1 files changed, 65 insertions, 0 deletions
diff --git a/third_party/rust/derive_more-impl/src/is_variant.rs b/third_party/rust/derive_more-impl/src/is_variant.rs
new file mode 100644
index 0000000000..123e3fb7bb
--- /dev/null
+++ b/third_party/rust/derive_more-impl/src/is_variant.rs
@@ -0,0 +1,65 @@
+use crate::utils::{AttrParams, DeriveType, State};
+use convert_case::{Case, Casing};
+use proc_macro2::TokenStream;
+use quote::{format_ident, quote};
+use syn::{DeriveInput, Fields, Result};
+
+pub fn expand(input: &DeriveInput, trait_name: &'static str) -> Result<TokenStream> {
+    let state = State::with_attr_params(
+        input,
+        trait_name,
+        "is_variant".into(),
+        AttrParams {
+            enum_: vec!["ignore"],
+            variant: vec!["ignore"],
+            struct_: vec!["ignore"],
+            field: vec!["ignore"],
+        },
+    )?;
+    assert!(
+        state.derive_type == DeriveType::Enum,
+        "IsVariant can only be derived for enums",
+    );
+
+    let enum_name = &input.ident;
+    let (imp_generics, type_generics, where_clause) = input.generics.split_for_impl();
+
+    let mut funcs = vec![];
+    for variant_state in state.enabled_variant_data().variant_states {
+        let variant = variant_state.variant.unwrap();
+        let fn_name = format_ident!(
+            "is_{}",
+            variant.ident.to_string().to_case(Case::Snake),
+            span = variant.ident.span(),
+        );
+        let variant_ident = &variant.ident;
+
+        let data_pattern = match variant.fields {
+            Fields::Named(_) => quote! { {..} },
+            Fields::Unnamed(_) => quote! { (..) },
+            Fields::Unit => quote! {},
+        };
+        let variant_name = stringify!(variant_ident);
+        let func = quote! {
+            #[doc = "Returns `true` if this value is of type `"]
+            #[doc = #variant_name]
+            #[doc = "`. Returns `false` otherwise"]
+            pub const fn #fn_name(&self) -> bool {
+                match self {
+                    #enum_name ::#variant_ident #data_pattern => true,
+                    _ => false
+                }
+            }
+        };
+        funcs.push(func);
+    }
+
+    let imp = quote! {
+        #[automatically_derived]
+        impl #imp_generics #enum_name #type_generics #where_clause {
+            #(#funcs)*
+        }
+    };
+
+    Ok(imp)
+}