1 files changed, 103 insertions, 0 deletions
diff --git a/src/tools/clippy/tests/ui/unnecessary_sort_by.rs b/src/tools/clippy/tests/ui/unnecessary_sort_by.rs
new file mode 100644
index 000000000..3365bf6e1
--- /dev/null
+++ b/src/tools/clippy/tests/ui/unnecessary_sort_by.rs
@@ -0,0 +1,103 @@
+// run-rustfix
+
+#![allow(clippy::stable_sort_primitive)]
+
+use std::cell::Ref;
+
+fn unnecessary_sort_by() {
+    fn id(x: isize) -> isize {
+        x
+    }
+
+    let mut vec: Vec<isize> = vec![3, 6, 1, 2, 5];
+    // Forward examples
+    vec.sort_by(|a, b| a.cmp(b));
+    vec.sort_unstable_by(|a, b| a.cmp(b));
+    vec.sort_by(|a, b| (a + 5).abs().cmp(&(b + 5).abs()));
+    vec.sort_unstable_by(|a, b| id(-a).cmp(&id(-b)));
+    // Reverse examples
+    vec.sort_by(|a, b| b.cmp(a)); // not linted to avoid suggesting `Reverse(b)` which would borrow
+    vec.sort_by(|a, b| (b + 5).abs().cmp(&(a + 5).abs()));
+    vec.sort_unstable_by(|a, b| id(-b).cmp(&id(-a)));
+    // Negative examples (shouldn't be changed)
+    let c = &7;
+    vec.sort_by(|a, b| (b - a).cmp(&(a - b)));
+    vec.sort_by(|_, b| b.cmp(&5));
+    vec.sort_by(|_, b| b.cmp(c));
+    vec.sort_unstable_by(|a, _| a.cmp(c));
+
+    // Vectors of references are fine as long as the resulting key does not borrow
+    let mut vec: Vec<&&&isize> = vec![&&&3, &&&6, &&&1, &&&2, &&&5];
+    vec.sort_by(|a, b| (***a).abs().cmp(&(***b).abs()));
+    vec.sort_unstable_by(|a, b| (***a).abs().cmp(&(***b).abs()));
+    // `Reverse(b)` would borrow in the following cases, don't lint
+    vec.sort_by(|a, b| b.cmp(a));
+    vec.sort_unstable_by(|a, b| b.cmp(a));
+
+    // No warning if element does not implement `Ord`
+    let mut vec: Vec<Ref<usize>> = Vec::new();
+    vec.sort_unstable_by(|a, b| a.cmp(b));
+}
+
+// Do not suggest returning a reference to the closure parameter of `Vec::sort_by_key`
+mod issue_5754 {
+    #[derive(Clone, Copy)]
+    struct Test(usize);
+
+    #[derive(PartialOrd, Ord, PartialEq, Eq)]
+    struct Wrapper<'a>(&'a usize);
+
+    impl Test {
+        fn name(&self) -> &usize {
+            &self.0
+        }
+
+        fn wrapped(&self) -> Wrapper<'_> {
+            Wrapper(&self.0)
+        }
+    }
+
+    pub fn test() {
+        let mut args: Vec<Test> = vec![];
+
+        // Forward
+        args.sort_by(|a, b| a.name().cmp(b.name()));
+        args.sort_by(|a, b| a.wrapped().cmp(&b.wrapped()));
+        args.sort_unstable_by(|a, b| a.name().cmp(b.name()));
+        args.sort_unstable_by(|a, b| a.wrapped().cmp(&b.wrapped()));
+        // Reverse
+        args.sort_by(|a, b| b.name().cmp(a.name()));
+        args.sort_by(|a, b| b.wrapped().cmp(&a.wrapped()));
+        args.sort_unstable_by(|a, b| b.name().cmp(a.name()));
+        args.sort_unstable_by(|a, b| b.wrapped().cmp(&a.wrapped()));
+    }
+}
+
+// The closure parameter is not dereferenced anymore, so non-Copy types can be linted
+mod issue_6001 {
+    struct Test(String);
+
+    impl Test {
+        // Return an owned type so that we don't hit the fix for 5754
+        fn name(&self) -> String {
+            self.0.clone()
+        }
+    }
+
+    pub fn test() {
+        let mut args: Vec<Test> = vec![];
+
+        // Forward
+        args.sort_by(|a, b| a.name().cmp(&b.name()));
+        args.sort_unstable_by(|a, b| a.name().cmp(&b.name()));
+        // Reverse
+        args.sort_by(|a, b| b.name().cmp(&a.name()));
+        args.sort_unstable_by(|a, b| b.name().cmp(&a.name()));
+    }
+}
+
+fn main() {
+    unnecessary_sort_by();
+    issue_5754::test();
+    issue_6001::test();
+}