Adding upstream version 115.7.0esr.upstream/115.7.0esr

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

1 files changed, 968 insertions, 0 deletions

diff --git a/third_party/rust/fallible_collections/src/vec.rs b/third_party/rust/fallible_collections/src/vec.rs
new file mode 100644
index 0000000000..6197b5b5d6
--- /dev/null
+++ b/third_party/rust/fallible_collections/src/vec.rs
@@ -0,0 +1,968 @@
+//! Implement Fallible Vec
+use super::TryClone;
+use crate::TryReserveError;
+#[allow(unused_imports)]
+use alloc::alloc::{alloc, realloc, Layout};
+use alloc::vec::Vec;
+use core::convert::TryInto as _;
+
+#[cfg(feature = "unstable")]
+#[macro_export]
+/// macro trying to create a vec, return a
+/// Result<Vec<T>,TryReserveError>
+macro_rules! try_vec {
+   ($elem:expr; $n:expr) => (
+        $crate::vec::try_from_elem($elem, $n)
+    );
+    ($($x:expr),*) => (
+        match <alloc::boxed::Box<_> as $crate::boxed::FallibleBox<_>>::try_new([$($x),*]) {
+            Err(e) => Err(e),
+            Ok(b) => Ok(<[_]>::into_vec(b)),
+        }
+    );
+    ($($x:expr,)*) => ($crate::try_vec![$($x),*])
+}
+
+/// trait implementing all fallible methods on vec
+pub trait FallibleVec<T> {
+    /// see reserve
+    fn try_reserve(&mut self, additional: usize) -> Result<(), TryReserveError>;
+    /// see push
+    fn try_push(&mut self, elem: T) -> Result<(), TryReserveError>;
+    /// try push and give back ownership in case of error
+    fn try_push_give_back(&mut self, elem: T) -> Result<(), (T, TryReserveError)>;
+    /// see with capacity, (Self must be sized by the constraint of Result)
+    fn try_with_capacity(capacity: usize) -> Result<Self, TryReserveError>
+    where
+        Self: core::marker::Sized;
+    /// see insert
+    fn try_insert(&mut self, index: usize, element: T) -> Result<(), (T, TryReserveError)>;
+    /// see append
+    fn try_append(&mut self, other: &mut Self) -> Result<(), TryReserveError>;
+    /// see resize, only works when the `value` implements Copy, otherwise, look at try_resize_no_copy
+    fn try_resize(&mut self, new_len: usize, value: T) -> Result<(), TryReserveError>
+    where
+        T: Copy + Clone;
+    fn try_resize_with<F>(&mut self, new_len: usize, f: F) -> Result<(), TryReserveError>
+    where
+        F: FnMut() -> T;
+    /// resize the vec by trying to clone the value repeatingly
+    fn try_resize_no_copy(&mut self, new_len: usize, value: T) -> Result<(), TryReserveError>
+    where
+        T: TryClone;
+    /// see resize, only works when the `value` implements Copy, otherwise, look at try_extend_from_slice_no_copy
+    fn try_extend_from_slice(&mut self, other: &[T]) -> Result<(), TryReserveError>
+    where
+        T: Copy + Clone;
+    /// extend the vec by trying to clone the value in `other`
+    fn try_extend_from_slice_no_copy(&mut self, other: &[T]) -> Result<(), TryReserveError>
+    where
+        T: TryClone;
+}
+
+/// TryVec is a thin wrapper around alloc::vec::Vec to provide support for
+/// fallible allocation.
+///
+/// See the crate documentation for more.
