macros: Add derive macro to implement as_str() from AsRef<str>

crates/ruma-macros/src/lib.rs

@@ -33,6 +33,7 @@ use self::{
     },
     identifiers::IdentifierInput,
     serde::{
+        as_str_as_ref_str::expand_as_str_as_ref_str,
         deserialize_from_cow_str::expand_deserialize_from_cow_str,
         display_as_ref_str::expand_display_as_ref_str,
         enum_as_ref_str::expand_enum_as_ref_str,
@@ -267,6 +268,13 @@ pub fn derive_enum_from_string(input: TokenStream) -> TokenStream {
 // FIXME: The following macros aren't actually interested in type details beyond name (and possibly
 //        generics in the future). They probably shouldn't use `DeriveInput`.
 
+/// Derive the `as_str()` method using the `AsRef<str>` implementation of the type.
+#[proc_macro_derive(AsStrAsRefStr, attributes(ruma_enum))]
+pub fn derive_as_str_as_ref_str(input: TokenStream) -> TokenStream {
+    let input = parse_macro_input!(input as DeriveInput);
+    expand_as_str_as_ref_str(&input.ident).unwrap_or_else(syn::Error::into_compile_error).into()
+}
+
 /// Derive the `fmt::Display` trait using the `AsRef<str>` implementation of the type.
 #[proc_macro_derive(DisplayAsRefStr)]
 pub fn derive_display_as_ref_str(input: TokenStream) -> TokenStream {

crates/ruma-macros/src/serde.rs

@@ -1,5 +1,6 @@
 //! Methods and types for (de)serialization.
 
+pub mod as_str_as_ref_str;
 pub mod attr;
 pub mod case;
 pub mod deserialize_from_cow_str;

crates/ruma-macros/src/serde/as_str_as_ref_str.rs

@@ -0,0 +1,16 @@
+use proc_macro2::{Ident, TokenStream};
+use quote::quote;
+
+pub fn expand_as_str_as_ref_str(ident: &Ident) -> syn::Result<TokenStream> {
+    let as_str_doc = format!("Creates a string slice from this `{}`.", ident);
+    Ok(quote! {
+        #[automatically_derived]
+        #[allow(deprecated)]
+        impl #ident {
+            #[doc = #as_str_doc]
+            pub fn as_str(&self) -> &str {
+                self.as_ref()
+            }
+        }
+    })
+}