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
256
257
258
259
260
261
262
263
264
// This file is part of ICU4X. For terms of use, please see the file
// called LICENSE at the top level of the ICU4X source tree
// (online at: https://github.com/unicode-org/icu4x/blob/main/LICENSE ).

use super::*;
use core::cmp::Ordering;
use core::marker::PhantomData;
use core::mem::{self, MaybeUninit};

/// This type is the [`ULE`] type for `Option<U>` where `U` is a [`ULE`] type
///
/// # Example
///
/// ```rust
/// use zerovec::ZeroVec;
///
/// let z = ZeroVec::alloc_from_slice(&[
///     Some('a'),
///     Some('á'),
///     Some('ø'),
///     None,
///     Some('ł'),
/// ]);
///
/// assert_eq!(z.get(2), Some(Some('ø')));
/// assert_eq!(z.get(3), Some(None));
/// ```
// Invariants:
// The MaybeUninit is zeroed when None (bool = false),
// and is valid when Some (bool = true)
#[repr(C, packed)]
pub struct OptionULE<U>(bool, MaybeUninit<U>);

impl<U: Copy> OptionULE<U> {
    /// Obtain this as an `Option<T>`
    pub fn get(self) -> Option<U> {
        if self.0 {
            unsafe {
                // safety: self.0 is true so the MaybeUninit is valid
                Some(self.1.assume_init())
            }
        } else {
            None
        }
    }

    /// Construct an `OptionULE<U>` from an equivalent `Option<T>`
    pub fn new(opt: Option<U>) -> Self {
        if let Some(inner) = opt {
            Self(true, MaybeUninit::new(inner))
        } else {
            Self(false, MaybeUninit::zeroed())
        }
    }
}

impl<U: Copy + core::fmt::Debug> core::fmt::Debug for OptionULE<U> {
    fn fmt(&self, f: &mut core::fmt::Formatter<'_>) -> core::fmt::Result {
        self.get().fmt(f)
    }
}

// Safety (based on the safety checklist on the ULE trait):
//  1. OptionULE does not include any uninitialized or padding bytes.
//     (achieved by `#[repr(C, packed)]` on a struct containing only ULE fields,
//     in the context of this impl. The MaybeUninit is valid for all byte sequences, and we only generate
///    zeroed or valid-T byte sequences to fill it)
//  2. OptionULE is aligned to 1 byte.
//     (achieved by `#[repr(C, packed)]` on a struct containing only ULE fields, in the context of this impl)
//  3. The impl of validate_byte_slice() returns an error if any byte is not valid.
//  4. The impl of validate_byte_slice() returns an error if there are extra bytes.
//  5. The other ULE methods use the default impl.
//  6. OptionULE byte equality is semantic equality by relying on the ULE equality
//     invariant on the subfields
unsafe impl<U: ULE> ULE for OptionULE<U> {
    fn validate_byte_slice(bytes: &[u8]) -> Result<(), ZeroVecError> {
        let size = mem::size_of::<Self>();
        if bytes.len() % size != 0 {
            return Err(ZeroVecError::length::<Self>(bytes.len()));
        }
        for chunk in bytes.chunks(size) {
            #[allow(clippy::indexing_slicing)] // `chunk` will have enough bytes to fit Self
            match chunk[0] {
                // https://doc.rust-lang.org/reference/types/boolean.html
                // Rust booleans are always size 1, align 1 values with valid bit patterns 0x0 or 0x1
                0 => {
                    if !chunk[1..].iter().all(|x| *x == 0) {
                        return Err(ZeroVecError::parse::<Self>());
                    }
                }
                1 => U::validate_byte_slice(&chunk[1..])?,
                _ => return Err(ZeroVecError::parse::<Self>()),
            }
        }
        Ok(())
    }
}

impl<T: AsULE> AsULE for Option<T> {
    type ULE = OptionULE<T::ULE>;
    fn to_unaligned(self) -> OptionULE<T::ULE> {
        OptionULE::new(self.map(T::to_unaligned))
    }

    fn from_unaligned(other: OptionULE<T::ULE>) -> Self {
        other.get().map(T::from_unaligned)
    }
}

impl<U: Copy> Copy for OptionULE<U> {}

impl<U: Copy> Clone for OptionULE<U> {
    fn clone(&self) -> Self {
        *self
    }
}

impl<U: Copy + PartialEq> PartialEq for OptionULE<U> {
    fn eq(&self, other: &Self) -> bool {
        self.get().eq(&other.get())
    }
}

impl<U: Copy + Eq> Eq for OptionULE<U> {}

/// A type allowing one to represent `Option<U>` for [`VarULE`] `U` types.
///
/// ```rust
/// use zerovec::ule::OptionVarULE;
/// use zerovec::VarZeroVec;
///
/// let mut zv: VarZeroVec<OptionVarULE<str>> = VarZeroVec::new();
///
/// zv.make_mut().push(&None::<&str>);
/// zv.make_mut().push(&Some("hello"));
/// zv.make_mut().push(&Some("world"));
/// zv.make_mut().push(&None::<&str>);
///
/// assert_eq!(zv.get(0).unwrap().as_ref(), None);
/// assert_eq!(zv.get(1).unwrap().as_ref(), Some("hello"));
/// ```
// The slice field is empty when None (bool = false),
// and is a valid T when Some (bool = true)
#[repr(C, packed)]
pub struct OptionVarULE<U: VarULE + ?Sized>(PhantomData<U>, bool, [u8]);

