fix(core): fix ng generate @angular/core:output-migration. Fixes angular#58650 (angular#60763)

Fixes angular#58650 - Insert a TODO comment for empty emit (without parameter).

PR Close angular#60763

Author: aparzi

packages/core/schematics/migrations/output-migration/output-migration.spec.ts

@@ -169,6 +169,65 @@ describe('outputs', () => {
         });
       });
 
+      it('should not insert a TODO comment for emit function with no type', async () => {
+        await verify({
+          before: `
+              import {Directive, Output, EventEmitter} from '@angular/core';
+
+              @Directive()
+              export class TestDir {
+                @Output() someChange = new EventEmitter();
+
+                someMethod(): void {
+                  this.someChange.emit();
+                }
+              }
+            `,
+          after: `
+              import {Directive, output} from '@angular/core';
+
+              @Directive()
+              export class TestDir {
+                readonly someChange = output();
+
+                someMethod(): void {
+                  this.someChange.emit();
+                }
+              }
+            `,
+        });
+      });
+
+      it('should insert a TODO comment for emit function with type', async () => {
+        await verify({
+          before: `
+              import {Directive, Output, EventEmitter} from '@angular/core';
+
+              @Directive()
+              export class TestDir {
+                @Output() someChange = new EventEmitter<string>();
+
+                someMethod(): void {
+                  this.someChange.emit();
+                }
+              }
+            `,
+          after: `
+              import {Directive, output} from '@angular/core';
+
+              @Directive()
+              export class TestDir {
+                readonly someChange = output<string>();
+
+                someMethod(): void {
+                  // TODO: The 'emit' function requires a mandatory string argument
+                  this.someChange.emit();
+                }
+              }
+            `,
+        });
+      });
+
       it('should migrate multiple outputs', async () => {
         await verifyDeclaration({
           before:

packages/core/schematics/migrations/output-migration/output-migration.ts

@@ -16,6 +16,7 @@ import {
   ProjectFileID,
   Replacement,
   Serializable,
+  TextUpdate,
   TsurgeFunnelMigration,
 } from '../../utils/tsurge';
 
@@ -216,6 +217,8 @@ export class OutputMigration extends TsurgeFunnelMigration<
         }
       }
 
+      addCommentForEmptyEmit(node, info, checker, reflector, dtsReader, outputFieldReplacements);
+
       // detect imports of test runners
       if (isTestRunnerImport(node)) {
         isTestFile = true;
@@ -449,3 +452,77 @@ function addOutputReplacement(
   }
   existingReplacements.replacements.push(...replacements);
 }
+
+function addCommentForEmptyEmit(
+  node: ts.Node,
+  info: ProgramInfo,
+  checker: ts.TypeChecker,
+  reflector: TypeScriptReflectionHost,
+  dtsReader: DtsMetadataReader,
+  outputFieldReplacements: Record<ClassFieldUniqueKey, OutputMigrationData>,
+): void {
+  if (!isEmptyEmitCall(node)) return;
+
+  const propertyAccess = getPropertyAccess(node);
+  if (!propertyAccess) return;
+
+  const symbol = checker.getSymbolAtLocation(propertyAccess.name);
+  if (!symbol || !symbol.declarations?.length) return;
+
+  const propertyDeclaration = isTargetOutputDeclaration(
+    propertyAccess,
+    checker,
+    reflector,
+    dtsReader,
+  );
+  if (!propertyDeclaration) return;
+
+  const eventEmitterType = getEventEmitterArgumentType(propertyDeclaration);
+  if (!eventEmitterType) return;
+
+  const id = getUniqueIdForProperty(info, propertyDeclaration);
+  const file = projectFile(node.getSourceFile(), info);
+  const formatter = getFormatterText(node);
+  const todoReplacement: TextUpdate = new TextUpdate({
+    toInsert: `${formatter.indent}// TODO: The 'emit' function requires a mandatory ${eventEmitterType} argument\n`,
+    end: formatter.lineStartPos,
+    position: formatter.lineStartPos,
+  });
+
+  addOutputReplacement(outputFieldReplacements, id, file, new Replacement(file, todoReplacement));
+}
+
+function isEmptyEmitCall(node: ts.Node): node is ts.CallExpression {
+  return (
+    ts.isCallExpression(node) &&
+    ts.isPropertyAccessExpression(node.expression) &&
+    node.expression.name.text === 'emit' &&
+    node.arguments.length === 0
+  );
+}
+
+function getPropertyAccess(node: ts.CallExpression): ts.PropertyAccessExpression | null {
+  const propertyAccessExpression = (node.expression as ts.PropertyAccessExpression).expression;
+  return ts.isPropertyAccessExpression(propertyAccessExpression) ? propertyAccessExpression : null;
+}
+
+function getEventEmitterArgumentType(propertyDeclaration: ts.PropertyDeclaration): string | null {
+  const initializer = propertyDeclaration.initializer;
+  if (!initializer || !ts.isNewExpression(initializer)) return null;
+
+  const isEventEmitter =
+    ts.isIdentifier(initializer.expression) && initializer.expression.getText() === 'EventEmitter';
+
+  if (!isEventEmitter) return null;
+
+  const [typeArg] = initializer.typeArguments ?? [];
+  return typeArg ? typeArg.getText() : null;
+}
+
+function getFormatterText(node: ts.Node): {indent: string; lineStartPos: number} {
+  const sourceFile = node.getSourceFile();
+  const {line} = sourceFile.getLineAndCharacterOfPosition(node.getStart());
+  const lineStartPos = sourceFile.getPositionOfLineAndCharacter(line, 0);
+  const indent = sourceFile.text.slice(lineStartPos, node.getStart());
+  return {indent, lineStartPos};
+}