Adding upstream version 1.64.0+dfsg1.upstream/1.64.0+dfsg1

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

1 files changed, 2664 insertions, 0 deletions

diff --git a/library/core/src/fmt/mod.rs b/library/core/src/fmt/mod.rs
new file mode 100644
index 000000000..372141e09
--- /dev/null
+++ b/library/core/src/fmt/mod.rs
@@ -0,0 +1,2664 @@
+//! Utilities for formatting and printing strings.
+
+#![stable(feature = "rust1", since = "1.0.0")]
+
+use crate::cell::{Cell, Ref, RefCell, RefMut, SyncUnsafeCell, UnsafeCell};
+use crate::char::EscapeDebugExtArgs;
+use crate::iter;
+use crate::marker::PhantomData;
+use crate::mem;
+use crate::num::fmt as numfmt;
+use crate::ops::Deref;
+use crate::result;
+use crate::str;
+
+mod builders;
+#[cfg(not(no_fp_fmt_parse))]
+mod float;
+#[cfg(no_fp_fmt_parse)]
+mod nofloat;
+mod num;
+
+#[stable(feature = "fmt_flags_align", since = "1.28.0")]
+#[cfg_attr(not(test), rustc_diagnostic_item = "Alignment")]
+/// Possible alignments returned by `Formatter::align`
+#[derive(Copy, Clone, Debug, PartialEq, Eq)]
+pub enum Alignment {
+    #[stable(feature = "fmt_flags_align", since = "1.28.0")]
+    /// Indication that contents should be left-aligned.
+    Left,
+    #[stable(feature = "fmt_flags_align", since = "1.28.0")]
+    /// Indication that contents should be right-aligned.
+    Right,
+    #[stable(feature = "fmt_flags_align", since = "1.28.0")]
+    /// Indication that contents should be center-aligned.
+    Center,
+}
+
+#[stable(feature = "debug_builders", since = "1.2.0")]
+pub use self::builders::{DebugList, DebugMap, DebugSet, DebugStruct, DebugTuple};
+
+#[unstable(feature = "fmt_internals", reason = "internal to format_args!", issue = "none")]
+#[doc(hidden)]
+pub mod rt {
+    pub mod v1;
+}
+
+/// The type returned by formatter methods.
+///
+/// # Examples
+///
+/// ```
+/// use std::fmt;
+///
+/// #[derive(Debug)]
+/// struct Triangle {
+///     a: f32,
+///     b: f32,
+///     c: f32
+/// }
+///
+/// impl fmt::Display for Triangle {
+///     fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+///         write!(f, "({}, {}, {})", self.a, self.b, self.c)
+///     }
+/// }
+///
+/// let pythagorean_triple = Triangle { a: 3.0, b: 4.0, c: 5.0 };
+///
+/// assert_eq!(format!("{pythagorean_triple}"), "(3, 4, 5)");
+/// ```
+#[stable(feature = "rust1", since = "1.0.0")]
+pub type Result = result::Result<(), Error>;
+
+/// The error type which is returned from formatting a message into a stream.
+///
+/// This type does not support transmission of an error other than that an error
+/// occurred. Any extra information must be arranged to be transmitted through
+/// some other means.
+///
+/// An important thing to remember is that the type `fmt::Error` should not be
+/// confused with [`std::io::Error`] or [`std::error::Error`], which you may also
+/// have in scope.
+///
+/// [`std::io::Error`]: ../../std/io/struct.Error.html
+/// [`std::error::Error`]: ../../std/error/trait.Error.html
+///
+/// # Examples
+///
+/// ```rust
+/// use std::fmt::{self, write};
+///
+/// let mut output = String::new();
+/// if let Err(fmt::Error) = write(&mut output, format_args!("Hello {}!", "world")) {
+///     panic!("An error occurred");
+/// }
+/// ```
+#[stable(feature = "rust1", since = "1.0.0")]
+#[derive(Copy, Clone, Debug, Default, Eq, Hash, Ord, PartialEq, PartialOrd)]
+pub struct Error;
+
+/// A trait for writing or formatting into Unicode-accepting buffers or streams.
+///
+/// This trait only accepts UTF-8–encoded data and is not [flushable]. If you only
+/// want to accept Unicode and you don't need flushing, you should implement this trait;
+/// otherwise you should implement [`std::io::Write`].
+///
+/// [`std::io::Write`]: ../../std/io/trait.Write.html
+/// [flushable]: ../../std/io/trait.Write.html#tymethod.flush
+#[stable(feature = "rust1", since = "1.0.0")]
+pub trait Write {
+    /// Writes a string slice into this writer, returning whether the write
+    /// succeeded.
+    ///
+    /// This method can only succeed if the entire string slice was successfully
+    /// written, and this method will not return until all data has been
+    /// written or an error occurs.
+    ///
+    /// # Errors
+    ///
+    /// This function will return an instance of [`Error`] on error.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use std::fmt::{Error, Write};
+    ///
+    /// fn writer<W: Write>(f: &mut W, s: &str) -> Result<(), Error> {
+    ///     f.write_str(s)
+    /// }
+    ///
+    /// let mut buf = String::new();
+    /// writer(&mut buf, "hola").unwrap();
+    /// assert_eq!(&buf, "hola");
+    /// ```
+    #[stable(feature = "rust1", since = "1.0.0")]
+    fn write_str(&mut self, s: &str) -> Result;
+
+    /// Writes a [`char`] into this writer, returning whether the write succeeded.
+    ///
+    /// A single [`char`] may be encoded as more than one byte.
+    /// This method can only succeed if the entire byte sequence was successfully
+    /// written, and this method will not return until all data has been
+    /// written or an error occurs.
+    ///
+    /// # Errors
+    ///
+    /// This function will return an instance of [`Error`] on error.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use std::fmt::{Error, Write};
+    ///
+    /// fn writer<W: Write>(f: &mut W, c: char) -> Result<(), Error> {
+    ///     f.write_char(c)
+    /// }
+    ///
+    /// let mut buf = String::new();
+    /// writer(&mut buf, 'a').unwrap();
+    /// writer(&mut buf, 'b').unwrap();
+    /// assert_eq!(&buf, "ab");
+    /// ```
+    #[stable(feature = "fmt_write_char", since = "1.1.0")]
+    fn write_char(&mut self, c: char) -> Result {
+        self.write_str(c.encode_utf8(&mut [0; 4]))
+    }
+
+    /// Glue for usage of the [`write!`] macro with implementors of this trait.
+    ///
+    /// This method should generally not be invoked manually, but rather through
+    /// the [`write!`] macro itself.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use std::fmt::{Error, Write};
+    ///
+    /// fn writer<W: Write>(f: &mut W, s: &str) -> Result<(), Error> {
+    ///     f.write_fmt(format_args!("{s}"))
+    /// }
+    ///
+    /// let mut buf = String::new();
+    /// writer(&mut buf, "world").unwrap();
+    /// assert_eq!(&buf, "world");
+    /// ```
+    #[stable(feature = "rust1", since = "1.0.0")]
+    fn write_fmt(mut self: &mut Self, args: Arguments<'_>) -> Result {
+        write(&mut self, args)
+    }
+}
+
+#[stable(feature = "fmt_write_blanket_impl", since = "1.4.0")]
+impl<W: Write + ?Sized> Write for &mut W {
+    fn write_str(&mut self, s: &str) -> Result {
+        (**self).write_str(s)
+    }
+
+    fn write_char(&mut self, c: char) -> Result {
+        (**self).write_char(c)
+    }
+
+    fn write_fmt(&mut self, args: Arguments<'_>) -> Result {
+        (**self).write_fmt(args)
+    }
+}
+
+/// Configuration for formatting.
+///
+/// A `Formatter` represents various options related to formatting. Users do not
+/// construct `Formatter`s directly; a mutable reference to one is passed to
+/// the `fmt` method of all formatting traits, like [`Debug`] and [`Display`].
+///
+/// To interact with a `Formatter`, you'll call various methods to change the
+/// various options related to formatting. For examples, please see the
+/// documentation of the methods defined on `Formatter` below.
+#[allow(missing_debug_implementations)]
+#[stable(feature = "rust1", since = "1.0.0")]
+pub struct Formatter<'a> {
+    flags: u32,
+    fill: char,
+    align: rt::v1::Alignment,
+    width: Option<usize>,
+    precision: Option<usize>,
+
+    buf: &'a mut (dyn Write + 'a),
+}
+
+impl<'a> Formatter<'a> {
+    /// Creates a new formatter with default settings.
+    ///
+    /// This can be used as a micro-optimization in cases where a full `Arguments`
+    /// structure (as created by `format_args!`) is not necessary; `Arguments`
+    /// is a little more expensive to use in simple formatting scenarios.
+    ///
+    /// Currently not intended for use outside of the standard library.
+    #[unstable(feature = "fmt_internals", reason = "internal to standard library", issue = "none")]
+    #[doc(hidden)]
+    pub fn new(buf: &'a mut (dyn Write + 'a)) -> Formatter<'a> {
+        Formatter {
+            flags: 0,
+            fill: ' ',
+            align: rt::v1::Alignment::Unknown,
+            width: None,
+            precision: None,
+            buf,
+        }
+    }
+}
+
+// NB. Argument is essentially an optimized partially applied formatting function,
+// equivalent to `exists T.(&T, fn(&T, &mut Formatter<'_>) -> Result`.
+
+extern "C" {
+    type Opaque;
+}
+
+/// This struct represents the generic "argument" which is taken by the Xprintf
+/// family of functions. It contains a function to format the given value. At
+/// compile time it is ensured that the function and the value have the correct
+/// types, and then this struct is used to canonicalize arguments to one type.
+#[derive(Copy, Clone)]
+#[allow(missing_debug_implementations)]
+#[unstable(feature = "fmt_internals", reason = "internal to format_args!", issue = "none")]
+#[doc(hidden)]
+pub struct ArgumentV1<'a> {
+    value: &'a Opaque,
+    formatter: fn(&Opaque, &mut Formatter<'_>) -> Result,
+}
+
+/// This struct represents the unsafety of constructing an `Arguments`.
+/// It exists, rather than an unsafe function, in order to simplify the expansion
+/// of `format_args!(..)` and reduce the scope of the `unsafe` block.
+#[allow(missing_debug_implementations)]
+#[doc(hidden)]
+#[unstable(feature = "fmt_internals", reason = "internal to format_args!", issue = "none")]
+pub struct UnsafeArg {
+    _private: (),
+}
+
+impl UnsafeArg {
+    /// See documentation where `UnsafeArg` is required to know when it is safe to
+    /// create and use `UnsafeArg`.
+    #[doc(hidden)]
+    #[unstable(feature = "fmt_internals", reason = "internal to format_args!", issue = "none")]
+    #[inline(always)]
+    pub unsafe fn new() -> Self {
+        Self { _private: () }
+    }
+}
+
+// This guarantees a single stable value for the function pointer associated with
+// indices/counts in the formatting infrastructure.
+//
+// Note that a function defined as such would not be correct as functions are
+// always tagged unnamed_addr with the current lowering to LLVM IR, so their
+// address is not considered important to LLVM and as such the as_usize cast
+// could have been miscompiled. In practice, we never call as_usize on non-usize
+// containing data (as a matter of static generation of the formatting
+// arguments), so this is merely an additional check.
+//
+// We primarily want to ensure that the function pointer at `USIZE_MARKER` has
+// an address corresponding *only* to functions that also take `&usize` as their
+// first argument. The read_volatile here ensures that we can safely ready out a
+// usize from the passed reference and that this address does not point at a
+// non-usize taking function.
