Rollup merge of rust-lang#130416 - BatmanAoD:130122-sort-by-docs, r=M…

…ark-Simulacrum

resolve rust-lang#130122: reword 'sort-by' edge-conditions documentation

See rust-lang#130122 for rationale & preliminary discussion.

library/alloc/src/slice.rs

@@ -180,10 +180,9 @@ impl<T> [T] {
     /// This sort is stable (i.e., does not reorder equal elements) and *O*(*n* \* log(*n*))
     /// worst-case.
     ///
-    /// If the implementation of [`Ord`] for `T` does not implement a [total order] the resulting
-    /// order of elements in the slice is unspecified. All original elements will remain in the
-    /// slice and any possible modifications via interior mutability are observed in the input. Same
-    /// is true if the implementation of [`Ord`] for `T` panics.
+    /// If the implementation of [`Ord`] for `T` does not implement a [total order], the function
+    /// may panic; even if the function exits normally, the resulting order of elements in the slice
+    /// is unspecified. See also the note on panicking below.
     ///
     /// When applicable, unstable sorting is preferred because it is generally faster than stable
     /// sorting and it doesn't allocate auxiliary memory. See
@@ -212,7 +211,15 @@ impl<T> [T] {
     ///
     /// # Panics
     ///
-    /// May panic if the implementation of [`Ord`] for `T` does not implement a [total order].
+    /// May panic if the implementation of [`Ord`] for `T` does not implement a [total order], or if
+    /// the [`Ord`] implementation itself panics.
+    ///
+    /// All safe functions on slices preserve the invariant that even if the function panics, all
+    /// original elements will remain in the slice and any possible modifications via interior
+    /// mutability are observed in the input. This ensures that recovery code (for instance inside
+    /// of a `Drop` or following a `catch_unwind`) will still have access to all the original
+    /// elements. For instance, if the slice belongs to a `Vec`, the `Vec::drop` method will be able
+    /// to dispose of all contained elements.
     ///
     /// # Examples
     ///
@@ -241,10 +248,9 @@ impl<T> [T] {
     /// This sort is stable (i.e., does not reorder equal elements) and *O*(*n* \* log(*n*))
     /// worst-case.
     ///
-    /// If the comparison function `compare` does not implement a [total order] the resulting order
-    /// of elements in the slice is unspecified. All original elements will remain in the slice and
-    /// any possible modifications via interior mutability are observed in the input. Same is true
-    /// if `compare` panics.
+    /// If the comparison function `compare` does not implement a [total order], the function may
+    /// panic; even if the function exits normally, the resulting order of elements in the slice is
+    /// unspecified. See also the note on panicking below.
     ///
     /// For example `|a, b| (a - b).cmp(a)` is a comparison function that is neither transitive nor
     /// reflexive nor total, `a < b < c < a` with `a = 1, b = 2, c = 3`. For more information and
@@ -263,7 +269,14 @@ impl<T> [T] {
     ///
     /// # Panics
     ///
-    /// May panic if `compare` does not implement a [total order].
+    /// May panic if `compare` does not implement a [total order], or if `compare` itself panics.
+    ///
+    /// All safe functions on slices preserve the invariant that even if the function panics, all
+    /// original elements will remain in the slice and any possible modifications via interior
+    /// mutability are observed in the input. This ensures that recovery code (for instance inside
+    /// of a `Drop` or following a `catch_unwind`) will still have access to all the original
+    /// elements. For instance, if the slice belongs to a `Vec`, the `Vec::drop` method will be able
+    /// to dispose of all contained elements.
     ///
     /// # Examples
     ///
@@ -295,10 +308,9 @@ impl<T> [T] {
     /// This sort is stable (i.e., does not reorder equal elements) and *O*(*m* \* *n* \* log(*n*))
     /// worst-case, where the key function is *O*(*m*).
     ///
-    /// If the implementation of [`Ord`] for `K` does not implement a [total order] the resulting
-    /// order of elements in the slice is unspecified. All original elements will remain in the
-    /// slice and any possible modifications via interior mutability are observed in the input. Same
-    /// is true if the implementation of [`Ord`] for `K` panics.
+    /// If the implementation of [`Ord`] for `K` does not implement a [total order], the function
+    /// may panic; even if the function exits normally, the resulting order of elements in the slice
+    /// is unspecified. See also the note on panicking below.
     ///
     /// # Current implementation
     ///
@@ -313,7 +325,15 @@ impl<T> [T] {
     ///
     /// # Panics
     ///
-    /// May panic if the implementation of [`Ord`] for `K` does not implement a [total order].
+    /// May panic if the implementation of [`Ord`] for `K` does not implement a [total order], or if
+    /// the [`Ord`] implementation or the key-function `f` panics.
+    ///
+    /// All safe functions on slices preserve the invariant that even if the function panics, all
+    /// original elements will remain in the slice and any possible modifications via interior
+    /// mutability are observed in the input. This ensures that recovery code (for instance inside
+    /// of a `Drop` or following a `catch_unwind`) will still have access to all the original
+    /// elements. For instance, if the slice belongs to a `Vec`, the `Vec::drop` method will be able
+    /// to dispose of all contained elements.
     ///
     /// # Examples
     ///
@@ -347,10 +367,9 @@ impl<T> [T] {
     /// storage to remember the results of key evaluation. The order of calls to the key function is
     /// unspecified and may change in future versions of the standard library.
     ///
-    /// If the implementation of [`Ord`] for `K` does not implement a [total order] the resulting
-    /// order of elements in the slice is unspecified. All original elements will remain in the
-    /// slice and any possible modifications via interior mutability are observed in the input. Same
-    /// is true if the implementation of [`Ord`] for `K` panics.
+    /// If the implementation of [`Ord`] for `K` does not implement a [total order], the function
+    /// may panic; even if the function exits normally, the resulting order of elements in the slice
+    /// is unspecified. See also the note on panicking below.
     ///
     /// For simple key functions (e.g., functions that are property accesses or basic operations),
     /// [`sort_by_key`](slice::sort_by_key) is likely to be faster.
@@ -369,7 +388,15 @@ impl<T> [T] {
     ///
     /// # Panics
     ///
-    /// May panic if the implementation of [`Ord`] for `K` does not implement a [total order].
+    /// May panic if the implementation of [`Ord`] for `K` does not implement a [total order], or if
+    /// the [`Ord`] implementation panics.
+    ///
+    /// All safe functions on slices preserve the invariant that even if the function panics, all
+    /// original elements will remain in the slice and any possible modifications via interior
+    /// mutability are observed in the input. This ensures that recovery code (for instance inside
+    /// of a `Drop` or following a `catch_unwind`) will still have access to all the original
+    /// elements. For instance, if the slice belongs to a `Vec`, the `Vec::drop` method will be able
+    /// to dispose of all contained elements.
     ///
     /// # Examples
     ///