move from non zero impls to `libcore/convert/num.rs`

2 files changed, 1115 insertions, 0 deletions

diff --git a/src/libcore/convert/mod.rs b/src/libcore/convert/mod.rs
new file mode 100644
index 00000000000..5414d9ac234
--- /dev/null
+++ b/src/libcore/convert/mod.rs
@@ -0,0 +1,666 @@
+//! Traits for conversions between types.
+//!
+//! The traits in this module provide a way to convert from one type to another type.
+//! Each trait serves a different purpose:
+//!
+//! - Implement the [`AsRef`] trait for cheap reference-to-reference conversions
+//! - Implement the [`AsMut`] trait for cheap mutable-to-mutable conversions
+//! - Implement the [`From`] trait for consuming value-to-value conversions
+//! - Implement the [`Into`] trait for consuming value-to-value conversions to types
+//!   outside the current crate
+//! - The [`TryFrom`] and [`TryInto`] traits behave like [`From`] and [`Into`],
+//!   but should be implemented when the conversion can fail.
+//!
+//! The traits in this module are often used as trait bounds for generic functions such that to
+//! arguments of multiple types are supported. See the documentation of each trait for examples.
+//!
+//! As a library author, you should always prefer implementing [`From<T>`][`From`] or
+//! [`TryFrom<T>`][`TryFrom`] rather than [`Into<U>`][`Into`] or [`TryInto<U>`][`TryInto`],
+//! as [`From`] and [`TryFrom`] provide greater flexibility and offer
+//! equivalent [`Into`] or [`TryInto`] implementations for free, thanks to a
+//! blanket implementation in the standard library. Only implement [`Into`] or [`TryInto`]
+//! when a conversion to a type outside the current crate is required.
+//!
+//! # Generic Implementations
+//!
+//! - [`AsRef`] and [`AsMut`] auto-dereference if the inner type is a reference
+//! - [`From`]`<U> for T` implies [`Into`]`<T> for U`
+//! - [`TryFrom`]`<U> for T` implies [`TryInto`]`<T> for U`
+//! - [`From`] and [`Into`] are reflexive, which means that all types can
+//!   `into` themselves and `from` themselves
+//!
+//! See each trait for usage examples.
+//!
+//! [`Into`]: trait.Into.html
+//! [`From`]: trait.From.html
+//! [`TryFrom`]: trait.TryFrom.html
+//! [`TryInto`]: trait.TryInto.html
+//! [`AsRef`]: trait.AsRef.html
+//! [`AsMut`]: trait.AsMut.html
+
+#![stable(feature = "rust1", since = "1.0.0")]
+
+mod num;
+
+#[unstable(feature = "convert_float_to_int", issue = "67057")]
+pub use num::FloatToInt;
+
+/// The identity function.
+///
+/// Two things are important to note about this function:
+///
+/// - It is not always equivalent to a closure like `|x| x`, since the
+///   closure may coerce `x` into a different type.
+///
+/// - It moves the input `x` passed to the function.
+///
+/// While it might seem strange to have a function that just returns back the
+/// input, there are some interesting uses.
+///
+/// # Examples
+///
+/// Using `identity` to do nothing in a sequence of other, interesting,
+/// functions:
+///
+/// ```rust
+/// use std::convert::identity;
+///
+/// fn manipulation(x: u32) -> u32 {
+///     // Let's pretend that adding one is an interesting function.
+///     x + 1
+/// }
+///
+/// let _arr = &[identity, manipulation];
+/// ```
+///
+/// Using `identity` as a "do nothing" base case in a conditional:
+///
+/// ```rust
+/// use std::convert::identity;
+///
+/// # let condition = true;
+/// #
+/// # fn manipulation(x: u32) -> u32 { x + 1 }
+/// #
+/// let do_stuff = if condition { manipulation } else { identity };
+///
+/// // Do more interesting stuff...
+///
+/// let _results = do_stuff(42);
+/// ```
+///
+/// Using `identity` to keep the `Some` variants of an iterator of `Option<T>`:
+///
+/// ```rust
+/// use std::convert::identity;
+///
+/// let iter = vec![Some(1), None, Some(3)].into_iter();
+/// let filtered = iter.filter_map(identity).collect::<Vec<_>>();
+/// assert_eq!(vec![1, 3], filtered);
+/// ```
+#[stable(feature = "convert_id", since = "1.33.0")]
+#[inline]
+pub const fn identity<T>(x: T) -> T {
+    x
+}
+
+/// Used to do a cheap reference-to-reference conversion.
+///
+/// This trait is similar to [`AsMut`] which is used for converting between mutable references.
+/// If you need to do a costly conversion it is better to implement [`From`] with type
+/// `&T` or write a custom function.
+///
+/// `AsRef` has the same signature as [`Borrow`], but [`Borrow`] is different in few aspects:
+///
+/// - Unlike `AsRef`, [`Borrow`] has a blanket impl for any `T`, and can be used to accept either
+///   a reference or a value.
+/// - [`Borrow`] also requires that [`Hash`], [`Eq`] and [`Ord`] for borrowed value are
+///   equivalent to those of the owned value. For this reason, if you want to
+///   borrow only a single field of a struct you can implement `AsRef`, but not [`Borrow`].
+///
+/// **Note: This trait must not fail**. If the conversion can fail, use a
+/// dedicated method which returns an [`Option<T>`] or a [`Result<T, E>`].
+///
+/// # Generic Implementations
+///
+/// - `AsRef` auto-dereferences if the inner type is a reference or a mutable
+///   reference (e.g.: `foo.as_ref()` will work the same if `foo` has type
+///   `&mut Foo` or `&&mut Foo`)
+///
+/// # Examples
+///
+/// By using trait bounds we can accept arguments of different types as long as they can be
+/// converted to the specified type `T`.
+///
+/// For example: By creating a generic function that takes an `AsRef<str>` we express that we
+/// want to accept all references that can be converted to [`&str`] as an argument.
+/// Since both [`String`] and [`&str`] implement `AsRef<str>` we can accept both as input argument.
