Remove DefaultLenType functionality and the ZeroLengthType implementation

Author: sosthene-nitrokey

CHANGELOG.md

@@ -20,6 +20,7 @@ and this project adheres to [Semantic Versioning](http://semver.org/).
 ### Removed
 
 - Removed invalid `bytes::Buf` implementation.
+- Removed `DefaultLenType` struct.
 
 ## [v0.9.0] - 2025-04-28 [YANKED]
 

src/len_type.rs

@@ -85,186 +85,6 @@ impl_lentype!(
     usize
 );
 
-macro_rules! impl_lentodefault {
-    ($LenT:ty: $($len:literal),*) => {$(
-        impl SmallestLenType for Const<$len> {
-            type Type = $LenT;
-        }
-    )*};
-}
-
-/// A struct to create individual types for mapping with [`SmallestLenType`].
-///
-/// See the documentation of [`DefaultLenType`] for a detailed explanation.
-pub struct Const<const N: usize>;
-
-/// A trait to map [`Const`] to it's respective [`LenType`].
-///
-/// See the documentation of [`DefaultLenType`] for a detailed explanation.
-#[diagnostic::on_unimplemented(
-    message = "Length `N` does not have a default `LenType` mapping",
-    note = "Provide the `LenType` explicitly, such as `usize`"
-)]
-pub trait SmallestLenType {
-    type Type: LenType;
-}
-
-/// A type alias to perform the `const N: usize` -> `LenType` mapping.
-///
-/// This is impossible to perform directly, but it is possible to write a `const N: usize` -> related `Type` mapping via a const generic argument,
-/// then map from that to an unrelated type via a trait with associated types.
-///
-/// [`Const`] is the "related type" in the above explaination, [`SmallestLenType`] is the mapping trait.
-#[allow(rustdoc::private_intra_doc_links)] // Only publically exposed via `crate::_export`
-pub type DefaultLenType<const N: usize> = <Const<N> as SmallestLenType>::Type;
-
-impl_lentodefault!(ZeroLenType: 0);
-impl_lentodefault!(u8: 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47, 48, 49, 50, 51, 52, 53, 54, 55, 56, 57, 58, 59, 60, 61, 62, 63, 64, 65, 66, 67, 68, 69, 70, 71, 72, 73, 74, 75, 76, 77, 78, 79, 80, 81, 82, 83, 84, 85, 86, 87, 88, 89, 90, 91, 92, 93, 94, 95, 96, 97, 98, 99, 100, 101, 102, 103, 104, 105, 106, 107, 108, 109, 110, 111, 112, 113, 114, 115, 116, 117, 118, 119, 120, 121, 122, 123, 124, 125, 126, 127, 128, 129, 130, 131, 132, 133, 134, 135, 136, 137, 138, 139, 140, 141, 142, 143, 144, 145, 146, 147, 148, 149, 150, 151, 152, 153, 154, 155, 156, 157, 158, 159, 160, 161, 162, 163, 164, 165, 166, 167, 168, 169, 170, 171, 172, 173, 174, 175, 176, 177, 178, 179, 180, 181, 182, 183, 184, 185, 186, 187, 188, 189, 190, 191, 192, 193, 194, 195, 196, 197, 198, 199, 200, 201, 202, 203, 204, 205, 206, 207, 208, 209, 210, 211, 212, 213, 214, 215, 216, 217, 218, 219, 220, 221, 222, 223, 224, 225, 226, 227, 228, 229, 230, 231, 232, 233, 234, 235, 236, 237, 238, 239, 240, 241, 242, 243, 244, 245, 246, 247, 248, 249, 250, 251, 252, 253, 254, 255);
-impl_lentodefault!(u16: 256, 300, 400, 500, 512, 600, 700, 800, 900, 1000, 1024, 2000, 2048, 4000, 4096, 8000, 8192, 16000, 16384, 32000, 32768, 65000, 65535);
-#[cfg(any(target_pointer_width = "32", target_pointer_width = "64"))]
-impl_lentodefault!(u32: 65536, 131072, 262144, 524288, 1048576, 2097152, 4194304, 8388608, 16777216, 33554432, 67108864, 134217728, 268435456, 536870912, 1073741824, 2147483648);
-
 pub const fn check_capacity_fits<LenT: LenType, const N: usize>() {
     assert!(LenT::MAX_USIZE >= N, "The capacity is larger than `LenT` can hold, increase the size of `LenT` or reduce the capacity");
 }
-
-/// Container with 0 capacity always has length 0, so there is no need to track length of such containers at all.
