Initial import of rayon-1.5.0.

Bug: 155309706
Change-Id: I6ff7de1cb89d093d7938abf78d586ed76da85b0d

3 files changed, 715 insertions, 0 deletions

diff --git a/src/iter/collect/consumer.rs b/src/iter/collect/consumer.rs
new file mode 100644
index 0000000..689f29c
--- /dev/null
+++ b/src/iter/collect/consumer.rs
@@ -0,0 +1,159 @@
+use super::super::plumbing::*;
+use std::marker::PhantomData;
+use std::ptr;
+use std::slice;
+
+pub(super) struct CollectConsumer<'c, T: Send> {
+    /// A slice covering the target memory, not yet initialized!
+    target: &'c mut [T],
+}
+
+pub(super) struct CollectFolder<'c, T: Send> {
+    /// The folder writes into `result` and must extend the result
+    /// up to exactly this number of elements.
+    final_len: usize,
+
+    /// The current written-to part of our slice of the target
+    result: CollectResult<'c, T>,
+}
+
+impl<'c, T: Send + 'c> CollectConsumer<'c, T> {
+    /// The target memory is considered uninitialized, and will be
+    /// overwritten without reading or dropping existing values.
+    pub(super) fn new(target: &'c mut [T]) -> Self {
+        CollectConsumer { target }
+    }
+}
+
+/// CollectResult represents an initialized part of the target slice.
+///
+/// This is a proxy owner of the elements in the slice; when it drops,
+/// the elements will be dropped, unless its ownership is released before then.
+#[must_use]
+pub(super) struct CollectResult<'c, T> {
+    start: *mut T,
+    len: usize,
+    invariant_lifetime: PhantomData<&'c mut &'c mut [T]>,
+}
+
+unsafe impl<'c, T> Send for CollectResult<'c, T> where T: Send {}
+
+impl<'c, T> CollectResult<'c, T> {
+    /// The current length of the collect result
+    pub(super) fn len(&self) -> usize {
+        self.len
+    }
+
+    /// Release ownership of the slice of elements, and return the length
+    pub(super) fn release_ownership(mut self) -> usize {
+        let ret = self.len;
+        self.len = 0;
+        ret
+    }
+}
+
+impl<'c, T> Drop for CollectResult<'c, T> {
+    fn drop(&mut self) {
+        // Drop the first `self.len` elements, which have been recorded
+        // to be initialized by the folder.
+        unsafe {
+            ptr::drop_in_place(slice::from_raw_parts_mut(self.start, self.len));
+        }
+    }
+}
+
+impl<'c, T: Send + 'c> Consumer<T> for CollectConsumer<'c, T> {
+    type Folder = CollectFolder<'c, T>;
+    type Reducer = CollectReducer;
+    type Result = CollectResult<'c, T>;
+
+    fn split_at(self, index: usize) -> (Self, Self, CollectReducer) {
+        let CollectConsumer { target } = self;
+
+        // Produce new consumers. Normal slicing ensures that the
+        // memory range given to each consumer is disjoint.
+        let (left, right) = target.split_at_mut(index);
+        (
+            CollectConsumer::new(left),
+            CollectConsumer::new(right),
+            CollectReducer,
+        )
+    }
+
+    fn into_folder(self) -> CollectFolder<'c, T> {
+        // Create a folder that consumes values and writes them
+        // into target. The initial result has length 0.
+        CollectFolder {
+            final_len: self.target.len(),
+            result: CollectResult {
+                start: self.target.as_mut_ptr(),
+                len: 0,
+                invariant_lifetime: PhantomData,
+            },
+        }
+    }
+
+    fn full(&self) -> bool {
+        false
+    }
+}
+
+impl<'c, T: Send + 'c> Folder<T> for CollectFolder<'c, T> {
+    type Result = CollectResult<'c, T>;
+
+    fn consume(mut self, item: T) -> CollectFolder<'c, T> {
+        if self.result.len >= self.final_len {
+            panic!("too many values pushed to consumer");
+        }
+
+        // Compute target pointer and write to it, and
+        // extend the current result by one element
+        unsafe {
+            self.result.start.add(self.result.len).write(item);
+            self.result.len += 1;
+        }
+
+        self
+    }
+
+    fn complete(self) -> Self::Result {
+        // NB: We don't explicitly check that the local writes were complete,
+        // but Collect will assert the total result length in the end.
