Add reorder_impl_items config option

Configurations.md

@@ -1413,6 +1413,42 @@ mod sit;
 **Note** `mod` with `#[macro_export]` will not be reordered since that could change the semantic
 of the original source code.
 
+## `reorder_impl_items`
+
+Reorder impl items. `type` and `const` are put first, then macros and methods.
+
+- **Default value**: `false`
+- **Possible values**: `true`, `false`
+- **Stable**: No
+
+#### `false` (default)
+
+```rust
+struct Dummy;
+
+impl Iterator for Dummy {
+    fn next(&mut self) -> Option<Self::Item> {
+        None
+    }
+
+    type Item = i32;
+}
+```
+
+#### `true`
+
+```rust
+struct Dummy;
+
+impl Iterator for Dummy {
+    type Item = i32;
+
+    fn next(&mut self) -> Option<Self::Item> {
+        None
+    }
+}
+```
+
 ## `report_todo`
 
 Report `TODO` items in comments.

src/config/mod.rs

@@ -75,6 +75,7 @@ create_config! {
     reorder_imported_names: bool, true, false,
         "Reorder lists of names in import statements alphabetically";
     reorder_modules: bool, true, false, "Reorder module statemtents alphabetically in group";
+    reorder_impl_items: bool, false, false, "Reorder impl items";
 
     // Spaces around punctuation
     binop_separator: SeparatorPlace, SeparatorPlace::Front, false,

tests/source/configs/reorder_impl_items/false.rs

@@ -0,0 +1,11 @@
+// rustfmt-reorder_impl_items: false
+
+struct Dummy;
+
+impl Iterator for Dummy {
+    fn next(&mut self) -> Option<Self::Item> {
+        None
+    }
+
+    type Item = i32;
+}

tests/source/configs/reorder_impl_items/true.rs

@@ -0,0 +1,11 @@
+// rustfmt-reorder_impl_items: true
+
+struct Dummy;
+
+impl Iterator for Dummy {
+    fn next(&mut self) -> Option<Self::Item> {
+        None
+    }
+
+    type Item = i32;
+}

tests/target/configs/reorder_impl_items/false.rs

@@ -0,0 +1,11 @@
+// rustfmt-reorder_impl_items: false
+
+struct Dummy;
+
+impl Iterator for Dummy {
+    fn next(&mut self) -> Option<Self::Item> {
+        None
+    }
+
+    type Item = i32;
+}

tests/target/configs/reorder_impl_items/true.rs

@@ -0,0 +1,11 @@
+// rustfmt-reorder_impl_items: true
+
+struct Dummy;
+
+impl Iterator for Dummy {
+    type Item = i32;
+
+    fn next(&mut self) -> Option<Self::Item> {
+        None
+    }
+}