+#[unstable(feature = "fmt_internals", reason = "internal to format_args!", issue = "none")]
+static USIZE_MARKER: fn(&usize, &mut Formatter<'_>) -> Result = |ptr, _| {
+    // SAFETY: ptr is a reference
+    let _v: usize = unsafe { crate::ptr::read_volatile(ptr) };
+    loop {}
+};
+
+macro_rules! arg_new {
+    ($f: ident, $t: ident) => {
+        #[doc(hidden)]
+        #[unstable(feature = "fmt_internals", reason = "internal to format_args!", issue = "none")]
+        #[inline]
+        pub fn $f<'b, T: $t>(x: &'b T) -> ArgumentV1<'_> {
+            Self::new(x, $t::fmt)
+        }
+    };
+}
+
+#[rustc_diagnostic_item = "ArgumentV1Methods"]
+impl<'a> ArgumentV1<'a> {
+    #[doc(hidden)]
+    #[unstable(feature = "fmt_internals", reason = "internal to format_args!", issue = "none")]
+    #[inline]
+    pub fn new<'b, T>(x: &'b T, f: fn(&T, &mut Formatter<'_>) -> Result) -> ArgumentV1<'b> {
+        // SAFETY: `mem::transmute(x)` is safe because
+        //     1. `&'b T` keeps the lifetime it originated with `'b`
+        //              (so as to not have an unbounded lifetime)
+        //     2. `&'b T` and `&'b Opaque` have the same memory layout
+        //              (when `T` is `Sized`, as it is here)
+        // `mem::transmute(f)` is safe since `fn(&T, &mut Formatter<'_>) -> Result`
+        // and `fn(&Opaque, &mut Formatter<'_>) -> Result` have the same ABI
+        // (as long as `T` is `Sized`)
+        unsafe { ArgumentV1 { formatter: mem::transmute(f), value: mem::transmute(x) } }
+    }
+
+    arg_new!(new_display, Display);
+    arg_new!(new_debug, Debug);
+    arg_new!(new_octal, Octal);
+    arg_new!(new_lower_hex, LowerHex);
+    arg_new!(new_upper_hex, UpperHex);
+    arg_new!(new_pointer, Pointer);
+    arg_new!(new_binary, Binary);
+    arg_new!(new_lower_exp, LowerExp);
+    arg_new!(new_upper_exp, UpperExp);
+
+    #[doc(hidden)]
+    #[unstable(feature = "fmt_internals", reason = "internal to format_args!", issue = "none")]
+    pub fn from_usize(x: &usize) -> ArgumentV1<'_> {
+        ArgumentV1::new(x, USIZE_MARKER)
+    }
+
+    fn as_usize(&self) -> Option<usize> {
+        // We are type punning a bit here: USIZE_MARKER only takes an &usize but
+        // formatter takes an &Opaque. Rust understandably doesn't think we should compare
+        // the function pointers if they don't have the same signature, so we cast to
+        // usizes to tell it that we just want to compare addresses.
+        if self.formatter as usize == USIZE_MARKER as usize {
+            // SAFETY: The `formatter` field is only set to USIZE_MARKER if
+            // the value is a usize, so this is safe
+            Some(unsafe { *(self.value as *const _ as *const usize) })
+        } else {
+            None
+        }
+    }
+}
+
+// flags available in the v1 format of format_args
+#[derive(Copy, Clone)]
+enum FlagV1 {
+    SignPlus,
+    SignMinus,
+    Alternate,
+    SignAwareZeroPad,
+    DebugLowerHex,
+    DebugUpperHex,
+}
+
+impl<'a> Arguments<'a> {
+    /// When using the format_args!() macro, this function is used to generate the
+    /// Arguments structure.
+    #[doc(hidden)]
+    #[inline]
+    #[unstable(feature = "fmt_internals", reason = "internal to format_args!", issue = "none")]
+    #[rustc_const_unstable(feature = "const_fmt_arguments_new", issue = "none")]
+    pub const fn new_v1(pieces: &'a [&'static str], args: &'a [ArgumentV1<'a>]) -> Arguments<'a> {
+        if pieces.len() < args.len() || pieces.len() > args.len() + 1 {
+            panic!("invalid args");
+        }
+        Arguments { pieces, fmt: None, args }
+    }
+
+    /// This function is used to specify nonstandard formatting parameters.
+    ///
+    /// An `UnsafeArg` is required because the following invariants must be held
+    /// in order for this function to be safe:
+    /// 1. The `pieces` slice must be at least as long as `fmt`.
+    /// 2. Every [`rt::v1::Argument::position`] value within `fmt` must be a
+    ///    valid index of `args`.
+    /// 3. Every [`Count::Param`] within `fmt` must contain a valid index of
+    ///    `args`.
+    #[doc(hidden)]
+    #[inline]
+    #[unstable(feature = "fmt_internals", reason = "internal to format_args!", issue = "none")]
+    #[rustc_const_unstable(feature = "const_fmt_arguments_new", issue = "none")]
+    pub const fn new_v1_formatted(
+        pieces: &'a [&'static str],
+        args: &'a [ArgumentV1<'a>],
+        fmt: &'a [rt::v1::Argument],
+        _unsafe_arg: UnsafeArg,
+    ) -> Arguments<'a> {
+        Arguments { pieces, fmt: Some(fmt), args }
+    }
+
+    /// Estimates the length of the formatted text.
+    ///
+    /// This is intended to be used for setting initial `String` capacity
+    /// when using `format!`. Note: this is neither the lower nor upper bound.
+    #[doc(hidden)]
+    #[inline]
+    #[unstable(feature = "fmt_internals", reason = "internal to format_args!", issue = "none")]
+    pub fn estimated_capacity(&self) -> usize {
+        let pieces_length: usize = self.pieces.iter().map(|x| x.len()).sum();
+
+        if self.args.is_empty() {
+            pieces_length
+        } else if !self.pieces.is_empty() && self.pieces[0].is_empty() && pieces_length < 16 {
+            // If the format string starts with an argument,
+            // don't preallocate anything, unless length
+            // of pieces is significant.
+            0
+        } else {
+            // There are some arguments, so any additional push
+            // will reallocate the string. To avoid that,
+            // we're "pre-doubling" the capacity here.
+            pieces_length.checked_mul(2).unwrap_or(0)
+        }
+    }
+}
+
+/// This structure represents a safely precompiled version of a format string
+/// and its arguments. This cannot be generated at runtime because it cannot
+/// safely be done, so no constructors are given and the fields are private
+/// to prevent modification.
+///
+/// The [`format_args!`] macro will safely create an instance of this structure.
+/// The macro validates the format string at compile-time so usage of the
+/// [`write()`] and [`format()`] functions can be safely performed.
+///
+/// You can use the `Arguments<'a>` that [`format_args!`] returns in `Debug`
+/// and `Display` contexts as seen below. The example also shows that `Debug`
+/// and `Display` format to the same thing: the interpolated format string
+/// in `format_args!`.
+///
+/// ```rust
+/// let debug = format!("{:?}", format_args!("{} foo {:?}", 1, 2));
+/// let display = format!("{}", format_args!("{} foo {:?}", 1, 2));
+/// assert_eq!("1 foo 2", display);
+/// assert_eq!(display, debug);
+/// ```
+///
+/// [`format()`]: ../../std/fmt/fn.format.html
+#[stable(feature = "rust1", since = "1.0.0")]
+#[cfg_attr(not(test), rustc_diagnostic_item = "Arguments")]
+#[derive(Copy, Clone)]
+pub struct Arguments<'a> {
+    // Format string pieces to print.
+    pieces: &'a [&'static str],
+
+    // Placeholder specs, or `None` if all specs are default (as in "{}{}").
+    fmt: Option<&'a [rt::v1::Argument]>,
+
+    // Dynamic arguments for interpolation, to be interleaved with string
+    // pieces. (Every argument is preceded by a string piece.)
+    args: &'a [ArgumentV1<'a>],
+}
+
+impl<'a> Arguments<'a> {
+    /// Get the formatted string, if it has no arguments to be formatted.
+    ///
+    /// This can be used to avoid allocations in the most trivial case.
+    ///
+    /// # Examples
+    ///
+    /// ```rust
+    /// use std::fmt::Arguments;
+    ///
+    /// fn write_str(_: &str) { /* ... */ }
+    ///
+    /// fn write_fmt(args: &Arguments) {
+    ///     if let Some(s) = args.as_str() {
+    ///         write_str(s)
+    ///     } else {
+    ///         write_str(&args.to_string());
+    ///     }
+    /// }
+    /// ```
+    ///
+    /// ```rust
+    /// assert_eq!(format_args!("hello").as_str(), Some("hello"));
+    /// assert_eq!(format_args!("").as_str(), Some(""));
+    /// assert_eq!(format_args!("{}", 1).as_str(), None);
+    /// ```
+    #[stable(feature = "fmt_as_str", since = "1.52.0")]
+    #[rustc_const_unstable(feature = "const_arguments_as_str", issue = "none")]
+    #[must_use]
+    #[inline]
+    pub const fn as_str(&self) -> Option<&'static str> {
+        match (self.pieces, self.args) {
+            ([], []) => Some(""),
+            ([s], []) => Some(s),
+            _ => None,
+        }
+    }
+}
+
+#[stable(feature = "rust1", since = "1.0.0")]
+impl Debug for Arguments<'_> {
+    fn fmt(&self, fmt: &mut Formatter<'_>) -> Result {
+        Display::fmt(self, fmt)
+    }
+}
+
+#[stable(feature = "rust1", since = "1.0.0")]
+impl Display for Arguments<'_> {
+    fn fmt(&self, fmt: &mut Formatter<'_>) -> Result {
+        write(fmt.buf, *self)
+    }
+}
+
+/// `?` formatting.
+///
+/// `Debug` should format the output in a programmer-facing, debugging context.
+///
+/// Generally speaking, you should just `derive` a `Debug` implementation.
+///
+/// When used with the alternate format specifier `#?`, the output is pretty-printed.
+///
+/// For more information on formatters, see [the module-level documentation][module].
+///
+/// [module]: ../../std/fmt/index.html
+///
+/// This trait can be used with `#[derive]` if all fields implement `Debug`. When
+/// `derive`d for structs, it will use the name of the `struct`, then `{`, then a
+/// comma-separated list of each field's name and `Debug` value, then `}`. For
+/// `enum`s, it will use the name of the variant and, if applicable, `(`, then the
+/// `Debug` values of the fields, then `)`.
+///
+/// # Stability
+///
+/// Derived `Debug` formats are not stable, and so may change with future Rust
+/// versions. Additionally, `Debug` implementations of types provided by the
+/// standard library (`libstd`, `libcore`, `liballoc`, etc.) are not stable, and
+/// may also change with future Rust versions.
+///
+/// # Examples
+///
+/// Deriving an implementation:
+///
+/// ```
+/// #[derive(Debug)]
+/// struct Point {
+///     x: i32,
+///     y: i32,
+/// }
+///
+/// let origin = Point { x: 0, y: 0 };
+///
+/// assert_eq!(format!("The origin is: {origin:?}"), "The origin is: Point { x: 0, y: 0 }");
+/// ```
+///
+/// Manually implementing:
+///
+/// ```
+/// use std::fmt;
+///
+/// struct Point {
+///     x: i32,
+///     y: i32,
+/// }
+///
+/// impl fmt::Debug for Point {
+///     fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+///         f.debug_struct("Point")
+///          .field("x", &self.x)
+///          .field("y", &self.y)
+///          .finish()
+///     }
+/// }
+///
+/// let origin = Point { x: 0, y: 0 };
+///
+/// assert_eq!(format!("The origin is: {origin:?}"), "The origin is: Point { x: 0, y: 0 }");
+/// ```
+///
+/// There are a number of helper methods on the [`Formatter`] struct to help you with manual
+/// implementations, such as [`debug_struct`].
+///
+/// [`debug_struct`]: Formatter::debug_struct
+///
+/// Types that do not wish to use the standard suite of debug representations
+/// provided by the `Formatter` trait (`debug_struct`, `debug_tuple`,
+/// `debug_list`, `debug_set`, `debug_map`) can do something totally custom by
+/// manually writing an arbitrary representation to the `Formatter`.