+        self.result
+    }
+
+    fn full(&self) -> bool {
+        false
+    }
+}
+
+/// Pretend to be unindexed for `special_collect_into_vec`,
+/// but we should never actually get used that way...
+impl<'c, T: Send + 'c> UnindexedConsumer<T> for CollectConsumer<'c, T> {
+    fn split_off_left(&self) -> Self {
+        unreachable!("CollectConsumer must be indexed!")
+    }
+    fn to_reducer(&self) -> Self::Reducer {
+        CollectReducer
+    }
+}
+
+/// CollectReducer combines adjacent chunks; the result must always
+/// be contiguous so that it is one combined slice.
+pub(super) struct CollectReducer;
+
+impl<'c, T> Reducer<CollectResult<'c, T>> for CollectReducer {
+    fn reduce(
+        self,
+        mut left: CollectResult<'c, T>,
+        right: CollectResult<'c, T>,
+    ) -> CollectResult<'c, T> {
+        // Merge if the CollectResults are adjacent and in left to right order
+        // else: drop the right piece now and total length will end up short in the end,
+        // when the correctness of the collected result is asserted.
+        if left.start.wrapping_add(left.len) == right.start {
+            left.len += right.release_ownership();
+        }
+        left
+    }
+}
diff --git a/src/iter/collect/mod.rs b/src/iter/collect/mod.rs
new file mode 100644
index 0000000..e18298e
--- /dev/null
+++ b/src/iter/collect/mod.rs
@@ -0,0 +1,171 @@
+use super::{IndexedParallelIterator, IntoParallelIterator, ParallelExtend, ParallelIterator};
+use std::slice;
+
+mod consumer;
+use self::consumer::CollectConsumer;
+use self::consumer::CollectResult;
+use super::unzip::unzip_indexed;
+
+mod test;
+
+/// Collects the results of the exact iterator into the specified vector.
+///
+/// This is called by `IndexedParallelIterator::collect_into_vec`.
+pub(super) fn collect_into_vec<I, T>(pi: I, v: &mut Vec<T>)
+where
+    I: IndexedParallelIterator<Item = T>,
+    T: Send,
+{
+    v.truncate(0); // clear any old data
+    let len = pi.len();
+    Collect::new(v, len).with_consumer(|consumer| pi.drive(consumer));
+}
+
+/// Collects the results of the iterator into the specified vector.
+///
+/// Technically, this only works for `IndexedParallelIterator`, but we're faking a
+/// bit of specialization here until Rust can do that natively.  Callers are
+/// using `opt_len` to find the length before calling this, and only exact
+/// iterators will return anything but `None` there.
+///
+/// Since the type system doesn't understand that contract, we have to allow
+/// *any* `ParallelIterator` here, and `CollectConsumer` has to also implement
+/// `UnindexedConsumer`.  That implementation panics `unreachable!` in case
+/// there's a bug where we actually do try to use this unindexed.
+fn special_extend<I, T>(pi: I, len: usize, v: &mut Vec<T>)
+where
+    I: ParallelIterator<Item = T>,
+    T: Send,
+{
+    Collect::new(v, len).with_consumer(|consumer| pi.drive_unindexed(consumer));
+}
+
+/// Unzips the results of the exact iterator into the specified vectors.
+///
+/// This is called by `IndexedParallelIterator::unzip_into_vecs`.
+pub(super) fn unzip_into_vecs<I, A, B>(pi: I, left: &mut Vec<A>, right: &mut Vec<B>)
+where
+    I: IndexedParallelIterator<Item = (A, B)>,
+    A: Send,
+    B: Send,
+{
+    // clear any old data
+    left.truncate(0);
+    right.truncate(0);
+
+    let len = pi.len();
+    Collect::new(right, len).with_consumer(|right_consumer| {
+        let mut right_result = None;
+        Collect::new(left, len).with_consumer(|left_consumer| {
+            let (left_r, right_r) = unzip_indexed(pi, left_consumer, right_consumer);
+            right_result = Some(right_r);
+            left_r
+        });
+        right_result.unwrap()
+    });
+}
+
+/// Manage the collection vector.
+struct Collect<'c, T: Send> {
+    vec: &'c mut Vec<T>,
+    len: usize,
+}
+
+impl<'c, T: Send + 'c> Collect<'c, T> {
+    fn new(vec: &'c mut Vec<T>, len: usize) -> Self {
+        Collect { vec, len }
+    }
+
+    /// Create a consumer on the slice of memory we are collecting into.
