Enhance PmpEmitter macro to support additional attributes and default handling

crates/pmp-emitter/src/lib.rs

@@ -3,34 +3,53 @@ use proc_macro::TokenStream;
 use syn::{ Lit, Path, Type, Ident, DeriveInput, parse_macro_input };
 use darling::{ ast, Error, Result, FromMeta, FromVariant, FromDeriveInput };
 
+// ---------------------------------------------------------------------------------------------- //
 
+#[derive(Debug, FromDeriveInput)]
+#[darling(forward_attrs(pmp_emitter))]
+struct EmitterInput {
+    ident: Ident,
+    data:  ast::Data<VariantReceiver, ()>,
+}
+
+#[derive(Debug, FromVariant)]
+#[darling(forward_attrs(pmp_emitter))]
+struct VariantReceiver {
+    ident:  Ident,
+    fields: ast::Fields<Type>,
+    attrs:  Vec<syn::Attribute>,
+}
+
+// ---------------------------------------------------------------------------------------------- //
 
 #[derive(Debug, Clone, Copy)]
 struct StrictBool(bool);
 
-#[derive(Debug, FromDeriveInput)]
+/// - `descriptor = "..."` - prefix shown before all variant messages (default: enum name)
-#[darling(attributes(PMPEmitter))]
+/// - `exit = true|false`  - whether to call process::exit (default: false)
-struct EmitterInput {
+#[derive(Debug, FromMeta)]
-    ident:      Ident,
+struct EnumAttrs {
-    data:       ast::Data<VariantReceiver, ()>,
+    #[darling(default)]
-    descriptor: String,
+    descriptor: Option<String>,
-    exit:       StrictBool,
+    #[darling(default)]
+    exit:       Option<StrictBool>,
 }
 
-#[derive(Debug, FromVariant)]
+/// - `message = "..."`   - error message (default: variant name as title case)
-#[darling(attributes(PMPEmitter))]
+/// - `colorizer = fn`    - optional fn(String) -> String for formatting
-struct VariantReceiver {
+/// - `exit = true|false` - overrides enum-level exit
-    ident:     Ident,
+#[derive(Debug, FromMeta)]
-    #[allow(unused)]
+struct VariantAttrs {
-    fields:    ast::Fields<Type>,
-
     #[darling(default)]
     exit:      Option<StrictBool>,
-    message:   String,
+    #[darling(default)]
+    message:   Option<String>,
     #[darling(default)]
     colorizer: Option<Path>,
 }
 
+// ---------------------------------------------------------------------------------------------- //
+
 impl FromMeta for StrictBool
 {
     fn from_value(value: &Lit) -> Result<Self>
@@ -44,6 +63,29 @@ impl FromMeta for StrictBool
     // intentionally NOT implementing from_word()
 }
 
+fn parse_pmp_attr<T: FromMeta>(attrs: &[syn::Attribute]) -> T
+where
+    T: Default,
+{
+    attrs
+        .iter()
+        .find(|a| a.path().is_ident("pmp_emitter"))
+        .map(|a| T::from_meta(&a.meta).expect("invalid pmp_emitter attribute"))
+        .unwrap_or_default()
+}
+
+impl Default for EnumAttrs {
+    fn default() -> Self {
+        Self { descriptor: None, exit: None }
+    }
+}
+
+impl Default for VariantAttrs {
+    fn default() -> Self {
+        Self { message: None, exit: None, colorizer: None }
+    }
+}
+
 // ---------------------------------------------------------------------------------------------- //
 
 fn pascal_to_title(s: &str) -> String 
@@ -61,60 +103,77 @@ fn pascal_to_title(s: &str) -> String
 
 // ---------------------------------------------------------------------------------------------- //
 
