feat(stream): Add AsciiChar

src/lib.rs

@@ -236,6 +236,7 @@ pub mod _tutorial;
 /// ```
 pub mod prelude {
     pub use crate::stream::StreamIsPartial as _;
+    pub use crate::stream::A;
     pub use crate::IResult;
     pub use crate::PResult;
     pub use crate::Parser;

src/parser.rs

@@ -5,6 +5,7 @@
 #[cfg(feature = "unstable-recover")]
 use crate::error::FromRecoverableError;
 use crate::error::{AddContext, FromExternalError, IResult, PResult, ParseError, ParserError};
+use crate::stream::AsciiChar;
 use crate::stream::{AsChar, Compare, Location, ParseSlice, Stream, StreamIsPartial};
 #[cfg(feature = "unstable-recover")]
 use crate::stream::{Recover, Recoverable};
@@ -743,6 +744,34 @@
     }
 }
 
+/// This is a shortcut for [`one_of`][crate::token::one_of].
+///
+/// # Example
+///
+/// ```
+/// # use winnow::prelude::*;
+/// # use winnow::{error::ErrMode, error::{ErrorKind, InputError}};
+/// fn parser<'s>(i: &mut &'s str) -> PResult<char, InputError<&'s str>> {
+///     A!('a').parse_next(i)
+/// }
+/// assert_eq!(parser.parse_peek("abc"), Ok(("bc", 'a')));
+/// assert_eq!(parser.parse_peek(" abc"), Err(ErrMode::Backtrack(InputError::new(" abc", ErrorKind::Verify))));
+/// assert_eq!(parser.parse_peek("bc"), Err(ErrMode::Backtrack(InputError::new("bc", ErrorKind::Verify))));
+/// assert_eq!(parser.parse_peek(""), Err(ErrMode::Backtrack(InputError::new("", ErrorKind::Token))));
+/// ```
+impl<I, E> Parser<I, <I as Stream>::Token, E> for AsciiChar
+where
+    I: StreamIsPartial,
+    I: Stream,
+    <I as Stream>::Token: AsChar + Clone,
+    E: ParserError<I>,
+{
+    #[inline(always)]
+    fn parse_next(&mut self, i: &mut I) -> PResult<<I as Stream>::Token, E> {
+        crate::token::one_of(*self).parse_next(i)
+    }
+}
+
 /// This is a shortcut for [`one_of`][crate::token::one_of].
 ///
 /// # Example

