Used existing macro code as a basis for implementing a source argumen…

…t for the derive macro. This should allow users to derive their own Source using the provided trait, which was previously missing from derive. (#225)

Co-authored-by: Maciej Hirsz <hello@maciej.codes>

logos-codegen/src/parser/mod.rs

@@ -25,6 +25,7 @@ use self::type_params::{replace_lifetime, traverse_type, TypeParams};
 pub struct Parser {
     pub errors: Errors,
     pub mode: Mode,
+    pub source: Option<TokenStream>,
     pub extras: MaybeVoid,
     pub error_type: MaybeVoid,
     pub subpatterns: Subpatterns,
@@ -96,6 +97,16 @@ impl Parser {
             };
 
             match (name.to_string().as_str(), value) {
+                ("source", NestedValue::Assign(value)) => {
+                    let span = value.span();
+                    if let Some(previous) = self.source.replace(value) {
+                        self.err("Source can be defined only once", span)
+                            .err("Previous definition here", previous.span());
+                    }
+                }
+                ("source", _) => {
+                    self.err("Expected: source = SomeType", name.span());
+                }
                 ("error", NestedValue::Assign(value)) => {
                     let span = value.span();
 

logos-derive/src/lib.rs

@@ -2,5 +2,5 @@ use proc_macro::TokenStream;
 
 #[proc_macro_derive(Logos, attributes(logos, extras, error, end, token, regex))]
 pub fn logos(input: TokenStream) -> TokenStream {
-    return logos_codegen::generate(input.into()).into();
+    logos_codegen::generate(input.into()).into()
 }