+///
+/// ```
+/// # use std::fmt;
+/// # struct Point {
+/// #     x: i32,
+/// #     y: i32,
+/// # }
+/// #
+/// impl fmt::Debug for Point {
+///     fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+///         write!(f, "Point [{} {}]", self.x, self.y)
+///     }
+/// }
+/// ```
+///
+/// `Debug` implementations using either `derive` or the debug builder API
+/// on [`Formatter`] support pretty-printing using the alternate flag: `{:#?}`.
+///
+/// Pretty-printing with `#?`:
+///
+/// ```
+/// #[derive(Debug)]
+/// struct Point {
+///     x: i32,
+///     y: i32,
+/// }
+///
+/// let origin = Point { x: 0, y: 0 };
+///
+/// assert_eq!(format!("The origin is: {origin:#?}"),
+/// "The origin is: Point {
+///     x: 0,
+///     y: 0,
+/// }");
+/// ```
+
+#[stable(feature = "rust1", since = "1.0.0")]
+#[rustc_on_unimplemented(
+    on(
+        crate_local,
+        label = "`{Self}` cannot be formatted using `{{:?}}`",
+        note = "add `#[derive(Debug)]` to `{Self}` or manually `impl {Debug} for {Self}`"
+    ),
+    message = "`{Self}` doesn't implement `{Debug}`",
+    label = "`{Self}` cannot be formatted using `{{:?}}` because it doesn't implement `{Debug}`"
+)]
+#[doc(alias = "{:?}")]
+#[rustc_diagnostic_item = "Debug"]
+#[rustc_trivial_field_reads]
+pub trait Debug {
+    /// Formats the value using the given formatter.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use std::fmt;
+    ///
+    /// struct Position {
+    ///     longitude: f32,
+    ///     latitude: f32,
+    /// }
+    ///
+    /// impl fmt::Debug for Position {
+    ///     fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+    ///         f.debug_tuple("")
+    ///          .field(&self.longitude)
+    ///          .field(&self.latitude)
+    ///          .finish()
+    ///     }
+    /// }
+    ///
+    /// let position = Position { longitude: 1.987, latitude: 2.983 };
+    /// assert_eq!(format!("{position:?}"), "(1.987, 2.983)");
+    ///
+    /// assert_eq!(format!("{position:#?}"), "(
+    ///     1.987,
+    ///     2.983,
+    /// )");
+    /// ```
+    #[stable(feature = "rust1", since = "1.0.0")]
+    fn fmt(&self, f: &mut Formatter<'_>) -> Result;
+}
+
+// Separate module to reexport the macro `Debug` from prelude without the trait `Debug`.
+pub(crate) mod macros {
+    /// Derive macro generating an impl of the trait `Debug`.
+    #[rustc_builtin_macro]
+    #[stable(feature = "builtin_macro_prelude", since = "1.38.0")]
+    #[allow_internal_unstable(core_intrinsics, fmt_helpers_for_derive)]
+    pub macro Debug($item:item) {
+        /* compiler built-in */
+    }
+}
+#[stable(feature = "builtin_macro_prelude", since = "1.38.0")]
+#[doc(inline)]
+pub use macros::Debug;
+
+/// Format trait for an empty format, `{}`.
+///
+/// `Display` is similar to [`Debug`], but `Display` is for user-facing
+/// output, and so cannot be derived.
+///
+/// For more information on formatters, see [the module-level documentation][module].
+///
+/// [module]: ../../std/fmt/index.html
+///
+/// # Examples
+///
+/// Implementing `Display` on a type:
+///
+/// ```
+/// use std::fmt;
+///
+/// struct Point {
+///     x: i32,
+///     y: i32,
+/// }
+///
+/// impl fmt::Display for Point {
+///     fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+///         write!(f, "({}, {})", self.x, self.y)
+///     }
+/// }
+///
+/// let origin = Point { x: 0, y: 0 };
+///
+/// assert_eq!(format!("The origin is: {origin}"), "The origin is: (0, 0)");
+/// ```
+#[rustc_on_unimplemented(
+    on(
+        any(_Self = "std::path::Path", _Self = "std::path::PathBuf"),
+        label = "`{Self}` cannot be formatted with the default formatter; call `.display()` on it",
+        note = "call `.display()` or `.to_string_lossy()` to safely print paths, \
+                as they may contain non-Unicode data"
+    ),
+    message = "`{Self}` doesn't implement `{Display}`",
+    label = "`{Self}` cannot be formatted with the default formatter",
+    note = "in format strings you may be able to use `{{:?}}` (or {{:#?}} for pretty-print) instead"
+)]
+#[doc(alias = "{}")]
+#[rustc_diagnostic_item = "Display"]
+#[stable(feature = "rust1", since = "1.0.0")]
+pub trait Display {
+    /// Formats the value using the given formatter.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use std::fmt;
+    ///
+    /// struct Position {
+    ///     longitude: f32,
+    ///     latitude: f32,
+    /// }
+    ///
+    /// impl fmt::Display for Position {
+    ///     fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+    ///         write!(f, "({}, {})", self.longitude, self.latitude)
+    ///     }
+    /// }
+    ///
+    /// assert_eq!("(1.987, 2.983)",
+    ///            format!("{}", Position { longitude: 1.987, latitude: 2.983, }));
+    /// ```
+    #[stable(feature = "rust1", since = "1.0.0")]
+    fn fmt(&self, f: &mut Formatter<'_>) -> Result;
+}
+
+/// `o` formatting.
+///
+/// The `Octal` trait should format its output as a number in base-8.
+///
+/// For primitive signed integers (`i8` to `i128`, and `isize`),
+/// negative values are formatted as the two’s complement representation.
+///
+/// The alternate flag, `#`, adds a `0o` in front of the output.
+///
+/// For more information on formatters, see [the module-level documentation][module].
+///
+/// [module]: ../../std/fmt/index.html
+///
+/// # Examples
+///
+/// Basic usage with `i32`:
+///
+/// ```
+/// let x = 42; // 42 is '52' in octal
+///
+/// assert_eq!(format!("{x:o}"), "52");
+/// assert_eq!(format!("{x:#o}"), "0o52");
+///
+/// assert_eq!(format!("{:o}", -16), "37777777760");
+/// ```
+///
+/// Implementing `Octal` on a type:
+///
+/// ```
+/// use std::fmt;
+///
+/// struct Length(i32);
+///
+/// impl fmt::Octal for Length {
+///     fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+///         let val = self.0;
+///
+///         fmt::Octal::fmt(&val, f) // delegate to i32's implementation
+///     }
+/// }
+///
+/// let l = Length(9);
+///
+/// assert_eq!(format!("l as octal is: {l:o}"), "l as octal is: 11");
+///
+/// assert_eq!(format!("l as octal is: {l:#06o}"), "l as octal is: 0o0011");
+/// ```
+#[stable(feature = "rust1", since = "1.0.0")]
+pub trait Octal {
+    /// Formats the value using the given formatter.
+    #[stable(feature = "rust1", since = "1.0.0")]
+    fn fmt(&self, f: &mut Formatter<'_>) -> Result;
+}
+
+/// `b` formatting.
+///
+/// The `Binary` trait should format its output as a number in binary.
+///
+/// For primitive signed integers ([`i8`] to [`i128`], and [`isize`]),
+/// negative values are formatted as the two’s complement representation.
+///
+/// The alternate flag, `#`, adds a `0b` in front of the output.
+///
+/// For more information on formatters, see [the module-level documentation][module].
+///
+/// [module]: ../../std/fmt/index.html
+///
+/// # Examples
+///
+/// Basic usage with [`i32`]:
+///
+/// ```
+/// let x = 42; // 42 is '101010' in binary
+///
+/// assert_eq!(format!("{x:b}"), "101010");
+/// assert_eq!(format!("{x:#b}"), "0b101010");
+///
+/// assert_eq!(format!("{:b}", -16), "11111111111111111111111111110000");
+/// ```
+///
+/// Implementing `Binary` on a type:
+///
+/// ```
+/// use std::fmt;
+///
+/// struct Length(i32);
+///
+/// impl fmt::Binary for Length {
+///     fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+///         let val = self.0;
+///
+///         fmt::Binary::fmt(&val, f) // delegate to i32's implementation
+///     }
+/// }
+///
+/// let l = Length(107);
+///
+/// assert_eq!(format!("l as binary is: {l:b}"), "l as binary is: 1101011");
+///
+/// assert_eq!(
+///     format!("l as binary is: {l:#032b}"),
+///     "l as binary is: 0b000000000000000000000001101011"
+/// );
+/// ```
+#[stable(feature = "rust1", since = "1.0.0")]
+pub trait Binary {
+    /// Formats the value using the given formatter.
+    #[stable(feature = "rust1", since = "1.0.0")]
+    fn fmt(&self, f: &mut Formatter<'_>) -> Result;
+}
+
+/// `x` formatting.
+///
+/// The `LowerHex` trait should format its output as a number in hexadecimal, with `a` through `f`
+/// in lower case.
+///
+/// For primitive signed integers (`i8` to `i128`, and `isize`),
+/// negative values are formatted as the two’s complement representation.
+///
+/// The alternate flag, `#`, adds a `0x` in front of the output.
+///
+/// For more information on formatters, see [the module-level documentation][module].
+///
+/// [module]: ../../std/fmt/index.html
+///
+/// # Examples
+///
+/// Basic usage with `i32`:
+///
+/// ```
+/// let x = 42; // 42 is '2a' in hex
+///
+/// assert_eq!(format!("{x:x}"), "2a");
+/// assert_eq!(format!("{x:#x}"), "0x2a");
+///
+/// assert_eq!(format!("{:x}", -16), "fffffff0");
+/// ```
+///
+/// Implementing `LowerHex` on a type:
+///
+/// ```
+/// use std::fmt;
+///
+/// struct Length(i32);
+///
+/// impl fmt::LowerHex for Length {
+///     fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+///         let val = self.0;
+///
+///         fmt::LowerHex::fmt(&val, f) // delegate to i32's implementation
+///     }
+/// }
+///
+/// let l = Length(9);
+///
+/// assert_eq!(format!("l as hex is: {l:x}"), "l as hex is: 9");
+///
+/// assert_eq!(format!("l as hex is: {l:#010x}"), "l as hex is: 0x00000009");
+/// ```
+#[stable(feature = "rust1", since = "1.0.0")]
+pub trait LowerHex {
+    /// Formats the value using the given formatter.
+    #[stable(feature = "rust1", since = "1.0.0")]
+    fn fmt(&self, f: &mut Formatter<'_>) -> Result;
+}
+
+/// `X` formatting.
+///
+/// The `UpperHex` trait should format its output as a number in hexadecimal, with `A` through `F`
+/// in upper case.
+///
+/// For primitive signed integers (`i8` to `i128`, and `isize`),
+/// negative values are formatted as the two’s complement representation.
+///
+/// The alternate flag, `#`, adds a `0x` in front of the output.
+///
+/// For more information on formatters, see [the module-level documentation][module].
+///
+/// [module]: ../../std/fmt/index.html
+///
+/// # Examples
+///
+/// Basic usage with `i32`:
+///
+/// ```
+/// let x = 42; // 42 is '2A' in hex
+///
+/// assert_eq!(format!("{x:X}"), "2A");
+/// assert_eq!(format!("{x:#X}"), "0x2A");
+///
+/// assert_eq!(format!("{:X}", -16), "FFFFFFF0");
+/// ```
+///
+/// Implementing `UpperHex` on a type:
+///
+/// ```
+/// use std::fmt;
+///
+/// struct Length(i32);
+///
+/// impl fmt::UpperHex for Length {
+///     fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+///         let val = self.0;
+///
+///         fmt::UpperHex::fmt(&val, f) // delegate to i32's implementation
+///     }
+/// }
+///
+/// let l = Length(i32::MAX);
+///
+/// assert_eq!(format!("l as hex is: {l:X}"), "l as hex is: 7FFFFFFF");
+///
+/// assert_eq!(format!("l as hex is: {l:#010X}"), "l as hex is: 0x7FFFFFFF");
+/// ```
+#[stable(feature = "rust1", since = "1.0.0")]
+pub trait UpperHex {
+    /// Formats the value using the given formatter.
