Off the rails with a proc macro

advent_derive/.gitignore

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+/target

advent_derive/Cargo.lock

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+# This file is automatically @generated by Cargo.
+# It is not intended for manual editing.
+version = 4
+
+[[package]]
+name = "advent_derive"
+version = "0.1.0"
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advent_derive/Cargo.toml

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+[package]
+name = "advent_derive"
+version = "0.1.0"
+edition = "2021"
+
+[lib]
+proc-macro = true
+
+[dependencies]
+syn = "2.0"
+quote = "1.0"
+darling = "0.20"
+

advent_derive/src/lib.rs

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+
+extern crate proc_macro;
+
+use proc_macro::{TokenStream, TokenTree};
+use quote::quote;
+use syn::{parse_macro_input, parse_quote, Expr, ItemStruct};
+
+#[proc_macro_attribute]
+pub fn advent_day(attrs: TokenStream, item: TokenStream, ) -> TokenStream {
+    let input = parse_macro_input!(item as ItemStruct);
+    let ident = &input.ident;
+
+    let mut parts = vec![];
+    for token in attrs.into_iter() {
+        match token {
+            TokenTree::Ident(ident) => parts.push(ident.to_string()),
+            _ => continue
+        }
+    }
+
+    let call1 = format!("{}::new()", parts[0]);
+    let call2 = format!("{}::new()", parts[1]);
+    let part1: Expr = parse_quote!(#call1);
+    let part2: Expr = parse_quote!(#call2);
+    
+    println!("{:?} {:?}", part1, part2);
+    
+    let output = quote! {
+        pub struct #ident {
+            part1: Box::<dyn AdventDayPart1>,
+            part2: Box::<dyn AdventDayPart2>
+        }
+
+        impl Day4 {
+            pub fn new() -> Self {
+                Day4 {
+                    part1: Box::new(#part1),
+                    part2: Box::new(#part2)
+                }
+            }
+        }          
+
+        impl AdventDay for #ident {
+            fn puzzle1(&mut self) -> Result<u64, AdventError> {
+                self.part1.read_input()?;
+                self.part1.solve()
+            }
+
+            fn puzzle2(&mut self) -> Result<u64, AdventError> {
+                self.part2.read_input()?;
+                self.part2.solve()
+            }
+        }
+    };
+    output.into()
+
+}