+    ///
+    /// The consumer needs to be used inside the scope function, and the
+    /// complete collect result passed back.
+    ///
+    /// This method will verify the collect result, and panic if the slice
+    /// was not fully written into. Otherwise, in the successful case,
+    /// the vector is complete with the collected result.
+    fn with_consumer<F>(mut self, scope_fn: F)
+    where
+        F: FnOnce(CollectConsumer<'_, T>) -> CollectResult<'_, T>,
+    {
+        unsafe {
+            let slice = Self::reserve_get_tail_slice(&mut self.vec, self.len);
+            let result = scope_fn(CollectConsumer::new(slice));
+
+            // The CollectResult represents a contiguous part of the
+            // slice, that has been written to.
+            // On unwind here, the CollectResult will be dropped.
+            // If some producers on the way did not produce enough elements,
+            // partial CollectResults may have been dropped without
+            // being reduced to the final result, and we will see
+            // that as the length coming up short.
+            //
+            // Here, we assert that `slice` is fully initialized. This is
+            // checked by the following assert, which verifies if a
+            // complete CollectResult was produced; if the length is
+            // correct, it is necessarily covering the target slice.
+            // Since we know that the consumer cannot have escaped from
+            // `drive` (by parametricity, essentially), we know that any
+            // stores that will happen, have happened. Unless some code is buggy,
+            // that means we should have seen `len` total writes.
+            let actual_writes = result.len();
+            assert!(
+                actual_writes == self.len,
+                "expected {} total writes, but got {}",
+                self.len,
+                actual_writes
+            );
+
+            // Release the result's mutable borrow and "proxy ownership"
+            // of the elements, before the vector takes it over.
+            result.release_ownership();
+
+            let new_len = self.vec.len() + self.len;
+            self.vec.set_len(new_len);
+        }
+    }
+
+    /// Reserve space for `len` more elements in the vector,
+    /// and return a slice to the uninitialized tail of the vector
+    ///
+    /// Safety: The tail slice is uninitialized
+    unsafe fn reserve_get_tail_slice(vec: &mut Vec<T>, len: usize) -> &mut [T] {
+        // Reserve the new space.
+        vec.reserve(len);
+
+        // Get a correct borrow, then extend it for the newly added length.
+        let start = vec.len();
+        let slice = &mut vec[start..];
+        slice::from_raw_parts_mut(slice.as_mut_ptr(), len)
+    }
+}
+
+/// Extends a vector with items from a parallel iterator.
+impl<T> ParallelExtend<T> for Vec<T>
+where
+    T: Send,
+{
+    fn par_extend<I>(&mut self, par_iter: I)
+    where
+        I: IntoParallelIterator<Item = T>,
+    {
+        // See the vec_collect benchmarks in rayon-demo for different strategies.
+        let par_iter = par_iter.into_par_iter();
+        match par_iter.opt_len() {
+            Some(len) => {
+                // When Rust gets specialization, we can get here for indexed iterators
+                // without relying on `opt_len`.  Until then, `special_extend()` fakes
+                // an unindexed mode on the promise that `opt_len()` is accurate.
+                special_extend(par_iter, len, self);
+            }
+            None => {
+                // This works like `extend`, but `Vec::append` is more efficient.
+                let list = super::extend::collect(par_iter);
+                self.reserve(super::extend::len(&list));
+                for mut vec in list {
+                    self.append(&mut vec);
+                }
+            }
+        }
+    }
+}
diff --git a/src/iter/collect/test.rs b/src/iter/collect/test.rs
new file mode 100644
index 0000000..00c16c4
--- /dev/null
+++ b/src/iter/collect/test.rs
@@ -0,0 +1,385 @@
+#![cfg(test)]
+#![allow(unused_assignments)]
+
+// These tests are primarily targeting "abusive" producers that will
+// try to drive the "collect consumer" incorrectly. These should
+// result in panics.
+
+use super::Collect;
+use crate::iter::plumbing::*;
+use rayon_core::join;
+
+use std::fmt;
+use std::panic;
+use std::sync::atomic::{AtomicUsize, Ordering};
+use std::thread::Result as ThreadResult;
+
+/// Promises to produce 2 items, but then produces 3.  Does not do any
+/// splits at all.