+    #[stable(feature = "rust1", since = "1.0.0")]
+    fn fmt(&self, f: &mut Formatter<'_>) -> Result;
+}
+
+/// `p` formatting.
+///
+/// The `Pointer` trait should format its output as a memory location. This is commonly presented
+/// as hexadecimal.
+///
+/// For more information on formatters, see [the module-level documentation][module].
+///
+/// [module]: ../../std/fmt/index.html
+///
+/// # Examples
+///
+/// Basic usage with `&i32`:
+///
+/// ```
+/// let x = &42;
+///
+/// let address = format!("{x:p}"); // this produces something like '0x7f06092ac6d0'
+/// ```
+///
+/// Implementing `Pointer` on a type:
+///
+/// ```
+/// use std::fmt;
+///
+/// struct Length(i32);
+///
+/// impl fmt::Pointer for Length {
+///     fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+///         // use `as` to convert to a `*const T`, which implements Pointer, which we can use
+///
+///         let ptr = self as *const Self;
+///         fmt::Pointer::fmt(&ptr, f)
+///     }
+/// }
+///
+/// let l = Length(42);
+///
+/// println!("l is in memory here: {l:p}");
+///
+/// let l_ptr = format!("{l:018p}");
+/// assert_eq!(l_ptr.len(), 18);
+/// assert_eq!(&l_ptr[..2], "0x");
+/// ```
+#[stable(feature = "rust1", since = "1.0.0")]
+#[rustc_diagnostic_item = "Pointer"]
+pub trait Pointer {
+    /// Formats the value using the given formatter.
+    #[stable(feature = "rust1", since = "1.0.0")]
+    #[rustc_diagnostic_item = "pointer_trait_fmt"]
+    fn fmt(&self, f: &mut Formatter<'_>) -> Result;
+}
+
+/// `e` formatting.
+///
+/// The `LowerExp` trait should format its output in scientific notation with a lower-case `e`.
+///
+/// For more information on formatters, see [the module-level documentation][module].
+///
+/// [module]: ../../std/fmt/index.html
+///
+/// # Examples
+///
+/// Basic usage with `f64`:
+///
+/// ```
+/// let x = 42.0; // 42.0 is '4.2e1' in scientific notation
+///
+/// assert_eq!(format!("{x:e}"), "4.2e1");
+/// ```
+///
+/// Implementing `LowerExp` on a type:
+///
+/// ```
+/// use std::fmt;
+///
+/// struct Length(i32);
+///
+/// impl fmt::LowerExp for Length {
+///     fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+///         let val = f64::from(self.0);
+///         fmt::LowerExp::fmt(&val, f) // delegate to f64's implementation
+///     }
+/// }
+///
+/// let l = Length(100);
+///
+/// assert_eq!(
+///     format!("l in scientific notation is: {l:e}"),
+///     "l in scientific notation is: 1e2"
+/// );
+///
+/// assert_eq!(
+///     format!("l in scientific notation is: {l:05e}"),
+///     "l in scientific notation is: 001e2"
+/// );
+/// ```
+#[stable(feature = "rust1", since = "1.0.0")]
+pub trait LowerExp {
+    /// Formats the value using the given formatter.
+    #[stable(feature = "rust1", since = "1.0.0")]
+    fn fmt(&self, f: &mut Formatter<'_>) -> Result;
+}
+
+/// `E` formatting.
+///
+/// The `UpperExp` trait should format its output in scientific notation with an upper-case `E`.
+///
+/// For more information on formatters, see [the module-level documentation][module].
+///
+/// [module]: ../../std/fmt/index.html
+///
+/// # Examples
+///
+/// Basic usage with `f64`:
+///
+/// ```
+/// let x = 42.0; // 42.0 is '4.2E1' in scientific notation
+///
+/// assert_eq!(format!("{x:E}"), "4.2E1");
+/// ```
+///
+/// Implementing `UpperExp` on a type:
+///
+/// ```
+/// use std::fmt;
+///
+/// struct Length(i32);
+///
+/// impl fmt::UpperExp for Length {
+///     fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+///         let val = f64::from(self.0);
+///         fmt::UpperExp::fmt(&val, f) // delegate to f64's implementation
+///     }
+/// }
+///
+/// let l = Length(100);
+///
+/// assert_eq!(
+///     format!("l in scientific notation is: {l:E}"),
+///     "l in scientific notation is: 1E2"
+/// );
+///
+/// assert_eq!(
+///     format!("l in scientific notation is: {l:05E}"),
+///     "l in scientific notation is: 001E2"
+/// );
+/// ```
+#[stable(feature = "rust1", since = "1.0.0")]
+pub trait UpperExp {
+    /// Formats the value using the given formatter.
+    #[stable(feature = "rust1", since = "1.0.0")]
+    fn fmt(&self, f: &mut Formatter<'_>) -> Result;
+}
+
+/// The `write` function takes an output stream, and an `Arguments` struct
+/// that can be precompiled with the `format_args!` macro.
+///
+/// The arguments will be formatted according to the specified format string
+/// into the output stream provided.
+///
+/// # Examples
+///
+/// Basic usage:
+///
+/// ```
+/// use std::fmt;
+///
+/// let mut output = String::new();
+/// fmt::write(&mut output, format_args!("Hello {}!", "world"))
+///     .expect("Error occurred while trying to write in String");
+/// assert_eq!(output, "Hello world!");
+/// ```
+///
+/// Please note that using [`write!`] might be preferable. Example:
+///
+/// ```
+/// use std::fmt::Write;
+///
+/// let mut output = String::new();
+/// write!(&mut output, "Hello {}!", "world")
+///     .expect("Error occurred while trying to write in String");
+/// assert_eq!(output, "Hello world!");
+/// ```
+///
+/// [`write!`]: crate::write!
+#[stable(feature = "rust1", since = "1.0.0")]
+pub fn write(output: &mut dyn Write, args: Arguments<'_>) -> Result {
+    let mut formatter = Formatter::new(output);
+    let mut idx = 0;
+
+    match args.fmt {
+        None => {
+            // We can use default formatting parameters for all arguments.
+            for (i, arg) in args.args.iter().enumerate() {
+                // SAFETY: args.args and args.pieces come from the same Arguments,
+                // which guarantees the indexes are always within bounds.
+                let piece = unsafe { args.pieces.get_unchecked(i) };
+                if !piece.is_empty() {
+                    formatter.buf.write_str(*piece)?;
+                }
+                (arg.formatter)(arg.value, &mut formatter)?;
+                idx += 1;
+            }
+        }
+        Some(fmt) => {
+            // Every spec has a corresponding argument that is preceded by
+            // a string piece.
+            for (i, arg) in fmt.iter().enumerate() {
+                // SAFETY: fmt and args.pieces come from the same Arguments,
+                // which guarantees the indexes are always within bounds.
+                let piece = unsafe { args.pieces.get_unchecked(i) };
+                if !piece.is_empty() {
+                    formatter.buf.write_str(*piece)?;
+                }
+                // SAFETY: arg and args.args come from the same Arguments,
+                // which guarantees the indexes are always within bounds.
+                unsafe { run(&mut formatter, arg, args.args) }?;
+                idx += 1;
+            }
+        }
+    }
+
+    // There can be only one trailing string piece left.
+    if let Some(piece) = args.pieces.get(idx) {
+        formatter.buf.write_str(*piece)?;
+    }
+
+    Ok(())
+}
+
+unsafe fn run(fmt: &mut Formatter<'_>, arg: &rt::v1::Argument, args: &[ArgumentV1<'_>]) -> Result {
+    fmt.fill = arg.format.fill;
+    fmt.align = arg.format.align;
+    fmt.flags = arg.format.flags;
+    // SAFETY: arg and args come from the same Arguments,
+    // which guarantees the indexes are always within bounds.
+    unsafe {
+        fmt.width = getcount(args, &arg.format.width);
+        fmt.precision = getcount(args, &arg.format.precision);
+    }
+
+    // Extract the correct argument
+    debug_assert!(arg.position < args.len());
+    // SAFETY: arg and args come from the same Arguments,
+    // which guarantees its index is always within bounds.
+    let value = unsafe { args.get_unchecked(arg.position) };
+
+    // Then actually do some printing
+    (value.formatter)(value.value, fmt)
+}
+
+unsafe fn getcount(args: &[ArgumentV1<'_>], cnt: &rt::v1::Count) -> Option<usize> {
+    match *cnt {
+        rt::v1::Count::Is(n) => Some(n),
+        rt::v1::Count::Implied => None,
+        rt::v1::Count::Param(i) => {
+            debug_assert!(i < args.len());
+            // SAFETY: cnt and args come from the same Arguments,
+            // which guarantees this index is always within bounds.
+            unsafe { args.get_unchecked(i).as_usize() }
+        }
+    }
+}
+
+/// Padding after the end of something. Returned by `Formatter::padding`.
+#[must_use = "don't forget to write the post padding"]
+pub(crate) struct PostPadding {
+    fill: char,
+    padding: usize,
+}
+
+impl PostPadding {
+    fn new(fill: char, padding: usize) -> PostPadding {
+        PostPadding { fill, padding }
+    }
+
+    /// Write this post padding.
+    pub(crate) fn write(self, f: &mut Formatter<'_>) -> Result {
+        for _ in 0..self.padding {
+            f.buf.write_char(self.fill)?;
+        }
+        Ok(())
+    }
+}
+
+impl<'a> Formatter<'a> {
+    fn wrap_buf<'b, 'c, F>(&'b mut self, wrap: F) -> Formatter<'c>
+    where
+        'b: 'c,
+        F: FnOnce(&'b mut (dyn Write + 'b)) -> &'c mut (dyn Write + 'c),
+    {
+        Formatter {
+            // We want to change this
+            buf: wrap(self.buf),
+
+            // And preserve these
+            flags: self.flags,
+            fill: self.fill,
+            align: self.align,
+            width: self.width,
+            precision: self.precision,
+        }
+    }
+
+    // Helper methods used for padding and processing formatting arguments that
+    // all formatting traits can use.
+
+    /// Performs the correct padding for an integer which has already been
+    /// emitted into a str. The str should *not* contain the sign for the
+    /// integer, that will be added by this method.
+    ///
+    /// # Arguments
+    ///
+    /// * is_nonnegative - whether the original integer was either positive or zero.
+    /// * prefix - if the '#' character (Alternate) is provided, this
+    ///   is the prefix to put in front of the number.
+    /// * buf - the byte array that the number has been formatted into
+    ///
+    /// This function will correctly account for the flags provided as well as
+    /// the minimum width. It will not take precision into account.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use std::fmt;
+    ///
+    /// struct Foo { nb: i32 }
+    ///
+    /// impl Foo {
+    ///     fn new(nb: i32) -> Foo {
+    ///         Foo {
+    ///             nb,
+    ///         }
+    ///     }
+    /// }
+    ///
+    /// impl fmt::Display for Foo {
+    ///     fn fmt(&self, formatter: &mut fmt::Formatter) -> fmt::Result {
+    ///         // We need to remove "-" from the number output.
+    ///         let tmp = self.nb.abs().to_string();
+    ///
+    ///         formatter.pad_integral(self.nb >= 0, "Foo ", &tmp)
+    ///     }
+    /// }
+    ///
+    /// assert_eq!(&format!("{}", Foo::new(2)), "2");
+    /// assert_eq!(&format!("{}", Foo::new(-1)), "-1");
+    /// assert_eq!(&format!("{}", Foo::new(0)), "0");
+    /// assert_eq!(&format!("{:#}", Foo::new(-1)), "-Foo 1");
+    /// assert_eq!(&format!("{:0>#8}", Foo::new(-1)), "00-Foo 1");
+    /// ```
+    #[stable(feature = "rust1", since = "1.0.0")]
+    pub fn pad_integral(&mut self, is_nonnegative: bool, prefix: &str, buf: &str) -> Result {
+        let mut width = buf.len();
+
+        let mut sign = None;
+        if !is_nonnegative {
+            sign = Some('-');
+            width += 1;
+        } else if self.sign_plus() {
+            sign = Some('+');
+            width += 1;
+        }
+
+        let prefix = if self.alternate() {
+            width += prefix.chars().count();
+            Some(prefix)
+        } else {
+            None
+        };
+
+        // Writes the sign if it exists, and then the prefix if it was requested
+        #[inline(never)]
+        fn write_prefix(f: &mut Formatter<'_>, sign: Option<char>, prefix: Option<&str>) -> Result {
+            if let Some(c) = sign {
+                f.buf.write_char(c)?;
+            }
+            if let Some(prefix) = prefix { f.buf.write_str(prefix) } else { Ok(()) }
+        }
+
+        // The `width` field is more of a `min-width` parameter at this point.
