Auto merge of #87408 - kornelski:try_reserve_error, r=yaahc

Hide allocator details from TryReserveError

I think there's [no need for TryReserveError to carry detailed information](https://github.com/rust-lang/rust/issues/48043#issuecomment-825139280), but I wouldn't want that issue to delay stabilization of the `try_reserve` feature.

So I'm proposing to stabilize `try_reserve` with a `TryReserveError` as an opaque structure, and if needed, expose error details later.

This PR moves the `enum` to an unstable inner `TryReserveErrorKind` that lives under a separate feature flag. `TryReserveErrorKind` could possibly be left as an implementation detail forever, and the `TryReserveError` get methods such as `allocation_size() -> Option<usize>` or `layout() -> Option<Layout>` instead, or the details could be dropped completely to make try-reserve errors just a unit struct, and thus smaller and cheaper.

4 files changed, 197 insertions, 87 deletions

diff --git a/library/alloc/tests/lib.rs b/library/alloc/tests/lib.rs
index 3143afa269d..b3e048a6587 100644
--- a/library/alloc/tests/lib.rs
+++ b/library/alloc/tests/lib.rs
@@ -8,6 +8,7 @@
 #![feature(pattern)]
 #![feature(trusted_len)]
 #![feature(try_reserve)]
+#![feature(try_reserve_kind)]
 #![feature(unboxed_closures)]
 #![feature(associated_type_bounds)]
 #![feature(binary_heap_into_iter_sorted)]
diff --git a/library/alloc/tests/string.rs b/library/alloc/tests/string.rs
index 9ec0ee97ab9..cf9d734a9d5 100644
--- a/library/alloc/tests/string.rs
+++ b/library/alloc/tests/string.rs
@@ -1,6 +1,6 @@
 use std::borrow::Cow;
 use std::cell::Cell;
-use std::collections::TryReserveError::*;
+use std::collections::TryReserveErrorKind::*;
 use std::ops::Bound;
 use std::ops::Bound::*;
 use std::ops::RangeBounds;
@@ -703,35 +703,42 @@ fn test_try_reserve() {
         let mut empty_string: String = String::new();
 
         // Check isize::MAX doesn't count as an overflow
-        if let Err(CapacityOverflow) = empty_string.try_reserve(MAX_CAP) {
+        if let Err(CapacityOverflow) = empty_string.try_reserve(MAX_CAP).map_err(|e| e.kind()) {
             panic!("isize::MAX shouldn't trigger an overflow!");
         }
         // Play it again, frank! (just to be sure)
-        if let Err(CapacityOverflow) = empty_string.try_reserve(MAX_CAP) {
+        if let Err(CapacityOverflow) = empty_string.try_reserve(MAX_CAP).map_err(|e| e.kind()) {
             panic!("isize::MAX shouldn't trigger an overflow!");
         }
 
         if guards_against_isize {
             // Check isize::MAX + 1 does count as overflow
-            if let Err(CapacityOverflow) = empty_string.try_reserve(MAX_CAP + 1) {
+            if let Err(CapacityOverflow) =
+                empty_string.try_reserve(MAX_CAP + 1).map_err(|e| e.kind())
+            {
             } else {
                 panic!("isize::MAX + 1 should trigger an overflow!")
             }
 
             // Check usize::MAX does count as overflow
-            if let Err(CapacityOverflow) = empty_string.try_reserve(MAX_USIZE) {
+            if let Err(CapacityOverflow) = empty_string.try_reserve(MAX_USIZE).map_err(|e| e.kind())
+            {
             } else {
                 panic!("usize::MAX should trigger an overflow!")
             }
         } else {
             // Check isize::MAX + 1 is an OOM
-            if let Err(AllocError { .. }) = empty_string.try_reserve(MAX_CAP + 1) {
+            if let Err(AllocError { .. }) =
+                empty_string.try_reserve(MAX_CAP + 1).map_err(|e| e.kind())
+            {
             } else {
                 panic!("isize::MAX + 1 should trigger an OOM!")
             }
 
             // Check usize::MAX is an OOM
-            if let Err(AllocError { .. }) = empty_string.try_reserve(MAX_USIZE) {
+            if let Err(AllocError { .. }) =
+                empty_string.try_reserve(MAX_USIZE).map_err(|e| e.kind())
+            {
             } else {
                 panic!("usize::MAX should trigger an OOM!")
             }
@@ -742,25 +749,27 @@ fn test_try_reserve() {
         // Same basic idea, but with non-zero len
         let mut ten_bytes: String = String::from("0123456789");
 
