check that the receiver type satisfies bounds

tests/ui/useless_conversion.fixed

@@ -206,11 +206,43 @@ mod issue11300 {
         assert_eq!(i.len(), 3);
     }
 
+    trait Helper<T: ?Sized> {}
+    impl Helper<i32> for [i32; 3] {}
+    impl Helper<i32> for std::array::IntoIter<i32, 3> {}
+    impl Helper<()> for std::array::IntoIter<i32, 3> {}
+
+    fn foo2<X: ?Sized, I>(_: I)
+    where
+        I: IntoIterator<Item = i32> + Helper<X>,
+    {
+    }
+
+    trait Helper2<T> {}
+    impl Helper2<std::array::IntoIter<i32, 3>> for i32 {}
+    impl Helper2<[i32; 3]> for i32 {}
+    fn foo3<I>(_: I)
+    where
+        I: IntoIterator<Item = i32>,
+        i32: Helper2<I>,
+    {
+    }
+
     pub fn bar() {
         // This should not trigger the lint:
         // `[i32, 3]` does not satisfy the `ExactSizeIterator` bound, so the into_iter call cannot be
         // removed and is not useless.
         foo([1, 2, 3].into_iter());
+
+        // This should trigger the lint, receiver type [i32; 3] also implements `Helper`
+        foo2::<i32, _>([1, 2, 3]);
+
+        // This again should *not* lint, since X = () and I = std::array::IntoIter<i32, 3>,
+        // and `[i32; 3]: Helper<()>` is not true (only `std::array::IntoIter<i32, 3>: Helper<()>` is).
+        foo2::<(), _>([1, 2, 3].into_iter());
+
+        // This should lint. Removing the `.into_iter()` means that `I` gets substituted with `[i32; 3]`,
+        // and `i32: Helper2<[i32, 3]>` is true, so this call is indeed unncessary.
+        foo3([1, 2, 3]);
     }
 }
 

tests/ui/useless_conversion.rs

@@ -206,11 +206,43 @@ mod issue11300 {
         assert_eq!(i.len(), 3);
     }
 
+    trait Helper<T: ?Sized> {}
+    impl Helper<i32> for [i32; 3] {}
+    impl Helper<i32> for std::array::IntoIter<i32, 3> {}
+    impl Helper<()> for std::array::IntoIter<i32, 3> {}
+
+    fn foo2<X: ?Sized, I>(_: I)
+    where
+        I: IntoIterator<Item = i32> + Helper<X>,
+    {
+    }
+
+    trait Helper2<T> {}
+    impl Helper2<std::array::IntoIter<i32, 3>> for i32 {}
+    impl Helper2<[i32; 3]> for i32 {}
+    fn foo3<I>(_: I)
+    where
+        I: IntoIterator<Item = i32>,
+        i32: Helper2<I>,
+    {
+    }
+
     pub fn bar() {
         // This should not trigger the lint:
         // `[i32, 3]` does not satisfy the `ExactSizeIterator` bound, so the into_iter call cannot be
         // removed and is not useless.
         foo([1, 2, 3].into_iter());
+
+        // This should trigger the lint, receiver type [i32; 3] also implements `Helper`
+        foo2::<i32, _>([1, 2, 3].into_iter());
+
+        // This again should *not* lint, since X = () and I = std::array::IntoIter<i32, 3>,
+        // and `[i32; 3]: Helper<()>` is not true (only `std::array::IntoIter<i32, 3>: Helper<()>` is).
+        foo2::<(), _>([1, 2, 3].into_iter());
+
+        // This should lint. Removing the `.into_iter()` means that `I` gets substituted with `[i32; 3]`,
+        // and `i32: Helper2<[i32, 3]>` is true, so this call is indeed unncessary.
+        foo3([1, 2, 3].into_iter());
     }
 }
 

tests/ui/useless_conversion.stderr

@@ -178,5 +178,29 @@ note: this parameter accepts any `IntoIterator`, so you don't need to call `.int
 LL |     fn b<T: IntoIterator<Item = i32>>(_: T) {}
    |             ^^^^^^^^^^^^^^^^^^^^^^^^
 
-error: aborting due to 24 previous errors
+error: explicit call to `.into_iter()` in function argument accepting `IntoIterator`
+  --> $DIR/useless_conversion.rs:237:24
+   |
+LL |         foo2::<i32, _>([1, 2, 3].into_iter());
+   |                        ^^^^^^^^^^^^^^^^^^^^^ help: consider removing the `.into_iter()`: `[1, 2, 3]`
+   |
+note: this parameter accepts any `IntoIterator`, so you don't need to call `.into_iter()`
+  --> $DIR/useless_conversion.rs:216:12
+   |
+LL |         I: IntoIterator<Item = i32> + Helper<X>,
+   |            ^^^^^^^^^^^^^^^^^^^^^^^^
+
+error: explicit call to `.into_iter()` in function argument accepting `IntoIterator`
+  --> $DIR/useless_conversion.rs:245:14
+   |
+LL |         foo3([1, 2, 3].into_iter());
+   |              ^^^^^^^^^^^^^^^^^^^^^ help: consider removing the `.into_iter()`: `[1, 2, 3]`
+   |
+note: this parameter accepts any `IntoIterator`, so you don't need to call `.into_iter()`
+  --> $DIR/useless_conversion.rs:225:12
+   |
+LL |         I: IntoIterator<Item = i32>,
+   |            ^^^^^^^^^^^^^^^^^^^^^^^^
+
+error: aborting due to 26 previous errors