fix: do not generate empty docstring for Rule (#987)

Author: sunng87

generator/src/generator.rs

@@ -223,10 +223,17 @@ fn generate_enum(
     });
 
     let grammar_doc = &doc_comment.grammar_doc;
-    let mut result = quote! {
-        #[doc = #grammar_doc]
-        #[allow(dead_code, non_camel_case_types, clippy::upper_case_acronyms)]
-        #[derive(Clone, Copy, Debug, Eq, Hash, Ord, PartialEq, PartialOrd)]
+    let mut result = if grammar_doc.is_empty() {
+        quote! {
+            #[allow(dead_code, non_camel_case_types, clippy::upper_case_acronyms)]
+            #[derive(Clone, Copy, Debug, Eq, Hash, Ord, PartialEq, PartialOrd)]
+        }
+    } else {
+        quote! {
+            #[doc = #grammar_doc]
+            #[allow(dead_code, non_camel_case_types, clippy::upper_case_acronyms)]
+            #[derive(Clone, Copy, Debug, Eq, Hash, Ord, PartialEq, PartialOrd)]
+        }
     };
     if non_exhaustive {
         result.append_all(quote! {
@@ -865,6 +872,41 @@ mod tests {
         );
     }
 
+    #[test]
+    fn rule_empty_doc() {
+        let rules = vec![OptimizedRule {
+            name: "f".to_owned(),
+            ty: RuleType::Normal,
+            expr: OptimizedExpr::Ident("g".to_owned()),
+        }];
+
+        let mut line_docs = HashMap::new();
+        line_docs.insert("f".to_owned(), "This is rule comment".to_owned());
+
+        let doc_comment = &DocComment {
+            grammar_doc: "".to_owned(),
+            line_docs,
+        };
+
+        assert_eq!(
+            generate_enum(&rules, doc_comment, false, false).to_string(),
+            quote! {
+                #[allow(dead_code, non_camel_case_types, clippy::upper_case_acronyms)]
+                #[derive(Clone, Copy, Debug, Eq, Hash, Ord, PartialEq, PartialOrd)]
+                pub enum Rule {
+                    #[doc = "This is rule comment"]
+                    r#f
+                }
+                impl Rule {
+                    pub fn all_rules() -> &'static [Rule] {
+                        &[Rule::r#f]
+                    }
+                }
+            }
+            .to_string()
+        );
+    }
+
     #[test]
     fn sequence() {
         let expr = OptimizedExpr::Seq(