+#[derive(PartialEq)]
+pub struct TryVec<T> {
+    inner: Vec<T>,
+}
+
+impl<T> Default for TryVec<T> {
+    #[inline(always)]
+    fn default() -> Self {
+        Self {
+            inner: Default::default(),
+        }
+    }
+}
+
+impl<T: core::fmt::Debug> core::fmt::Debug for TryVec<T> {
+    #[inline]
+    fn fmt(&self, f: &mut core::fmt::Formatter<'_>) -> core::fmt::Result {
+        self.inner.fmt(f)
+    }
+}
+
+impl<T> TryVec<T> {
+    #[inline(always)]
+    pub fn new() -> Self {
+        Self { inner: Vec::new() }
+    }
+
+    #[inline]
+    pub fn with_capacity(capacity: usize) -> Result<Self, TryReserveError> {
+        Ok(Self {
+            inner: FallibleVec::try_with_capacity(capacity)?,
+        })
+    }
+
+    #[inline(always)]
+    pub fn append(&mut self, other: &mut Self) -> Result<(), TryReserveError> {
+        FallibleVec::try_append(&mut self.inner, &mut other.inner)
+    }
+
+    #[inline(always)]
+    pub fn as_mut_slice(&mut self) -> &mut [T] {
+        self
+    }
+
+    #[inline(always)]
+    pub fn as_slice(&self) -> &[T] {
+        self
+    }
+
+    #[inline(always)]
+    pub fn clear(&mut self) {
+        self.inner.clear()
+    }
+
+    #[cfg(test)]
+    pub fn into_inner(self) -> Vec<T> {
+        self.inner
+    }
+
+    #[inline(always)]
+    pub fn is_empty(&self) -> bool {
+        self.inner.is_empty()
+    }
+
+    #[inline(always)]
+    pub fn iter_mut(&mut self) -> IterMut<T> {
+        IterMut {
+            inner: self.inner.iter_mut(),
+        }
+    }
+
+    #[inline(always)]
+    pub fn iter(&self) -> Iter<T> {
+        Iter {
+            inner: self.inner.iter(),
+        }
+    }
+
+    #[inline(always)]
+    pub fn pop(&mut self) -> Option<T> {
+        self.inner.pop()
+    }
+
+    #[inline(always)]
+    pub fn push(&mut self, value: T) -> Result<(), TryReserveError> {
+        FallibleVec::try_push(&mut self.inner, value)
+    }
+
+    #[inline(always)]
+    pub fn reserve(&mut self, additional: usize) -> Result<(), TryReserveError> {
+        FallibleVec::try_reserve(&mut self.inner, additional)
+    }
+
+    #[inline(always)]
+    pub fn resize_with<F>(&mut self, new_len: usize, f: F) -> Result<(), TryReserveError>
+    where
+        F: FnMut() -> T,
+    {
+        FallibleVec::try_resize_with(&mut self.inner, new_len, f)
+    }
+}
+
+impl<T: TryClone> TryClone for TryVec<T> {
+    #[inline]
+    fn try_clone(&self) -> Result<Self, TryReserveError> {
+        self.as_slice().try_into()
+    }
+}
+
+impl<T: TryClone> TryVec<TryVec<T>> {
+    pub fn concat(&self) -> Result<TryVec<T>, TryReserveError> {
+        let size = self.iter().map(|v| v.inner.len()).sum();
+        let mut result = TryVec::with_capacity(size)?;
+        for v in self.iter() {
+            result.inner.try_extend_from_slice_no_copy(&v.inner)?;
+        }
+        Ok(result)
+    }
+}
+
+impl<T: TryClone> TryVec<T> {
+    #[inline(always)]
+    pub fn extend_from_slice(&mut self, other: &[T]) -> Result<(), TryReserveError> {
+        self.inner.try_extend_from_slice_no_copy(other)
+    }
+}
+
+impl<T> IntoIterator for TryVec<T> {
+    type Item = T;
+    type IntoIter = alloc::vec::IntoIter<T>;
+
+    #[inline(always)]
+    fn into_iter(self) -> Self::IntoIter {
+        self.inner.into_iter()
+    }
+}
+
+impl<'a, T> IntoIterator for &'a TryVec<T> {
+    type Item = &'a T;
+    type IntoIter = alloc::slice::Iter<'a, T>;
+
+    #[inline(always)]
+    fn into_iter(self) -> Self::IntoIter {
+        self.inner.iter()
+    }
+}
+
+#[cfg(feature = "std_io")]
+pub mod std_io {
+    use super::*;
+    use std::io::{self, Read, Take, Write};
+
+    pub trait TryRead {
+        fn try_read_to_end(&mut self, buf: &mut TryVec<u8>) -> io::Result<usize>;
+
+        #[inline]
+        fn read_into_try_vec(&mut self) -> io::Result<TryVec<u8>> {
+            let mut buf = TryVec::new();
+            self.try_read_to_end(&mut buf)?;
+            Ok(buf)
+        }
+    }
+
+    impl<T: Read> TryRead for Take<T> {
+        /// This function reserves the upper limit of what `src` can generate before
+        /// reading all bytes until EOF in this source, placing them into `buf`. If the
+        /// allocation is unsuccessful, or reading from the source generates an error
+        /// before reaching EOF, this will return an error. Otherwise, it will return
+        /// the number of bytes read.