src/stream/ascii.rs

@@ -0,0 +1,180 @@
+/// One of the 128 Unicode characters from U+0000 through U+007F,
+/// often known as the [ASCII] subset.
+///
+/// Officially, this is the first [block] in Unicode, _Basic Latin_.
+/// For details, see the [*C0 Controls and Basic Latin*][chart] code chart.
+///
+/// This block was based on older 7-bit character code standards such as
+/// ANSI X3.4-1977, ISO 646-1973, and [NIST FIPS 1-2].
+///
+/// **Note:** This is a polyfill for [`ascii::Char`][std::ascii::Char].
+///
+/// # When to use this
+///
+/// The main advantage of this subset is that it's always valid UTF-8.  As such,
+/// the `&[ascii::Char]` -> `&str` conversion function (as well as other related
+/// ones) are O(1): *no* runtime checks are needed.
+///
+/// If you're consuming strings, you should usually handle Unicode and thus
+/// accept `str`s, not limit yourself to `ascii::Char`s.
+///
+/// However, certain formats are intentionally designed to produce ASCII-only
+/// output in order to be 8-bit-clean.  In those cases, it can be simpler and
+/// faster to generate `ascii::Char`s instead of dealing with the variable width
+/// properties of general UTF-8 encoded strings, while still allowing the result
+/// to be used freely with other Rust things that deal in general `str`s.
+///
+/// For example, a UUID library might offer a way to produce the string
+/// representation of a UUID as an `[ascii::Char; 36]` to avoid memory
+/// allocation yet still allow it to be used as UTF-8 via `as_str` without
+/// paying for validation (or needing `unsafe` code) the way it would if it
+/// were provided as a `[u8; 36]`.
+///
+/// # Layout
+///
+/// This type is guaranteed to have a size and alignment of 1 byte.
+///
+/// # Names
+///
+/// The variants on this type are [Unicode names][NamesList] of the characters
+/// in upper camel case, with a few tweaks:
+/// - For `<control>` characters, the primary alias name is used.
+/// - `LATIN` is dropped, as this block has no non-latin letters.
+/// - `LETTER` is dropped, as `CAPITAL`/`SMALL` suffices in this block.
+/// - `DIGIT`s use a single digit rather than writing out `ZERO`, `ONE`, etc.
+///
+/// [ASCII]: https://www.unicode.org/glossary/index.html#ASCII
+/// [block]: https://www.unicode.org/glossary/index.html#block
+/// [chart]: https://www.unicode.org/charts/PDF/U0000.pdf
+/// [NIST FIPS 1-2]: https://nvlpubs.nist.gov/nistpubs/Legacy/FIPS/fipspub1-2-1977.pdf
+/// [NamesList]: https://www.unicode.org/Public/15.0.0/ucd/NamesList.txt
+#[derive(Copy, Clone, PartialEq, Eq, PartialOrd, Ord, Hash)]
+pub struct AsciiChar(u8);
+
+impl AsciiChar {
+    /// Creates an ascii character from the byte `b`,
+    /// or returns `None` if it's too large.
+    #[inline(always)]
+    pub const fn from_u8(b: u8) -> Option<Self> {
+        if b <= 127 {
+            // SAFETY: Just checked that `b` is in-range
+            Some(unsafe { Self::from_u8_unchecked(b) })
+        } else {
+            None
+        }
+    }
+
+    /// Creates an ASCII character from the byte `b`,
+    /// without checking whether it's valid.
+    ///
+    /// # Safety
+    ///
+    /// `b` must be in `0..=127`, or else this is UB.
+    #[inline(always)]
+    pub const unsafe fn from_u8_unchecked(b: u8) -> Self {
+        Self(b)
+    }
+
+    /// Gets this ASCII character as a byte.
+    #[inline(always)]
+    pub const fn to_u8(self) -> u8 {
+        self.0 as u8
+    }
+
+    /// Gets this ASCII character as a `char` Unicode Scalar Value.
+    #[inline(always)]
+    pub const fn to_char(self) -> char {
+        self.0 as char
+    }
+}
+
+impl crate::lib::std::fmt::Display for AsciiChar {
+    fn fmt(&self, f: &mut crate::lib::std::fmt::Formatter<'_>) -> crate::lib::std::fmt::Result {
+        self.to_char().fmt(f)
+    }
+}
+
+impl crate::lib::std::fmt::Debug for AsciiChar {
+    fn fmt(&self, f: &mut crate::lib::std::fmt::Formatter<'_>) -> crate::lib::std::fmt::Result {
+        self.to_char().fmt(f)
+    }
+}
+
+/// Create an [`AsciiChar`] with compile-time validation
+#[macro_export]
+#[doc(hidden)] // forced to be visible in intended location
+macro_rules! A {
+    ($byte: literal) => {{
+        #![allow(clippy::unnecessary_cast)] // not always the same type
+
+        const BYTE: char = $byte as char;
+        const MAX: char = 127 as char;
+        const C: $crate::stream::AsciiChar = if BYTE <= MAX {
+            unsafe { $crate::stream::AsciiChar::from_u8_unchecked(BYTE as u8) }
+        } else {
+            panic!()
+        };
+        C
+    }};
+}
+
+/// Create an [`&[AsciiChar]`] with compile-time validation
+#[macro_export]
+#[doc(hidden)] // forced to be visible in intended location
+macro_rules! AS {
+    ($s: literal) => {{
+        #![allow(clippy::unnecessary_cast)] // not always the same type
+
+        const S: &'static str = $s;
+        const BYTES: &'static [u8] = unsafe { core::mem::transmute(S) };
+        let mut i = 0;
+        while i < BYTES.len() {
+            let byte = BYTES[0];
+            if byte <= 127 {
+            } else {
+                panic!()
+            };
+            i += 1;
+        }
+        const AS: &'static [$crate::stream::AsciiChar] = unsafe { core::mem::transmute(BYTES) };
+        AS
+    }};
+}
+
+#[cfg(test)]
+mod test {
+    use super::*;
+
+    #[test]
+    fn const_number() {
+        const fn gen() -> AsciiChar {
+            crate::stream::A!(97)
+        }
+        assert_eq!(gen(), AsciiChar::from_u8(b'a').unwrap());
+    }
+
+    #[test]
+    fn const_u8() {
+        const fn gen() -> AsciiChar {
+            crate::stream::A!(b'a')
+        }
+        assert_eq!(gen(), AsciiChar::from_u8(b'a').unwrap());
+    }
+
+    #[test]
+    fn const_char() {
+        const fn gen() -> AsciiChar {
+            crate::stream::A!('a')
+        }
+        assert_eq!(gen(), AsciiChar::from_u8(b'a').unwrap());
+    }
+
+    #[test]
+    fn const_str() {
+        const fn gen() -> &'static [AsciiChar] {
+            crate::stream::AS!("a")
+        }
+        const S: &'static [AsciiChar] = gen();
+        dbg!(S);
+    }
+}