Rollup merge of #130090 - RalfJung:result-copied, r=Noratrieb

make Result::copied unstably const
The corresponding `Option::copied` is unstably const, so seems reasonable to do the same here.

Author: workingjubilee

library/core/src/option.rs

@@ -1893,7 +1893,7 @@ impl<T> Option<&T> {
 where
 T:Copy,
 {
-// FIXME: this implementation, which sidesteps using `Option::map` since it's not const
+// FIXME(const-hack): this implementation, which sidesteps using `Option::map` since it's not const
 // ready yet, should be reverted when possible to avoid code repetition
 matchself{
 Some(&v) => Some(v),
@@ -1941,7 +1941,7 @@ impl<T> Option<&mut T> {
 /// ```
 #[must_use = "`self` will be dropped if the result is not used"]
 #[stable(feature = "copied", since = "1.35.0")]
-#[rustc_const_unstable(feature = "const_option_ext", issue = "91930")]
+#[rustc_const_unstable(feature = "const_option", issue = "67441")]
 pubconstfncopied(self) -> Option<T>
 where
 T:Copy,

library/core/src/result.rs

@@ -1535,11 +1535,17 @@ impl<T, E> Result<&T, E> {
 /// ```
 #[inline]
 #[stable(feature = "result_copied", since = "1.59.0")]
-pubfncopied(self) -> Result<T,E>
+#[rustc_const_unstable(feature = "const_result", issue = "82814")]
+pubconstfncopied(self) -> Result<T,E>
 where
 T:Copy,
 {
-self.map(|&t| t)
+// FIXME(const-hack): this implementation, which sidesteps using `Result::map` since it's not const
+// ready yet, should be reverted when possible to avoid code repetition
+matchself{
+Ok(&v) => Ok(v),
+Err(e) => Err(e),
+}
 }
 
 /// Maps a `Result<&T, E>` to a `Result<T, E>` by cloning the contents of the
@@ -1579,11 +1585,17 @@ impl<T, E> Result<&mut T, E> {
 /// ```
 #[inline]
 #[stable(feature = "result_copied", since = "1.59.0")]
-pubfncopied(self) -> Result<T,E>
+#[rustc_const_unstable(feature = "const_result", issue = "82814")]
+pubconstfncopied(self) -> Result<T,E>
 where
 T:Copy,
 {
-self.map(|&mut t| t)
+// FIXME(const-hack): this implementation, which sidesteps using `Result::map` since it's not const
+// ready yet, should be reverted when possible to avoid code repetition
+matchself{
+Ok(&mut v) => Ok(v),
+Err(e) => Err(e),
+}
 }
 
 /// Maps a `Result<&mut T, E>` to a `Result<T, E>` by cloning the contents of the