feat(AstVisitor): add onStart, onFinish callbacks to AstVisitor. It allows to add logging/reporting when you apply it to your AST.

Author: nodkz

src/astVisitor.ts

@@ -30,6 +30,14 @@ export type AstVisitor = {
   DIR?: VisitKindFn<AstDirNode>;
   FILE?: VisitKindFn<AstFileNode>;
   ROOT_TYPE?: VisitKindFn<AstRootTypeNode>;
+  /**
+   * Callback will be called when you start apply visitor to AST.
+   */
+  onStart?: (ast: AstRootNode, visitor: AstVisitor) => void;
+  /**
+   * Callback will be called when visitor finishes traversing AST.
+   */
+  onFinish?: (ast: AstRootNode, visitor: AstVisitor) => void;
 };
 
 export interface VisitInfo {
@@ -40,6 +48,10 @@ export interface VisitInfo {
 }
 
 export function astVisitor(ast: AstRootNode, visitor: AstVisitor): void {
+  if (visitor?.onStart) {
+    visitor.onStart(ast, visitor);
+  }
+
   (Object.keys(ast.children) as Array<keyof typeof ast.children>).forEach((operation) => {
     const rootNode = ast.children[operation];
     if (!rootNode) return;
@@ -51,6 +63,10 @@ export function astVisitor(ast: AstRootNode, visitor: AstVisitor): void {
       operation,
     });
   });
+
+  if (visitor?.onFinish) {
+    visitor.onFinish(ast, visitor);
+  }
 }
 
 export function visitNode(