-        if let Err(CapacityOverflow) = ten_bytes.try_reserve(MAX_CAP - 10) {
+        if let Err(CapacityOverflow) = ten_bytes.try_reserve(MAX_CAP - 10).map_err(|e| e.kind()) {
             panic!("isize::MAX shouldn't trigger an overflow!");
         }
-        if let Err(CapacityOverflow) = ten_bytes.try_reserve(MAX_CAP - 10) {
+        if let Err(CapacityOverflow) = ten_bytes.try_reserve(MAX_CAP - 10).map_err(|e| e.kind()) {
             panic!("isize::MAX shouldn't trigger an overflow!");
         }
         if guards_against_isize {
-            if let Err(CapacityOverflow) = ten_bytes.try_reserve(MAX_CAP - 9) {
+            if let Err(CapacityOverflow) = ten_bytes.try_reserve(MAX_CAP - 9).map_err(|e| e.kind())
+            {
             } else {
                 panic!("isize::MAX + 1 should trigger an overflow!");
             }
         } else {
-            if let Err(AllocError { .. }) = ten_bytes.try_reserve(MAX_CAP - 9) {
+            if let Err(AllocError { .. }) = ten_bytes.try_reserve(MAX_CAP - 9).map_err(|e| e.kind())
+            {
             } else {
                 panic!("isize::MAX + 1 should trigger an OOM!")
             }
         }
         // Should always overflow in the add-to-len
-        if let Err(CapacityOverflow) = ten_bytes.try_reserve(MAX_USIZE) {
+        if let Err(CapacityOverflow) = ten_bytes.try_reserve(MAX_USIZE).map_err(|e| e.kind()) {
         } else {
             panic!("usize::MAX should trigger an overflow!")
         }
@@ -782,30 +791,40 @@ fn test_try_reserve_exact() {
     {
         let mut empty_string: String = String::new();
 
-        if let Err(CapacityOverflow) = empty_string.try_reserve_exact(MAX_CAP) {
+        if let Err(CapacityOverflow) = empty_string.try_reserve_exact(MAX_CAP).map_err(|e| e.kind())
+        {
             panic!("isize::MAX shouldn't trigger an overflow!");
         }
-        if let Err(CapacityOverflow) = empty_string.try_reserve_exact(MAX_CAP) {
+        if let Err(CapacityOverflow) = empty_string.try_reserve_exact(MAX_CAP).map_err(|e| e.kind())
+        {
             panic!("isize::MAX shouldn't trigger an overflow!");
         }
 
         if guards_against_isize {
-            if let Err(CapacityOverflow) = empty_string.try_reserve_exact(MAX_CAP + 1) {
+            if let Err(CapacityOverflow) =
+                empty_string.try_reserve_exact(MAX_CAP + 1).map_err(|e| e.kind())
+            {
             } else {
                 panic!("isize::MAX + 1 should trigger an overflow!")
             }
 
-            if let Err(CapacityOverflow) = empty_string.try_reserve_exact(MAX_USIZE) {
+            if let Err(CapacityOverflow) =
+                empty_string.try_reserve_exact(MAX_USIZE).map_err(|e| e.kind())
+            {
             } else {
                 panic!("usize::MAX should trigger an overflow!")
             }
         } else {
-            if let Err(AllocError { .. }) = empty_string.try_reserve_exact(MAX_CAP + 1) {
+            if let Err(AllocError { .. }) =
+                empty_string.try_reserve_exact(MAX_CAP + 1).map_err(|e| e.kind())
+            {
             } else {
                 panic!("isize::MAX + 1 should trigger an OOM!")
             }
 
-            if let Err(AllocError { .. }) = empty_string.try_reserve_exact(MAX_USIZE) {
+            if let Err(AllocError { .. }) =
+                empty_string.try_reserve_exact(MAX_USIZE).map_err(|e| e.kind())
+            {
             } else {
                 panic!("usize::MAX should trigger an OOM!")
             }
@@ -815,24 +834,33 @@ fn test_try_reserve_exact() {
     {
         let mut ten_bytes: String = String::from("0123456789");
 
