feat(stackable-versioned): Use attribute instead of derive macro (#793)

* Update changelog

* Add basic adjustements to support attribute macro

* Add type alias for latest version

* Remove unused code

Author: Techassi

crates/stackable-versioned/CHANGELOG.md

@@ -4,9 +4,12 @@ All notable changes to this project will be documented in this file.
 
 ## [Unreleased]
 
+- Change from derive macro to attribute macro to be able to generate code
+  _in place_ instead of _appending_ new code ([#CHANGEME]).
 - Improve action chain generation ([#784]).
 
-[#784](ttps://github.com/stackabletech/operator-rs/pull/784)
+[#784](https://github.com/stackabletech/operator-rs/pull/784)
+[#CHANGEME](https://github.com/stackabletech/operator-rs/pull/CHANGEME)
 
 ## [0.1.0] - 2024-05-08
 

crates/stackable-versioned/src/attrs/container.rs

@@ -2,7 +2,7 @@ use std::{cmp::Ordering, collections::HashSet, ops::Deref};
 
 use darling::{
     util::{Flag, SpannedValue},
-    Error, FromDeriveInput, FromMeta, Result,
+    Error, FromMeta, Result,
 };
 use k8s_version::Version;
 
@@ -12,13 +12,8 @@ use k8s_version::Version;
 ///
 /// - `version`, which can occur one or more times. See [`VersionAttributes`].
 /// - `options`, which allow further customization of the generated code. See [`ContainerOptions`].
-#[derive(Clone, Debug, FromDeriveInput)]
-#[darling(
-    attributes(versioned),
-    supports(struct_named),
-    forward_attrs(allow, doc, cfg, serde),
-    and_then = ContainerAttributes::validate
-)]
+#[derive(Debug, FromMeta)]
+#[darling(and_then = ContainerAttributes::validate)]
 pub(crate) struct ContainerAttributes {
     #[darling(multiple, rename = "version")]
     pub(crate) versions: SpannedValue<Vec<VersionAttributes>>,

crates/stackable-versioned/src/gen/mod.rs

@@ -1,16 +1,14 @@
-use darling::FromDeriveInput;
 use proc_macro2::TokenStream;
 use quote::ToTokens;
 use syn::{spanned::Spanned, Data, DeriveInput, Error, Result};
 
 use crate::{
     attrs::container::ContainerAttributes,
-    gen::{venum::VersionedEnum, version::ContainerVersion, vstruct::VersionedStruct},
+    gen::{version::ContainerVersion, vstruct::VersionedStruct},
 };
 
 pub(crate) mod field;
 pub(crate) mod neighbors;
-pub(crate) mod venum;
 pub(crate) mod version;
 pub(crate) mod vstruct;
 
@@ -26,20 +24,13 @@ pub(crate) mod vstruct;
 // TODO (@Techassi): Think about how we can handle nested structs / enums which
 // are also versioned.
 
-pub(crate) fn expand(input: DeriveInput) -> Result<TokenStream> {
-    // Extract container attributes
-    let attributes = ContainerAttributes::from_derive_input(&input)?;
-
-    // Validate container shape and generate code
+pub(crate) fn expand(attrs: ContainerAttributes, input: DeriveInput) -> Result<TokenStream> {
     let expanded = match input.data {
-        Data::Struct(data) => {
-            VersionedStruct::new(input.ident, data, attributes)?.to_token_stream()
-        }
-        Data::Enum(data) => VersionedEnum::new(input.ident, data, attributes)?.to_token_stream(),
-        Data::Union(_) => {
+        Data::Struct(data) => VersionedStruct::new(input.ident, data, attrs)?.to_token_stream(),
+        _ => {
             return Err(Error::new(
                 input.span(),
-                "derive macro `Versioned` only supports structs and enums",
+                "attribute macro `versioned` only supports structs",
             ))
         }
     };

crates/stackable-versioned/src/gen/venum.rs

@@ -27,10 +27,11 @@ pub(crate) struct VersionedStruct {
 }
 
 impl ToTokens for VersionedStruct {
-    fn to_tokens(&self, _tokens: &mut TokenStream) {
-        let mut versions = self.versions.iter().peekable();
+    fn to_tokens(&self, tokens: &mut TokenStream) {
+        let versions = self.versions.iter().peekable();
+        let struct_name = &self.ident;
 