+///
+/// [`Option<T>`]: ../../std/option/enum.Option.html
+/// [`Result<T, E>`]: ../../std/result/enum.Result.html
+/// [`Borrow`]: ../../std/borrow/trait.Borrow.html
+/// [`Hash`]: ../../std/hash/trait.Hash.html
+/// [`Eq`]: ../../std/cmp/trait.Eq.html
+/// [`Ord`]: ../../std/cmp/trait.Ord.html
+/// [`&str`]: ../../std/primitive.str.html
+/// [`String`]: ../../std/string/struct.String.html
+///
+/// ```
+/// fn is_hello<T: AsRef<str>>(s: T) {
+///    assert_eq!("hello", s.as_ref());
+/// }
+///
+/// let s = "hello";
+/// is_hello(s);
+///
+/// let s = "hello".to_string();
+/// is_hello(s);
+/// ```
+#[stable(feature = "rust1", since = "1.0.0")]
+pub trait AsRef<T: ?Sized> {
+    /// Performs the conversion.
+    #[stable(feature = "rust1", since = "1.0.0")]
+    fn as_ref(&self) -> &T;
+}
+
+/// Used to do a cheap mutable-to-mutable reference conversion.
+///
+/// This trait is similar to [`AsRef`] but used for converting between mutable
+/// references. If you need to do a costly conversion it is better to
+/// implement [`From`] with type `&mut T` or write a custom function.
+///
+/// **Note: This trait must not fail**. If the conversion can fail, use a
+/// dedicated method which returns an [`Option<T>`] or a [`Result<T, E>`].
+///
+/// [`Option<T>`]: ../../std/option/enum.Option.html
+/// [`Result<T, E>`]: ../../std/result/enum.Result.html
+///
+/// # Generic Implementations
+///
+/// - `AsMut` auto-dereferences if the inner type is a mutable reference
+///   (e.g.: `foo.as_mut()` will work the same if `foo` has type `&mut Foo`
+///   or `&mut &mut Foo`)
+///
+/// # Examples
+///
+/// Using `AsMut` as trait bound for a generic function we can accept all mutable references
+/// that can be converted to type `&mut T`. Because [`Box<T>`] implements `AsMut<T>` we can
+/// write a function `add_one` that takes all arguments that can be converted to `&mut u64`.
+/// Because [`Box<T>`] implements `AsMut<T>`, `add_one` accepts arguments of type
+/// `&mut Box<u64>` as well:
+///
+/// ```
+/// fn add_one<T: AsMut<u64>>(num: &mut T) {
+///     *num.as_mut() += 1;
+/// }
+///
+/// let mut boxed_num = Box::new(0);
+/// add_one(&mut boxed_num);
+/// assert_eq!(*boxed_num, 1);
+/// ```
+///
+/// [`Box<T>`]: ../../std/boxed/struct.Box.html
+#[stable(feature = "rust1", since = "1.0.0")]
+pub trait AsMut<T: ?Sized> {
+    /// Performs the conversion.
+    #[stable(feature = "rust1", since = "1.0.0")]
+    fn as_mut(&mut self) -> &mut T;
+}
+
+/// A value-to-value conversion that consumes the input value. The
+/// opposite of [`From`].
+///
+/// One should avoid implementing [`Into`] and implement [`From`] instead.
+/// Implementing [`From`] automatically provides one with an implementation of [`Into`]
+/// thanks to the blanket implementation in the standard library.
+///
+/// Prefer using [`Into`] over [`From`] when specifying trait bounds on a generic function
+/// to ensure that types that only implement [`Into`] can be used as well.
+///
+/// **Note: This trait must not fail**. If the conversion can fail, use [`TryInto`].
+///
+/// # Generic Implementations
+///
+/// - [`From`]`<T> for U` implies `Into<U> for T`
+/// - [`Into`] is reflexive, which means that `Into<T> for T` is implemented
+///
+/// # Implementing [`Into`] for conversions to external types in old versions of Rust
+///
+/// Prior to Rust 1.40, if the destination type was not part of the current crate
+/// then you couldn't implement [`From`] directly.
+/// For example, take this code:
+///
+/// ```
+/// struct Wrapper<T>(Vec<T>);
+/// impl<T> From<Wrapper<T>> for Vec<T> {
+///     fn from(w: Wrapper<T>) -> Vec<T> {
+///         w.0
+///     }
+/// }
+/// ```
+/// This will fail to compile in older versions of the language because Rust's orphaning rules
+/// used to be a little bit more strict. To bypass this, you could implement [`Into`] directly:
+///
+/// ```
+/// struct Wrapper<T>(Vec<T>);
+/// impl<T> Into<Vec<T>> for Wrapper<T> {
+///     fn into(self) -> Vec<T> {
+///         self.0
+///     }
+/// }
+/// ```
+///
+/// It is important to understand that [`Into`] does not provide a [`From`] implementation
+/// (as [`From`] does with [`Into`]). Therefore, you should always try to implement [`From`]
+/// and then fall back to [`Into`] if [`From`] can't be implemented.
+///
+/// # Examples
+///
+/// [`String`] implements [`Into`]`<`[`Vec`]`<`[`u8`]`>>`:
+///
+/// In order to express that we want a generic function to take all arguments that can be
+/// converted to a specified type `T`, we can use a trait bound of [`Into`]`<T>`.
+/// For example: The function `is_hello` takes all arguments that can be converted into a
+/// [`Vec`]`<`[`u8`]`>`.
+///
+/// ```
+/// fn is_hello<T: Into<Vec<u8>>>(s: T) {
+///    let bytes = b"hello".to_vec();
+///    assert_eq!(bytes, s.into());
+/// }
+///
+/// let s = "hello".to_string();
+/// is_hello(s);
+/// ```
+///
+/// [`TryInto`]: trait.TryInto.html
+/// [`Option<T>`]: ../../std/option/enum.Option.html
+/// [`Result<T, E>`]: ../../std/result/enum.Result.html
+/// [`String`]: ../../std/string/struct.String.html
+/// [`From`]: trait.From.html
+/// [`Into`]: trait.Into.html
+/// [`Vec`]: ../../std/vec/struct.Vec.html
+#[stable(feature = "rust1", since = "1.0.0")]
+pub trait Into<T>: Sized {
+    /// Performs the conversion.
+    #[stable(feature = "rust1", since = "1.0.0")]
+    fn into(self) -> T;
+}
+
+/// Used to do value-to-value conversions while consuming the input value. It is the reciprocal of
+/// [`Into`].
+///
+/// One should always prefer implementing `From` over [`Into`]
+/// because implementing `From` automatically provides one with a implementation of [`Into`]
+/// thanks to the blanket implementation in the standard library.
+///
+/// Only implement [`Into`] if a conversion to a type outside the current crate is required.