-        if let Err(CapacityOverflow) = ten_bytes.try_reserve_exact(MAX_CAP - 10) {
+        if let Err(CapacityOverflow) =
+            ten_bytes.try_reserve_exact(MAX_CAP - 10).map_err(|e| e.kind())
+        {
             panic!("isize::MAX shouldn't trigger an overflow!");
         }
-        if let Err(CapacityOverflow) = ten_bytes.try_reserve_exact(MAX_CAP - 10) {
+        if let Err(CapacityOverflow) =
+            ten_bytes.try_reserve_exact(MAX_CAP - 10).map_err(|e| e.kind())
+        {
             panic!("isize::MAX shouldn't trigger an overflow!");
         }
         if guards_against_isize {
-            if let Err(CapacityOverflow) = ten_bytes.try_reserve_exact(MAX_CAP - 9) {
+            if let Err(CapacityOverflow) =
+                ten_bytes.try_reserve_exact(MAX_CAP - 9).map_err(|e| e.kind())
+            {
             } else {
                 panic!("isize::MAX + 1 should trigger an overflow!");
             }
         } else {
-            if let Err(AllocError { .. }) = ten_bytes.try_reserve_exact(MAX_CAP - 9) {
+            if let Err(AllocError { .. }) =
+                ten_bytes.try_reserve_exact(MAX_CAP - 9).map_err(|e| e.kind())
+            {
             } else {
                 panic!("isize::MAX + 1 should trigger an OOM!")
             }
         }
-        if let Err(CapacityOverflow) = ten_bytes.try_reserve_exact(MAX_USIZE) {
+        if let Err(CapacityOverflow) = ten_bytes.try_reserve_exact(MAX_USIZE).map_err(|e| e.kind())
+        {
         } else {
             panic!("usize::MAX should trigger an overflow!")
         }
diff --git a/library/alloc/tests/vec.rs b/library/alloc/tests/vec.rs
index 3b723701680..d3a6dcfddc5 100644
--- a/library/alloc/tests/vec.rs
+++ b/library/alloc/tests/vec.rs
@@ -1,6 +1,6 @@
 use std::borrow::Cow;
 use std::cell::Cell;
-use std::collections::TryReserveError::*;
+use std::collections::TryReserveErrorKind::*;
 use std::fmt::Debug;
 use std::iter::InPlaceIterable;
 use std::mem::{size_of, swap};
@@ -1478,35 +1478,41 @@ fn test_try_reserve() {
         let mut empty_bytes: Vec<u8> = Vec::new();
 
         // Check isize::MAX doesn't count as an overflow
-        if let Err(CapacityOverflow) = empty_bytes.try_reserve(MAX_CAP) {
+        if let Err(CapacityOverflow) = empty_bytes.try_reserve(MAX_CAP).map_err(|e| e.kind()) {
             panic!("isize::MAX shouldn't trigger an overflow!");
         }
         // Play it again, frank! (just to be sure)
-        if let Err(CapacityOverflow) = empty_bytes.try_reserve(MAX_CAP) {
+        if let Err(CapacityOverflow) = empty_bytes.try_reserve(MAX_CAP).map_err(|e| e.kind()) {
             panic!("isize::MAX shouldn't trigger an overflow!");
         }
 
         if guards_against_isize {
             // Check isize::MAX + 1 does count as overflow
-            if let Err(CapacityOverflow) = empty_bytes.try_reserve(MAX_CAP + 1) {
+            if let Err(CapacityOverflow) =
+                empty_bytes.try_reserve(MAX_CAP + 1).map_err(|e| e.kind())
+            {
             } else {
                 panic!("isize::MAX + 1 should trigger an overflow!")
             }
 
             // Check usize::MAX does count as overflow
-            if let Err(CapacityOverflow) = empty_bytes.try_reserve(MAX_USIZE) {
+            if let Err(CapacityOverflow) = empty_bytes.try_reserve(MAX_USIZE).map_err(|e| e.kind())
+            {
             } else {
                 panic!("usize::MAX should trigger an overflow!")
             }
         } else {
             // Check isize::MAX + 1 is an OOM
-            if let Err(AllocError { .. }) = empty_bytes.try_reserve(MAX_CAP + 1) {
+            if let Err(AllocError { .. }) =
+                empty_bytes.try_reserve(MAX_CAP + 1).map_err(|e| e.kind())
+            {
             } else {
                 panic!("isize::MAX + 1 should trigger an OOM!")
             }
 
             // Check usize::MAX is an OOM
-            if let Err(AllocError { .. }) = empty_bytes.try_reserve(MAX_USIZE) {
+            if let Err(AllocError { .. }) = empty_bytes.try_reserve(MAX_USIZE).map_err(|e| e.kind())
+            {
             } else {
                 panic!("usize::MAX should trigger an OOM!")
             }
@@ -1517,25 +1523,27 @@ fn test_try_reserve() {
         // Same basic idea, but with non-zero len
         let mut ten_bytes: Vec<u8> = vec![1, 2, 3, 4, 5, 6, 7, 8, 9, 10];
 
