Fix redundant_closure_for_method_calls suggestion

Certain types must be enclosed in angle brackets and must have generic
arguments substituted to create a working suggestion. For example, if
`s` has type `&[u8]`, then `|s| s.len()` may be replaced with
`<[u8]>::len`. Previously, Clippy erroneously suggested `[T]::len`.

tests/ui/eta.fixed

@@ -316,3 +316,25 @@ pub fn mutable_impl_fn_mut(mut f: impl FnMut(), mut f_used_once: impl FnMut()) -
 
     move || takes_fn_mut(&mut f_used_once)
 }
+
+impl dyn TestTrait + '_ {
+    fn method_on_dyn(&self) -> bool {
+        false
+    }
+}
+
+// https://github.com/rust-lang/rust-clippy/issues/7746
+fn angle_brackets_and_substs() {
+    let array_opt: Option<&[u8; 3]> = Some(&[4, 8, 7]);
+    array_opt.map(<[u8; 3]>::as_slice);
+
+    let slice_opt: Option<&[u8]> = Some(b"slice");
+    slice_opt.map(<[u8]>::len);
+
+    let ptr_opt: Option<*const usize> = Some(&487);
+    ptr_opt.map(<*const usize>::is_null);
+
+    let test_struct = TestStruct { some_ref: &487 };
+    let dyn_opt: Option<&dyn TestTrait> = Some(&test_struct);
+    dyn_opt.map(<dyn TestTrait>::method_on_dyn);
+}

tests/ui/eta.rs

@@ -316,3 +316,25 @@ pub fn mutable_impl_fn_mut(mut f: impl FnMut(), mut f_used_once: impl FnMut()) -
 
     move || takes_fn_mut(|| f_used_once())
 }
+
+impl dyn TestTrait + '_ {
+    fn method_on_dyn(&self) -> bool {
+        false
+    }
+}
+
+// https://github.com/rust-lang/rust-clippy/issues/7746
+fn angle_brackets_and_substs() {
+    let array_opt: Option<&[u8; 3]> = Some(&[4, 8, 7]);
+    array_opt.map(|a| a.as_slice());
+
+    let slice_opt: Option<&[u8]> = Some(b"slice");
+    slice_opt.map(|s| s.len());
+
+    let ptr_opt: Option<*const usize> = Some(&487);
+    ptr_opt.map(|p| p.is_null());
+
+    let test_struct = TestStruct { some_ref: &487 };
+    let dyn_opt: Option<&dyn TestTrait> = Some(&test_struct);
+    dyn_opt.map(|d| d.method_on_dyn());
+}

tests/ui/eta.stderr

@@ -134,5 +134,29 @@ error: redundant closure
 LL |     move || takes_fn_mut(|| f_used_once())
    |                          ^^^^^^^^^^^^^^^^ help: replace the closure with the function itself: `&mut f_used_once`
 
-error: aborting due to 22 previous errors
+error: redundant closure
+  --> $DIR/eta.rs:329:19
+   |
+LL |     array_opt.map(|a| a.as_slice());
+   |                   ^^^^^^^^^^^^^^^^ help: replace the closure with the method itself: `<[u8; 3]>::as_slice`
+
+error: redundant closure
+  --> $DIR/eta.rs:332:19
+   |
+LL |     slice_opt.map(|s| s.len());
+   |                   ^^^^^^^^^^^ help: replace the closure with the method itself: `<[u8]>::len`
+
+error: redundant closure
+  --> $DIR/eta.rs:335:17
+   |
+LL |     ptr_opt.map(|p| p.is_null());
+   |                 ^^^^^^^^^^^^^^^ help: replace the closure with the method itself: `<*const usize>::is_null`
+
+error: redundant closure
+  --> $DIR/eta.rs:339:17
+   |
+LL |     dyn_opt.map(|d| d.method_on_dyn());
+   |                 ^^^^^^^^^^^^^^^^^^^^^ help: replace the closure with the method itself: `<dyn TestTrait>::method_on_dyn`
+
+error: aborting due to 26 previous errors