+        ///
+        /// Since `Take::limit()` may return a value greater than the number of bytes
+        /// which can be read from the source, it's possible this function may fail
+        /// in the allocation phase even though allocating the number of bytes available
+        /// to read would have succeeded. In general, it is assumed that the callers
+        /// have accurate knowledge of the number of bytes of interest and have created
+        /// `src` accordingly.
+        #[inline]
+        fn try_read_to_end(&mut self, buf: &mut TryVec<u8>) -> io::Result<usize> {
+            try_read_up_to(self, self.limit(), buf)
+        }
+    }
+
+    /// Read up to `limit` bytes from `src`, placing them into `buf` and returning the
+    /// number of bytes read. Space for `limit` additional bytes is reserved in `buf`, so
+    /// this function will return an error if the allocation fails.
+    pub fn try_read_up_to<R: Read>(
+        src: &mut R,
+        limit: u64,
+        buf: &mut TryVec<u8>,
+    ) -> io::Result<usize> {
+        let additional = limit
+            .try_into()
+            .map_err(|e| io::Error::new(io::ErrorKind::Other, e))?;
+        buf.reserve(additional)
+            .map_err(|_| io::Error::new(io::ErrorKind::Other, "reserve allocation failed"))?;
+        let bytes_read = src.take(limit).read_to_end(&mut buf.inner)?;
+        Ok(bytes_read)
+    }
+
+    impl Write for TryVec<u8> {
+        fn write(&mut self, buf: &[u8]) -> io::Result<usize> {
+            self.extend_from_slice(buf)
+                .map_err(|_| io::Error::new(io::ErrorKind::Other, "extend_from_slice failed"))?;
+            Ok(buf.len())
+        }
+
+        #[inline(always)]
+        fn flush(&mut self) -> io::Result<()> {
+            Ok(())
+        }
+    }
+
+    #[cfg(test)]
+    mod tests {
+        use super::*;
+
+        #[test]
+        fn try_read_to_end() {
+            let mut src = b"1234567890".take(5);
+            let mut buf = TryVec::new();
+            src.try_read_to_end(&mut buf).unwrap();
+            assert_eq!(buf.len(), 5);
+            assert_eq!(buf, b"12345".as_ref());
+        }
+
+        #[test]
+        fn read_into_try_vec() {
+            let mut src = b"1234567890".take(5);
+            let buf = src.read_into_try_vec().unwrap();
+            assert_eq!(buf.len(), 5);
+            assert_eq!(buf, b"12345".as_ref());
+        }
+
+        #[test]
+        fn read_into_try_vec_oom() {
+            let mut src = b"1234567890".take(core::usize::MAX.try_into().expect("usize < u64"));
+            assert!(src.read_into_try_vec().is_err());
+        }
+
+        #[test]
+        fn try_read_up_to() {
+            let src = b"1234567890";
+            let mut buf = TryVec::new();
+            super::try_read_up_to(&mut src.as_ref(), 5, &mut buf).unwrap();
+            assert_eq!(buf.len(), 5);
+            assert_eq!(buf, b"12345".as_ref());
+        }
+
+        #[test]
+        fn try_read_up_to_oom() {
+            let src = b"1234567890";
+            let mut buf = TryVec::new();
+            let limit = core::usize::MAX.try_into().expect("usize < u64");
+            let res = super::try_read_up_to(&mut src.as_ref(), limit, &mut buf);
+            assert!(res.is_err());
+        }
+    }
+}
+
+impl<T: PartialEq> PartialEq<Vec<T>> for TryVec<T> {
+    #[inline(always)]
+    fn eq(&self, other: &Vec<T>) -> bool {
+        self.inner.eq(other)
+    }
+}
+
+impl<'a, T: PartialEq> PartialEq<&'a [T]> for TryVec<T> {
+    #[inline(always)]
+    fn eq(&self, other: &&[T]) -> bool {
+        self.inner.eq(other)
+    }
+}
+
+impl PartialEq<&str> for TryVec<u8> {
+    #[inline]
+    fn eq(&self, other: &&str) -> bool {
+        self.as_slice() == other.as_bytes()