-        if let Err(CapacityOverflow) = ten_bytes.try_reserve(MAX_CAP - 10) {
+        if let Err(CapacityOverflow) = ten_bytes.try_reserve(MAX_CAP - 10).map_err(|e| e.kind()) {
             panic!("isize::MAX shouldn't trigger an overflow!");
         }
-        if let Err(CapacityOverflow) = ten_bytes.try_reserve(MAX_CAP - 10) {
+        if let Err(CapacityOverflow) = ten_bytes.try_reserve(MAX_CAP - 10).map_err(|e| e.kind()) {
             panic!("isize::MAX shouldn't trigger an overflow!");
         }
         if guards_against_isize {
-            if let Err(CapacityOverflow) = ten_bytes.try_reserve(MAX_CAP - 9) {
+            if let Err(CapacityOverflow) = ten_bytes.try_reserve(MAX_CAP - 9).map_err(|e| e.kind())
+            {
             } else {
                 panic!("isize::MAX + 1 should trigger an overflow!");
             }
         } else {
-            if let Err(AllocError { .. }) = ten_bytes.try_reserve(MAX_CAP - 9) {
+            if let Err(AllocError { .. }) = ten_bytes.try_reserve(MAX_CAP - 9).map_err(|e| e.kind())
+            {
             } else {
                 panic!("isize::MAX + 1 should trigger an OOM!")
             }
         }
         // Should always overflow in the add-to-len
-        if let Err(CapacityOverflow) = ten_bytes.try_reserve(MAX_USIZE) {
+        if let Err(CapacityOverflow) = ten_bytes.try_reserve(MAX_USIZE).map_err(|e| e.kind()) {
         } else {
             panic!("usize::MAX should trigger an overflow!")
         }
@@ -1545,25 +1553,31 @@ fn test_try_reserve() {
         // Same basic idea, but with interesting type size
         let mut ten_u32s: Vec<u32> = vec![1, 2, 3, 4, 5, 6, 7, 8, 9, 10];
 
-        if let Err(CapacityOverflow) = ten_u32s.try_reserve(MAX_CAP / 4 - 10) {
+        if let Err(CapacityOverflow) = ten_u32s.try_reserve(MAX_CAP / 4 - 10).map_err(|e| e.kind())
+        {
             panic!("isize::MAX shouldn't trigger an overflow!");
         }
-        if let Err(CapacityOverflow) = ten_u32s.try_reserve(MAX_CAP / 4 - 10) {
+        if let Err(CapacityOverflow) = ten_u32s.try_reserve(MAX_CAP / 4 - 10).map_err(|e| e.kind())
+        {
             panic!("isize::MAX shouldn't trigger an overflow!");
         }
         if guards_against_isize {
-            if let Err(CapacityOverflow) = ten_u32s.try_reserve(MAX_CAP / 4 - 9) {
+            if let Err(CapacityOverflow) =
+                ten_u32s.try_reserve(MAX_CAP / 4 - 9).map_err(|e| e.kind())
+            {
             } else {
                 panic!("isize::MAX + 1 should trigger an overflow!");
             }
         } else {
-            if let Err(AllocError { .. }) = ten_u32s.try_reserve(MAX_CAP / 4 - 9) {
+            if let Err(AllocError { .. }) =
+                ten_u32s.try_reserve(MAX_CAP / 4 - 9).map_err(|e| e.kind())
+            {
             } else {
                 panic!("isize::MAX + 1 should trigger an OOM!")
             }
         }
         // Should fail in the mul-by-size
-        if let Err(CapacityOverflow) = ten_u32s.try_reserve(MAX_USIZE - 20) {
+        if let Err(CapacityOverflow) = ten_u32s.try_reserve(MAX_USIZE - 20).map_err(|e| e.kind()) {
         } else {
             panic!("usize::MAX should trigger an overflow!");
         }
@@ -1585,30 +1599,40 @@ fn test_try_reserve_exact() {
     {
         let mut empty_bytes: Vec<u8> = Vec::new();
 
-        if let Err(CapacityOverflow) = empty_bytes.try_reserve_exact(MAX_CAP) {
+        if let Err(CapacityOverflow) = empty_bytes.try_reserve_exact(MAX_CAP).map_err(|e| e.kind())
+        {
             panic!("isize::MAX shouldn't trigger an overflow!");
         }
-        if let Err(CapacityOverflow) = empty_bytes.try_reserve_exact(MAX_CAP) {
+        if let Err(CapacityOverflow) = empty_bytes.try_reserve_exact(MAX_CAP).map_err(|e| e.kind())
+        {
             panic!("isize::MAX shouldn't trigger an overflow!");
         }
 
         if guards_against_isize {
-            if let Err(CapacityOverflow) = empty_bytes.try_reserve_exact(MAX_CAP + 1) {
+            if let Err(CapacityOverflow) =
+                empty_bytes.try_reserve_exact(MAX_CAP + 1).map_err(|e| e.kind())
+            {
             } else {
                 panic!("isize::MAX + 1 should trigger an overflow!")
             }
 