-#[proc_macro_attribute]
+#[proc_macro_derive(PmpEmitter, attributes(pmp_emitter))]
-pub fn pmp_emitter(_attr: TokenStream, item: TokenStream) -> TokenStream
+pub fn pmp_emitter(item: TokenStream) -> TokenStream
 {
     let input = parse_macro_input!(item as DeriveInput);
-    let args  = match EmitterInput::from_derive_input(&input) {
+
+    // parse enum shape
+    let shape = match EmitterInput::from_derive_input(&input) {
         Ok(a)  => a,
         Err(e) => return e.write_errors().into(),
     };
 
-    let enum_ident  = &args.ident;
+    // parse enum-level #[pmp_emitter(...)] directly from the raw attrs
-    let descriptor  = &args.descriptor;
+    let enum_attrs: EnumAttrs = parse_pmp_attr(&input.attrs);
-    let global_exit = args.exit.0;
 
-    let variants = args
+    let enum_ident  = &shape.ident;
+    let descriptor  = enum_attrs.descriptor
+        .unwrap_or_else(|| pascal_to_title(&enum_ident.to_string()));
+    let global_exit = enum_attrs.exit.map(|b| b.0).unwrap_or(false);
+
+    let variants = shape
         .data
         .take_enum()
-        .expect("pmp_emitter can only be applied to enums");
+        .expect("PmpEmitter can only be derived on enums");
 
-    let match_arms = variants.iter().map(|v| 
+    let match_arms = variants.iter().map(|v|
-    {
-        let var_ident   = &v.ident;
-        let message     = &v.message;
-        let should_exit = v.exit.map(|b| b.0).unwrap_or(global_exit);
-        let title       = pascal_to_title(&var_ident.to_string());
-
-        // ┌─ Output format ───────────────────────────────┐
-        // │  {descriptor}: {Variant Title} ("{message}")  │
-        // │                                               │
-        // │  {stacktrace}                                 │
-        // └───────────────────────────────────────────────┘
-        let header = format!("{}: {} (\"{}\")", descriptor, title, message);
-
-        // Apply colorizer fn if provided, otherwise plain string
-        let formatted_header = match &v.colorizer 
         {
-            Some(path) => quote! { #path(#header) },
+            let var_ident = &v.ident;
-            None       => quote! { #header.to_string() },
+            let title     = pascal_to_title(&var_ident.to_string());
-        };
 
-        let exit_tokens = if should_exit { quote! { std::process::exit(1); } } else { quote! {} };
+            // parse variant-level #[pmp_emitter(...)] from the variant's raw attrs
+            let vattrs: VariantAttrs = parse_pmp_attr(&v.attrs);
 
-        quote! {
+            let message     = vattrs.message.unwrap_or_else(|| title.clone());
-            #enum_ident::#var_ident(trace) => 
+            let should_exit = vattrs.exit.map(|b| b.0).unwrap_or(global_exit);
+
+            // ┌─ Output format ───────────────────────────────┐
+            // │  {descriptor}: {Variant Title} ("{message}")  │
+            // │                                               │
+            // │  {stacktrace}                                 │
+            // └───────────────────────────────────────────────┘
+            let header = format!("{}: {} (\"{}\")", descriptor, title, message);
+
+            let formatted_header = match &vattrs.colorizer
             {
-                println!("{}\n\n{}", #formatted_header, trace);
+                Some(path) => quote! { #path(#header) },
-                #exit_tokens
+                None       => quote! { #header.to_string() },
+            };
+
+            let exit_tokens = if should_exit { quote! { std::process::exit(1); } } else { quote! {} };
+
+            match v.fields.style
+            {
+                ast::Style::Tuple => quote! {
+                #enum_ident::#var_ident(trace) =>
+                {
+                    println!("{}\n\n{}", #formatted_header, trace);
+                    #exit_tokens
+                }
+            },
+                _ => quote! {
+                #enum_ident::#var_ident =>
+                {
+                    println!("{}", #formatted_header);
+                    #exit_tokens
+                }
+            },
             }
-        }
+        });
-    });
 
     quote! {
-        #input  // re-emit the original enum untouched
+        impl #enum_ident
-
-        impl #enum_ident 
         {
             pub fn emit(&self) {
                 match self {