+    }
+}
+
+impl core::convert::AsRef<[u8]> for TryVec<u8> {
+    #[inline(always)]
+    fn as_ref(&self) -> &[u8] {
+        self.inner.as_ref()
+    }
+}
+
+impl<T> core::convert::From<Vec<T>> for TryVec<T> {
+    #[inline(always)]
+    fn from(value: Vec<T>) -> Self {
+        Self { inner: value }
+    }
+}
+
+impl<T: TryClone> core::convert::TryFrom<&[T]> for TryVec<T> {
+    type Error = TryReserveError;
+
+    #[inline]
+    fn try_from(value: &[T]) -> Result<Self, Self::Error> {
+        let mut v = Self::new();
+        v.inner.try_extend_from_slice_no_copy(value)?;
+        Ok(v)
+    }
+}
+
+impl core::convert::TryFrom<&str> for TryVec<u8> {
+    type Error = TryReserveError;
+
+    #[inline]
+    fn try_from(value: &str) -> Result<Self, Self::Error> {
+        let mut v = Self::new();
+        v.extend_from_slice(value.as_bytes())?;
+        Ok(v)
+    }
+}
+
+impl<T> core::ops::Deref for TryVec<T> {
+    type Target = [T];
+
+    #[inline(always)]
+    fn deref(&self) -> &[T] {
+        self.inner.deref()
+    }
+}
+
+impl<T> core::ops::DerefMut for TryVec<T> {
+    fn deref_mut(&mut self) -> &mut [T] {
+        self.inner.deref_mut()
+    }
+}
+
+pub struct Iter<'a, T> {
+    inner: alloc::slice::Iter<'a, T>,
+}
+
+impl<'a, T> Iterator for Iter<'a, T> {
+    type Item = &'a T;
+
+    #[inline(always)]
+    fn next(&mut self) -> Option<Self::Item> {
+        self.inner.next()
+    }
+
+    #[inline(always)]
+    fn size_hint(&self) -> (usize, Option<usize>) {
+        self.inner.size_hint()
+    }
+}
+
+pub struct IterMut<'a, T> {
+    inner: alloc::slice::IterMut<'a, T>,
+}
+
+impl<'a, T> Iterator for IterMut<'a, T> {
+    type Item = &'a mut T;
+
+    #[inline(always)]
+    fn next(&mut self) -> Option<Self::Item> {
+        self.inner.next()
+    }
+
+    #[inline(always)]
+    fn size_hint(&self) -> (usize, Option<usize>) {
+        self.inner.size_hint()
+    }
+}
+
+/// Grow capacity exponentially
+#[cold]
+fn vec_try_reserve_for_growth<T>(v: &mut Vec<T>, additional: usize) -> Result<(), TryReserveError> {
+    // saturating, because can't use CapacityOverflow here if rust_1_57 flag is enabled
+    FallibleVec::try_reserve(v, additional.max(v.capacity().saturating_mul(2) - v.len()))
+}
+
+fn needs_to_grow<T>(v: &Vec<T>, len: usize) -> bool {
+    v.len().checked_add(len).map_or(true, |needed| needed > v.capacity())
+}
+
+#[cfg(not(any(feature = "unstable", feature = "rust_1_57")))]
+fn vec_try_reserve<T>(v: &mut Vec<T>, additional: usize) -> Result<(), TryReserveError> {
+    let available = v.capacity().checked_sub(v.len()).expect("capacity >= len");
+    if additional > available {
+        let increase = additional
+            .checked_sub(available)
+            .expect("additional > available");
+        let new_cap = v
+            .capacity()
+            .checked_add(increase)
+            .ok_or(TryReserveError::CapacityOverflow)?;
+        vec_try_extend(v, new_cap)?;
+        debug_assert!(v.capacity() == new_cap);
+    }
+
+    Ok(())
+}
+
+#[cfg(not(any(feature = "unstable", feature = "rust_1_57")))]
+fn vec_try_extend<T>(v: &mut Vec<T>, new_cap: usize) -> Result<(), TryReserveError> {
+    let old_len = v.len();
+    let old_cap: usize = v.capacity();
+
+    if old_cap >= new_cap {
+        return Ok(());
+    }
+
+    let elem_size = core::mem::size_of::<T>();
+    let new_alloc_size = new_cap
+        .checked_mul(elem_size)
+        .filter(|size| *size <= isize::MAX as usize)
+        .ok_or(TryReserveError::CapacityOverflow)?;
+
+    // required for alloc safety
+    // See https://doc.rust-lang.org/stable/std/alloc/trait.GlobalAlloc.html#safety-1
+    // Should be unreachable given prior `old_cap >= new_cap` check.