-            if let Err(CapacityOverflow) = empty_bytes.try_reserve_exact(MAX_USIZE) {
+            if let Err(CapacityOverflow) =
+                empty_bytes.try_reserve_exact(MAX_USIZE).map_err(|e| e.kind())
+            {
             } else {
                 panic!("usize::MAX should trigger an overflow!")
             }
         } else {
-            if let Err(AllocError { .. }) = empty_bytes.try_reserve_exact(MAX_CAP + 1) {
+            if let Err(AllocError { .. }) =
+                empty_bytes.try_reserve_exact(MAX_CAP + 1).map_err(|e| e.kind())
+            {
             } else {
                 panic!("isize::MAX + 1 should trigger an OOM!")
             }
 
-            if let Err(AllocError { .. }) = empty_bytes.try_reserve_exact(MAX_USIZE) {
+            if let Err(AllocError { .. }) =
+                empty_bytes.try_reserve_exact(MAX_USIZE).map_err(|e| e.kind())
+            {
             } else {
                 panic!("usize::MAX should trigger an OOM!")
             }
@@ -1618,24 +1642,33 @@ fn test_try_reserve_exact() {
     {
         let mut ten_bytes: Vec<u8> = vec![1, 2, 3, 4, 5, 6, 7, 8, 9, 10];
 
-        if let Err(CapacityOverflow) = ten_bytes.try_reserve_exact(MAX_CAP - 10) {
+        if let Err(CapacityOverflow) =
+            ten_bytes.try_reserve_exact(MAX_CAP - 10).map_err(|e| e.kind())
+        {
             panic!("isize::MAX shouldn't trigger an overflow!");
         }
-        if let Err(CapacityOverflow) = ten_bytes.try_reserve_exact(MAX_CAP - 10) {
+        if let Err(CapacityOverflow) =
+            ten_bytes.try_reserve_exact(MAX_CAP - 10).map_err(|e| e.kind())
+        {
             panic!("isize::MAX shouldn't trigger an overflow!");
         }
         if guards_against_isize {
-            if let Err(CapacityOverflow) = ten_bytes.try_reserve_exact(MAX_CAP - 9) {
+            if let Err(CapacityOverflow) =
+                ten_bytes.try_reserve_exact(MAX_CAP - 9).map_err(|e| e.kind())
+            {
             } else {
                 panic!("isize::MAX + 1 should trigger an overflow!");
             }
         } else {
-            if let Err(AllocError { .. }) = ten_bytes.try_reserve_exact(MAX_CAP - 9) {
+            if let Err(AllocError { .. }) =
+                ten_bytes.try_reserve_exact(MAX_CAP - 9).map_err(|e| e.kind())
+            {
             } else {
                 panic!("isize::MAX + 1 should trigger an OOM!")
             }
         }
-        if let Err(CapacityOverflow) = ten_bytes.try_reserve_exact(MAX_USIZE) {
+        if let Err(CapacityOverflow) = ten_bytes.try_reserve_exact(MAX_USIZE).map_err(|e| e.kind())
+        {
         } else {
             panic!("usize::MAX should trigger an overflow!")
         }
@@ -1644,24 +1677,34 @@ fn test_try_reserve_exact() {
     {
         let mut ten_u32s: Vec<u32> = vec![1, 2, 3, 4, 5, 6, 7, 8, 9, 10];
 