+        match self.width {
+            // If there's no minimum length requirements then we can just
+            // write the bytes.
+            None => {
+                write_prefix(self, sign, prefix)?;
+                self.buf.write_str(buf)
+            }
+            // Check if we're over the minimum width, if so then we can also
+            // just write the bytes.
+            Some(min) if width >= min => {
+                write_prefix(self, sign, prefix)?;
+                self.buf.write_str(buf)
+            }
+            // The sign and prefix goes before the padding if the fill character
+            // is zero
+            Some(min) if self.sign_aware_zero_pad() => {
+                let old_fill = crate::mem::replace(&mut self.fill, '0');
+                let old_align = crate::mem::replace(&mut self.align, rt::v1::Alignment::Right);
+                write_prefix(self, sign, prefix)?;
+                let post_padding = self.padding(min - width, rt::v1::Alignment::Right)?;
+                self.buf.write_str(buf)?;
+                post_padding.write(self)?;
+                self.fill = old_fill;
+                self.align = old_align;
+                Ok(())
+            }
+            // Otherwise, the sign and prefix goes after the padding
+            Some(min) => {
+                let post_padding = self.padding(min - width, rt::v1::Alignment::Right)?;
+                write_prefix(self, sign, prefix)?;
+                self.buf.write_str(buf)?;
+                post_padding.write(self)
+            }
+        }
+    }
+
+    /// This function takes a string slice and emits it to the internal buffer
+    /// after applying the relevant formatting flags specified. The flags
+    /// recognized for generic strings are:
+    ///
+    /// * width - the minimum width of what to emit
+    /// * fill/align - what to emit and where to emit it if the string
+    ///                provided needs to be padded
+    /// * precision - the maximum length to emit, the string is truncated if it
+    ///               is longer than this length
+    ///
+    /// Notably this function ignores the `flag` parameters.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use std::fmt;
+    ///
+    /// struct Foo;
+    ///
+    /// impl fmt::Display for Foo {
+    ///     fn fmt(&self, formatter: &mut fmt::Formatter) -> fmt::Result {
+    ///         formatter.pad("Foo")
+    ///     }
+    /// }
+    ///
+    /// assert_eq!(&format!("{Foo:<4}"), "Foo ");
+    /// assert_eq!(&format!("{Foo:0>4}"), "0Foo");
+    /// ```
+    #[stable(feature = "rust1", since = "1.0.0")]
+    pub fn pad(&mut self, s: &str) -> Result {
+        // Make sure there's a fast path up front
+        if self.width.is_none() && self.precision.is_none() {
+            return self.buf.write_str(s);
+        }
+        // The `precision` field can be interpreted as a `max-width` for the
+        // string being formatted.
+        let s = if let Some(max) = self.precision {
+            // If our string is longer that the precision, then we must have
+            // truncation. However other flags like `fill`, `width` and `align`
+            // must act as always.
+            if let Some((i, _)) = s.char_indices().nth(max) {
+                // LLVM here can't prove that `..i` won't panic `&s[..i]`, but
+                // we know that it can't panic. Use `get` + `unwrap_or` to avoid
+                // `unsafe` and otherwise don't emit any panic-related code
+                // here.
+                s.get(..i).unwrap_or(s)
+            } else {
+                &s
+            }
+        } else {
+            &s
+        };
+        // The `width` field is more of a `min-width` parameter at this point.
+        match self.width {
+            // If we're under the maximum length, and there's no minimum length
+            // requirements, then we can just emit the string
+            None => self.buf.write_str(s),
+            Some(width) => {
+                let chars_count = s.chars().count();
+                // If we're under the maximum width, check if we're over the minimum
+                // width, if so it's as easy as just emitting the string.
+                if chars_count >= width {
+                    self.buf.write_str(s)
+                }
+                // If we're under both the maximum and the minimum width, then fill
+                // up the minimum width with the specified string + some alignment.
+                else {
+                    let align = rt::v1::Alignment::Left;
+                    let post_padding = self.padding(width - chars_count, align)?;
+                    self.buf.write_str(s)?;
+                    post_padding.write(self)
+                }
+            }
+        }
+    }
+
+    /// Write the pre-padding and return the unwritten post-padding. Callers are
+    /// responsible for ensuring post-padding is written after the thing that is
+    /// being padded.
+    pub(crate) fn padding(
+        &mut self,
+        padding: usize,
+        default: rt::v1::Alignment,
+    ) -> result::Result<PostPadding, Error> {
+        let align = match self.align {
+            rt::v1::Alignment::Unknown => default,
+            _ => self.align,
+        };
+
+        let (pre_pad, post_pad) = match align {
+            rt::v1::Alignment::Left => (0, padding),
+            rt::v1::Alignment::Right | rt::v1::Alignment::Unknown => (padding, 0),
+            rt::v1::Alignment::Center => (padding / 2, (padding + 1) / 2),
+        };
+
+        for _ in 0..pre_pad {
+            self.buf.write_char(self.fill)?;
+        }
+
+        Ok(PostPadding::new(self.fill, post_pad))
+    }
+
+    /// Takes the formatted parts and applies the padding.
+    /// Assumes that the caller already has rendered the parts with required precision,
+    /// so that `self.precision` can be ignored.
+    fn pad_formatted_parts(&mut self, formatted: &numfmt::Formatted<'_>) -> Result {
+        if let Some(mut width) = self.width {
+            // for the sign-aware zero padding, we render the sign first and
+            // behave as if we had no sign from the beginning.
+            let mut formatted = formatted.clone();
+            let old_fill = self.fill;
+            let old_align = self.align;
+            let mut align = old_align;
+            if self.sign_aware_zero_pad() {
+                // a sign always goes first
+                let sign = formatted.sign;
+                self.buf.write_str(sign)?;
+
+                // remove the sign from the formatted parts
+                formatted.sign = "";
+                width = width.saturating_sub(sign.len());
+                align = rt::v1::Alignment::Right;
+                self.fill = '0';
+                self.align = rt::v1::Alignment::Right;
+            }
+
+            // remaining parts go through the ordinary padding process.
+            let len = formatted.len();
+            let ret = if width <= len {
+                // no padding
+                self.write_formatted_parts(&formatted)
+            } else {
+                let post_padding = self.padding(width - len, align)?;
+                self.write_formatted_parts(&formatted)?;
+                post_padding.write(self)
+            };
+            self.fill = old_fill;
+            self.align = old_align;
+            ret
+        } else {
+            // this is the common case and we take a shortcut
+            self.write_formatted_parts(formatted)
+        }
+    }
+
+    fn write_formatted_parts(&mut self, formatted: &numfmt::Formatted<'_>) -> Result {
+        fn write_bytes(buf: &mut dyn Write, s: &[u8]) -> Result {
+            // SAFETY: This is used for `numfmt::Part::Num` and `numfmt::Part::Copy`.
+            // It's safe to use for `numfmt::Part::Num` since every char `c` is between
+            // `b'0'` and `b'9'`, which means `s` is valid UTF-8.
+            // It's also probably safe in practice to use for `numfmt::Part::Copy(buf)`
+            // since `buf` should be plain ASCII, but it's possible for someone to pass
+            // in a bad value for `buf` into `numfmt::to_shortest_str` since it is a
+            // public function.
+            // FIXME: Determine whether this could result in UB.
+            buf.write_str(unsafe { str::from_utf8_unchecked(s) })
+        }
+
+        if !formatted.sign.is_empty() {
+            self.buf.write_str(formatted.sign)?;
+        }
+        for part in formatted.parts {
+            match *part {
+                numfmt::Part::Zero(mut nzeroes) => {
+                    const ZEROES: &str = // 64 zeroes
+                        "0000000000000000000000000000000000000000000000000000000000000000";
+                    while nzeroes > ZEROES.len() {
+                        self.buf.write_str(ZEROES)?;
+                        nzeroes -= ZEROES.len();
+                    }
+                    if nzeroes > 0 {
+                        self.buf.write_str(&ZEROES[..nzeroes])?;
+                    }
+                }
+                numfmt::Part::Num(mut v) => {
+                    let mut s = [0; 5];
+                    let len = part.len();
+                    for c in s[..len].iter_mut().rev() {
+                        *c = b'0' + (v % 10) as u8;
+                        v /= 10;
+                    }
+                    write_bytes(self.buf, &s[..len])?;
+                }
+                numfmt::Part::Copy(buf) => {
+                    write_bytes(self.buf, buf)?;
+                }
+            }
+        }
+        Ok(())
+    }
+
+    /// Writes some data to the underlying buffer contained within this
+    /// formatter.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use std::fmt;
+    ///
+    /// struct Foo;
+    ///
+    /// impl fmt::Display for Foo {
+    ///     fn fmt(&self, formatter: &mut fmt::Formatter) -> fmt::Result {
+    ///         formatter.write_str("Foo")
+    ///         // This is equivalent to:
+    ///         // write!(formatter, "Foo")
+    ///     }
+    /// }
+    ///
+    /// assert_eq!(&format!("{Foo}"), "Foo");
+    /// assert_eq!(&format!("{Foo:0>8}"), "Foo");
+    /// ```
+    #[stable(feature = "rust1", since = "1.0.0")]
+    pub fn write_str(&mut self, data: &str) -> Result {
+        self.buf.write_str(data)
+    }
+
+    /// Writes some formatted information into this instance.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use std::fmt;
+    ///
+    /// struct Foo(i32);
+    ///
+    /// impl fmt::Display for Foo {
+    ///     fn fmt(&self, formatter: &mut fmt::Formatter) -> fmt::Result {
+    ///         formatter.write_fmt(format_args!("Foo {}", self.0))
+    ///     }
+    /// }
+    ///
+    /// assert_eq!(&format!("{}", Foo(-1)), "Foo -1");
+    /// assert_eq!(&format!("{:0>8}", Foo(2)), "Foo 2");
+    /// ```
+    #[stable(feature = "rust1", since = "1.0.0")]
+    pub fn write_fmt(&mut self, fmt: Arguments<'_>) -> Result {
+        write(self.buf, fmt)
+    }
+
+    /// Flags for formatting
+    #[must_use]
+    #[stable(feature = "rust1", since = "1.0.0")]
+    #[deprecated(
+        since = "1.24.0",
+        note = "use the `sign_plus`, `sign_minus`, `alternate`, \
+                or `sign_aware_zero_pad` methods instead"
+    )]
+    pub fn flags(&self) -> u32 {
+        self.flags
+    }
+
+    /// Character used as 'fill' whenever there is alignment.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use std::fmt;
+    ///
+    /// struct Foo;
+    ///
+    /// impl fmt::Display for Foo {
+    ///     fn fmt(&self, formatter: &mut fmt::Formatter) -> fmt::Result {
+    ///         let c = formatter.fill();
+    ///         if let Some(width) = formatter.width() {
+    ///             for _ in 0..width {
+    ///                 write!(formatter, "{c}")?;
+    ///             }
+    ///             Ok(())
+    ///         } else {
+    ///             write!(formatter, "{c}")
+    ///         }
+    ///     }
+    /// }
+    ///
+    /// // We set alignment to the right with ">".