impl<U: VarULE + ?Sized> OptionVarULE<U> {
    /// Obtain this as an `Option<&U>`
    pub fn as_ref(&self) -> Option<&U> {
        if self.1 {
            unsafe {
                // Safety: byte field is a valid T if boolean field is true
                Some(U::from_byte_slice_unchecked(&self.2))
            }
        } else {
            None
        }
    }
}

impl<U: VarULE + ?Sized + core::fmt::Debug> core::fmt::Debug for OptionVarULE<U> {
    fn fmt(&self, f: &mut core::fmt::Formatter<'_>) -> core::fmt::Result {
        self.as_ref().fmt(f)
    }
}

// Safety (based on the safety checklist on the VarULE trait):
//  1. OptionVarULE<T> does not include any uninitialized or padding bytes
//     (achieved by being repr(C, packed) on ULE types)
//  2. OptionVarULE<T> is aligned to 1 byte (achieved by being repr(C, packed) on ULE types)
//  3. The impl of `validate_byte_slice()` returns an error if any byte is not valid.
//  4. The impl of `validate_byte_slice()` returns an error if the slice cannot be used in its entirety
//  5. The impl of `from_byte_slice_unchecked()` returns a reference to the same data.
//  6. All other methods are defaulted
//  7. OptionVarULE<T> byte equality is semantic equality (achieved by being an aggregate)
unsafe impl<U: VarULE + ?Sized> VarULE for OptionVarULE<U> {
    #[inline]
    fn validate_byte_slice(slice: &[u8]) -> Result<(), ZeroVecError> {
        if slice.is_empty() {
            return Err(ZeroVecError::length::<Self>(slice.len()));
        }
        #[allow(clippy::indexing_slicing)] // slice already verified to be nonempty
        match slice[0] {
            // https://doc.rust-lang.org/reference/types/boolean.html
            // Rust booleans are always size 1, align 1 values with valid bit patterns 0x0 or 0x1
            0 => {
                if slice.len() != 1 {
                    Err(ZeroVecError::length::<Self>(slice.len()))
                } else {
                    Ok(())
                }
            }
            1 => U::validate_byte_slice(&slice[1..]),
            _ => Err(ZeroVecError::parse::<Self>()),
        }
    }

    #[inline]
    unsafe fn from_byte_slice_unchecked(bytes: &[u8]) -> &Self {
        let entire_struct_as_slice: *const [u8] =
            ::core::ptr::slice_from_raw_parts(bytes.as_ptr(), bytes.len() - 1);
        &*(entire_struct_as_slice as *const Self)
    }
}

unsafe impl<T, U> EncodeAsVarULE<OptionVarULE<U>> for Option<T>
where
    T: EncodeAsVarULE<U>,
    U: VarULE + ?Sized,
{
    fn encode_var_ule_as_slices<R>(&self, _: impl FnOnce(&[&[u8]]) -> R) -> R {
        // unnecessary if the other two are implemented
        unreachable!()
    }

    #[inline]
    fn encode_var_ule_len(&self) -> usize {
        if let Some(ref inner) = *self {
            // slice + boolean
            1 + inner.encode_var_ule_len()
        } else {
            // boolean + empty slice
            1
        }
    }

    #[allow(clippy::indexing_slicing)] // This method is allowed to panic when lengths are invalid
    fn encode_var_ule_write(&self, dst: &mut [u8]) {
        if let Some(ref inner) = *self {
            debug_assert!(
                !dst.is_empty(),
                "OptionVarULE must have at least one byte when Some"
            );
            dst[0] = 1;
            inner.encode_var_ule_write(&mut dst[1..]);
        } else {
            debug_assert!(
                dst.len() == 1,
                "OptionVarULE must have exactly one byte when None"
            );
            dst[0] = 0;
        }
    }
}

impl<U: VarULE + ?Sized + PartialEq> PartialEq for OptionVarULE<U> {
    fn eq(&self, other: &Self) -> bool {
        self.as_ref().eq(&other.as_ref())
    }
}

impl<U: VarULE + ?Sized + Eq> Eq for OptionVarULE<U> {}

impl<U: VarULE + ?Sized + PartialOrd> PartialOrd for OptionVarULE<U> {
    fn partial_cmp(&self, other: &Self) -> Option<Ordering> {
        self.as_ref().partial_cmp(&other.as_ref())
    }
}

impl<U: VarULE + ?Sized + Ord> Ord for OptionVarULE<U> {
    fn cmp(&self, other: &Self) -> Ordering {
        self.as_ref().cmp(&other.as_ref())
    }
}