-        if let Err(CapacityOverflow) = ten_u32s.try_reserve_exact(MAX_CAP / 4 - 10) {
+        if let Err(CapacityOverflow) =
+            ten_u32s.try_reserve_exact(MAX_CAP / 4 - 10).map_err(|e| e.kind())
+        {
             panic!("isize::MAX shouldn't trigger an overflow!");
         }
-        if let Err(CapacityOverflow) = ten_u32s.try_reserve_exact(MAX_CAP / 4 - 10) {
+        if let Err(CapacityOverflow) =
+            ten_u32s.try_reserve_exact(MAX_CAP / 4 - 10).map_err(|e| e.kind())
+        {
             panic!("isize::MAX shouldn't trigger an overflow!");
         }
         if guards_against_isize {
-            if let Err(CapacityOverflow) = ten_u32s.try_reserve_exact(MAX_CAP / 4 - 9) {
+            if let Err(CapacityOverflow) =
+                ten_u32s.try_reserve_exact(MAX_CAP / 4 - 9).map_err(|e| e.kind())
+            {
             } else {
                 panic!("isize::MAX + 1 should trigger an overflow!");
             }
         } else {
-            if let Err(AllocError { .. }) = ten_u32s.try_reserve_exact(MAX_CAP / 4 - 9) {
+            if let Err(AllocError { .. }) =
+                ten_u32s.try_reserve_exact(MAX_CAP / 4 - 9).map_err(|e| e.kind())
+            {
             } else {
                 panic!("isize::MAX + 1 should trigger an OOM!")
             }
         }
-        if let Err(CapacityOverflow) = ten_u32s.try_reserve_exact(MAX_USIZE - 20) {
+        if let Err(CapacityOverflow) =
+            ten_u32s.try_reserve_exact(MAX_USIZE - 20).map_err(|e| e.kind())
+        {
         } else {
             panic!("usize::MAX should trigger an overflow!")
         }
diff --git a/library/alloc/tests/vec_deque.rs b/library/alloc/tests/vec_deque.rs
index d7140cf9759..e9fd19d76ea 100644
--- a/library/alloc/tests/vec_deque.rs
+++ b/library/alloc/tests/vec_deque.rs
@@ -1,4 +1,4 @@
-use std::collections::TryReserveError::*;
+use std::collections::TryReserveErrorKind::*;
 use std::collections::{vec_deque::Drain, VecDeque};
 use std::fmt::Debug;
 use std::mem::size_of;
@@ -1171,23 +1171,26 @@ fn test_try_reserve() {
         let mut empty_bytes: VecDeque<u8> = VecDeque::new();
 
         // Check isize::MAX doesn't count as an overflow
-        if let Err(CapacityOverflow) = empty_bytes.try_reserve(MAX_CAP) {
+        if let Err(CapacityOverflow) = empty_bytes.try_reserve(MAX_CAP).map_err(|e| e.kind()) {
             panic!("isize::MAX shouldn't trigger an overflow!");
         }
         // Play it again, frank! (just to be sure)
-        if let Err(CapacityOverflow) = empty_bytes.try_reserve(MAX_CAP) {
+        if let Err(CapacityOverflow) = empty_bytes.try_reserve(MAX_CAP).map_err(|e| e.kind()) {
             panic!("isize::MAX shouldn't trigger an overflow!");
         }
 
         if guards_against_isize {
             // Check isize::MAX + 1 does count as overflow
-            if let Err(CapacityOverflow) = empty_bytes.try_reserve(MAX_CAP + 1) {
+            if let Err(CapacityOverflow) =
+                empty_bytes.try_reserve(MAX_CAP + 1).map_err(|e| e.kind())
+            {
             } else {
                 panic!("isize::MAX + 1 should trigger an overflow!")
             }
 
             // Check usize::MAX does count as overflow
-            if let Err(CapacityOverflow) = empty_bytes.try_reserve(MAX_USIZE) {
+            if let Err(CapacityOverflow) = empty_bytes.try_reserve(MAX_USIZE).map_err(|e| e.kind())
+            {
             } else {
                 panic!("usize::MAX should trigger an overflow!")
             }
@@ -1196,7 +1199,7 @@ fn test_try_reserve() {
             // VecDeque starts with capacity 7, always adds 1 to the capacity
             // and also rounds the number to next power of 2 so this is the
             // furthest we can go without triggering CapacityOverflow
-            if let Err(AllocError { .. }) = empty_bytes.try_reserve(MAX_CAP) {
+            if let Err(AllocError { .. }) = empty_bytes.try_reserve(MAX_CAP).map_err(|e| e.kind()) {
             } else {
                 panic!("isize::MAX + 1 should trigger an OOM!")
             }
@@ -1207,25 +1210,27 @@ fn test_try_reserve() {
         // Same basic idea, but with non-zero len
         let mut ten_bytes: VecDeque<u8> = vec![1, 2, 3, 4, 5, 6, 7, 8, 9, 10].into_iter().collect();
 
