Remove Iterator::is_sorted_by_key

This method can be trivially replaced by `iter.map(...).is_sorted()`.
There has been some discussion about this, but the only reason for
having that method that has been brought up is to have a more symmetry
between the methods of `[T]` and `Iterator`. `[T]::is_sorted_by_key` is
necessary, as there is not a simple replacement for it. But I don't
think API symmetry is a strong enough argument for adding methods that
are essentially superfluous or "a tiny bit convenient" at most.

Finally, this method can always be added in the future. For the initial
stabilization of the `is_sorted` API, it is not necessary.

Author: LukasKalbertodt

compiler/rustc_typeck/src/astconv/generics.rs

@@ -270,13 +270,16 @@ impl<'o, 'tcx> dyn AstConv<'tcx> + 'o {
                                         tcx,
                                         arg,
                                         param,
-                                        !args_iter.clone().is_sorted_by_key(|arg| match arg {
-                                            GenericArg::Lifetime(_) => ParamKindOrd::Lifetime,
-                                            GenericArg::Type(_) => ParamKindOrd::Type,
-                                            GenericArg::Const(_) => ParamKindOrd::Const {
-                                                unordered: tcx.features().const_generics,
-                                            },
-                                        }),
+                                        !args_iter
+                                            .clone()
+                                            .map(|arg| match arg {
+                                                GenericArg::Lifetime(_) => ParamKindOrd::Lifetime,
+                                                GenericArg::Type(_) => ParamKindOrd::Type,
+                                                GenericArg::Const(_) => ParamKindOrd::Const {
+                                                    unordered: tcx.features().const_generics,
+                                                },
+                                            })
+                                            .is_sorted(),
                                         Some(&format!(
                                             "reorder the arguments: {}: `<{}>`",
                                             param_types_present

library/core/src/iter/traits/iterator.rs

@@ -3337,34 +3337,6 @@ pub trait Iterator {
         true
     }
 
-    /// Checks if the elements of this iterator are sorted using the given key extraction
-    /// function.
-    ///
-    /// Instead of comparing the iterator's elements directly, this function compares the keys of
-    /// the elements, as determined by `f`. Apart from that, it's equivalent to [`is_sorted`]; see
-    /// its documentation for more information.
-    ///
-    /// [`is_sorted`]: Iterator::is_sorted
-    ///
-    /// # Examples
-    ///
-    /// ```
-    /// #![feature(is_sorted)]
-    ///
-    /// assert!(["c", "bb", "aaa"].iter().is_sorted_by_key(|s| s.len()));
-    /// assert!(![-2i32, -1, 0, 3].iter().is_sorted_by_key(|n| n.abs()));
-    /// ```
-    #[inline]
-    #[unstable(feature = "is_sorted", reason = "new API", issue = "53485")]
-    fn is_sorted_by_key<F, K>(self, f: F) -> bool
-    where
-        Self: Sized,
-        F: FnMut(Self::Item) -> K,
-        K: PartialOrd,
-    {
-        self.map(f).is_sorted()
-    }
-
     /// See [TrustedRandomAccess]
     // The unusual name is to avoid name collisions in method resolution
     // see #76479.

library/core/src/slice/mod.rs

@@ -3385,7 +3385,7 @@ impl<T> [T] {
         F: FnMut(&T) -> K,
         K: PartialOrd,
     {
-        self.iter().is_sorted_by_key(f)
+        self.iter().map(f).is_sorted()
     }
 
     /// Returns the index of the partition point according to the given predicate

library/core/tests/iter/traits/iterator.rs

@@ -375,9 +375,7 @@ fn test_is_sorted() {
     assert!(std::iter::empty::<i32>().is_sorted());
     assert!(![0.0, 1.0, f32::NAN].iter().is_sorted());
     assert!([-2, -1, 0, 3].iter().is_sorted());
-    assert!(![-2i32, -1, 0, 3].iter().is_sorted_by_key(|n| n.abs()));
     assert!(!["c", "bb", "aaa"].iter().is_sorted());
-    assert!(["c", "bb", "aaa"].iter().is_sorted_by_key(|s| s.len()));
 }
 
 #[test]

src/test/ui/feature-gates/feature-gate-is_sorted.rs

@@ -2,8 +2,6 @@ fn main() {
     // Assert `Iterator` methods are unstable
     assert!([1, 2, 2, 9].iter().is_sorted());
     //~^ ERROR: use of unstable library feature 'is_sorted': new API
-    assert!(![-2i32, -1, 0, 3].iter().is_sorted_by_key(|n| n.abs()));
-    //~^ ERROR: use of unstable library feature 'is_sorted': new API
 
     // Assert `[T]` methods are unstable
     assert!([1, 2, 2, 9].is_sorted());

src/test/ui/feature-gates/feature-gate-is_sorted.stderr

@@ -8,16 +8,7 @@ LL |     assert!([1, 2, 2, 9].iter().is_sorted());
    = help: add `#![feature(is_sorted)]` to the crate attributes to enable
 
 error[E0658]: use of unstable library feature 'is_sorted': new API
-  --> $DIR/feature-gate-is_sorted.rs:5:39
-   |
-LL |     assert!(![-2i32, -1, 0, 3].iter().is_sorted_by_key(|n| n.abs()));
-   |                                       ^^^^^^^^^^^^^^^^
-   |
-   = note: see issue #53485 <https://github.com/rust-lang/rust/issues/53485> for more information
-   = help: add `#![feature(is_sorted)]` to the crate attributes to enable
-
-error[E0658]: use of unstable library feature 'is_sorted': new API
-  --> $DIR/feature-gate-is_sorted.rs:9:26
+  --> $DIR/feature-gate-is_sorted.rs:7:26
    |
 LL |     assert!([1, 2, 2, 9].is_sorted());
    |                          ^^^^^^^^^
@@ -26,14 +17,14 @@ LL |     assert!([1, 2, 2, 9].is_sorted());
    = help: add `#![feature(is_sorted)]` to the crate attributes to enable
 
 error[E0658]: use of unstable library feature 'is_sorted': new API
-  --> $DIR/feature-gate-is_sorted.rs:11:32
+  --> $DIR/feature-gate-is_sorted.rs:9:32
    |
 LL |     assert!(![-2i32, -1, 0, 3].is_sorted_by_key(|n| n.abs()));
    |                                ^^^^^^^^^^^^^^^^
    |
    = note: see issue #53485 <https://github.com/rust-lang/rust/issues/53485> for more information
    = help: add `#![feature(is_sorted)]` to the crate attributes to enable
 
-error: aborting due to 4 previous errors
+error: aborting due to 3 previous errors
 
 For more information about this error, try `rustc --explain E0658`.