+#[test]
+#[should_panic(expected = "too many values")]
+fn produce_too_many_items() {
+    let mut v = vec![];
+    Collect::new(&mut v, 2).with_consumer(|consumer| {
+        let mut folder = consumer.into_folder();
+        folder = folder.consume(22);
+        folder = folder.consume(23);
+        folder.consume(24);
+        unreachable!("folder does not complete")
+    });
+}
+
+/// Produces fewer items than promised. Does not do any
+/// splits at all.
+#[test]
+#[should_panic(expected = "expected 5 total writes, but got 2")]
+fn produce_fewer_items() {
+    let mut v = vec![];
+    let collect = Collect::new(&mut v, 5);
+    collect.with_consumer(|consumer| {
+        let mut folder = consumer.into_folder();
+        folder = folder.consume(22);
+        folder = folder.consume(23);
+        folder.complete()
+    });
+}
+
+// Complete is not called by the consumer. Hence,the collection vector is not fully initialized.
+#[test]
+#[should_panic(expected = "expected 4 total writes, but got 2")]
+fn left_produces_items_with_no_complete() {
+    let mut v = vec![];
+    let collect = Collect::new(&mut v, 4);
+    collect.with_consumer(|consumer| {
+        let (left_consumer, right_consumer, _) = consumer.split_at(2);
+        let mut left_folder = left_consumer.into_folder();
+        let mut right_folder = right_consumer.into_folder();
+        left_folder = left_folder.consume(0).consume(1);
+        right_folder = right_folder.consume(2).consume(3);
+        right_folder.complete()
+    });
+}
+
+// Complete is not called by the right consumer. Hence,the
+// collection vector is not fully initialized.
+#[test]
+#[should_panic(expected = "expected 4 total writes, but got 2")]
+fn right_produces_items_with_no_complete() {
+    let mut v = vec![];
+    let collect = Collect::new(&mut v, 4);
+    collect.with_consumer(|consumer| {
+        let (left_consumer, right_consumer, _) = consumer.split_at(2);
+        let mut left_folder = left_consumer.into_folder();
+        let mut right_folder = right_consumer.into_folder();
+        left_folder = left_folder.consume(0).consume(1);
+        right_folder = right_folder.consume(2).consume(3);
+        left_folder.complete()
+    });
+}
+
+// Complete is not called by the consumer. Hence,the collection vector is not fully initialized.
+#[test]
+fn produces_items_with_no_complete() {
+    let counter = DropCounter::default();
+    let mut v = vec![];
+    let panic_result = panic::catch_unwind(panic::AssertUnwindSafe(|| {
+        let collect = Collect::new(&mut v, 2);
+        collect.with_consumer(|consumer| {
+            let mut folder = consumer.into_folder();
+            folder = folder.consume(counter.element());
+            folder = folder.consume(counter.element());
+            panic!("folder does not complete");
+        });
+    }));
+    assert!(v.is_empty());
+    assert_is_panic_with_message(&panic_result, "folder does not complete");
+    counter.assert_drop_count();
+}
+
+// The left consumer produces too many items while the right
+// consumer produces correct number.
+#[test]
+#[should_panic(expected = "too many values")]
+fn left_produces_too_many_items() {
+    let mut v = vec![];
+    let collect = Collect::new(&mut v, 4);
+    collect.with_consumer(|consumer| {
+        let (left_consumer, right_consumer, _) = consumer.split_at(2);
+        let mut left_folder = left_consumer.into_folder();
+        let mut right_folder = right_consumer.into_folder();
+        left_folder = left_folder.consume(0).consume(1).consume(2);
+        right_folder = right_folder.consume(2).consume(3);
+        let _ = right_folder.complete();
+        unreachable!("folder does not complete");
+    });
+}
+
+// The right consumer produces too many items while the left
+// consumer produces correct number.
+#[test]
+#[should_panic(expected = "too many values")]
+fn right_produces_too_many_items() {
+    let mut v = vec![];
+    let collect = Collect::new(&mut v, 4);
+    collect.with_consumer(|consumer| {
+        let (left_consumer, right_consumer, _) = consumer.split_at(2);
+        let mut left_folder = left_consumer.into_folder();
+        let mut right_folder = right_consumer.into_folder();
+        left_folder = left_folder.consume(0).consume(1);
+        right_folder = right_folder.consume(2).consume(3).consume(4);
+        let _ = left_folder.complete();
+        unreachable!("folder does not complete");
+    });
+}
+
+// The left consumer produces fewer items while the right
+// consumer produces correct number.