-///
-/// This type is used as a placeholder for length of container with 0 capacity. It allows optimizing total size of
-/// containers like this to 0 bytes.
-///
-/// Logically, this type always stores value 0. Because of this ZeroLenType::one() panics and should never be called.
-#[doc(hidden)]
-#[derive(Copy, Clone, PartialEq, PartialOrd)]
-pub struct ZeroLenType;
-
-impl Debug for ZeroLenType {
-    fn fmt(&self, f: &mut core::fmt::Formatter<'_>) -> core::fmt::Result {
-        write!(f, "0")
-    }
-}
-
-impl Display for ZeroLenType {
-    fn fmt(&self, f: &mut core::fmt::Formatter<'_>) -> core::fmt::Result {
-        write!(f, "0")
-    }
-}
-
-impl Sealed for ZeroLenType {
-    const ZERO: Self = Self;
-
-    const MAX: Self = Self;
-    const MAX_USIZE: usize = 0;
-
-    #[inline]
-    fn one() -> Self {
-        panic!("ZeroLenType cannot represent value 1");
-    }
-}
-
-impl LenType for ZeroLenType {}
-
-impl Add for ZeroLenType {
-    type Output = Self;
-
-    fn add(self, _rhs: Self) -> Self::Output {
-        Self::ZERO
-    }
-}
-
-impl AddAssign for ZeroLenType {
-    fn add_assign(&mut self, _rhs: Self) {}
-}
-
-impl Sub for ZeroLenType {
-    type Output = Self;
-
-    fn sub(self, _rhs: Self) -> Self::Output {
-        Self::ZERO
-    }
-}
-
-impl SubAssign for ZeroLenType {
-    fn sub_assign(&mut self, _rhs: Self) {}
-}
-
-#[doc(hidden)]
-#[derive(Debug, PartialEq)]
-pub struct ZeroLenTypeTryFromError;
-
-impl TryFrom<usize> for ZeroLenType {
-    type Error = ZeroLenTypeTryFromError;
-
-    fn try_from(value: usize) -> Result<Self, Self::Error> {
-        if value > 0 {
-            return Err(ZeroLenTypeTryFromError);
-        }
-
-        Ok(Self::ZERO)
-    }
-}
-
-impl TryInto<usize> for ZeroLenType {
-    type Error = ();
-
-    fn try_into(self) -> Result<usize, Self::Error> {
-        Ok(0)
-    }
-}
-
-#[cfg(test)]
-mod tests {
-    use crate::len_type::{Sealed, ZeroLenType, ZeroLenTypeTryFromError};
-
-    #[test]
-    pub fn test_zero_len_type_conversions() {
-        assert_eq!(ZeroLenType::into_usize(ZeroLenType::ZERO), 0_usize);
-        assert_eq!(ZeroLenType::from_usize(0_usize), ZeroLenType::ZERO);
-
-        assert_eq!(ZeroLenType::ZERO.try_into(), Ok(0_usize));
-        assert_eq!(ZeroLenType::try_from(0_usize), Ok(ZeroLenType::ZERO));
-        assert_eq!(ZeroLenType::try_from(1_usize), Err(ZeroLenTypeTryFromError));
-    }
-
-    #[test]
-    #[should_panic]
-    pub fn test_zero_len_type_one() {
-        ZeroLenType::one();
-    }
-
-    #[test]
-    #[should_panic]
-    pub fn test_zero_len_type_one_usize() {
-        ZeroLenType::from_usize(1);
-    }
-
-    #[test]
-    pub fn test_zero_len_type_constants() {
-        assert_eq!(ZeroLenType::ZERO, ZeroLenType);
-        assert_eq!(ZeroLenType::MAX, ZeroLenType);
-        assert_eq!(ZeroLenType::MAX_USIZE, 0_usize);
-    }
-
-    #[test]
-    pub fn test_zero_len_type_size() {
-        assert_eq!(core::mem::size_of::<ZeroLenType>(), 0);
-    }
-
-    #[test]
-    pub fn test_zero_len_type_ops() {
-        assert_eq!(ZeroLenType::ZERO + ZeroLenType::ZERO, ZeroLenType::ZERO);
-        assert_eq!(ZeroLenType::ZERO - ZeroLenType::ZERO, ZeroLenType::ZERO);
-
-        let mut zero = ZeroLenType::ZERO;
-        zero += ZeroLenType::ZERO;
-        assert_eq!(zero, ZeroLenType::ZERO);
-        zero -= ZeroLenType::ZERO;
-        assert_eq!(zero, ZeroLenType::ZERO);
-    }
-
-    #[test]
-    pub fn test_zero_len_type_debug() {
-        assert_eq!(format!("{}", ZeroLenType), "0");
-        assert_eq!(format!("{:?}", ZeroLenType), "0");
-    }
-}