+    /// assert_eq!(&format!("{Foo:G>3}"), "GGG");
+    /// assert_eq!(&format!("{Foo:t>6}"), "tttttt");
+    /// ```
+    #[must_use]
+    #[stable(feature = "fmt_flags", since = "1.5.0")]
+    pub fn fill(&self) -> char {
+        self.fill
+    }
+
+    /// Flag indicating what form of alignment was requested.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// extern crate core;
+    ///
+    /// use std::fmt::{self, Alignment};
+    ///
+    /// struct Foo;
+    ///
+    /// impl fmt::Display for Foo {
+    ///     fn fmt(&self, formatter: &mut fmt::Formatter) -> fmt::Result {
+    ///         let s = if let Some(s) = formatter.align() {
+    ///             match s {
+    ///                 Alignment::Left    => "left",
+    ///                 Alignment::Right   => "right",
+    ///                 Alignment::Center  => "center",
+    ///             }
+    ///         } else {
+    ///             "into the void"
+    ///         };
+    ///         write!(formatter, "{s}")
+    ///     }
+    /// }
+    ///
+    /// assert_eq!(&format!("{Foo:<}"), "left");
+    /// assert_eq!(&format!("{Foo:>}"), "right");
+    /// assert_eq!(&format!("{Foo:^}"), "center");
+    /// assert_eq!(&format!("{Foo}"), "into the void");
+    /// ```
+    #[must_use]
+    #[stable(feature = "fmt_flags_align", since = "1.28.0")]
+    pub fn align(&self) -> Option<Alignment> {
+        match self.align {
+            rt::v1::Alignment::Left => Some(Alignment::Left),
+            rt::v1::Alignment::Right => Some(Alignment::Right),
+            rt::v1::Alignment::Center => Some(Alignment::Center),
+            rt::v1::Alignment::Unknown => None,
+        }
+    }
+
+    /// Optionally specified integer width that the output should be.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use std::fmt;
+    ///
+    /// struct Foo(i32);
+    ///
+    /// impl fmt::Display for Foo {
+    ///     fn fmt(&self, formatter: &mut fmt::Formatter) -> fmt::Result {
+    ///         if let Some(width) = formatter.width() {
+    ///             // If we received a width, we use it
+    ///             write!(formatter, "{:width$}", &format!("Foo({})", self.0), width = width)
+    ///         } else {
+    ///             // Otherwise we do nothing special
+    ///             write!(formatter, "Foo({})", self.0)
+    ///         }
+    ///     }
+    /// }
+    ///
+    /// assert_eq!(&format!("{:10}", Foo(23)), "Foo(23)   ");
+    /// assert_eq!(&format!("{}", Foo(23)), "Foo(23)");
+    /// ```
+    #[must_use]
+    #[stable(feature = "fmt_flags", since = "1.5.0")]
+    pub fn width(&self) -> Option<usize> {
+        self.width
+    }
+
+    /// Optionally specified precision for numeric types. Alternatively, the
+    /// maximum width for string types.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use std::fmt;
+    ///
+    /// struct Foo(f32);
+    ///
+    /// impl fmt::Display for Foo {
+    ///     fn fmt(&self, formatter: &mut fmt::Formatter) -> fmt::Result {
+    ///         if let Some(precision) = formatter.precision() {
+    ///             // If we received a precision, we use it.
+    ///             write!(formatter, "Foo({1:.*})", precision, self.0)
+    ///         } else {
+    ///             // Otherwise we default to 2.
+    ///             write!(formatter, "Foo({:.2})", self.0)
+    ///         }
+    ///     }
+    /// }
+    ///
+    /// assert_eq!(&format!("{:.4}", Foo(23.2)), "Foo(23.2000)");
+    /// assert_eq!(&format!("{}", Foo(23.2)), "Foo(23.20)");
+    /// ```
+    #[must_use]
+    #[stable(feature = "fmt_flags", since = "1.5.0")]
+    pub fn precision(&self) -> Option<usize> {
+        self.precision
+    }
+
+    /// Determines if the `+` flag was specified.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use std::fmt;
+    ///
+    /// struct Foo(i32);
+    ///
+    /// impl fmt::Display for Foo {
+    ///     fn fmt(&self, formatter: &mut fmt::Formatter) -> fmt::Result {
+    ///         if formatter.sign_plus() {
+    ///             write!(formatter,
+    ///                    "Foo({}{})",
+    ///                    if self.0 < 0 { '-' } else { '+' },
+    ///                    self.0)
+    ///         } else {
+    ///             write!(formatter, "Foo({})", self.0)
+    ///         }
+    ///     }
+    /// }
+    ///
+    /// assert_eq!(&format!("{:+}", Foo(23)), "Foo(+23)");
+    /// assert_eq!(&format!("{}", Foo(23)), "Foo(23)");
+    /// ```
+    #[must_use]
+    #[stable(feature = "fmt_flags", since = "1.5.0")]
+    pub fn sign_plus(&self) -> bool {
+        self.flags & (1 << FlagV1::SignPlus as u32) != 0
+    }
+
+    /// Determines if the `-` flag was specified.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use std::fmt;
+    ///
+    /// struct Foo(i32);
+    ///
+    /// impl fmt::Display for Foo {
+    ///     fn fmt(&self, formatter: &mut fmt::Formatter) -> fmt::Result {
+    ///         if formatter.sign_minus() {
+    ///             // You want a minus sign? Have one!
+    ///             write!(formatter, "-Foo({})", self.0)
+    ///         } else {
+    ///             write!(formatter, "Foo({})", self.0)
+    ///         }
+    ///     }
+    /// }
+    ///
+    /// assert_eq!(&format!("{:-}", Foo(23)), "-Foo(23)");
+    /// assert_eq!(&format!("{}", Foo(23)), "Foo(23)");
+    /// ```
+    #[must_use]
+    #[stable(feature = "fmt_flags", since = "1.5.0")]
+    pub fn sign_minus(&self) -> bool {
+        self.flags & (1 << FlagV1::SignMinus as u32) != 0
+    }
+
+    /// Determines if the `#` flag was specified.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use std::fmt;
+    ///
+    /// struct Foo(i32);
+    ///
+    /// impl fmt::Display for Foo {
+    ///     fn fmt(&self, formatter: &mut fmt::Formatter) -> fmt::Result {
+    ///         if formatter.alternate() {
+    ///             write!(formatter, "Foo({})", self.0)
+    ///         } else {
+    ///             write!(formatter, "{}", self.0)
+    ///         }
+    ///     }
+    /// }
+    ///
+    /// assert_eq!(&format!("{:#}", Foo(23)), "Foo(23)");
+    /// assert_eq!(&format!("{}", Foo(23)), "23");
+    /// ```
+    #[must_use]
+    #[stable(feature = "fmt_flags", since = "1.5.0")]
+    pub fn alternate(&self) -> bool {
+        self.flags & (1 << FlagV1::Alternate as u32) != 0
+    }
+
+    /// Determines if the `0` flag was specified.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use std::fmt;
+    ///
+    /// struct Foo(i32);
+    ///
+    /// impl fmt::Display for Foo {
+    ///     fn fmt(&self, formatter: &mut fmt::Formatter) -> fmt::Result {
+    ///         assert!(formatter.sign_aware_zero_pad());
+    ///         assert_eq!(formatter.width(), Some(4));
+    ///         // We ignore the formatter's options.
+    ///         write!(formatter, "{}", self.0)
+    ///     }
+    /// }
+    ///
+    /// assert_eq!(&format!("{:04}", Foo(23)), "23");
+    /// ```
+    #[must_use]
+    #[stable(feature = "fmt_flags", since = "1.5.0")]
+    pub fn sign_aware_zero_pad(&self) -> bool {
+        self.flags & (1 << FlagV1::SignAwareZeroPad as u32) != 0
+    }
+
+    // FIXME: Decide what public API we want for these two flags.
+    // https://github.com/rust-lang/rust/issues/48584
+    fn debug_lower_hex(&self) -> bool {
+        self.flags & (1 << FlagV1::DebugLowerHex as u32) != 0
+    }
+
+    fn debug_upper_hex(&self) -> bool {
+        self.flags & (1 << FlagV1::DebugUpperHex as u32) != 0
+    }
+
+    /// Creates a [`DebugStruct`] builder designed to assist with creation of
+    /// [`fmt::Debug`] implementations for structs.
+    ///
+    /// [`fmt::Debug`]: self::Debug
+    ///
+    /// # Examples
+    ///
+    /// ```rust
+    /// use std::fmt;
+    /// use std::net::Ipv4Addr;
+    ///
+    /// struct Foo {
+    ///     bar: i32,
+    ///     baz: String,
+    ///     addr: Ipv4Addr,
+    /// }
+    ///
+    /// impl fmt::Debug for Foo {
+    ///     fn fmt(&self, fmt: &mut fmt::Formatter) -> fmt::Result {
+    ///         fmt.debug_struct("Foo")
+    ///             .field("bar", &self.bar)
+    ///             .field("baz", &self.baz)
+    ///             .field("addr", &format_args!("{}", self.addr))
+    ///             .finish()
+    ///     }
+    /// }
+    ///
+    /// assert_eq!(
+    ///     "Foo { bar: 10, baz: \"Hello World\", addr: 127.0.0.1 }",
+    ///     format!("{:?}", Foo {
+    ///         bar: 10,
+    ///         baz: "Hello World".to_string(),
+    ///         addr: Ipv4Addr::new(127, 0, 0, 1),
+    ///     })
+    /// );
+    /// ```
+    #[stable(feature = "debug_builders", since = "1.2.0")]
+    pub fn debug_struct<'b>(&'b mut self, name: &str) -> DebugStruct<'b, 'a> {
+        builders::debug_struct_new(self, name)
+    }
+
+    /// Used to shrink `derive(Debug)` code, for faster compilation and smaller binaries.
+    /// `debug_struct_fields_finish` is more general, but this is faster for 1 field.
+    #[doc(hidden)]
+    #[unstable(feature = "fmt_helpers_for_derive", issue = "none")]
+    pub fn debug_struct_field1_finish<'b>(
+        &'b mut self,
+        name: &str,
+        name1: &str,
+        value1: &dyn Debug,
+    ) -> Result {
+        let mut builder = builders::debug_struct_new(self, name);
+        builder.field(name1, value1);
+        builder.finish()
+    }
+
+    /// Used to shrink `derive(Debug)` code, for faster compilation and smaller binaries.
+    /// `debug_struct_fields_finish` is more general, but this is faster for 2 fields.
+    #[doc(hidden)]
+    #[unstable(feature = "fmt_helpers_for_derive", issue = "none")]
+    pub fn debug_struct_field2_finish<'b>(
+        &'b mut self,
+        name: &str,
+        name1: &str,
+        value1: &dyn Debug,
+        name2: &str,
+        value2: &dyn Debug,
+    ) -> Result {
+        let mut builder = builders::debug_struct_new(self, name);
+        builder.field(name1, value1);
+        builder.field(name2, value2);
+        builder.finish()
+    }
+
+    /// Used to shrink `derive(Debug)` code, for faster compilation and smaller binaries.
+    /// `debug_struct_fields_finish` is more general, but this is faster for 3 fields.
+    #[doc(hidden)]
+    #[unstable(feature = "fmt_helpers_for_derive", issue = "none")]
+    pub fn debug_struct_field3_finish<'b>(
+        &'b mut self,
+        name: &str,
+        name1: &str,
+        value1: &dyn Debug,
+        name2: &str,
+        value2: &dyn Debug,
+        name3: &str,
+        value3: &dyn Debug,
+    ) -> Result {
+        let mut builder = builders::debug_struct_new(self, name);
+        builder.field(name1, value1);
+        builder.field(name2, value2);
+        builder.field(name3, value3);
+        builder.finish()
+    }
+
+    /// Used to shrink `derive(Debug)` code, for faster compilation and smaller binaries.
+    /// `debug_struct_fields_finish` is more general, but this is faster for 4 fields.