-        while let Some(version) = versions.next() {
+        for version in versions {
             let mut fields = TokenStream::new();
 
             for field in &self.fields {
@@ -43,24 +44,27 @@ impl ToTokens for VersionedStruct {
 
             let deprecated_attr = version.deprecated.then_some(quote! {#[deprecated]});
             let module_name = format_ident!("{version}", version = version.inner.to_string());
-            let struct_name = &self.ident;
-
-            // Only generate a module when there is at least one more version.
-            // This skips generating a module for the latest version, because
-            // the base struct always represents the latest version.
-            if versions.peek().is_some() {
-                _tokens.extend(quote! {
-                    #[automatically_derived]
-                    #deprecated_attr
-                    pub mod #module_name {
-
-                        pub struct #struct_name {
-                            #fields
-                        }
+
+            tokens.extend(quote! {
+                #[automatically_derived]
+                #deprecated_attr
+                pub mod #module_name {
+
+                    pub struct #struct_name {
+                        #fields
                     }
-                });
-            }
+                }
+            });
         }
+
+        // Special handling for the last (and thus latest) version
+        let module_name = format_ident!(
+            "{version}",
+            version = self.versions.last().unwrap().inner.to_string()
+        );
+        tokens.extend(quote! {
+            pub type #struct_name = #module_name::#struct_name;
+        })
     }
 }
 

crates/stackable-versioned/src/gen/vstruct.rs

@@ -1,15 +1,32 @@
+use darling::{ast::NestedMeta, FromMeta};
 use proc_macro::TokenStream;
 use syn::{DeriveInput, Error};
 
+use crate::attrs::container::ContainerAttributes;
+
 mod attrs;
 mod consts;
 mod gen;
 
-#[proc_macro_derive(Versioned, attributes(versioned))]
-pub fn versioned_macro_derive(input: TokenStream) -> TokenStream {
+#[proc_macro_attribute]
+pub fn versioned(attrs: TokenStream, input: TokenStream) -> TokenStream {
+    let attrs = match NestedMeta::parse_meta_list(attrs.into()) {
+        Ok(attrs) => match ContainerAttributes::from_list(&attrs) {
+            Ok(attrs) => attrs,
+            Err(err) => return err.write_errors().into(),
+        },
+        Err(err) => return darling::Error::from(err).write_errors().into(),
+    };
+
+    // NOTE (@Techassi): For now, we can just use the DeriveInput type here,
+    // because we only support structs (and eventually enums) to be versioned.
+    // In the future - if we decide to support modules - this requires
+    // adjustments to also support modules. One possible solution might be to
+    // use an enum with two variants: Container(DeriveInput) and
+    // Module(ItemMod).
     let input = syn::parse_macro_input!(input as DeriveInput);
 
-    gen::expand(input)
+    gen::expand(attrs, input)
         .unwrap_or_else(Error::into_compile_error)
         .into()
 }

crates/stackable-versioned/src/lib.rs

@@ -1,9 +1,8 @@
-use stackable_versioned::Versioned;
+use stackable_versioned::versioned;
 
 // To expand the generated code (for debugging and testing), it is recommended
 // to first change directory via `cd crates/stackable-versioned` and to then
 // run `cargo expand --test basic --all-features`.
-#[derive(Versioned)]
 #[allow(dead_code)]
 #[versioned(
     version(name = "v1alpha1"),
@@ -27,6 +26,16 @@ struct Foo {
 fn basic() {
     let _ = v1alpha1::Foo { jjj: 0, baz: false };
     let _ = v1beta1::Foo { bar: 0, baz: false };
+    let _ = v1::Foo { bar: 0, baz: false };
+
+    #[allow(deprecated)]
+    let _ = v2::Foo {
+        deprecated_bar: 0,
+        baz: false,
+    };
+
+    // The latest version (v3)
+    #[allow(deprecated)]
     let _ = Foo {
         deprecated_bar: 0,
         baz: false,