Generate grammar comments

examples/domainmodel/src/language-server/domain-model.langium

@@ -22,8 +22,11 @@ Entity:
         (features+=Feature)*
     '}';
 
+/**
+ * This is a parser rule
+ */
 Feature:
-    (many?='many')? name=ID ':' type=[Type:QualifiedName];
+    (many?='many')? name=ID ':' /** This is an assignment */ type=[Type:QualifiedName];
 
 QualifiedName returns string:
     ID ('.' ID)*;

examples/domainmodel/src/language-server/generated/grammar.ts

@@ -306,7 +306,8 @@ export const DomainModelGrammar = (): Grammar => loadedDomainModelGrammar ?? (lo
                 "arguments": []
               },
               "deprecatedSyntax": false
-            }
+            },
+            "$comment": "/** This is an assignment */"
           }
         ]
       },
@@ -315,7 +316,8 @@ export const DomainModelGrammar = (): Grammar => loadedDomainModelGrammar ?? (lo
       "fragment": false,
       "hiddenTokens": [],
       "parameters": [],
-      "wildcard": false
+      "wildcard": false,
+      "$comment": "/**\\n * This is a parser rule\\n */"
     },
     {
       "$type": "ParserRule",

packages/langium-cli/src/generator/grammar-serializer.ts

@@ -36,6 +36,7 @@ export function serializeGrammar(services: LangiumServices, grammars: Grammar[],
                 };
                 const serializedGrammar = services.serializer.JsonSerializer.serialize(grammar, {
                     space: production ? undefined : 2,
+                    comments: true,
                     uriConverter
                 });
                 // The json serializer returns strings with \n line delimiter by default

packages/langium/src/grammar/langium-grammar.langium

@@ -1,8 +1,9 @@
-/******************************************************************************
- * Copyright 2021 TypeFox GmbH
- * This program and the accompanying materials are made available under the
- * terms of the MIT License, which is available in the project root.
- ******************************************************************************/
+// ******************************************************************************
+// Copyright 2021 TypeFox GmbH
+// This program and the accompanying materials are made available under the
+// terms of the MIT License, which is available in the project root.
+// *****************************************************************************
+
 grammar LangiumGrammar
 
 entry Grammar:

packages/langium/src/serializer/json-serializer.ts

@@ -188,7 +188,10 @@ export class DefaultJsonSerializer implements JsonSerializer {
             }
             if (comments) {
                 astNode ??= { ...value };
-                (astNode as AstNodeWithComment).$comment = this.commentProvider.getComment(value);
+                const comment = this.commentProvider.getComment(value);
+                if (comment) {
+                    (astNode as AstNodeWithComment).$comment = comment.replace(/\r/g, '');
+                }
             }
             return astNode ?? value;
         } else {