num/wrapping.rs
@@ -638,6 +638,7 @@ macro_rules! wrapping_int_impl {
/// }
/// ```
#[inline]
+ #[must_use]
#[unstable(feature = "wrapping_int_impl", issue = "32463")]
pub const fn from_be(x: Self) -> Self {
Wrapping(<$t>::from_be(x.0))
@@ -665,6 +666,7 @@ macro_rules! wrapping_int_impl {
/// }
/// ```
#[inline]
+ #[must_use]
#[unstable(feature = "wrapping_int_impl", issue = "32463")]
pub const fn from_le(x: Self) -> Self {
Wrapping(<$t>::from_le(x.0))
diff --git a/library/core/src/str/converts.rs b/library/core/src/str/converts.rs
index da6ef1b6678c6..ed9f49f159611 100644
--- a/library/core/src/str/converts.rs
+++ b/library/core/src/str/converts.rs
@@ -155,6 +155,7 @@ pub fn from_utf8_mut(v: &mut [u8]) -> Result<&mut str, Utf8Error> {
/// assert_eq!("💖", sparkle_heart);
/// ```
#[inline]
+#[must_use]
#[stable(feature = "rust1", since = "1.0.0")]
#[rustc_const_stable(feature = "const_str_from_utf8_unchecked", since = "1.55.0")]
pub const unsafe fn from_utf8_unchecked(v: &[u8]) -> &str {
@@ -181,6 +182,7 @@ pub const unsafe fn from_utf8_unchecked(v: &[u8]) -> &str {
/// assert_eq!("💖", heart);
/// ```
#[inline]
+#[must_use]
#[stable(feature = "str_mut_extras", since = "1.20.0")]
pub unsafe fn from_utf8_unchecked_mut(v: &mut [u8]) -> &mut str {
// SAFETY: the caller must guarantee that the bytes `v`
diff --git a/library/core/src/str/lossy.rs b/library/core/src/str/lossy.rs
index 720a35bbc8f2c..d3c9d21c3c756 100644
--- a/library/core/src/str/lossy.rs
+++ b/library/core/src/str/lossy.rs
@@ -12,10 +12,12 @@ pub struct Utf8Lossy {
}
impl Utf8Lossy {
+ #[must_use]
pub fn from_str(s: &str) -> &Utf8Lossy {
Utf8Lossy::from_bytes(s.as_bytes())
}
+ #[must_use]
pub fn from_bytes(bytes: &[u8]) -> &Utf8Lossy {
// SAFETY: Both use the same memory layout, and UTF-8 correctness isn't required.
unsafe { mem::transmute(bytes) }
diff --git a/library/core/src/task/wake.rs b/library/core/src/task/wake.rs
index b775e022a54b4..e1bbdfaef8016 100644
--- a/library/core/src/task/wake.rs
+++ b/library/core/src/task/wake.rs
@@ -158,6 +158,7 @@ pub struct Context<'a> {
impl<'a> Context<'a> {
/// Create a new `Context` from a `&Waker`.
#[stable(feature = "futures_api", since = "1.36.0")]
+ #[must_use]
#[inline]
pub fn from_waker(waker: &'a Waker) -> Self {
Context { waker, _marker: PhantomData }
@@ -251,6 +252,7 @@ impl Waker {
/// in [`RawWaker`]'s and [`RawWakerVTable`]'s documentation is not upheld.
/// Therefore this method is unsafe.
