From fb6348b9932ba3adbce631106d96686444c7df8f Mon Sep 17 00:00:00 2001
From: Alan Agius <17563226+alan-agius4@users.noreply.github.com>
Date: Fri, 5 Dec 2025 10:42:31 +0000
Subject: [PATCH] fix(@angular/build): ensure locale base href retains leading
 slash

When baseHref is provided, getLocaleBaseHref was incorrectly stripping the leading slash from the joined path. This commit removes the stripLeadingSlash call to ensure the leading slash is preserved when appropriate.

Closes #32030
---
 .../build/src/builders/application/options.ts |  15 ++-
 .../src/builders/application/options_spec.ts  | 106 ++++++++++++++++++
 2 files changed, 117 insertions(+), 4 deletions(-)
 create mode 100644 packages/angular/build/src/builders/application/options_spec.ts

diff --git a/packages/angular/build/src/builders/application/options.ts b/packages/angular/build/src/builders/application/options.ts
index 25bd87253357..83b7ea428f35 100644
--- a/packages/angular/build/src/builders/application/options.ts
+++ b/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;
 }
 
 /**
diff --git a/packages/angular/build/src/builders/application/options_spec.ts b/packages/angular/build/src/builders/application/options_spec.ts
new file mode 100644
index 000000000000..ac6320905019
--- /dev/null
+++ b/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/');
+  });
+});