+/// `From` cannot do these type of conversions because of Rust's orphaning rules.
+/// See [`Into`] for more details.
+///
+/// Prefer using [`Into`] over using `From` when specifying trait bounds on a generic function.
+/// This way, types that directly implement [`Into`] can be used as arguments as well.
+///
+/// The `From` is also very useful when performing error handling. When constructing a function
+/// that is capable of failing, the return type will generally be of the form `Result<T, E>`.
+/// The `From` trait simplifies error handling by allowing a function to return a single error type
+/// that encapsulate multiple error types. See the "Examples" section and [the book][book] for more
+/// details.
+///
+/// **Note: This trait must not fail**. If the conversion can fail, use [`TryFrom`].
+///
+/// # Generic Implementations
+///
+/// - `From<T> for U` implies [`Into`]`<U> for T`
+/// - `From` is reflexive, which means that `From<T> for T` is implemented
+///
+/// # Examples
+///
+/// [`String`] implements `From<&str>`:
+///
+/// An explicit conversion from a `&str` to a String is done as follows:
+///
+/// ```
+/// let string = "hello".to_string();
+/// let other_string = String::from("hello");
+///
+/// assert_eq!(string, other_string);
+/// ```
+///
+/// While performing error handling it is often useful to implement `From` for your own error type.
+/// By converting underlying error types to our own custom error type that encapsulates the
+/// underlying error type, we can return a single error type without losing information on the
+/// underlying cause. The '?' operator automatically converts the underlying error type to our
+/// custom error type by calling `Into<CliError>::into` which is automatically provided when
+/// implementing `From`. The compiler then infers which implementation of `Into` should be used.
+///
+/// ```
+/// use std::fs;
+/// use std::io;
+/// use std::num;
+///
+/// enum CliError {
+///     IoError(io::Error),
+///     ParseError(num::ParseIntError),
+/// }
+///
+/// impl From<io::Error> for CliError {
+///     fn from(error: io::Error) -> Self {
+///         CliError::IoError(error)
+///     }
+/// }
+///
+/// impl From<num::ParseIntError> for CliError {
+///     fn from(error: num::ParseIntError) -> Self {
+///         CliError::ParseError(error)
+///     }
+/// }
+///
+/// fn open_and_parse_file(file_name: &str) -> Result<i32, CliError> {
+///     let mut contents = fs::read_to_string(&file_name)?;
+///     let num: i32 = contents.trim().parse()?;
+///     Ok(num)
+/// }
+/// ```
+///
+/// [`TryFrom`]: trait.TryFrom.html
+/// [`Option<T>`]: ../../std/option/enum.Option.html
+/// [`Result<T, E>`]: ../../std/result/enum.Result.html
+/// [`String`]: ../../std/string/struct.String.html
+/// [`Into`]: trait.Into.html
+/// [`from`]: trait.From.html#tymethod.from
+/// [book]: ../../book/ch09-00-error-handling.html
+#[stable(feature = "rust1", since = "1.0.0")]
+#[rustc_on_unimplemented(on(
+    all(_Self = "&str", T = "std::string::String"),
+    note = "to coerce a `{T}` into a `{Self}`, use `&*` as a prefix",
+))]
+pub trait From<T>: Sized {
+    /// Performs the conversion.
+    #[stable(feature = "rust1", since = "1.0.0")]
+    fn from(_: T) -> Self;
+}
+
+/// An attempted conversion that consumes `self`, which may or may not be
+/// expensive.
+///
+/// Library authors should usually not directly implement this trait,
+/// but should prefer implementing the [`TryFrom`] trait, which offers
+/// greater flexibility and provides an equivalent `TryInto`
+/// implementation for free, thanks to a blanket implementation in the
+/// standard library. For more information on this, see the
+/// documentation for [`Into`].
+///
+/// # Implementing `TryInto`
+///
+/// This suffers the same restrictions and reasoning as implementing
+/// [`Into`], see there for details.
+///
+/// [`TryFrom`]: trait.TryFrom.html
+/// [`Into`]: trait.Into.html
+#[stable(feature = "try_from", since = "1.34.0")]
+pub trait TryInto<T>: Sized {
+    /// The type returned in the event of a conversion error.
+    #[stable(feature = "try_from", since = "1.34.0")]
+    type Error;
+
+    /// Performs the conversion.
+    #[stable(feature = "try_from", since = "1.34.0")]
+    fn try_into(self) -> Result<T, Self::Error>;
+}
+
+/// Simple and safe type conversions that may fail in a controlled
+/// way under some circumstances. It is the reciprocal of [`TryInto`].
+///
+/// This is useful when you are doing a type conversion that may
+/// trivially succeed but may also need special handling.
+/// For example, there is no way to convert an [`i64`] into an [`i32`]
+/// using the [`From`] trait, because an [`i64`] may contain a value
+/// that an [`i32`] cannot represent and so the conversion would lose data.
+/// This might be handled by truncating the [`i64`] to an [`i32`] (essentially
+/// giving the [`i64`]'s value modulo [`i32::MAX`]) or by simply returning
+/// [`i32::MAX`], or by some other method.  The [`From`] trait is intended
+/// for perfect conversions, so the `TryFrom` trait informs the
+/// programmer when a type conversion could go bad and lets them
+/// decide how to handle it.
+///
+/// # Generic Implementations
+///
+/// - `TryFrom<T> for U` implies [`TryInto`]`<U> for T`
+/// - [`try_from`] is reflexive, which means that `TryFrom<T> for T`
+/// is implemented and cannot fail -- the associated `Error` type for
+/// calling `T::try_from()` on a value of type `T` is [`!`].
+///
+/// `TryFrom<T>` can be implemented as follows:
+///
+/// ```
+/// use std::convert::TryFrom;
+///
+/// struct GreaterThanZero(i32);
+///
+/// impl TryFrom<i32> for GreaterThanZero {
+///     type Error = &'static str;
+///
+///     fn try_from(value: i32) -> Result<Self, Self::Error> {
+///         if value <= 0 {
+///             Err("GreaterThanZero only accepts value superior than zero!")
+///         } else {
+///             Ok(GreaterThanZero(value))
+///         }
+///     }
+/// }
+/// ```
+///
+/// # Examples
+///
+/// As described, [`i32`] implements `TryFrom<`[`i64`]`>`:
+///
+/// ```
+/// use std::convert::TryFrom;
+///
+/// let big_number = 1_000_000_000_000i64;
+/// // Silently truncates `big_number`, requires detecting
+/// // and handling the truncation after the fact.