#[inline]
+ #[must_use]
#[stable(feature = "futures_api", since = "1.36.0")]
pub unsafe fn from_raw(waker: RawWaker) -> Waker {
Waker { waker }
diff --git a/library/core/src/time.rs b/library/core/src/time.rs
index d1533b8d67a6b..d57c959820d8d 100644
--- a/library/core/src/time.rs
+++ b/library/core/src/time.rs
@@ -203,6 +203,7 @@ impl Duration {
/// assert_eq!(0, duration.subsec_nanos());
/// ```
#[stable(feature = "duration", since = "1.3.0")]
+ #[must_use]
#[inline]
#[rustc_const_stable(feature = "duration_consts", since = "1.32.0")]
pub const fn from_secs(secs: u64) -> Duration {
@@ -222,6 +223,7 @@ impl Duration {
/// assert_eq!(569_000_000, duration.subsec_nanos());
/// ```
#[stable(feature = "duration", since = "1.3.0")]
+ #[must_use]
#[inline]
#[rustc_const_stable(feature = "duration_consts", since = "1.32.0")]
pub const fn from_millis(millis: u64) -> Duration {
@@ -244,6 +246,7 @@ impl Duration {
/// assert_eq!(2000, duration.subsec_nanos());
/// ```
#[stable(feature = "duration_from_micros", since = "1.27.0")]
+ #[must_use]
#[inline]
#[rustc_const_stable(feature = "duration_consts", since = "1.32.0")]
pub const fn from_micros(micros: u64) -> Duration {
@@ -266,6 +269,7 @@ impl Duration {
/// assert_eq!(123, duration.subsec_nanos());
/// ```
#[stable(feature = "duration_extras", since = "1.27.0")]
+ #[must_use]
#[inline]
#[rustc_const_stable(feature = "duration_consts", since = "1.32.0")]
pub const fn from_nanos(nanos: u64) -> Duration {
@@ -692,6 +696,7 @@ impl Duration {
/// assert_eq!(dur, Duration::new(2, 700_000_000));
/// ```
#[stable(feature = "duration_float", since = "1.38.0")]
+ #[must_use]
#[inline]
#[rustc_const_unstable(feature = "duration_consts_2", issue = "72440")]
pub const fn from_secs_f64(secs: f64) -> Duration {
@@ -753,6 +758,7 @@ impl Duration {
/// assert_eq!(dur, Duration::new(2, 700_000_000));
/// ```
#[stable(feature = "duration_float", since = "1.38.0")]
+ #[must_use]
#[inline]
#[rustc_const_unstable(feature = "duration_consts_2", issue = "72440")]
pub const fn from_secs_f32(secs: f32) -> Duration {
diff --git a/library/std/src/ffi/c_str.rs b/library/std/src/ffi/c_str.rs
index fe1f28f00c403..e290350993d73 100644
--- a/library/std/src/ffi/c_str.rs
+++ b/library/std/src/ffi/c_str.rs
@@ -425,6 +425,7 @@ impl CString {
/// let c_string = CString::from_vec_unchecked(raw);
/// }
/// ```
+ #[must_use]
#[stable(feature = "rust1", since = "1.0.0")]
pub unsafe fn from_vec_unchecked(mut v: Vec<u8>) -> CString {
v.reserve_exact(1);
@@ -476,6 +477,7 @@ impl CString {
/// let c_string = CString::from_raw(raw);
/// }
/// ```
+ #[must_use = "call `drop(from_raw(ptr))` if you intend to drop the `CString`"]
#[stable(feature = "cstr_memory", since = "1.4.0")]
pub unsafe fn from_raw(ptr: *mut c_char) -> CString {
// SAFETY: This is called with a pointer that was obtained from a call
@@ -701,6 +703,7 @@ impl CString {
/// unsafe { CString::from_vec_unchecked(b"abc".to_vec()) }
/// );
/// ```
+ #[must_use]
#[unstable(feature = "cstring_from_vec_with_nul", issue = "73179")]
pub unsafe fn from_vec_with_nul_unchecked(v: Vec<u8>) -> Self {
Self { inner: v.into_boxed_slice() }
@@ -1162,6 +1165,7 @@ impl CStr {
/// }
/// # }
/// ```
+ #[must_use]
#[stable(feature = "rust1", since = "1.0.0")]
pub unsafe fn from_ptr<'a>(ptr: *const c_char) -> &'a CStr {
// SAFETY: The caller has provided a pointer that points to a valid C
@@ -1244,6 +1248,7 @@ impl CStr {
/// }
/// ```
#[inline]
+ #[must_use]
#[stable(feature = "cstr_from_bytes", since = "1.10.0")]
#[rustc_const_unstable(feature = "const_cstr_unchecked", issue = "none")]
pub const unsafe fn from_bytes_with_nul_unchecked(bytes: &[u8]) -> &CStr {
diff --git a/library/std/src/io/error.rs b/library/std/src/io/error.rs
index 51666c0a3c7f1..57b5c28430f1e 100644
--- a/library/std/src/io/error.rs
+++ b/library/std/src/io/error.rs
@@ -473,6 +473,7 @@ impl Error {
/// # }
/// ```
#[stable(feature = "rust1", since = "1.0.0")]
+ #[must_use]
#[inline]
pub fn from_raw_os_error(code: i32) -> Error {
Error { repr: Repr::Os(code) }