+    assert!(new_alloc_size > 0);
+
+    let align = core::mem::align_of::<T>();
+
+    let (new_ptr, layout) = {
+        if old_cap == 0 {
+            let layout = Layout::from_size_align(new_alloc_size, align).expect("Invalid layout");
+            let new_ptr = unsafe { alloc(layout) };
+            (new_ptr, layout)
+        } else {
+            let old_alloc_size = old_cap
+                .checked_mul(elem_size)
+                .ok_or(TryReserveError::CapacityOverflow)?;
+            let layout = Layout::from_size_align(old_alloc_size, align).expect("Invalid layout");
+            let new_ptr = unsafe { realloc(v.as_mut_ptr() as *mut u8, layout, new_alloc_size) };
+            (new_ptr, layout)
+        }
+    };
+
+    if new_ptr.is_null() {
+        return Err(TryReserveError::AllocError { layout });
+    }
+
+    let new_vec = unsafe { Vec::from_raw_parts(new_ptr.cast(), old_len, new_cap) };
+
+    core::mem::forget(core::mem::replace(v, new_vec));
+    Ok(())
+}
+
+impl<T> FallibleVec<T> for Vec<T> {
+    #[inline(always)]
+    fn try_reserve(&mut self, additional: usize) -> Result<(), TryReserveError> {
+        #[cfg(all(feature = "unstable", not(feature = "rust_1_57")))]
+        {
+            self.try_reserve(additional)
+        }
+
+        #[cfg(not(feature = "rust_1_57"))]
+        {
+            vec_try_reserve(self, additional)
+        }
+
+        #[cfg(feature = "rust_1_57")]
+        {
+            // TryReserveError is an opaque type in 1.57
+            self.try_reserve(additional).map_err(|_| {
+                crate::make_try_reserve_error(self.len(), additional, core::mem::size_of::<T>(), core::mem::align_of::<T>())
+            })
+        }
+    }
+
+    #[inline]
+    fn try_push(&mut self, elem: T) -> Result<(), TryReserveError> {
+        if self.len() == self.capacity() {
+            vec_try_reserve_for_growth(self, 1)?;
+        }
+        Ok(self.push(elem))
+    }
+
+    #[inline]
+    fn try_push_give_back(&mut self, elem: T) -> Result<(), (T, TryReserveError)> {
+        if self.len() == self.capacity() {
+            if let Err(e) = vec_try_reserve_for_growth(self, 1) {
+                return Err((elem, e));
+            }
+        }
+        Ok(self.push(elem))
+    }
+
+    #[inline]
+    fn try_with_capacity(capacity: usize) -> Result<Self, TryReserveError>
+    where
+        Self: core::marker::Sized,
+    {
+        let mut n = Self::new();
+        FallibleVec::try_reserve(&mut n, capacity)?;
+        Ok(n)
+    }
+
+    #[inline]
+    fn try_insert(&mut self, index: usize, element: T) -> Result<(), (T, TryReserveError)> {
+        if self.len() == self.capacity() {
+            if let Err(e) = vec_try_reserve_for_growth(self, 1) {
+                return Err((element, e));
+            }
+        }
+        Ok(self.insert(index, element))
+    }
+    #[inline]
+    fn try_append(&mut self, other: &mut Self) -> Result<(), TryReserveError> {
+        FallibleVec::try_reserve(self, other.len())?;
+        Ok(self.append(other))
+    }
+    fn try_resize(&mut self, new_len: usize, value: T) -> Result<(), TryReserveError>
+    where
+        T: Copy + Clone,
+    {
+        let len = self.len();
+        if new_len > len {
+            FallibleVec::try_reserve(self, new_len - len)?;
+        }
+        Ok(self.resize(new_len, value))
+    }
+    fn try_resize_with<F>(&mut self, new_len: usize, f: F) -> Result<(), TryReserveError>
+    where
+        F: FnMut() -> T,
+    {
+        let len = self.len();
+        if new_len > len {
+            FallibleVec::try_reserve(self, new_len - len)?;
+        }
+        Ok(self.resize_with(new_len, f))
+    }
+    fn try_resize_no_copy(&mut self, new_len: usize, value: T) -> Result<(), TryReserveError>
+    where