+/// let smaller_number = big_number as i32;
+/// assert_eq!(smaller_number, -727379968);
+///
+/// // Returns an error because `big_number` is too big to
+/// // fit in an `i32`.
+/// let try_smaller_number = i32::try_from(big_number);
+/// assert!(try_smaller_number.is_err());
+///
+/// // Returns `Ok(3)`.
+/// let try_successful_smaller_number = i32::try_from(3);
+/// assert!(try_successful_smaller_number.is_ok());
+/// ```
+///
+/// [`try_from`]: trait.TryFrom.html#tymethod.try_from
+/// [`TryInto`]: trait.TryInto.html
+/// [`i32::MAX`]: ../../std/i32/constant.MAX.html
+/// [`!`]: ../../std/primitive.never.html
+#[stable(feature = "try_from", since = "1.34.0")]
+pub trait TryFrom<T>: Sized {
+    /// The type returned in the event of a conversion error.
+    #[stable(feature = "try_from", since = "1.34.0")]
+    type Error;
+
+    /// Performs the conversion.
+    #[stable(feature = "try_from", since = "1.34.0")]
+    fn try_from(value: T) -> Result<Self, Self::Error>;
+}
+
+////////////////////////////////////////////////////////////////////////////////
+// GENERIC IMPLS
+////////////////////////////////////////////////////////////////////////////////
+
+// As lifts over &
+#[stable(feature = "rust1", since = "1.0.0")]
+impl<T: ?Sized, U: ?Sized> AsRef<U> for &T
+where
+    T: AsRef<U>,
+{
+    fn as_ref(&self) -> &U {
+        <T as AsRef<U>>::as_ref(*self)
+    }
+}
+
+// As lifts over &mut
+#[stable(feature = "rust1", since = "1.0.0")]
+impl<T: ?Sized, U: ?Sized> AsRef<U> for &mut T
+where
+    T: AsRef<U>,
+{
+    fn as_ref(&self) -> &U {
+        <T as AsRef<U>>::as_ref(*self)
+    }
+}
+
+// FIXME (#45742): replace the above impls for &/&mut with the following more general one:
+// // As lifts over Deref
+// impl<D: ?Sized + Deref<Target: AsRef<U>>, U: ?Sized> AsRef<U> for D {
+//     fn as_ref(&self) -> &U {
+//         self.deref().as_ref()
+//     }
+// }
+
+// AsMut lifts over &mut
+#[stable(feature = "rust1", since = "1.0.0")]
+impl<T: ?Sized, U: ?Sized> AsMut<U> for &mut T
+where
+    T: AsMut<U>,
+{
+    fn as_mut(&mut self) -> &mut U {
+        (*self).as_mut()
+    }
+}
+
+// FIXME (#45742): replace the above impl for &mut with the following more general one:
+// // AsMut lifts over DerefMut
+// impl<D: ?Sized + Deref<Target: AsMut<U>>, U: ?Sized> AsMut<U> for D {
+//     fn as_mut(&mut self) -> &mut U {
+//         self.deref_mut().as_mut()
+//     }
+// }
+
+// From implies Into
+#[stable(feature = "rust1", since = "1.0.0")]
+impl<T, U> Into<U> for T
+where
+    U: From<T>,
+{
+    fn into(self) -> U {
+        U::from(self)
+    }
+}
+
+// From (and thus Into) is reflexive
+#[stable(feature = "rust1", since = "1.0.0")]
+impl<T> From<T> for T {
+    fn from(t: T) -> T {
+        t
+    }
+}
+
+/// **Stability note:** This impl does not yet exist, but we are
+/// "reserving space" to add it in the future. See
+/// [rust-lang/rust#64715][#64715] for details.
+///
+/// [#64715]: https://github.com/rust-lang/rust/issues/64715
+#[stable(feature = "convert_infallible", since = "1.34.0")]
+#[allow(unused_attributes)] // FIXME(#58633): do a principled fix instead.
+#[rustc_reservation_impl = "permitting this impl would forbid us from adding \
+                            `impl<T> From<!> for T` later; see rust-lang/rust#64715 for details"]
+impl<T> From<!> for T {
+    fn from(t: !) -> T {
+        t
+    }
+}
+
+// TryFrom implies TryInto
+#[stable(feature = "try_from", since = "1.34.0")]
+impl<T, U> TryInto<U> for T
+where
+    U: TryFrom<T>,
+{
+    type Error = U::Error;
+
+    fn try_into(self) -> Result<U, U::Error> {
+        U::try_from(self)
+    }
+}
+
+// Infallible conversions are semantically equivalent to fallible conversions
+// with an uninhabited error type.
+#[stable(feature = "try_from", since = "1.34.0")]
+impl<T, U> TryFrom<U> for T
+where
+    U: Into<T>,
+{
+    type Error = Infallible;
+
+    fn try_from(value: U) -> Result<Self, Self::Error> {
+        Ok(U::into(value))
+    }
+}
+
+////////////////////////////////////////////////////////////////////////////////
+// CONCRETE IMPLS
+////////////////////////////////////////////////////////////////////////////////
+
+#[stable(feature = "rust1", since = "1.0.0")]
+impl<T> AsRef<[T]> for [T] {
+    fn as_ref(&self) -> &[T] {
+        self
+    }
+}
+
+#[stable(feature = "rust1", since = "1.0.0")]
+impl<T> AsMut<[T]> for [T] {
+    fn as_mut(&mut self) -> &mut [T] {
+        self
+    }
+}
+
+#[stable(feature = "rust1", since = "1.0.0")]
+impl AsRef<str> for str {
+    #[inline]
+    fn as_ref(&self) -> &str {
+        self
+    }
+}
+
+////////////////////////////////////////////////////////////////////////////////
+// THE NO-ERROR ERROR TYPE
+////////////////////////////////////////////////////////////////////////////////
+
+/// A type alias for [the `!` “never” type][never].
+///
+/// `Infallible` represents types of errors that can never happen since `!` has no valid values.
+/// This can be useful for generic APIs that use [`Result`] and parameterize the error type,
+/// to indicate that the result is always [`Ok`].
+///
+/// For example, the [`TryFrom`] trait (conversion that returns a [`Result`])
+/// has a blanket implementation for all types where a reverse [`Into`] implementation exists.
