Replace simple_event_shunt macro with proc macro

This macro is pretty complicated and I needed to add the ability to
clean keywords, so it makes more sense to have this be a proc macro.

macros/Cargo.toml

@@ -0,0 +1,11 @@
+[package]
+name = "macros"
+version = "0.1.0"
+edition = "2021"
+
+[lib]
+proc-macro = true
+
+[dependencies]
+quote = "1.0.37"
+syn = "2.0.79"

macros/src/lib.rs

@@ -0,0 +1,133 @@
+use proc_macro::TokenStream;
+
+use quote::{format_ident, quote};
+use syn::{
+    braced, bracketed, parse::Parse, parse_macro_input, parse_quote, punctuated::Punctuated, Token,
+};
+
+enum FieldOrClosure {
+    Field(syn::Ident),
+    Closure(syn::Ident, syn::Expr),
+}
+
+impl Parse for FieldOrClosure {
+    fn parse(input: syn::parse::ParseStream) -> syn::Result<Self> {
+        input.parse().map(|ident| Self::Field(ident)).or_else(|_| {
+            input.parse().map(|mut closure: syn::ExprClosure| {
+                assert_eq!(closure.inputs.len(), 1);
+                let syn::Pat::Ident(arg) = closure.inputs.pop().unwrap().into_value() else {
+                    panic!("expected ident for closure argument");
+                };
+
+                Self::Closure(arg.ident, *closure.body)
+            })
+        })
+    }
+}
+
+struct EventVariant {
+    name: syn::Ident,
+    fields: Option<Punctuated<FieldOrClosure, Token![,]>>,
+}
+
+impl Parse for EventVariant {
+    fn parse(input: syn::parse::ParseStream) -> syn::Result<Self> {
+        let name = input.parse()?;
+        let fields = if input.peek(syn::token::Brace) {
+            let f;
+            braced!(f in input);
+            let f = Punctuated::parse_terminated(&f)?;
+            Some(f)
+        } else {
+            None
+        };
+
+        Ok(Self { name, fields })
+    }
+}
+
+struct Input {
+    object: syn::Expr,
+    event_object: syn::Ident,
+    event_type: syn::Type,
+    events: Punctuated<EventVariant, Token![,]>,
+}
+
+impl Parse for Input {
+    fn parse(input: syn::parse::ParseStream) -> syn::Result<Self> {
+        let object = input.parse()?;
+        input.parse::<Token![,]>()?;
+        let event_object = input.parse()?;
+        input.parse::<Token![:]>()?;
+        let event_type = input.parse()?;
+        input.parse::<Token![=>]>()?;
+        let events;
+        bracketed!(events in input);
+        let events = Punctuated::parse_terminated(&events)?;
+        Ok(Self {
+            object,
+            event_object,
+            event_type,
+            events,
+        })
+    }
+}
+
+#[proc_macro]
+pub fn simple_event_shunt(tokens: TokenStream) -> TokenStream {
+    let Input {
+        object,
+        event_object,
+        event_type,
+        events,
+    } = parse_macro_input!(tokens as Input);
+
+    let match_arms = events.into_iter().map(|e| {
+        let mut field_names = Punctuated::<_, Token![,]>::new();
+        let mut fn_args = Punctuated::<syn::Expr, Token![,]>::new();
+        if let Some(fields) = e.fields {
+            for field in fields {
+                match field {
+                    FieldOrClosure::Field(name) => {
+                        fn_args.push(parse_quote! { #name });
+                        field_names.push(name);
+                    }
+                    FieldOrClosure::Closure(name, expr) => {
+                        field_names.push(name);
+                        fn_args.push(expr);
+                    }
+                }
+            }
+        }
+
+        let name = e.name;
+        let fn_name = String::from_utf8(
+            name.to_string()
+                .bytes()
+                .enumerate()
+                .flat_map(|(idx, c)| {
+                    if idx != 0 && c.is_ascii_uppercase() {
+                        vec![b'_', c.to_ascii_lowercase()]
+                    } else {
+                        vec![c.to_ascii_lowercase()]
+                    }
+                })
+                .collect::<Vec<_>>(),
+        )
+        .unwrap();
+        let keyword_pfx = if fn_name == "type" { "_" } else { "" };
+        let fn_name = format_ident!("{keyword_pfx}{fn_name}");
+
+        quote! {
+            #name { #field_names } => { #object.#fn_name(#fn_args); }
+        }
+    });
+    quote! {{
+        use #event_type::*;
+        match #event_object {
+            #(#match_arms)*
+            _ => log::warn!(concat!("unhandled ", stringify!(#event_type), ": {:?}"), #event_object)
+        }
+    }}
+    .into()
+}