1 files changed, 74 insertions, 0 deletions
diff --git a/third_party/rust/derive_more-impl/doc/index.md b/third_party/rust/derive_more-impl/doc/index.md
new file mode 100644
index 0000000000..c45fb46df5
--- /dev/null
+++ b/third_party/rust/derive_more-impl/doc/index.md
@@ -0,0 +1,74 @@
+# What `#[derive(Index)]` generates
+
+Deriving `Index` only works for a single field of a struct.
+The result is that you will index it's member directly.
+
+With `#[index]` or `#[index(ignore)]` it's possible to indicate the field that
+you want to derive `Index` for.
+
+
+
+
+## Example usage
+
+```rust
+# use derive_more::Index;
+#
+#[derive(Index)]
+struct MyVec(Vec<i32>);
+
+// You can specify the field you want to derive Index for
+#[derive(Index)]
+struct Numbers {
+    #[index]
+    numbers: Vec<i32>,
+    useless: bool,
+}
+
+assert_eq!(5, MyVec(vec![5, 8])[0]);
+assert_eq!(200, Numbers { numbers: vec![100, 200], useless: false }[1]);
+```
+
+
+
+
+## Structs
+
+When deriving `Index` for a struct:
+
+```rust
+# use derive_more::Index;
+#
+#[derive(Index)]
+struct Numbers {
+    #[index]
+    numbers: Vec<i32>,
+    useless: bool,
+}
+```
+
+Code like this will be generated:
+
+```rust
+# struct Numbers {
+#     numbers: Vec<i32>,
+#     useless: bool,
+# }
+impl<__IdxT> ::core::ops::Index<__IdxT> for Numbers
+where
+    Vec<i32>: ::core::ops::Index<__IdxT>,
+{
+    type Output = <Vec<i32> as ::core::ops::Index<__IdxT>>::Output;
+    #[inline]
+    fn index(&self, idx: __IdxT) -> &Self::Output {
+        <Vec<i32> as ::core::ops::Index<__IdxT>>::index(&self.numbers, idx)
+    }
+}
+```
+
+
+
+
+## Enums
+
+Deriving `Index` is not supported for enums.