add test::stress_test

Cargo.toml

@@ -7,5 +7,8 @@ edition = "2021"
 
 [dependencies]
 
+[dev-dependencies]
+rand = "0.8.5"
+
 [features]
-unstable = []
+unstable = []

src/lib.rs

@@ -103,7 +103,7 @@
 //! │    │          └──────────────────────────────────────────┘   │ │
 //! │    └─────────────────────────────────────────────────────────┘ │
 //! │                                                                │
-//! └─ aligned to usize                       also aligned to usize ─┘
+//! └─ aligned to align_of::<*const T>()   also aligned to *const T ─┘
 //! ```
 //!
 //! [`Vec<T: ?Sized>`]: Vec
@@ -142,7 +142,7 @@ use std::{
     alloc::{alloc, dealloc, Layout},
     any::Any,
     marker::PhantomData,
-    mem::{self, align_of_val, size_of, size_of_val},
+    mem::{self, align_of, align_of_val, size_of, size_of_val},
     ops::{Index, IndexMut},
     ptr::{drop_in_place, NonNull},
     slice,
@@ -312,7 +312,7 @@ impl<T: ?Sized> Vec<T> {
     }
 
     unsafe fn realloc(&mut self, size: usize) {
-        let layout = Layout::from_size_align_unchecked(size, 8).pad_to_align();
+        let layout = Layout::from_size_align_unchecked(size, align_of::<Extra<T>>()).pad_to_align();
         if self.capacity == 0 {
             // will panic if OOM
             self.ptr = NonNull::new(alloc(layout)).unwrap();
@@ -519,7 +519,7 @@ impl<T: ?Sized> Vec<T> {
         if self.capacity != 0 {
             dealloc(
                 self.ptr.as_ptr(),
-                Layout::from_size_align_unchecked(self.capacity, 8),
+                Layout::from_size_align_unchecked(self.capacity, align_of::<Extra<T>>()),
             );
         }
     }

src/test.rs

@@ -1,5 +1,7 @@
 //! Always use `cargo miri test`, and never just `cargo test`.
 
+use rand::{thread_rng, Rng};
+
 use super::prelude::{vec, *};
 use std::{
     any::Any,
@@ -211,3 +213,33 @@ fn remove() {
     assert_eq!(vec.remove(1).unwrap().debug(), "\"foo\"");
     assert_eq!(vec.debug(), "[1, true]");
 }
+
+#[test]
+fn stress_test() {
+    let mut vec: Vec<dyn Debug> = Vec::new();
+
+    let mut rng = thread_rng();
+
+    let mut len = 0;
+
+    let iterations = if cfg!(miri) { 100_000 } else { 1_000_000 };
+
+    for _ in 0..iterations {
+        if len == 0 || rng.gen_bool(0.7) {
+            len += 1;
+
+            match rng.gen_range(1..=3) {
+                1 => vec.push_unsize_stable("a string", |v| v as _),
+                2 => vec.push_unsize_stable(1, |v| v as _),
+                3 => vec.push_unsize_stable(true, |v| v as _),
+                _ => unreachable!(),
+            }
+        } else {
+            len -= 1;
+
+            vec.pop();
+        }
+
+        assert_eq!(len, vec.len());
+    }
+}