+#[test]
+#[should_panic(expected = "expected 4 total writes, but got 1")]
+fn left_produces_fewer_items() {
+    let mut v = vec![];
+    let collect = Collect::new(&mut v, 4);
+    collect.with_consumer(|consumer| {
+        let reducer = consumer.to_reducer();
+        let (left_consumer, right_consumer, _) = consumer.split_at(2);
+        let mut left_folder = left_consumer.into_folder();
+        let mut right_folder = right_consumer.into_folder();
+        left_folder = left_folder.consume(0);
+        right_folder = right_folder.consume(2).consume(3);
+        let left_result = left_folder.complete();
+        let right_result = right_folder.complete();
+        reducer.reduce(left_result, right_result)
+    });
+}
+
+// The left and right consumer produce the correct number but
+// only left result is returned
+#[test]
+#[should_panic(expected = "expected 4 total writes, but got 2")]
+fn only_left_result() {
+    let mut v = vec![];
+    let collect = Collect::new(&mut v, 4);
+    collect.with_consumer(|consumer| {
+        let (left_consumer, right_consumer, _) = consumer.split_at(2);
+        let mut left_folder = left_consumer.into_folder();
+        let mut right_folder = right_consumer.into_folder();
+        left_folder = left_folder.consume(0).consume(1);
+        right_folder = right_folder.consume(2).consume(3);
+        let left_result = left_folder.complete();
+        let _ = right_folder.complete();
+        left_result
+    });
+}
+
+// The left and right consumer produce the correct number but
+// only right result is returned
+#[test]
+#[should_panic(expected = "expected 4 total writes, but got 2")]
+fn only_right_result() {
+    let mut v = vec![];
+    let collect = Collect::new(&mut v, 4);
+    collect.with_consumer(|consumer| {
+        let (left_consumer, right_consumer, _) = consumer.split_at(2);
+        let mut left_folder = left_consumer.into_folder();
+        let mut right_folder = right_consumer.into_folder();
+        left_folder = left_folder.consume(0).consume(1);
+        right_folder = right_folder.consume(2).consume(3);
+        let _ = left_folder.complete();
+        right_folder.complete()
+    });
+}
+
+// The left and right consumer produce the correct number but reduce
+// in the wrong order.
+#[test]
+#[should_panic(expected = "expected 4 total writes, but got 2")]
+fn reducer_does_not_preserve_order() {
+    let mut v = vec![];
+    let collect = Collect::new(&mut v, 4);
+    collect.with_consumer(|consumer| {
+        let reducer = consumer.to_reducer();
+        let (left_consumer, right_consumer, _) = consumer.split_at(2);
+        let mut left_folder = left_consumer.into_folder();
+        let mut right_folder = right_consumer.into_folder();
+        left_folder = left_folder.consume(0).consume(1);
+        right_folder = right_folder.consume(2).consume(3);
+        let left_result = left_folder.complete();
+        let right_result = right_folder.complete();
+        reducer.reduce(right_result, left_result)
+    });
+}
+
+// The right consumer produces fewer items while the left
+// consumer produces correct number.
+#[test]
+#[should_panic(expected = "expected 4 total writes, but got 3")]
+fn right_produces_fewer_items() {
+    let mut v = vec![];
+    let collect = Collect::new(&mut v, 4);
+    collect.with_consumer(|consumer| {
+        let reducer = consumer.to_reducer();
+        let (left_consumer, right_consumer, _) = consumer.split_at(2);
+        let mut left_folder = left_consumer.into_folder();
+        let mut right_folder = right_consumer.into_folder();
+        left_folder = left_folder.consume(0).consume(1);
+        right_folder = right_folder.consume(2);
+        let left_result = left_folder.complete();
+        let right_result = right_folder.complete();
+        reducer.reduce(left_result, right_result)
+    });
+}
+
+// The left consumer panics and the right stops short, like `panic_fuse()`.
+// We should get the left panic without finishing `Collect::with_consumer`.
+#[test]
+#[should_panic(expected = "left consumer panic")]
+fn left_panics() {
+    let mut v = vec![];
+    let collect = Collect::new(&mut v, 4);
+    collect.with_consumer(|consumer| {
+        let reducer = consumer.to_reducer();
+        let (left_consumer, right_consumer, _) = consumer.split_at(2);
+        let (left_result, right_result) = join(
+            || {
+                let mut left_folder = left_consumer.into_folder();
+                left_folder = left_folder.consume(0);
+                panic!("left consumer panic");
+            },
+            || {
+                let mut right_folder = right_consumer.into_folder();
+                right_folder = right_folder.consume(2);
+                right_folder.complete() // early return
+            },
+        );
+        reducer.reduce(left_result, right_result)
+    });
+    unreachable!();
+}
+
+// The right consumer panics and the left stops short, like `panic_fuse()`.
