Add support for plugins to change parsing, printing, and visiting behaviors

.gitignore

@@ -1,3 +1,6 @@
 **/target
 **/*.rs.bk
-Cargo.lock
+Cargo.lock
+
+# I `cargo expand > EXPAND.rs` sometimes
+EXPAND.rs

full-moon-derive/src/lib.rs

@@ -4,7 +4,6 @@ extern crate proc_macro;
 
 mod derive;
 mod node;
-mod symbols;
 mod visit;
 
 use derive::DeriveGenerator;
@@ -20,8 +19,3 @@ pub fn derive_visit(input: TokenStream) -> TokenStream {
 pub fn derive_node(input: TokenStream) -> TokenStream {
     node::NodeGenerator::derive(input)
 }
-
-#[proc_macro]
-pub fn symbols(input: TokenStream) -> TokenStream {
-    symbols::parse(input)
-}

full-moon-derive/src/node.rs

@@ -75,7 +75,7 @@ impl DeriveGenerator for NodeGenerator {
                 }
             }
 
-            impl #impl_generics crate::node::Node #impl_generics for #input_ident #ty_generics #where_clause {
+            impl #impl_generics crate::node::Node for #input_ident #ty_generics #where_clause {
                 fn start_position(&self) -> Option<crate::tokenizer::Position> {
                     Some(#macro_name!("range", { #tokens })?.0)
                 }

full-moon-derive/src/visit.rs

@@ -58,6 +58,14 @@ impl VisitGenerator {
         for field in data_fields
             .iter()
             .filter(|field| search_hint("visit", &field.attrs) != Some(VisitHint::Skip))
+            .filter(|field| {
+                field
+                    .ident
+                    .as_ref()
+                    .expect("field requires an ident")
+                    .to_string()
+                    != "plugin_info"
+            })
         {
             let ident = field.ident.as_ref().unwrap();
             let token_stream = quote! { #prefix#ident };
@@ -95,7 +103,7 @@ impl VisitGenerator {
 impl DeriveGenerator for VisitGenerator {
     fn complete(input: &syn::DeriveInput, tokens: TokenStream) -> TokenStream {
         let input_ident = &input.ident;
-        let (impl_generics, ty_generics, where_clause) = input.generics.split_for_impl();
+        let (_, ty_generics, where_clause) = input.generics.split_for_impl();
 
         let (visit_self, visit_self_end) = match search_hint("visit", &input.attrs) {
             Some(VisitHint::SkipVisitSelf) => (quote! {}, quote! {}),
@@ -137,8 +145,8 @@ impl DeriveGenerator for VisitGenerator {
         };
 
         quote! {
-            impl #impl_generics crate::visitors::Visit for #input_ident #ty_generics #where_clause {
-                fn visit<V: crate::visitors::Visitor>(&self, visitor: &mut V) {
+            impl<P: crate::plugins::Plugin> crate::visitors::Visit<P> for #input_ident #ty_generics #where_clause {
+                fn visit<V: crate::visitors::Visitor<P>>(&self, visitor: &mut V) {
                     macro_rules! visit {
                         ($visit_what: expr, $visitor: expr) => {
                             $visit_what.visit($visitor);
@@ -171,8 +179,8 @@ impl DeriveGenerator for VisitGenerator {
                 }
             }
 
-            impl #impl_generics crate::visitors::VisitMut for #input_ident #ty_generics #where_clause {
-                fn visit_mut<V: crate::visitors::VisitorMut>(mut self, visitor: &mut V) -> Self {
+            impl<P: crate::plugins::Plugin> crate::visitors::VisitMut<P> for #input_ident #ty_generics #where_clause {
+                fn visit_mut<V: crate::visitors::VisitorMut<P>>(mut self, visitor: &mut V) -> Self {
                     macro_rules! visit {
                         ($visit_what: expr, $visitor: expr) => {
                             $visit_what = $visit_what.visit_mut($visitor);
@@ -225,6 +233,12 @@ impl MatchEnumGenerator for VisitGenerator {
         variant: &syn::Ident,
         named: &syn::FieldsNamed,
     ) -> TokenStream {
+        // Plugins should create their own visitors, there's no good way
+        // to handle this generically.
+        if *variant == "Plugin" {
+            panic!("Plugin wasn't expected as a named variant");
+        }
+
         let fields: Vec<_> = named
             .named
             .iter()
@@ -255,6 +269,17 @@ impl MatchEnumGenerator for VisitGenerator {
         variant: &syn::Ident,
         fields: &syn::FieldsUnnamed,
     ) -> TokenStream {
+        // Plugins should create their own visitors, there's no good way
+        // to handle this generically.
+        if *variant == "Plugin" {
+            return quote! {
+                #input::#variant(node_info) => {
+                    // TODO: This is probably wrong
+                    unimplemented!("Plugin variant should not be being matched, plugins need to handle their own visit behavior");
+                }
+            };
+        }
+
         let fields: Vec<_> = fields
             .unnamed
             .iter()

full-moon/Cargo.toml

@@ -31,7 +31,7 @@ smol_str = { version = "0.1.17", features = ["serde"] }
 
 [dev-dependencies]
 criterion = "0.2"
-insta = { version = "1.7.0", features = ["glob"] }
+insta = { version = "1.8.0", features = ["glob"] }
 pretty_assertions = "0.6.1"
 
 [[bench]]