1 files changed, 83 insertions, 0 deletions
diff --git a/third_party/rust/derive_more/src/into.rs b/third_party/rust/derive_more/src/into.rs
new file mode 100644
index 0000000000..61d820e9b8
--- /dev/null
+++ b/third_party/rust/derive_more/src/into.rs
@@ -0,0 +1,83 @@
+use std::iter;
+
+use proc_macro2::TokenStream;
+use quote::{quote, ToTokens};
+use syn::{parse::Result, DeriveInput};
+
+use crate::utils::{add_extra_generic_param, AttrParams, MultiFieldData, State};
+
+/// Provides the hook to expand `#[derive(Into)]` into an implementation of `Into`
+pub fn expand(input: &DeriveInput, trait_name: &'static str) -> Result<TokenStream> {
+    let state = State::with_attr_params(
+        input,
+        trait_name,
+        quote!(::core::convert),
+        trait_name.to_lowercase(),
+        AttrParams {
+            enum_: vec!["ignore", "owned", "ref", "ref_mut"],
+            variant: vec!["ignore", "owned", "ref", "ref_mut"],
+            struct_: vec!["ignore", "owned", "ref", "ref_mut", "types"],
+            field: vec!["ignore"],
+        },
+    )?;
+    let MultiFieldData {
+        variant_info,
+        field_types,
+        field_idents,
+        input_type,
+        ..
+    } = state.enabled_fields_data();
+
+    let mut tokens = TokenStream::new();
+
+    for ref_type in variant_info.ref_types() {
+        let reference = ref_type.reference();
+        let lifetime = ref_type.lifetime();
+        let reference_with_lifetime = ref_type.reference_with_lifetime();
+
+        let generics_impl;
+        let (_, ty_generics, where_clause) = input.generics.split_for_impl();
+        let (impl_generics, _, _) = if ref_type.is_ref() {
+            generics_impl = add_extra_generic_param(&input.generics, lifetime);
+            generics_impl.split_for_impl()
+        } else {
+            input.generics.split_for_impl()
+        };
+
+        let additional_types = variant_info.additional_types(ref_type);
+        for explicit_type in iter::once(None).chain(additional_types.iter().map(Some)) {
+            let into_types: Vec<_> = field_types
+                .iter()
+                .map(|field_type| {
+                    // No, `.unwrap_or()` won't work here, because we use different types.
+                    if let Some(type_) = explicit_type {
+                        quote! { #reference_with_lifetime #type_ }
+                    } else {
+                        quote! { #reference_with_lifetime #field_type }
+                    }
+                })
+                .collect();
+
+            let initializers = field_idents.iter().map(|field_ident| {
+                if let Some(type_) = explicit_type {
+                    quote! { <#reference #type_>::from(#reference original.#field_ident) }
+                } else {
+                    quote! { #reference original.#field_ident }
+                }
+            });
+
+            (quote! {
+                #[automatically_derived]
+                impl#impl_generics ::core::convert::From<#reference_with_lifetime #input_type#ty_generics> for
+                    (#(#into_types),*) #where_clause {
+
+                    #[inline]
+                    fn from(original: #reference_with_lifetime #input_type#ty_generics) -> Self {
+                        (#(#initializers),*)
+                    }
+                }
+            }).to_tokens(&mut tokens);
+        }
+    }
+    Ok(tokens)
+}