+///
+/// ```ignore (illustrates std code, duplicating the impl in a doctest would be an error)
+/// impl<T, U> TryFrom<U> for T where U: Into<T> {
+///     type Error = Infallible;
+///
+///     fn try_from(value: U) -> Result<Self, Infallible> {
+///         Ok(U::into(value))  // Never returns `Err`
+///     }
+/// }
+/// ```
+///
+/// # Eventual deprecation
+///
+/// Previously, `Infallible` was defined as `enum Infallible {}`.
+/// Now that it is merely a type alias to `!`, we will eventually deprecate `Infallible`.
+///
+/// [`Ok`]: ../result/enum.Result.html#variant.Ok
+/// [`Result`]: ../result/enum.Result.html
+/// [`TryFrom`]: trait.TryFrom.html
+/// [`Into`]: trait.Into.html
+/// [never]: ../../std/primitive.never.html
+#[stable(feature = "convert_infallible", since = "1.34.0")]
+pub type Infallible = !;
diff --git a/src/libcore/convert/num.rs b/src/libcore/convert/num.rs
new file mode 100644
index 00000000000..6f5ee756f58
--- /dev/null
+++ b/src/libcore/convert/num.rs
@@ -0,0 +1,449 @@
+use super::{From, TryFrom};
+use crate::num::TryFromIntError;
+
+mod private {
+    /// This trait being unreachable from outside the crate
+    /// prevents other implementations of the `FloatToInt` trait,
+    /// which allows potentially adding more trait methods after the trait is `#[stable]`.
+    #[unstable(feature = "convert_float_to_int", issue = "67057")]
+    pub trait Sealed {}
+}
+
+/// Supporting trait for inherent methods of `f32` and `f64` such as `round_unchecked_to`.
+/// Typically doesn’t need to be used directly.
+#[unstable(feature = "convert_float_to_int", issue = "67057")]
+pub trait FloatToInt<Int>: private::Sealed + Sized {
+    #[cfg(not(bootstrap))]
+    #[unstable(feature = "float_approx_unchecked_to", issue = "67058")]
+    #[doc(hidden)]
+    unsafe fn approx_unchecked(self) -> Int;
+}
+
+macro_rules! impl_float_to_int {
+    ( $Float: ident => $( $Int: ident )+ ) => {
+        #[unstable(feature = "convert_float_to_int", issue = "67057")]
+        impl private::Sealed for $Float {}
+        $(
+            #[unstable(feature = "convert_float_to_int", issue = "67057")]
+            impl FloatToInt<$Int> for $Float {
+                #[cfg(not(bootstrap))]
+                #[doc(hidden)]
+                #[inline]
+                unsafe fn approx_unchecked(self) -> $Int {
+                    crate::intrinsics::float_to_int_approx_unchecked(self)
+                }
+            }
+        )+
+    }
+}
+
+impl_float_to_int!(f32 => u8 u16 u32 u64 u128 usize i8 i16 i32 i64 i128 isize);
+impl_float_to_int!(f64 => u8 u16 u32 u64 u128 usize i8 i16 i32 i64 i128 isize);
+
+// Conversion traits for primitive integer and float types
+// Conversions T -> T are covered by a blanket impl and therefore excluded
+// Some conversions from and to usize/isize are not implemented due to portability concerns
+macro_rules! impl_from {
+    ($Small: ty, $Large: ty, #[$attr:meta], $doc: expr) => {
+        #[$attr]
+        #[doc = $doc]
+        impl From<$Small> for $Large {
+            #[inline]
+            fn from(small: $Small) -> $Large {
+                small as $Large
+            }
+        }
+    };
+    ($Small: ty, $Large: ty, #[$attr:meta]) => {
+        impl_from!($Small,
+                   $Large,
+                   #[$attr],
+                   concat!("Converts `",
+                           stringify!($Small),
+                           "` to `",
+                           stringify!($Large),
+                           "` losslessly."));
+    }
+}
+
+macro_rules! impl_from_bool {
+    ($target: ty, #[$attr:meta]) => {
+        impl_from!(bool, $target, #[$attr], concat!("Converts a `bool` to a `",
+            stringify!($target), "`. The resulting value is `0` for `false` and `1` for `true`
+values.
+
+# Examples
+
+```
+assert_eq!(", stringify!($target), "::from(true), 1);
+assert_eq!(", stringify!($target), "::from(false), 0);
+```"));
+    };
+}
+
+// Bool -> Any
+impl_from_bool! { u8, #[stable(feature = "from_bool", since = "1.28.0")] }
+impl_from_bool! { u16, #[stable(feature = "from_bool", since = "1.28.0")] }
+impl_from_bool! { u32, #[stable(feature = "from_bool", since = "1.28.0")] }
+impl_from_bool! { u64, #[stable(feature = "from_bool", since = "1.28.0")] }
+impl_from_bool! { u128, #[stable(feature = "from_bool", since = "1.28.0")] }
+impl_from_bool! { usize, #[stable(feature = "from_bool", since = "1.28.0")] }
+impl_from_bool! { i8, #[stable(feature = "from_bool", since = "1.28.0")] }
+impl_from_bool! { i16, #[stable(feature = "from_bool", since = "1.28.0")] }
+impl_from_bool! { i32, #[stable(feature = "from_bool", since = "1.28.0")] }
+impl_from_bool! { i64, #[stable(feature = "from_bool", since = "1.28.0")] }
+impl_from_bool! { i128, #[stable(feature = "from_bool", since = "1.28.0")] }
+impl_from_bool! { isize, #[stable(feature = "from_bool", since = "1.28.0")] }
+
+// Unsigned -> Unsigned
+impl_from! { u8, u16, #[stable(feature = "lossless_int_conv", since = "1.5.0")] }
+impl_from! { u8, u32, #[stable(feature = "lossless_int_conv", since = "1.5.0")] }
+impl_from! { u8, u64, #[stable(feature = "lossless_int_conv", since = "1.5.0")] }
+impl_from! { u8, u128, #[stable(feature = "i128", since = "1.26.0")] }
+impl_from! { u8, usize, #[stable(feature = "lossless_int_conv", since = "1.5.0")] }
+impl_from! { u16, u32, #[stable(feature = "lossless_int_conv", since = "1.5.0")] }
+impl_from! { u16, u64, #[stable(feature = "lossless_int_conv", since = "1.5.0")] }
+impl_from! { u16, u128, #[stable(feature = "i128", since = "1.26.0")] }
+impl_from! { u32, u64, #[stable(feature = "lossless_int_conv", since = "1.5.0")] }
+impl_from! { u32, u128, #[stable(feature = "i128", since = "1.26.0")] }