+        T: TryClone,
+    {
+        let len = self.len();
+
+        if new_len > len {
+            self.try_extend_with(new_len - len, TryExtendElement(value))
+        } else {
+            Ok(self.truncate(new_len))
+        }
+    }
+    #[inline]
+    fn try_extend_from_slice(&mut self, other: &[T]) -> Result<(), TryReserveError>
+    where
+        T: Clone,
+    {
+        if needs_to_grow(self, other.len()) {
+            vec_try_reserve_for_growth(self, other.len())?;
+        }
+        Ok(self.extend_from_slice(other))
+    }
+    fn try_extend_from_slice_no_copy(&mut self, other: &[T]) -> Result<(), TryReserveError>
+    where
+        T: TryClone,
+    {
+        if needs_to_grow(self, other.len()) {
+            vec_try_reserve_for_growth(self, other.len())?;
+        }
+        let mut len = self.len();
+        let mut iterator = other.iter();
+        while let Some(element) = iterator.next() {
+            unsafe {
+                core::ptr::write(self.get_unchecked_mut(len), element.try_clone()?);
+                // NB can't overflow since we would have had to alloc the address space
+                len += 1;
+                self.set_len(len);
+            }
+        }
+        Ok(())
+    }
+}
+
+trait ExtendWith<T> {
+    fn next(&mut self) -> Result<T, TryReserveError>;
+    fn last(self) -> T;
+}
+
+struct TryExtendElement<T: TryClone>(T);
+impl<T: TryClone> ExtendWith<T> for TryExtendElement<T> {
+    #[inline(always)]
+    fn next(&mut self) -> Result<T, TryReserveError> {
+        self.0.try_clone()
+    }
+    #[inline(always)]
+    fn last(self) -> T {
+        self.0
+    }
+}
+
+trait TryExtend<T> {
+    fn try_extend_with<E: ExtendWith<T>>(
+        &mut self,
+        n: usize,
+        value: E,
+    ) -> Result<(), TryReserveError>;
+}
+
+impl<T> TryExtend<T> for Vec<T> {
+    /// Extend the vector by `n` values, using the given generator.
+    fn try_extend_with<E: ExtendWith<T>>(
+        &mut self,
+        n: usize,
+        mut value: E,
+    ) -> Result<(), TryReserveError> {
+        if needs_to_grow(self, n) {
+            vec_try_reserve_for_growth(self, n)?;
+        }
+
+        unsafe {
+            let mut ptr = self.as_mut_ptr().add(self.len());
+
+            let mut local_len = self.len();
+            // Write all elements except the last one
+            for _ in 1..n {
+                core::ptr::write(ptr, value.next()?);
+                ptr = ptr.offset(1);
+                // Increment the length in every step in case next() panics
+                local_len += 1;
+                self.set_len(local_len);
+            }
+
+            if n > 0 {
+                // We can write the last element directly without cloning needlessly
+                core::ptr::write(ptr, value.last());
+                local_len += 1;
+                self.set_len(local_len);
+            }
+
+            // len set by scope guard
+        }
+        Ok(())
+    }
+}
+
+trait Truncate {
+    fn truncate(&mut self, len: usize);
+}
+
+impl<T> Truncate for Vec<T> {
+    fn truncate(&mut self, len: usize) {
+        let current_len = self.len();
+        unsafe {
+            let mut ptr = self.as_mut_ptr().add(current_len);
+            // Set the final length at the end, keeping in mind that
+            // dropping an element might panic. Works around a missed
+            // optimization, as seen in the following issue:
+            // https://github.com/rust-lang/rust/issues/51802
+            let mut local_len = self.len();
+
+            // drop any extra elements
+            for _ in len..current_len {
+                ptr = ptr.offset(-1);
+                core::ptr::drop_in_place(ptr);
+                local_len -= 1;
+                self.set_len(local_len);