+    #[doc(hidden)]
+    #[unstable(feature = "fmt_helpers_for_derive", issue = "none")]
+    pub fn debug_struct_field4_finish<'b>(
+        &'b mut self,
+        name: &str,
+        name1: &str,
+        value1: &dyn Debug,
+        name2: &str,
+        value2: &dyn Debug,
+        name3: &str,
+        value3: &dyn Debug,
+        name4: &str,
+        value4: &dyn Debug,
+    ) -> Result {
+        let mut builder = builders::debug_struct_new(self, name);
+        builder.field(name1, value1);
+        builder.field(name2, value2);
+        builder.field(name3, value3);
+        builder.field(name4, value4);
+        builder.finish()
+    }
+
+    /// Used to shrink `derive(Debug)` code, for faster compilation and smaller binaries.
+    /// `debug_struct_fields_finish` is more general, but this is faster for 5 fields.
+    #[doc(hidden)]
+    #[unstable(feature = "fmt_helpers_for_derive", issue = "none")]
+    pub fn debug_struct_field5_finish<'b>(
+        &'b mut self,
+        name: &str,
+        name1: &str,
+        value1: &dyn Debug,
+        name2: &str,
+        value2: &dyn Debug,
+        name3: &str,
+        value3: &dyn Debug,
+        name4: &str,
+        value4: &dyn Debug,
+        name5: &str,
+        value5: &dyn Debug,
+    ) -> Result {
+        let mut builder = builders::debug_struct_new(self, name);
+        builder.field(name1, value1);
+        builder.field(name2, value2);
+        builder.field(name3, value3);
+        builder.field(name4, value4);
+        builder.field(name5, value5);
+        builder.finish()
+    }
+
+    /// Used to shrink `derive(Debug)` code, for faster compilation and smaller binaries.
+    /// For the cases not covered by `debug_struct_field[12345]_finish`.
+    #[doc(hidden)]
+    #[unstable(feature = "fmt_helpers_for_derive", issue = "none")]
+    pub fn debug_struct_fields_finish<'b>(
+        &'b mut self,
+        name: &str,
+        names: &[&str],
+        values: &[&dyn Debug],
+    ) -> Result {
+        assert_eq!(names.len(), values.len());
+        let mut builder = builders::debug_struct_new(self, name);
+        for (name, value) in iter::zip(names, values) {
+            builder.field(name, value);
+        }
+        builder.finish()
+    }
+
+    /// Creates a `DebugTuple` builder designed to assist with creation of
+    /// `fmt::Debug` implementations for tuple structs.
+    ///
+    /// # Examples
+    ///
+    /// ```rust
+    /// use std::fmt;
+    /// use std::marker::PhantomData;
+    ///
+    /// struct Foo<T>(i32, String, PhantomData<T>);
+    ///
+    /// impl<T> fmt::Debug for Foo<T> {
+    ///     fn fmt(&self, fmt: &mut fmt::Formatter) -> fmt::Result {
+    ///         fmt.debug_tuple("Foo")
+    ///             .field(&self.0)
+    ///             .field(&self.1)
+    ///             .field(&format_args!("_"))
+    ///             .finish()
+    ///     }
+    /// }
+    ///
+    /// assert_eq!(
+    ///     "Foo(10, \"Hello\", _)",
+    ///     format!("{:?}", Foo(10, "Hello".to_string(), PhantomData::<u8>))
+    /// );
+    /// ```
+    #[stable(feature = "debug_builders", since = "1.2.0")]
+    pub fn debug_tuple<'b>(&'b mut self, name: &str) -> DebugTuple<'b, 'a> {
+        builders::debug_tuple_new(self, name)
+    }
+
+    /// Used to shrink `derive(Debug)` code, for faster compilation and smaller binaries.
+    /// `debug_tuple_fields_finish` is more general, but this is faster for 1 field.
+    #[doc(hidden)]
+    #[unstable(feature = "fmt_helpers_for_derive", issue = "none")]
+    pub fn debug_tuple_field1_finish<'b>(&'b mut self, name: &str, value1: &dyn Debug) -> Result {
+        let mut builder = builders::debug_tuple_new(self, name);
+        builder.field(value1);
+        builder.finish()
+    }
+
+    /// Used to shrink `derive(Debug)` code, for faster compilation and smaller binaries.
+    /// `debug_tuple_fields_finish` is more general, but this is faster for 2 fields.
+    #[doc(hidden)]
+    #[unstable(feature = "fmt_helpers_for_derive", issue = "none")]
+    pub fn debug_tuple_field2_finish<'b>(
+        &'b mut self,
+        name: &str,
+        value1: &dyn Debug,
+        value2: &dyn Debug,
+    ) -> Result {
+        let mut builder = builders::debug_tuple_new(self, name);
+        builder.field(value1);
+        builder.field(value2);
+        builder.finish()
+    }
+
+    /// Used to shrink `derive(Debug)` code, for faster compilation and smaller binaries.
+    /// `debug_tuple_fields_finish` is more general, but this is faster for 3 fields.
+    #[doc(hidden)]
+    #[unstable(feature = "fmt_helpers_for_derive", issue = "none")]
+    pub fn debug_tuple_field3_finish<'b>(
+        &'b mut self,
+        name: &str,
+        value1: &dyn Debug,
+        value2: &dyn Debug,
+        value3: &dyn Debug,
+    ) -> Result {
+        let mut builder = builders::debug_tuple_new(self, name);
+        builder.field(value1);
+        builder.field(value2);
+        builder.field(value3);
+        builder.finish()
+    }
+
+    /// Used to shrink `derive(Debug)` code, for faster compilation and smaller binaries.
+    /// `debug_tuple_fields_finish` is more general, but this is faster for 4 fields.
+    #[doc(hidden)]
+    #[unstable(feature = "fmt_helpers_for_derive", issue = "none")]
+    pub fn debug_tuple_field4_finish<'b>(
+        &'b mut self,
+        name: &str,
+        value1: &dyn Debug,
+        value2: &dyn Debug,
+        value3: &dyn Debug,
+        value4: &dyn Debug,
+    ) -> Result {
+        let mut builder = builders::debug_tuple_new(self, name);
+        builder.field(value1);
+        builder.field(value2);
+        builder.field(value3);
+        builder.field(value4);
+        builder.finish()
+    }
+
+    /// Used to shrink `derive(Debug)` code, for faster compilation and smaller binaries.
+    /// `debug_tuple_fields_finish` is more general, but this is faster for 5 fields.
+    #[doc(hidden)]
+    #[unstable(feature = "fmt_helpers_for_derive", issue = "none")]
+    pub fn debug_tuple_field5_finish<'b>(
+        &'b mut self,
+        name: &str,
+        value1: &dyn Debug,
+        value2: &dyn Debug,
+        value3: &dyn Debug,
+        value4: &dyn Debug,
+        value5: &dyn Debug,
+    ) -> Result {
+        let mut builder = builders::debug_tuple_new(self, name);
+        builder.field(value1);
+        builder.field(value2);
+        builder.field(value3);
+        builder.field(value4);
+        builder.field(value5);
+        builder.finish()
+    }
+
+    /// Used to shrink `derive(Debug)` code, for faster compilation and smaller binaries.
+    /// For the cases not covered by `debug_tuple_field[12345]_finish`.
+    #[doc(hidden)]
+    #[unstable(feature = "fmt_helpers_for_derive", issue = "none")]
+    pub fn debug_tuple_fields_finish<'b>(
+        &'b mut self,
+        name: &str,
+        values: &[&dyn Debug],
+    ) -> Result {
+        let mut builder = builders::debug_tuple_new(self, name);
+        for value in values {
+            builder.field(value);
+        }
+        builder.finish()
+    }
+
+    /// Creates a `DebugList` builder designed to assist with creation of
+    /// `fmt::Debug` implementations for list-like structures.
+    ///
+    /// # Examples
+    ///
+    /// ```rust
+    /// use std::fmt;
+    ///
+    /// struct Foo(Vec<i32>);
+    ///
+    /// impl fmt::Debug for Foo {
+    ///     fn fmt(&self, fmt: &mut fmt::Formatter) -> fmt::Result {
+    ///         fmt.debug_list().entries(self.0.iter()).finish()
+    ///     }
+    /// }
+    ///
+    /// assert_eq!(format!("{:?}", Foo(vec![10, 11])), "[10, 11]");
+    /// ```
+    #[stable(feature = "debug_builders", since = "1.2.0")]
+    pub fn debug_list<'b>(&'b mut self) -> DebugList<'b, 'a> {
+        builders::debug_list_new(self)
+    }
+
+    /// Creates a `DebugSet` builder designed to assist with creation of
+    /// `fmt::Debug` implementations for set-like structures.
+    ///
+    /// # Examples
+    ///
+    /// ```rust
+    /// use std::fmt;
+    ///
+    /// struct Foo(Vec<i32>);
+    ///
+    /// impl fmt::Debug for Foo {
+    ///     fn fmt(&self, fmt: &mut fmt::Formatter) -> fmt::Result {
+    ///         fmt.debug_set().entries(self.0.iter()).finish()
+    ///     }
+    /// }
+    ///
+    /// assert_eq!(format!("{:?}", Foo(vec![10, 11])), "{10, 11}");
+    /// ```
+    ///
+    /// [`format_args!`]: crate::format_args
+    ///
+    /// In this more complex example, we use [`format_args!`] and `.debug_set()`
+    /// to build a list of match arms:
+    ///
+    /// ```rust
+    /// use std::fmt;
+    ///
+    /// struct Arm<'a, L: 'a, R: 'a>(&'a (L, R));
+    /// struct Table<'a, K: 'a, V: 'a>(&'a [(K, V)], V);
+    ///
+    /// impl<'a, L, R> fmt::Debug for Arm<'a, L, R>
+    /// where
+    ///     L: 'a + fmt::Debug, R: 'a + fmt::Debug
+    /// {
+    ///     fn fmt(&self, fmt: &mut fmt::Formatter) -> fmt::Result {
+    ///         L::fmt(&(self.0).0, fmt)?;
+    ///         fmt.write_str(" => ")?;
+    ///         R::fmt(&(self.0).1, fmt)
+    ///     }
+    /// }
+    ///
+    /// impl<'a, K, V> fmt::Debug for Table<'a, K, V>
+    /// where
+    ///     K: 'a + fmt::Debug, V: 'a + fmt::Debug
+    /// {
+    ///     fn fmt(&self, fmt: &mut fmt::Formatter) -> fmt::Result {
+    ///         fmt.debug_set()
+    ///         .entries(self.0.iter().map(Arm))
+    ///         .entry(&Arm(&(format_args!("_"), &self.1)))
+    ///         .finish()
+    ///     }
+    /// }
+    /// ```
+    #[stable(feature = "debug_builders", since = "1.2.0")]
+    pub fn debug_set<'b>(&'b mut self) -> DebugSet<'b, 'a> {
+        builders::debug_set_new(self)
+    }
+
+    /// Creates a `DebugMap` builder designed to assist with creation of
+    /// `fmt::Debug` implementations for map-like structures.
