feat(compiler): support AstVisitor.visitEmptyExpr()

Add support for `AstVisitor.visitEmptyExpr()`

Author: fisker

packages/compiler-cli/src/ngtsc/typecheck/src/expression.ts

@@ -129,13 +129,6 @@ class AstTranslator implements AstVisitor {
       ast = ast.ast;
     }
 
-    // The `EmptyExpr` doesn't have a dedicated method on `AstVisitor`, so it's special cased here.
-    if (ast instanceof EmptyExpr) {
-      const res = ts.factory.createIdentifier('undefined');
-      addParseSpanInfo(res, ast.sourceSpan);
-      return res;
-    }
-
     // First attempt to let any custom resolution logic provide a translation for the given node.
     const resolved = this.maybeResolve(ast);
     if (resolved !== null) {
@@ -494,6 +487,12 @@ class AstTranslator implements AstVisitor {
     return node;
   }
 
+  visitEmptyExpr(ast: EmptyExpr, context: any) {
+    const node = ts.factory.createIdentifier('undefined');
+    addParseSpanInfo(node, ast.sourceSpan);
+    return node;
+  }
+
   private convertToSafeCall(
     ast: Call | SafeCall,
     expr: ts.Expression,

packages/compiler/src/expression_parser/ast.ts

@@ -47,7 +47,7 @@ export abstract class ASTWithName extends AST {
 
 export class EmptyExpr extends AST {
   override visit(visitor: AstVisitor, context: any = null) {
-    // do nothing
+    return visitor.visitEmptyExpr?.(this, context);
   }
 }
 
@@ -651,6 +651,7 @@ export interface AstVisitor {
   visitRegularExpressionLiteral(ast: RegularExpressionLiteral, context: any): any;
   visitSpreadElement(ast: SpreadElement, context: any): any;
   visitASTWithSource?(ast: ASTWithSource, context: any): any;
+  visitEmptyExpr?(ast: EmptyExpr, context: any): any;
   /**
    * This function is optionally defined to allow classes that implement this
    * interface to selectively decide if the specified `ast` should be visited.
@@ -756,6 +757,7 @@ export class RecursiveAstVisitor implements AstVisitor {
   visitSpreadElement(ast: SpreadElement, context: any) {
     this.visit(ast.expression, context);
   }
+  visitEmptyExpr(ast: EmptyExpr, context: any): any {}
   // This is not part of the AstVisitor interface, just a helper method
   visitAll(asts: AST[], context: any): any {
     for (const ast of asts) {