refactor(migrations): keep the http-xhr-backend migration idempotent

Our migrations should be idempotent in case they are run multiple times.

Author: JeanMeche

packages/core/schematics/migrations/http-xhr-backend/http-xhr-backend.spec.ts

@@ -59,7 +59,7 @@ describe('http fetch backend migration', () => {
     expect(actual).toMatch(/import \{.*withXhr.*\}/);
   });
 
-  it('should update provideHttpClient to remove withFetch', async () => {
+  it('should not update provideHttpClient to remove withFetch', async () => {
     const {fs} = await runTsurgeMigration(new XhrBackendMigration(), [
       {
         name: absoluteFrom('/index.ts'),
@@ -77,30 +77,9 @@ describe('http fetch backend migration', () => {
 
     const actual = fs.readFile(absoluteFrom('/index.ts'));
     expect(actual).toContain(
-      'provideHttpClient(withInterceptorsFromDi(), withXsrfConfiguration({}))',
+      'provideHttpClient(withFetch(), withInterceptorsFromDi(), withXsrfConfiguration({}))',
     );
-    expect(actual).not.toContain('withFetch');
-  });
-
-  it('should update provideHttpClient to remove withFetch as only arg', async () => {
-    const {fs} = await runTsurgeMigration(new XhrBackendMigration(), [
-      {
-        name: absoluteFrom('/index.ts'),
-        isProgramRootFile: true,
-        contents: `
-        import {AppConfig} from '@angular/core';
-        import {provideHttpClient, withFetch, withInterceptorsFromDi, withXsrfConfiguration} from '@angular/common/http';
-
-        const config: AppConfig = [
-          provideHttpClient(withFetch()),
-        ]
-          `,
-      },
-    ]);
-
-    const actual = fs.readFile(absoluteFrom('/index.ts'));
-    expect(actual).toContain('provideHttpClient()');
-    expect(actual).not.toContain('withFetch');
+    expect(actual).toContain('withFetch');
   });
 
   it('should not update provideHttpClient if withXhr is already present', async () => {

packages/core/schematics/migrations/http-xhr-backend/migration.ts

@@ -26,9 +26,7 @@ const provideHttpClient = 'provideHttpClient';
 
 const WITH_FETCH = 'withFetch';
 const WITH_XHR = 'withXhr';
-const CORE_PACKAGE = '@angular/core';
 const HTTP_PACKAGE = '@angular/common/http';
-const PROVIDE_HTTP_CLIENT = 'provideHttpClient';
 
 export interface CompilationUnitData {
   replacements: Replacement[];
@@ -41,8 +39,11 @@ export interface MigrationConfig {
   shouldMigrate?: (containingFile: ProjectFile) => boolean;
 }
 
-const provideHttpClientIdentifier = ts.factory.createIdentifier('provideHttpClient');
-
+/**
+ * Prior to v22, provideHttpClient() had a Xhr backend by default. In v22, the default was switched to a Fetch backend.
+ * This migration adds the withXhr() option to any provideHttpClient() calls that do not already have either withFetch() or withXhr() specified,
+ * to preserve the Xhr backend behavior.
+ */
 export class XhrBackendMigration extends TsurgeFunnelMigration<
   CompilationUnitData,
   CompilationUnitData
@@ -107,19 +108,6 @@ export class XhrBackendMigration extends TsurgeFunnelMigration<
             exportSymbolName: WITH_XHR,
             requestedFile: sourceFile,
           });
-        } else if (withFetchNode) {
-          const isLastArg = node.arguments[node.arguments.length - 1] === withFetchNode;
-          replacements.push(
-            new Replacement(
-              projectFile(sourceFile, info),
-              new TextUpdate({
-                position: withFetchNode.getStart(),
-                end: isLastArg ? withFetchNode.getEnd() : withFetchNode.getEnd() + 2, // +2 to remove the comma and space, could be improved
-                toInsert: '',
-              }),
-            ),
-          );
-          importManager.removeImport(sourceFile, 'withFetch', HTTP_PACKAGE);
         }
       };
       sourceFile.forEachChild(walk);