+    ///
+    /// # Examples
+    ///
+    /// ```rust
+    /// use std::fmt;
+    ///
+    /// struct Foo(Vec<(String, i32)>);
+    ///
+    /// impl fmt::Debug for Foo {
+    ///     fn fmt(&self, fmt: &mut fmt::Formatter) -> fmt::Result {
+    ///         fmt.debug_map().entries(self.0.iter().map(|&(ref k, ref v)| (k, v))).finish()
+    ///     }
+    /// }
+    ///
+    /// assert_eq!(
+    ///     format!("{:?}",  Foo(vec![("A".to_string(), 10), ("B".to_string(), 11)])),
+    ///     r#"{"A": 10, "B": 11}"#
+    ///  );
+    /// ```
+    #[stable(feature = "debug_builders", since = "1.2.0")]
+    pub fn debug_map<'b>(&'b mut self) -> DebugMap<'b, 'a> {
+        builders::debug_map_new(self)
+    }
+}
+
+#[stable(since = "1.2.0", feature = "formatter_write")]
+impl Write for Formatter<'_> {
+    fn write_str(&mut self, s: &str) -> Result {
+        self.buf.write_str(s)
+    }
+
+    fn write_char(&mut self, c: char) -> Result {
+        self.buf.write_char(c)
+    }
+
+    fn write_fmt(&mut self, args: Arguments<'_>) -> Result {
+        write(self.buf, args)
+    }
+}
+
+#[stable(feature = "rust1", since = "1.0.0")]
+impl Display for Error {
+    fn fmt(&self, f: &mut Formatter<'_>) -> Result {
+        Display::fmt("an error occurred when formatting an argument", f)
+    }
+}
+
+// Implementations of the core formatting traits
+
+macro_rules! fmt_refs {
+    ($($tr:ident),*) => {
+        $(
+        #[stable(feature = "rust1", since = "1.0.0")]
+        impl<T: ?Sized + $tr> $tr for &T {
+            fn fmt(&self, f: &mut Formatter<'_>) -> Result { $tr::fmt(&**self, f) }
+        }
+        #[stable(feature = "rust1", since = "1.0.0")]
+        impl<T: ?Sized + $tr> $tr for &mut T {
+            fn fmt(&self, f: &mut Formatter<'_>) -> Result { $tr::fmt(&**self, f) }
+        }
+        )*
+    }
+}
+
+fmt_refs! { Debug, Display, Octal, Binary, LowerHex, UpperHex, LowerExp, UpperExp }
+
+#[unstable(feature = "never_type", issue = "35121")]
+impl Debug for ! {
+    fn fmt(&self, _: &mut Formatter<'_>) -> Result {
+        *self
+    }
+}
+
+#[unstable(feature = "never_type", issue = "35121")]
+impl Display for ! {
+    fn fmt(&self, _: &mut Formatter<'_>) -> Result {
+        *self
+    }
+}
+
+#[stable(feature = "rust1", since = "1.0.0")]
+impl Debug for bool {
+    #[inline]
+    fn fmt(&self, f: &mut Formatter<'_>) -> Result {
+        Display::fmt(self, f)
+    }
+}
+
+#[stable(feature = "rust1", since = "1.0.0")]
+impl Display for bool {
+    fn fmt(&self, f: &mut Formatter<'_>) -> Result {
+        Display::fmt(if *self { "true" } else { "false" }, f)
+    }
+}
+
+#[stable(feature = "rust1", since = "1.0.0")]
+impl Debug for str {
+    fn fmt(&self, f: &mut Formatter<'_>) -> Result {
+        f.write_char('"')?;
+        let mut from = 0;
+        for (i, c) in self.char_indices() {
+            let esc = c.escape_debug_ext(EscapeDebugExtArgs {
+                escape_grapheme_extended: true,
+                escape_single_quote: false,
+                escape_double_quote: true,
+            });
+            // If char needs escaping, flush backlog so far and write, else skip
+            if esc.len() != 1 {
+                f.write_str(&self[from..i])?;
+                for c in esc {
+                    f.write_char(c)?;
+                }
+                from = i + c.len_utf8();
+            }
+        }
+        f.write_str(&self[from..])?;
+        f.write_char('"')
+    }
+}
+
+#[stable(feature = "rust1", since = "1.0.0")]
+impl Display for str {
+    fn fmt(&self, f: &mut Formatter<'_>) -> Result {
+        f.pad(self)
+    }
+}
+
+#[stable(feature = "rust1", since = "1.0.0")]
+impl Debug for char {
+    fn fmt(&self, f: &mut Formatter<'_>) -> Result {
+        f.write_char('\'')?;
+        for c in self.escape_debug_ext(EscapeDebugExtArgs {
+            escape_grapheme_extended: true,
+            escape_single_quote: true,
+            escape_double_quote: false,
+        }) {
+            f.write_char(c)?
+        }
+        f.write_char('\'')
+    }
+}
+
+#[stable(feature = "rust1", since = "1.0.0")]
+impl Display for char {
+    fn fmt(&self, f: &mut Formatter<'_>) -> Result {
+        if f.width.is_none() && f.precision.is_none() {
+            f.write_char(*self)
+        } else {
+            f.pad(self.encode_utf8(&mut [0; 4]))
+        }
+    }
+}
+
+#[stable(feature = "rust1", since = "1.0.0")]
+impl<T: ?Sized> Pointer for *const T {
+    fn fmt(&self, f: &mut Formatter<'_>) -> Result {
+        // Cast is needed here because `.addr()` requires `T: Sized`.
+        pointer_fmt_inner((*self as *const ()).addr(), f)
+    }
+}
+
+/// Since the formatting will be identical for all pointer types, use a non-monomorphized
+/// implementation for the actual formatting to reduce the amount of codegen work needed.
+///
+/// This uses `ptr_addr: usize` and not `ptr: *const ()` to be able to use this for
+/// `fn(...) -> ...` without using [problematic] "Oxford Casts".
+///
+/// [problematic]: https://github.com/rust-lang/rust/issues/95489
+pub(crate) fn pointer_fmt_inner(ptr_addr: usize, f: &mut Formatter<'_>) -> Result {
+    let old_width = f.width;
+    let old_flags = f.flags;
+
+    // The alternate flag is already treated by LowerHex as being special-
+    // it denotes whether to prefix with 0x. We use it to work out whether
+    // or not to zero extend, and then unconditionally set it to get the
+    // prefix.
+    if f.alternate() {
+        f.flags |= 1 << (FlagV1::SignAwareZeroPad as u32);
+
+        if f.width.is_none() {
+            f.width = Some((usize::BITS / 4) as usize + 2);
+        }
+    }
+    f.flags |= 1 << (FlagV1::Alternate as u32);
+
+    let ret = LowerHex::fmt(&ptr_addr, f);
+
+    f.width = old_width;
+    f.flags = old_flags;
+
+    ret
+}
+
+#[stable(feature = "rust1", since = "1.0.0")]
+impl<T: ?Sized> Pointer for *mut T {
+    fn fmt(&self, f: &mut Formatter<'_>) -> Result {
+        Pointer::fmt(&(*self as *const T), f)
+    }
+}
+
+#[stable(feature = "rust1", since = "1.0.0")]
+impl<T: ?Sized> Pointer for &T {
+    fn fmt(&self, f: &mut Formatter<'_>) -> Result {
+        Pointer::fmt(&(*self as *const T), f)
+    }
+}
+
+#[stable(feature = "rust1", since = "1.0.0")]
+impl<T: ?Sized> Pointer for &mut T {
+    fn fmt(&self, f: &mut Formatter<'_>) -> Result {
+        Pointer::fmt(&(&**self as *const T), f)
+    }
+}
+
+// Implementation of Display/Debug for various core types
+
+#[stable(feature = "rust1", since = "1.0.0")]
+impl<T: ?Sized> Debug for *const T {
+    fn fmt(&self, f: &mut Formatter<'_>) -> Result {
+        Pointer::fmt(self, f)
+    }
+}
+#[stable(feature = "rust1", since = "1.0.0")]
+impl<T: ?Sized> Debug for *mut T {
+    fn fmt(&self, f: &mut Formatter<'_>) -> Result {
+        Pointer::fmt(self, f)
+    }
+}
+
+macro_rules! peel {
+    ($name:ident, $($other:ident,)*) => (tuple! { $($other,)* })
+}
+
+macro_rules! tuple {
+    () => ();
+    ( $($name:ident,)+ ) => (
+        maybe_tuple_doc! {
+            $($name)+ @
+            #[stable(feature = "rust1", since = "1.0.0")]
+            impl<$($name:Debug),+> Debug for ($($name,)+) where last_type!($($name,)+): ?Sized {
+                #[allow(non_snake_case, unused_assignments)]
+                fn fmt(&self, f: &mut Formatter<'_>) -> Result {
+                    let mut builder = f.debug_tuple("");
+                    let ($(ref $name,)+) = *self;
+                    $(
+                        builder.field(&$name);
+                    )+
+
+                    builder.finish()
+                }
+            }
+        }
+        peel! { $($name,)+ }
+    )
+}
+
+macro_rules! maybe_tuple_doc {
+    ($a:ident @ #[$meta:meta] $item:item) => {
+        #[cfg_attr(not(bootstrap), doc(fake_variadic))]
+        #[doc = "This trait is implemented for tuples up to twelve items long."]
+        #[$meta]
+        $item
+    };
+    ($a:ident $($rest_a:ident)+ @ #[$meta:meta] $item:item) => {
+        #[doc(hidden)]
+        #[$meta]
+        $item
+    };
+}
+
+macro_rules! last_type {
+    ($a:ident,) => { $a };
+    ($a:ident, $($rest_a:ident,)+) => { last_type!($($rest_a,)+) };
+}
+
+tuple! { E, D, C, B, A, Z, Y, X, W, V, U, T, }
+
+#[stable(feature = "rust1", since = "1.0.0")]
+impl<T: Debug> Debug for [T] {
+    fn fmt(&self, f: &mut Formatter<'_>) -> Result {
+        f.debug_list().entries(self.iter()).finish()
+    }
+}
+
+#[stable(feature = "rust1", since = "1.0.0")]
+impl Debug for () {
+    #[inline]
+    fn fmt(&self, f: &mut Formatter<'_>) -> Result {
+        f.pad("()")
+    }
+}
+#[stable(feature = "rust1", since = "1.0.0")]
+impl<T: ?Sized> Debug for PhantomData<T> {
+    fn fmt(&self, f: &mut Formatter<'_>) -> Result {
+        f.debug_struct("PhantomData").finish()
+    }
+}
+
+#[stable(feature = "rust1", since = "1.0.0")]
+impl<T: Copy + Debug> Debug for Cell<T> {
+    fn fmt(&self, f: &mut Formatter<'_>) -> Result {
+        f.debug_struct("Cell").field("value", &self.get()).finish()
+    }
+}
+
+#[stable(feature = "rust1", since = "1.0.0")]
+impl<T: ?Sized + Debug> Debug for RefCell<T> {
+    fn fmt(&self, f: &mut Formatter<'_>) -> Result {
+        match self.try_borrow() {
+            Ok(borrow) => f.debug_struct("RefCell").field("value", &borrow).finish(),
+            Err(_) => {
+                // The RefCell is mutably borrowed so we can't look at its value
+                // here. Show a placeholder instead.
+                struct BorrowedPlaceholder;
+
+                impl Debug for BorrowedPlaceholder {
+                    fn fmt(&self, f: &mut Formatter<'_>) -> Result {
+                        f.write_str("<borrowed>")
+                    }
+                }
+
+                f.debug_struct("RefCell").field("value", &BorrowedPlaceholder).finish()
+            }
+        }
+    }
+}
+
+#[stable(feature = "rust1", since = "1.0.0")]
+impl<T: ?Sized + Debug> Debug for Ref<'_, T> {
+    fn fmt(&self, f: &mut Formatter<'_>) -> Result {
+        Debug::fmt(&**self, f)
+    }
+}
+
+#[stable(feature = "rust1", since = "1.0.0")]
+impl<T: ?Sized + Debug> Debug for RefMut<'_, T> {
+    fn fmt(&self, f: &mut Formatter<'_>) -> Result {
+        Debug::fmt(&*(self.deref()), f)
+    }
+}
+
+#[stable(feature = "core_impl_debug", since = "1.9.0")]
+impl<T: ?Sized> Debug for UnsafeCell<T> {
+    fn fmt(&self, f: &mut Formatter<'_>) -> Result {
+        f.debug_struct("UnsafeCell").finish_non_exhaustive()
+    }
+}
+
+#[unstable(feature = "sync_unsafe_cell", issue = "95439")]
+impl<T: ?Sized> Debug for SyncUnsafeCell<T> {
+    fn fmt(&self, f: &mut Formatter<'_>) -> Result {
+        f.debug_struct("SyncUnsafeCell").finish_non_exhaustive()
+    }
+}
+
+// If you expected tests to be here, look instead at the core/tests/fmt.rs file,
+// it's a lot easier than creating all of the rt::Piece structures here.
+// There are also tests in the alloc crate, for those that need allocations.