+// We should get the right panic without finishing `Collect::with_consumer`.
+#[test]
+#[should_panic(expected = "right consumer panic")]
+fn right_panics() {
+    let mut v = vec![];
+    let collect = Collect::new(&mut v, 4);
+    collect.with_consumer(|consumer| {
+        let reducer = consumer.to_reducer();
+        let (left_consumer, right_consumer, _) = consumer.split_at(2);
+        let (left_result, right_result) = join(
+            || {
+                let mut left_folder = left_consumer.into_folder();
+                left_folder = left_folder.consume(0);
+                left_folder.complete() // early return
+            },
+            || {
+                let mut right_folder = right_consumer.into_folder();
+                right_folder = right_folder.consume(2);
+                panic!("right consumer panic");
+            },
+        );
+        reducer.reduce(left_result, right_result)
+    });
+    unreachable!();
+}
+
+// The left consumer produces fewer items while the right
+// consumer produces correct number; check that created elements are dropped
+#[test]
+fn left_produces_fewer_items_drops() {
+    let counter = DropCounter::default();
+    let mut v = vec![];
+    let panic_result = panic::catch_unwind(panic::AssertUnwindSafe(|| {
+        let collect = Collect::new(&mut v, 4);
+        collect.with_consumer(|consumer| {
+            let reducer = consumer.to_reducer();
+            let (left_consumer, right_consumer, _) = consumer.split_at(2);
+            let mut left_folder = left_consumer.into_folder();
+            let mut right_folder = right_consumer.into_folder();
+            left_folder = left_folder.consume(counter.element());
+            right_folder = right_folder
+                .consume(counter.element())
+                .consume(counter.element());
+            let left_result = left_folder.complete();
+            let right_result = right_folder.complete();
+            reducer.reduce(left_result, right_result)
+        });
+    }));
+    assert!(v.is_empty());
+    assert_is_panic_with_message(&panic_result, "expected 4 total writes, but got 1");
+    counter.assert_drop_count();
+}
+
+/// This counter can create elements, and then count and verify
+/// the number of which have actually been dropped again.
+#[derive(Default)]
+struct DropCounter {
+    created: AtomicUsize,
+    dropped: AtomicUsize,
+}
+
+struct Element<'a>(&'a AtomicUsize);
+
+impl DropCounter {
+    fn created(&self) -> usize {
+        self.created.load(Ordering::SeqCst)
+    }
+
+    fn dropped(&self) -> usize {
+        self.dropped.load(Ordering::SeqCst)
+    }
+
+    fn element(&self) -> Element<'_> {
+        self.created.fetch_add(1, Ordering::SeqCst);
+        Element(&self.dropped)
+    }
+
+    fn assert_drop_count(&self) {
+        assert_eq!(
+            self.created(),
+            self.dropped(),
+            "Expected {} dropped elements, but found {}",
+            self.created(),
+            self.dropped()
+        );
+    }
+}
+
+impl<'a> Drop for Element<'a> {
+    fn drop(&mut self) {
+        self.0.fetch_add(1, Ordering::SeqCst);
+    }
+}
+
+/// Assert that the result from catch_unwind is a panic that contains expected message
+fn assert_is_panic_with_message<T>(result: &ThreadResult<T>, expected: &str)
+where
+    T: fmt::Debug,
+{
+    match result {
+        Ok(value) => {
+            panic!(
+                "assertion failure: Expected panic, got successful {:?}",
+                value
+            );
+        }
+        Err(error) => {
+            let message_str = error.downcast_ref::<&'static str>().cloned();
+            let message_string = error.downcast_ref::<String>().map(String::as_str);
+            if let Some(message) = message_str.or(message_string) {
+                if !message.contains(expected) {
+                    panic!(
+                        "assertion failure: Expected {:?}, but found panic with {:?}",
+                        expected, message
+                    );
+                }
+            // assertion passes
+            } else {
+                panic!(
+                    "assertion failure: Expected {:?}, but found panic with unknown value",
+                    expected
+                );
+            }
+        }
+    }
+}