+impl_from! { u64, u128, #[stable(feature = "i128", since = "1.26.0")] }
+
+// Signed -> Signed
+impl_from! { i8, i16, #[stable(feature = "lossless_int_conv", since = "1.5.0")] }
+impl_from! { i8, i32, #[stable(feature = "lossless_int_conv", since = "1.5.0")] }
+impl_from! { i8, i64, #[stable(feature = "lossless_int_conv", since = "1.5.0")] }
+impl_from! { i8, i128, #[stable(feature = "i128", since = "1.26.0")] }
+impl_from! { i8, isize, #[stable(feature = "lossless_int_conv", since = "1.5.0")] }
+impl_from! { i16, i32, #[stable(feature = "lossless_int_conv", since = "1.5.0")] }
+impl_from! { i16, i64, #[stable(feature = "lossless_int_conv", since = "1.5.0")] }
+impl_from! { i16, i128, #[stable(feature = "i128", since = "1.26.0")] }
+impl_from! { i32, i64, #[stable(feature = "lossless_int_conv", since = "1.5.0")] }
+impl_from! { i32, i128, #[stable(feature = "i128", since = "1.26.0")] }
+impl_from! { i64, i128, #[stable(feature = "i128", since = "1.26.0")] }
+
+// Unsigned -> Signed
+impl_from! { u8, i16, #[stable(feature = "lossless_int_conv", since = "1.5.0")] }
+impl_from! { u8, i32, #[stable(feature = "lossless_int_conv", since = "1.5.0")] }
+impl_from! { u8, i64, #[stable(feature = "lossless_int_conv", since = "1.5.0")] }
+impl_from! { u8, i128, #[stable(feature = "i128", since = "1.26.0")] }
+impl_from! { u16, i32, #[stable(feature = "lossless_int_conv", since = "1.5.0")] }
+impl_from! { u16, i64, #[stable(feature = "lossless_int_conv", since = "1.5.0")] }
+impl_from! { u16, i128, #[stable(feature = "i128", since = "1.26.0")] }
+impl_from! { u32, i64, #[stable(feature = "lossless_int_conv", since = "1.5.0")] }
+impl_from! { u32, i128, #[stable(feature = "i128", since = "1.26.0")] }
+impl_from! { u64, i128, #[stable(feature = "i128", since = "1.26.0")] }
+
+// The C99 standard defines bounds on INTPTR_MIN, INTPTR_MAX, and UINTPTR_MAX
+// which imply that pointer-sized integers must be at least 16 bits:
+// https://port70.net/~nsz/c/c99/n1256.html#7.18.2.4
+impl_from! { u16, usize, #[stable(feature = "lossless_iusize_conv", since = "1.26.0")] }
+impl_from! { u8, isize, #[stable(feature = "lossless_iusize_conv", since = "1.26.0")] }
+impl_from! { i16, isize, #[stable(feature = "lossless_iusize_conv", since = "1.26.0")] }
+
+// RISC-V defines the possibility of a 128-bit address space (RV128).
+
+// CHERI proposes 256-bit “capabilities”. Unclear if this would be relevant to usize/isize.
+// https://www.cl.cam.ac.uk/research/security/ctsrd/pdfs/20171017a-cheri-poster.pdf
+// http://www.csl.sri.com/users/neumann/2012resolve-cheri.pdf
+
+// Note: integers can only be represented with full precision in a float if
+// they fit in the significand, which is 24 bits in f32 and 53 bits in f64.
+// Lossy float conversions are not implemented at this time.
+
+// Signed -> Float
+impl_from! { i8, f32, #[stable(feature = "lossless_float_conv", since = "1.6.0")] }
+impl_from! { i8, f64, #[stable(feature = "lossless_float_conv", since = "1.6.0")] }
+impl_from! { i16, f32, #[stable(feature = "lossless_float_conv", since = "1.6.0")] }
+impl_from! { i16, f64, #[stable(feature = "lossless_float_conv", since = "1.6.0")] }
+impl_from! { i32, f64, #[stable(feature = "lossless_float_conv", since = "1.6.0")] }
+
+// Unsigned -> Float
+impl_from! { u8, f32, #[stable(feature = "lossless_float_conv", since = "1.6.0")] }
+impl_from! { u8, f64, #[stable(feature = "lossless_float_conv", since = "1.6.0")] }
+impl_from! { u16, f32, #[stable(feature = "lossless_float_conv", since = "1.6.0")] }
+impl_from! { u16, f64, #[stable(feature = "lossless_float_conv", since = "1.6.0")] }
+impl_from! { u32, f64, #[stable(feature = "lossless_float_conv", since = "1.6.0")] }
+
+// Float -> Float
+impl_from! { f32, f64, #[stable(feature = "lossless_float_conv", since = "1.6.0")] }
+
+// no possible bounds violation
+macro_rules! try_from_unbounded {
+    ($source:ty, $($target:ty),*) => {$(
+        #[stable(feature = "try_from", since = "1.34.0")]
+        impl TryFrom<$source> for $target {
+            type Error = TryFromIntError;
+
+            /// Try to create the target number type from a source
+            /// number type. This returns an error if the source value
+            /// is outside of the range of the target type.
+            #[inline]
+            fn try_from(value: $source) -> Result<Self, Self::Error> {
+                Ok(value as $target)
+            }
+        }
+    )*}
+}
+
+// only negative bounds
+macro_rules! try_from_lower_bounded {
+    ($source:ty, $($target:ty),*) => {$(
+        #[stable(feature = "try_from", since = "1.34.0")]
+        impl TryFrom<$source> for $target {
+            type Error = TryFromIntError;
+
+            /// Try to create the target number type from a source
+            /// number type. This returns an error if the source value
+            /// is outside of the range of the target type.
+            #[inline]
+            fn try_from(u: $source) -> Result<$target, TryFromIntError> {
+                if u >= 0 {
+                    Ok(u as $target)
+                } else {
+                    Err(TryFromIntError(()))
+                }
+            }
+        }
+    )*}
+}
+
+// unsigned to signed (only positive bound)
+macro_rules! try_from_upper_bounded {
+    ($source:ty, $($target:ty),*) => {$(
+        #[stable(feature = "try_from", since = "1.34.0")]
+        impl TryFrom<$source> for $target {
+            type Error = TryFromIntError;
+
+            /// Try to create the target number type from a source
+            /// number type. This returns an error if the source value
+            /// is outside of the range of the target type.