-        if let Err(CapacityOverflow) = ten_bytes.try_reserve(MAX_CAP - 10) {
+        if let Err(CapacityOverflow) = ten_bytes.try_reserve(MAX_CAP - 10).map_err(|e| e.kind()) {
             panic!("isize::MAX shouldn't trigger an overflow!");
         }
-        if let Err(CapacityOverflow) = ten_bytes.try_reserve(MAX_CAP - 10) {
+        if let Err(CapacityOverflow) = ten_bytes.try_reserve(MAX_CAP - 10).map_err(|e| e.kind()) {
             panic!("isize::MAX shouldn't trigger an overflow!");
         }
         if guards_against_isize {
-            if let Err(CapacityOverflow) = ten_bytes.try_reserve(MAX_CAP - 9) {
+            if let Err(CapacityOverflow) = ten_bytes.try_reserve(MAX_CAP - 9).map_err(|e| e.kind())
+            {
             } else {
                 panic!("isize::MAX + 1 should trigger an overflow!");
             }
         } else {
-            if let Err(AllocError { .. }) = ten_bytes.try_reserve(MAX_CAP - 9) {
+            if let Err(AllocError { .. }) = ten_bytes.try_reserve(MAX_CAP - 9).map_err(|e| e.kind())
+            {
             } else {
                 panic!("isize::MAX + 1 should trigger an OOM!")
             }
         }
         // Should always overflow in the add-to-len
-        if let Err(CapacityOverflow) = ten_bytes.try_reserve(MAX_USIZE) {
+        if let Err(CapacityOverflow) = ten_bytes.try_reserve(MAX_USIZE).map_err(|e| e.kind()) {
         } else {
             panic!("usize::MAX should trigger an overflow!")
         }
@@ -1235,25 +1240,31 @@ fn test_try_reserve() {
         // Same basic idea, but with interesting type size
         let mut ten_u32s: VecDeque<u32> = vec![1, 2, 3, 4, 5, 6, 7, 8, 9, 10].into_iter().collect();
 
-        if let Err(CapacityOverflow) = ten_u32s.try_reserve(MAX_CAP / 4 - 10) {
+        if let Err(CapacityOverflow) = ten_u32s.try_reserve(MAX_CAP / 4 - 10).map_err(|e| e.kind())
+        {
             panic!("isize::MAX shouldn't trigger an overflow!");
         }
-        if let Err(CapacityOverflow) = ten_u32s.try_reserve(MAX_CAP / 4 - 10) {
+        if let Err(CapacityOverflow) = ten_u32s.try_reserve(MAX_CAP / 4 - 10).map_err(|e| e.kind())
+        {
             panic!("isize::MAX shouldn't trigger an overflow!");
         }
         if guards_against_isize {
-            if let Err(CapacityOverflow) = ten_u32s.try_reserve(MAX_CAP / 4 - 9) {
+            if let Err(CapacityOverflow) =
+                ten_u32s.try_reserve(MAX_CAP / 4 - 9).map_err(|e| e.kind())
+            {
             } else {
                 panic!("isize::MAX + 1 should trigger an overflow!");
             }
         } else {
-            if let Err(AllocError { .. }) = ten_u32s.try_reserve(MAX_CAP / 4 - 9) {
+            if let Err(AllocError { .. }) =
+                ten_u32s.try_reserve(MAX_CAP / 4 - 9).map_err(|e| e.kind())
+            {
             } else {
                 panic!("isize::MAX + 1 should trigger an OOM!")
             }
         }
         // Should fail in the mul-by-size
-        if let Err(CapacityOverflow) = ten_u32s.try_reserve(MAX_USIZE - 20) {
+        if let Err(CapacityOverflow) = ten_u32s.try_reserve(MAX_USIZE - 20).map_err(|e| e.kind()) {
         } else {
             panic!("usize::MAX should trigger an overflow!");
         }
@@ -1275,20 +1286,26 @@ fn test_try_reserve_exact() {
     {
         let mut empty_bytes: VecDeque<u8> = VecDeque::new();
 
-        if let Err(CapacityOverflow) = empty_bytes.try_reserve_exact(MAX_CAP) {
+        if let Err(CapacityOverflow) = empty_bytes.try_reserve_exact(MAX_CAP).map_err(|e| e.kind())
+        {
             panic!("isize::MAX shouldn't trigger an overflow!");
         }
-        if let Err(CapacityOverflow) = empty_bytes.try_reserve_exact(MAX_CAP) {
+        if let Err(CapacityOverflow) = empty_bytes.try_reserve_exact(MAX_CAP).map_err(|e| e.kind())
+        {
             panic!("isize::MAX shouldn't trigger an overflow!");
         }
 
         if guards_against_isize {
-            if let Err(CapacityOverflow) = empty_bytes.try_reserve_exact(MAX_CAP + 1) {
+            if let Err(CapacityOverflow) =
+                empty_bytes.try_reserve_exact(MAX_CAP + 1).map_err(|e| e.kind())
+            {
             } else {
                 panic!("isize::MAX + 1 should trigger an overflow!")
             }
 