+            }
+        }
+    }
+}
+
+/// try creating a vec from an `elem` cloned `n` times, see std::from_elem
+#[cfg(feature = "unstable")]
+pub fn try_from_elem<T: TryClone>(elem: T, n: usize) -> Result<Vec<T>, TryReserveError> {
+    <T as SpecFromElem>::try_from_elem(elem, n)
+}
+
+// Specialization trait used for Vec::from_elem
+#[cfg(feature = "unstable")]
+trait SpecFromElem: Sized {
+    fn try_from_elem(elem: Self, n: usize) -> Result<Vec<Self>, TryReserveError>;
+}
+
+#[cfg(feature = "unstable")]
+impl<T: TryClone> SpecFromElem for T {
+    default fn try_from_elem(elem: Self, n: usize) -> Result<Vec<T>, TryReserveError> {
+        let mut v = Vec::new();
+        v.try_resize_no_copy(n, elem)?;
+        Ok(v)
+    }
+}
+
+#[cfg(feature = "unstable")]
+impl SpecFromElem for u8 {
+    #[inline]
+    fn try_from_elem(elem: u8, n: usize) -> Result<Vec<u8>, TryReserveError> {
+        unsafe {
+            let mut v: Vec<u8> = FallibleVec::try_with_capacity(n)?;
+            core::ptr::write_bytes(v.as_mut_ptr(), elem, n);
+            v.set_len(n);
+            Ok(v)
+        }
+    }
+}
+
+impl<T: TryClone> TryClone for Vec<T> {
+    #[inline]
+    fn try_clone(&self) -> Result<Self, TryReserveError>
+    where
+        Self: core::marker::Sized,
+    {
+        let mut v = Vec::new();
+        v.try_extend_from_slice_no_copy(self)?;
+        Ok(v)
+    }
+}
+
+pub trait TryFromIterator<I>: Sized {
+    fn try_from_iterator<T: IntoIterator<Item = I>>(iterator: T) -> Result<Self, TryReserveError>;
+}
+
+impl<I> TryFromIterator<I> for Vec<I> {
+    fn try_from_iterator<T: IntoIterator<Item = I>>(iterator: T) -> Result<Self, TryReserveError>
+    where
+        T: IntoIterator<Item = I>,
+    {
+        let mut new = Self::new();
+        for i in iterator {
+            new.try_push(i)?;
+        }
+        Ok(new)
+    }
+}
+
+pub trait TryCollect<I> {
+    fn try_collect<C: TryFromIterator<I>>(self) -> Result<C, TryReserveError>;
+}
+
+impl<I, T> TryCollect<I> for T
+where
+    T: IntoIterator<Item = I>,
+{
+    #[inline(always)]
+    fn try_collect<C: TryFromIterator<I>>(self) -> Result<C, TryReserveError> {
+        C::try_from_iterator(self)
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    #[cfg(feature = "unstable")]
+    fn vec() {
+        // let v: Vec<u8> = from_elem(1, 10);
+        let v: Vec<Vec<u8>> = try_vec![try_vec![42; 10].unwrap(); 100].unwrap();
+        println!("{:?}", v);
+        let v2 = try_vec![0, 1, 2];
+        println!("{:?}", v2);
+        assert_eq!(2 + 2, 4);
+    }
+
+    #[test]
+    fn try_clone_vec() {
+        // let v: Vec<u8> = from_elem(1, 10);
+        let v = vec![42; 100];
+        assert_eq!(v.try_clone().unwrap(), v);
+    }
+
+    #[test]
+    fn try_clone_oom() {
+        let layout = Layout::new::<u8>();
+        let v =
+            unsafe { Vec::<u8>::from_raw_parts(alloc(layout), core::isize::MAX as usize, core::isize::MAX as usize) };
+        assert!(v.try_clone().is_err());
+    }
+
+    #[test]
+    fn tryvec_try_clone_oom() {
+        let layout = Layout::new::<u8>();
+        let inner =
+            unsafe { Vec::<u8>::from_raw_parts(alloc(layout), core::isize::MAX as usize, core::isize::MAX as usize) };
+        let tv = TryVec { inner };
+        assert!(tv.try_clone().is_err());
+    }
+
+    // #[test]
+    // fn try_out_of_mem() {
+    //     let v = try_vec![42_u8; 1000000000];
+    //     assert_eq!(v.try_clone().unwrap(), v);
+    // }
+
+    #[test]
+    fn oom() {
+        let mut vec: Vec<char> = Vec::new();
+        match FallibleVec::try_reserve(&mut vec, core::usize::MAX / std::mem::size_of::<char>()) {
+            Ok(_) => panic!("it should be OOM"),
+            _ => (),
+        }
