fix(@angular/build): ensure locale base href retains leading slash (angular#32040)

When baseHref is provided, getLocaleBaseHref was incorrectly adding a leading slash from the joined path. This commit removes calls `stripLeadingSlash` to ensure the leading slash is removed when appropriate.

Author: alan-agius4

packages/angular/build/src/builders/application/options.ts

@@ -25,7 +25,7 @@ import {
   loadPostcssConfiguration,
 } from '../../utils/postcss-configuration';
 import { getProjectRootPaths, normalizeDirectoryPath } from '../../utils/project-metadata';
-import { addTrailingSlash, joinUrlParts } from '../../utils/url';
+import { addTrailingSlash, joinUrlParts, stripLeadingSlash } from '../../utils/url';
 import {
   Schema as ApplicationBuilderOptions,
   ExperimentalPlatform,
@@ -681,9 +681,16 @@ export function getLocaleBaseHref(
 
   const baseHrefSuffix = localeData.baseHref ?? localeData.subPath + '/';
 
-  return baseHrefSuffix !== ''
-    ? addTrailingSlash(joinUrlParts(baseHref, baseHrefSuffix))
-    : undefined;
+  let joinedBaseHref: string | undefined;
+  if (baseHrefSuffix !== '') {
+    joinedBaseHref = addTrailingSlash(joinUrlParts(baseHref, baseHrefSuffix));
+
+    if (baseHref && baseHref[0] !== '/') {
+      joinedBaseHref = stripLeadingSlash(joinedBaseHref);
+    }
+  }
+
+  return joinedBaseHref;
 }
 
 /**

packages/angular/build/src/builders/application/options_spec.ts

@@ -0,0 +1,106 @@
+/**
+ * @license
+ * Copyright Google LLC All Rights Reserved.
+ *
+ * Use of this source code is governed by an MIT-style license that can be
+ * found in the LICENSE file at https://angular.dev/license
+ */
+
+import { NormalizedApplicationBuildOptions, getLocaleBaseHref } from './options';
+
+describe('getLocaleBaseHref', () => {
+  const baseI18nOptions: NormalizedApplicationBuildOptions['i18nOptions'] = {
+    inlineLocales: new Set(),
+    sourceLocale: 'en-US',
+    locales: {},
+    flatOutput: false,
+    shouldInline: false,
+    hasDefinedSourceLocale: false,
+  };
+
+  it('should return undefined if flatOutput is true', () => {
+    const result = getLocaleBaseHref(undefined, { ...baseI18nOptions, flatOutput: true }, 'fr');
+    expect(result).toBeUndefined();
+  });
+
+  it('should return undefined if locale is not found', () => {
+    const result = getLocaleBaseHref(undefined, baseI18nOptions, 'fr');
+    expect(result).toBeUndefined();
+  });
+
+  it('should return baseHref from locale data if present', () => {
+    const i18nOptions = {
+      ...baseI18nOptions,
+      locales: {
+        fr: {
+          files: [],
+          translation: {},
+          subPath: 'fr',
+          baseHref: '/fr/',
+        },
+      },
+    };
+    const result = getLocaleBaseHref(undefined, i18nOptions, 'fr');
+    expect(result).toBe('/fr/');
+  });
+
+  it('should join baseHref and locale subPath if baseHref is provided', () => {
+    const i18nOptions = {
+      ...baseI18nOptions,
+      locales: {
+        fr: {
+          files: [],
+          translation: {},
+          subPath: 'fr',
+        },
+      },
+    };
+    const result = getLocaleBaseHref('/app/', i18nOptions, 'fr');
+    expect(result).toBe('/app/fr/');
+  });
+
+  it('should handle missing baseHref (undefined) correctly', () => {
+    const i18nOptions = {
+      ...baseI18nOptions,
+      locales: {
+        fr: {
+          files: [],
+          translation: {},
+          subPath: 'fr',
+        },
+      },
+    };
+    const result = getLocaleBaseHref(undefined, i18nOptions, 'fr');
+    expect(result).toBe('/fr/');
+  });
+
+  it('should handle empty baseHref correctly', () => {
+    const i18nOptions = {
+      ...baseI18nOptions,
+      locales: {
+        fr: {
+          files: [],
+          translation: {},
+          subPath: 'fr',
+        },
+      },
+    };
+    const result = getLocaleBaseHref('', i18nOptions, 'fr');
+    expect(result).toBe('/fr/');
+  });
+
+  it('should strip leading slash if baseHref does not start with slash', () => {
+    const i18nOptions = {
+      ...baseI18nOptions,
+      locales: {
+        fr: {
+          files: [],
+          translation: {},
+          subPath: 'fr',
+        },
+      },
+    };
+    const result = getLocaleBaseHref('app/', i18nOptions, 'fr');
+    expect(result).toBe('app/fr/');
+  });
+});