+            #[inline]
+            fn try_from(u: $source) -> Result<$target, TryFromIntError> {
+                if u > (<$target>::max_value() as $source) {
+                    Err(TryFromIntError(()))
+                } else {
+                    Ok(u as $target)
+                }
+            }
+        }
+    )*}
+}
+
+// all other cases
+macro_rules! try_from_both_bounded {
+    ($source:ty, $($target:ty),*) => {$(
+        #[stable(feature = "try_from", since = "1.34.0")]
+        impl TryFrom<$source> for $target {
+            type Error = TryFromIntError;
+
+            /// Try to create the target number type from a source
+            /// number type. This returns an error if the source value
+            /// is outside of the range of the target type.
+            #[inline]
+            fn try_from(u: $source) -> Result<$target, TryFromIntError> {
+                let min = <$target>::min_value() as $source;
+                let max = <$target>::max_value() as $source;
+                if u < min || u > max {
+                    Err(TryFromIntError(()))
+                } else {
+                    Ok(u as $target)
+                }
+            }
+        }
+    )*}
+}
+
+macro_rules! rev {
+    ($mac:ident, $source:ty, $($target:ty),*) => {$(
+        $mac!($target, $source);
+    )*}
+}
+
+// intra-sign conversions
+try_from_upper_bounded!(u16, u8);
+try_from_upper_bounded!(u32, u16, u8);
+try_from_upper_bounded!(u64, u32, u16, u8);
+try_from_upper_bounded!(u128, u64, u32, u16, u8);
+
+try_from_both_bounded!(i16, i8);
+try_from_both_bounded!(i32, i16, i8);
+try_from_both_bounded!(i64, i32, i16, i8);
+try_from_both_bounded!(i128, i64, i32, i16, i8);
+
+// unsigned-to-signed
+try_from_upper_bounded!(u8, i8);
+try_from_upper_bounded!(u16, i8, i16);
+try_from_upper_bounded!(u32, i8, i16, i32);
+try_from_upper_bounded!(u64, i8, i16, i32, i64);
+try_from_upper_bounded!(u128, i8, i16, i32, i64, i128);
+
+// signed-to-unsigned
+try_from_lower_bounded!(i8, u8, u16, u32, u64, u128);
+try_from_lower_bounded!(i16, u16, u32, u64, u128);
+try_from_lower_bounded!(i32, u32, u64, u128);
+try_from_lower_bounded!(i64, u64, u128);
+try_from_lower_bounded!(i128, u128);
+try_from_both_bounded!(i16, u8);
+try_from_both_bounded!(i32, u16, u8);
+try_from_both_bounded!(i64, u32, u16, u8);
+try_from_both_bounded!(i128, u64, u32, u16, u8);
+
+// usize/isize
+try_from_upper_bounded!(usize, isize);
+try_from_lower_bounded!(isize, usize);
+
+#[cfg(target_pointer_width = "16")]
+mod ptr_try_from_impls {
+    use super::TryFromIntError;
+    use crate::convert::TryFrom;
+
+    try_from_upper_bounded!(usize, u8);
+    try_from_unbounded!(usize, u16, u32, u64, u128);
+    try_from_upper_bounded!(usize, i8, i16);
+    try_from_unbounded!(usize, i32, i64, i128);
+
+    try_from_both_bounded!(isize, u8);
+    try_from_lower_bounded!(isize, u16, u32, u64, u128);
+    try_from_both_bounded!(isize, i8);
+    try_from_unbounded!(isize, i16, i32, i64, i128);
+
+    rev!(try_from_upper_bounded, usize, u32, u64, u128);
+    rev!(try_from_lower_bounded, usize, i8, i16);
+    rev!(try_from_both_bounded, usize, i32, i64, i128);
+
+    rev!(try_from_upper_bounded, isize, u16, u32, u64, u128);
+    rev!(try_from_both_bounded, isize, i32, i64, i128);
+}
+
+#[cfg(target_pointer_width = "32")]
+mod ptr_try_from_impls {
+    use super::TryFromIntError;
+    use crate::convert::TryFrom;
+
+    try_from_upper_bounded!(usize, u8, u16);
+    try_from_unbounded!(usize, u32, u64, u128);
+    try_from_upper_bounded!(usize, i8, i16, i32);
+    try_from_unbounded!(usize, i64, i128);
+
+    try_from_both_bounded!(isize, u8, u16);
+    try_from_lower_bounded!(isize, u32, u64, u128);
+    try_from_both_bounded!(isize, i8, i16);
+    try_from_unbounded!(isize, i32, i64, i128);
+
+    rev!(try_from_unbounded, usize, u32);
+    rev!(try_from_upper_bounded, usize, u64, u128);
+    rev!(try_from_lower_bounded, usize, i8, i16, i32);
+    rev!(try_from_both_bounded, usize, i64, i128);
+
+    rev!(try_from_unbounded, isize, u16);
+    rev!(try_from_upper_bounded, isize, u32, u64, u128);
+    rev!(try_from_unbounded, isize, i32);
+    rev!(try_from_both_bounded, isize, i64, i128);
+}
+
+#[cfg(target_pointer_width = "64")]
+mod ptr_try_from_impls {
+    use super::TryFromIntError;
+    use crate::convert::TryFrom;
+
+    try_from_upper_bounded!(usize, u8, u16, u32);
+    try_from_unbounded!(usize, u64, u128);
+    try_from_upper_bounded!(usize, i8, i16, i32, i64);
+    try_from_unbounded!(usize, i128);
+
+    try_from_both_bounded!(isize, u8, u16, u32);
+    try_from_lower_bounded!(isize, u64, u128);
+    try_from_both_bounded!(isize, i8, i16, i32);
+    try_from_unbounded!(isize, i64, i128);
+
+    rev!(try_from_unbounded, usize, u32, u64);
+    rev!(try_from_upper_bounded, usize, u128);
+    rev!(try_from_lower_bounded, usize, i8, i16, i32, i64);
+    rev!(try_from_both_bounded, usize, i128);
+
+    rev!(try_from_unbounded, isize, u16, u32);