src/lib.rs

@@ -241,7 +241,6 @@ mod ufmt;
 /// Do not use. Used for macros only. Not covered by semver guarantees.
 #[doc(hidden)]
 pub mod _export {
-    pub use crate::len_type::DefaultLenType;
     pub use crate::string::format;
 }
 

src/string/mod.rs

@@ -977,7 +977,7 @@ impl_try_from_num!(u64, 20);
 
 #[cfg(test)]
 mod tests {
-    use crate::{len_type::ZeroLenType, CapacityError, String, Vec};
+    use crate::{CapacityError, String, Vec};
 
     #[test]
     fn static_new() {
@@ -1240,29 +1240,4 @@ mod tests {
         let formatted = format!(2; "123");
         assert_eq!(formatted, Err(core::fmt::Error));
     }
-
-    #[test]
-    fn zero_capacity() {
-        let mut s: String<0, ZeroLenType> = String::new();
-        // Validate capacity
-        assert_eq!(s.capacity(), 0);
-
-        // Make sure there is no capacity
-        assert!(s.push('a').is_err());
-
-        // Validate length
-        assert_eq!(s.len(), 0);
-
-        // Validate pop
-        assert_eq!(s.pop(), None);
-
-        // Validate slice
-        assert_eq!(s.as_str(), "");
-
-        // Validate empty
-        assert!(s.is_empty());
-
-        // Size of string with zero capacity should be 0 bytes because of `ZeroLenType` optimization
-        assert_eq!(core::mem::size_of_val(&s), 0);
-    }
 }

src/vec/mod.rs

@@ -1737,8 +1737,6 @@ mod tests {
 
     use static_assertions::assert_not_impl_any;
 
-    use crate::len_type::ZeroLenType;
-
     use super::{Vec, VecView};
 
     // Ensure a `Vec` containing `!Send` values stays `!Send` itself.
@@ -2182,34 +2180,6 @@ mod tests {
         assert!(!v.ends_with(b"a"));
     }
 
-    #[test]
-    fn zero_capacity() {
-        let mut v: Vec<u8, 0, ZeroLenType> = Vec::new();
-        // Validate capacity
-        assert_eq!(v.capacity(), 0);
-
-        // Make sure there is no capacity
-        assert!(v.push(1).is_err());
-
-        // Validate length
-        assert_eq!(v.len(), 0);
-
-        // Validate pop
-        assert_eq!(v.pop(), None);
-
-        // Validate slice
-        assert_eq!(v.as_slice(), &[]);
-
-        // Validate empty
-        assert!(v.is_empty());
-
-        // Validate full
-        assert!(v.is_full());
-
-        // Size of vector with zero capacity should be 0 bytes because of `ZeroLenType` optimization
-        assert_eq!(core::mem::size_of_val(&v), 0);
-    }
-
     #[test]
     fn spare_capacity_mut() {
         let mut v: Vec<_, 4> = Vec::new();