Rollup merge of #69792 - LenaWil:try_reserve_error/impl-error, r=sfackler

Implement Error for TryReserveError

I noticed that the Error trait wasn't implemented for TryReserveError. (#48043)

Not sure if the error messages and code style are 100% correct, it's my first time contributing to the Rust std.

1 files changed, 18 insertions, 0 deletions

diff --git a/src/liballoc/collections/mod.rs b/src/liballoc/collections/mod.rs
index 0bb62373fab..6b21e54f66a 100644
--- a/src/liballoc/collections/mod.rs
+++ b/src/liballoc/collections/mod.rs
@@ -42,6 +42,7 @@ pub use linked_list::LinkedList;
 pub use vec_deque::VecDeque;
 
 use crate::alloc::{Layout, LayoutErr};
+use core::fmt::Display;
 
 /// The error type for `try_reserve` methods.
 #[derive(Clone, PartialEq, Eq, Debug)]
@@ -77,6 +78,23 @@ impl From<LayoutErr> for TryReserveError {
     }
 }
 
+#[unstable(feature = "try_reserve", reason = "new API", issue = "48043")]
+impl Display for TryReserveError {
+    fn fmt(
+        &self,
+        fmt: &mut core::fmt::Formatter<'_>,
+    ) -> core::result::Result<(), core::fmt::Error> {
+        fmt.write_str("memory allocation failed")?;
+        let reason = match &self {
+            TryReserveError::CapacityOverflow => {
+                " because the computed capacity exceeded the collection's maximum"
+            }
+            TryReserveError::AllocError { .. } => " because the memory allocator returned a error",
+        };
+        fmt.write_str(reason)
+    }
+}
+
 /// An intermediate trait for specialization of `Extend`.
 #[doc(hidden)]
 trait SpecExtend<I: IntoIterator> {