+    rev!(try_from_upper_bounded, isize, u64, u128);
+    rev!(try_from_unbounded, isize, i32, i64);
+    rev!(try_from_both_bounded, isize, i128);
+}
+
+// Conversion traits for non-zero integer types
+use crate::num::NonZeroI128;
+use crate::num::NonZeroI16;
+use crate::num::NonZeroI32;
+use crate::num::NonZeroI64;
+use crate::num::NonZeroI8;
+use crate::num::NonZeroIsize;
+use crate::num::NonZeroU128;
+use crate::num::NonZeroU16;
+use crate::num::NonZeroU32;
+use crate::num::NonZeroU64;
+use crate::num::NonZeroU8;
+use crate::num::NonZeroUsize;
+
+macro_rules! nzint_impl_from {
+    ($Small: ty, $Large: ty, #[$attr:meta], $doc: expr) => {
+        #[$attr]
+        #[doc = $doc]
+        impl From<$Small> for $Large {
+            #[inline]
+            fn from(small: $Small) -> $Large {
+                // SAFETY: input type guarantees the value is non-zero
+                unsafe {
+                    <$Large>::new_unchecked(small.get().into())
+                }
+            }
+        }
+    };
+    ($Small: ty, $Large: ty, #[$attr:meta]) => {
+        nzint_impl_from!($Small,
+                   $Large,
+                   #[$attr],
+                   concat!("Converts `",
+                           stringify!($Small),
+                           "` to `",
+                           stringify!($Large),
+                           "` losslessly."));
+    }
+}
+
+// Non-zero Unsigned -> Non-zero Unsigned
+nzint_impl_from! { NonZeroU8, NonZeroU16, #[stable(feature = "nz_int_conv", since = "1.41.0")] }
+nzint_impl_from! { NonZeroU8, NonZeroU32, #[stable(feature = "nz_int_conv", since = "1.41.0")] }
+nzint_impl_from! { NonZeroU8, NonZeroU64, #[stable(feature = "nz_int_conv", since = "1.41.0")] }
+nzint_impl_from! { NonZeroU8, NonZeroU128, #[stable(feature = "nz_int_conv", since = "1.41.0")] }
+nzint_impl_from! { NonZeroU8, NonZeroUsize, #[stable(feature = "nz_int_conv", since = "1.41.0")] }
+nzint_impl_from! { NonZeroU16, NonZeroU32, #[stable(feature = "nz_int_conv", since = "1.41.0")] }
+nzint_impl_from! { NonZeroU16, NonZeroU64, #[stable(feature = "nz_int_conv", since = "1.41.0")] }
+nzint_impl_from! { NonZeroU16, NonZeroU128, #[stable(feature = "nz_int_conv", since = "1.41.0")] }
+nzint_impl_from! { NonZeroU16, NonZeroUsize, #[stable(feature = "nz_int_conv", since = "1.41.0")] }
+nzint_impl_from! { NonZeroU32, NonZeroU64, #[stable(feature = "nz_int_conv", since = "1.41.0")] }
+nzint_impl_from! { NonZeroU32, NonZeroU128, #[stable(feature = "nz_int_conv", since = "1.41.0")] }
+nzint_impl_from! { NonZeroU64, NonZeroU128, #[stable(feature = "nz_int_conv", since = "1.41.0")] }
+
+// Non-zero Signed -> Non-zero Signed
+nzint_impl_from! { NonZeroI8, NonZeroI16, #[stable(feature = "nz_int_conv", since = "1.41.0")] }
+nzint_impl_from! { NonZeroI8, NonZeroI32, #[stable(feature = "nz_int_conv", since = "1.41.0")] }
+nzint_impl_from! { NonZeroI8, NonZeroI64, #[stable(feature = "nz_int_conv", since = "1.41.0")] }
+nzint_impl_from! { NonZeroI8, NonZeroI128, #[stable(feature = "nz_int_conv", since = "1.41.0")] }
+nzint_impl_from! { NonZeroI8, NonZeroIsize, #[stable(feature = "nz_int_conv", since = "1.41.0")] }
+nzint_impl_from! { NonZeroI16, NonZeroI32, #[stable(feature = "nz_int_conv", since = "1.41.0")] }
+nzint_impl_from! { NonZeroI16, NonZeroI64, #[stable(feature = "nz_int_conv", since = "1.41.0")] }
+nzint_impl_from! { NonZeroI16, NonZeroI128, #[stable(feature = "nz_int_conv", since = "1.41.0")] }
+nzint_impl_from! { NonZeroI16, NonZeroIsize, #[stable(feature = "nz_int_conv", since = "1.41.0")] }
+nzint_impl_from! { NonZeroI32, NonZeroI64, #[stable(feature = "nz_int_conv", since = "1.41.0")] }
+nzint_impl_from! { NonZeroI32, NonZeroI128, #[stable(feature = "nz_int_conv", since = "1.41.0")] }
+nzint_impl_from! { NonZeroI64, NonZeroI128, #[stable(feature = "nz_int_conv", since = "1.41.0")] }
+
+// NonZero UnSigned -> Non-zero Signed
+nzint_impl_from! { NonZeroU8, NonZeroI16, #[stable(feature = "nz_int_conv", since = "1.41.0")] }
+nzint_impl_from! { NonZeroU8, NonZeroI32, #[stable(feature = "nz_int_conv", since = "1.41.0")] }
+nzint_impl_from! { NonZeroU8, NonZeroI64, #[stable(feature = "nz_int_conv", since = "1.41.0")] }
+nzint_impl_from! { NonZeroU8, NonZeroI128, #[stable(feature = "nz_int_conv", since = "1.41.0")] }
+nzint_impl_from! { NonZeroU8, NonZeroIsize, #[stable(feature = "nz_int_conv", since = "1.41.0")] }
+nzint_impl_from! { NonZeroU16, NonZeroI32, #[stable(feature = "nz_int_conv", since = "1.41.0")] }
+nzint_impl_from! { NonZeroU16, NonZeroI64, #[stable(feature = "nz_int_conv", since = "1.41.0")] }
+nzint_impl_from! { NonZeroU16, NonZeroI128, #[stable(feature = "nz_int_conv", since = "1.41.0")] }
+nzint_impl_from! { NonZeroU32, NonZeroI64, #[stable(feature = "nz_int_conv", since = "1.41.0")] }
+nzint_impl_from! { NonZeroU32, NonZeroI128, #[stable(feature = "nz_int_conv", since = "1.41.0")] }
+nzint_impl_from! { NonZeroU64, NonZeroI128, #[stable(feature = "nz_int_conv", since = "1.41.0")] }