-            if let Err(CapacityOverflow) = empty_bytes.try_reserve_exact(MAX_USIZE) {
+            if let Err(CapacityOverflow) =
+                empty_bytes.try_reserve_exact(MAX_USIZE).map_err(|e| e.kind())
+            {
             } else {
                 panic!("usize::MAX should trigger an overflow!")
             }
@@ -1297,7 +1314,9 @@ fn test_try_reserve_exact() {
             // VecDeque starts with capacity 7, always adds 1 to the capacity
             // and also rounds the number to next power of 2 so this is the
             // furthest we can go without triggering CapacityOverflow
-            if let Err(AllocError { .. }) = empty_bytes.try_reserve_exact(MAX_CAP) {
+            if let Err(AllocError { .. }) =
+                empty_bytes.try_reserve_exact(MAX_CAP).map_err(|e| e.kind())
+            {
             } else {
                 panic!("isize::MAX + 1 should trigger an OOM!")
             }
@@ -1307,24 +1326,33 @@ fn test_try_reserve_exact() {
     {
         let mut ten_bytes: VecDeque<u8> = vec![1, 2, 3, 4, 5, 6, 7, 8, 9, 10].into_iter().collect();
 
-        if let Err(CapacityOverflow) = ten_bytes.try_reserve_exact(MAX_CAP - 10) {
+        if let Err(CapacityOverflow) =
+            ten_bytes.try_reserve_exact(MAX_CAP - 10).map_err(|e| e.kind())
+        {
             panic!("isize::MAX shouldn't trigger an overflow!");
         }
-        if let Err(CapacityOverflow) = ten_bytes.try_reserve_exact(MAX_CAP - 10) {
+        if let Err(CapacityOverflow) =
+            ten_bytes.try_reserve_exact(MAX_CAP - 10).map_err(|e| e.kind())
+        {
             panic!("isize::MAX shouldn't trigger an overflow!");
         }
         if guards_against_isize {
-            if let Err(CapacityOverflow) = ten_bytes.try_reserve_exact(MAX_CAP - 9) {
+            if let Err(CapacityOverflow) =
+                ten_bytes.try_reserve_exact(MAX_CAP - 9).map_err(|e| e.kind())
+            {
             } else {
                 panic!("isize::MAX + 1 should trigger an overflow!");
             }
         } else {
-            if let Err(AllocError { .. }) = ten_bytes.try_reserve_exact(MAX_CAP - 9) {
+            if let Err(AllocError { .. }) =
+                ten_bytes.try_reserve_exact(MAX_CAP - 9).map_err(|e| e.kind())
+            {
             } else {
                 panic!("isize::MAX + 1 should trigger an OOM!")
             }
         }
-        if let Err(CapacityOverflow) = ten_bytes.try_reserve_exact(MAX_USIZE) {
+        if let Err(CapacityOverflow) = ten_bytes.try_reserve_exact(MAX_USIZE).map_err(|e| e.kind())
+        {
         } else {
             panic!("usize::MAX should trigger an overflow!")
         }
@@ -1333,24 +1361,34 @@ fn test_try_reserve_exact() {
     {
         let mut ten_u32s: VecDeque<u32> = vec![1, 2, 3, 4, 5, 6, 7, 8, 9, 10].into_iter().collect();
 
-        if let Err(CapacityOverflow) = ten_u32s.try_reserve_exact(MAX_CAP / 4 - 10) {
+        if let Err(CapacityOverflow) =
+            ten_u32s.try_reserve_exact(MAX_CAP / 4 - 10).map_err(|e| e.kind())
+        {
             panic!("isize::MAX shouldn't trigger an overflow!");
         }
-        if let Err(CapacityOverflow) = ten_u32s.try_reserve_exact(MAX_CAP / 4 - 10) {
+        if let Err(CapacityOverflow) =
+            ten_u32s.try_reserve_exact(MAX_CAP / 4 - 10).map_err(|e| e.kind())
+        {
             panic!("isize::MAX shouldn't trigger an overflow!");
         }
         if guards_against_isize {
-            if let Err(CapacityOverflow) = ten_u32s.try_reserve_exact(MAX_CAP / 4 - 9) {
+            if let Err(CapacityOverflow) =
+                ten_u32s.try_reserve_exact(MAX_CAP / 4 - 9).map_err(|e| e.kind())
+            {
             } else {
                 panic!("isize::MAX + 1 should trigger an overflow!");
             }
         } else {
-            if let Err(AllocError { .. }) = ten_u32s.try_reserve_exact(MAX_CAP / 4 - 9) {
+            if let Err(AllocError { .. }) =
+                ten_u32s.try_reserve_exact(MAX_CAP / 4 - 9).map_err(|e| e.kind())
+            {
             } else {
                 panic!("isize::MAX + 1 should trigger an OOM!")
             }
         }
-        if let Err(CapacityOverflow) = ten_u32s.try_reserve_exact(MAX_USIZE - 20) {
+        if let Err(CapacityOverflow) =
+            ten_u32s.try_reserve_exact(MAX_USIZE - 20).map_err(|e| e.kind())
+        {
         } else {
             panic!("usize::MAX should trigger an overflow!")
         }