+        match FallibleVec::try_reserve(&mut vec, core::usize::MAX) {
+            Ok(_) => panic!("it should be OOM"),
+            _ => (),
+        }
+    }
+
+    #[test]
+    fn tryvec_oom() {
+        let mut vec: TryVec<char> = TryVec::new();
+        match vec.reserve(core::usize::MAX / std::mem::size_of::<char>()) {
+            Ok(_) => panic!("it should be OOM"),
+            _ => (),
+        }
+        match vec.reserve(core::usize::MAX) {
+            Ok(_) => panic!("it should be OOM"),
+            _ => (),
+        }
+    }
+
+    #[test]
+    fn try_reserve() {
+        let mut vec: Vec<_> = vec![1];
+        let additional_room = vec.capacity() - vec.len();
+        let additional = additional_room + 1;
+        let old_cap = vec.capacity();
+        FallibleVec::try_reserve(&mut vec, additional).unwrap();
+        assert!(vec.capacity() > old_cap);
+    }
+
+    #[test]
+    fn tryvec_reserve() {
+        let mut vec: TryVec<_> = vec![1].into();
+        let old_cap = vec.inner.capacity();
+        let new_cap = old_cap + 1;
+        vec.reserve(new_cap).unwrap();
+        assert!(vec.inner.capacity() >= new_cap);
+    }
+
+    #[test]
+    fn try_reserve_idempotent() {
+        let mut vec: Vec<_> = vec![1];
+        let additional_room = vec.capacity() - vec.len();
+        let additional = additional_room + 1;
+        FallibleVec::try_reserve(&mut vec, additional).unwrap();
+        let cap_after_reserve = vec.capacity();
+        FallibleVec::try_reserve(&mut vec, additional).unwrap();
+        assert_eq!(vec.capacity(), cap_after_reserve);
+    }
+
+    #[test]
+    fn tryvec_reserve_idempotent() {
+        let mut vec: TryVec<_> = vec![1].into();
+        let old_cap = vec.inner.capacity();
+        let new_cap = old_cap + 1;
+        vec.reserve(new_cap).unwrap();
+        let cap_after_reserve = vec.inner.capacity();
+        vec.reserve(new_cap).unwrap();
+        assert_eq!(cap_after_reserve, vec.inner.capacity());
+    }
+
+    #[test]
+    fn capacity_overflow() {
+        let mut vec: Vec<_> = vec![1];
+        match FallibleVec::try_reserve(&mut vec, core::usize::MAX) {
+            Ok(_) => panic!("capacity calculation should overflow"),
+            _ => (),
+        }
+    }
+
+    #[test]
+    fn tryvec_capacity_overflow() {
+        let mut vec: TryVec<_> = vec![1].into();
+        match vec.reserve(core::usize::MAX) {
+            Ok(_) => panic!("capacity calculation should overflow"),
+            _ => (),
+        }
+    }
+
+    #[test]
+    fn extend_from_slice() {
+        let mut vec: Vec<u8> = b"foo".as_ref().into();
+        vec.shrink_to_fit();
+        vec.reserve(5);
+        assert_eq!(8, vec.capacity());
+        vec.try_extend_from_slice(b"bar").unwrap();
+        assert_eq!(vec, b"foobar".as_ref());
+        vec.try_extend_from_slice(b"1").unwrap();
+        assert_eq!(vec, b"foobar1".as_ref());
+        assert_eq!(8, vec.capacity());
+        vec.try_extend_from_slice(b"11").unwrap();
+        assert_eq!(16, vec.capacity());
+    }
+
+    #[test]
+    fn tryvec_extend_from_slice() {
+        let mut vec: TryVec<u8> = b"foo".as_ref().try_into().unwrap();
+        vec.extend_from_slice(b"bar").unwrap();
+        assert_eq!(vec, b"foobar".as_ref());
+    }
+
+    #[test]
+    #[cfg(not(any(feature = "unstable", feature = "rust_1_57")))]
+    fn try_extend_zst() {
+        let mut vec: Vec<()> = Vec::new();
+        assert_eq!(vec.capacity(), core::usize::MAX);
+        assert!(vec_try_extend(&mut vec, 10).is_ok());
+        assert!(vec_try_extend(&mut vec, core::usize::MAX).is_ok());
+    }
+
+    #[test]
+    fn try_reserve_zst() {
+        let mut vec: Vec<()> = Vec::new();
+        assert!(FallibleVec::try_reserve(&mut vec, core::usize::MAX).is_ok());
+    }
+}