Not using href values from alternaateRefs array and instead original URL path for all hreflang entries

[markojak]

Describe the bug

When generating a sitemap for a Next.js application with multiple languages we incorrectly generates the hreflang attributes in the sitemap XML. It seems to have a limitation or bug in how it handles the alternateRefs array when generating the sitemap XML. The package is not correctly using the href values from the alternateRefs array and is instead using the original URL path for all hreflang entries.

To Reproduce

• Define a custom transform function that generates alternateRefs array for each URL using a bunch of constants specifying the correct hreflang and href values for each alternate language
• generate sitemap
• Inspect sitemap

(code below)

In the generated sitemap XML, the xhtml:link elements for alternate language URLs should have the correct hreflang and href attributes. The href attribute should contain the appropriate URL for each alternate language, matching the hreflang value.

For example, for a URL like https://example.com/fr/blog, the expected xhtml:link elements should be:

<xhtml:link rel="alternate" hreflang="en" href="https://example.com/en/blog"/>
<xhtml:link rel="alternate" hreflang="es" href="https://example.com/es/blog"/>
<xhtml:link rel="alternate" hreflang="de" href="https://example/de/blog"/>

Actual behavior

In the generated sitemap XML, the xhtml:link elements for alternate language URLs have incorrect href attributes. The href attribute contains the same URL as the main URL, instead of the corresponding alternate language URL.

For example, for a URL like https://example.com/fr/blog, the actual xhtml:link elements in the sitemap XML are:

<xhtml:link rel="alternate" hreflang="en" href="https://example.com/fr/blog"/>
<xhtml:link rel="alternate" hreflang="es" href="https://example.com/fr/blog"/>
<xhtml:link rel="alternate" hreflang="de" href="https://example.com/fr/blog"/>
<xhtml:link rel="alternate" hreflang="fr" href="https://example.com/fr/blog"/>

Additional context

Next.js version: "next": "13.4.10-canary.1",
Latest sitemap version

Implementation

require('ts-node').register();
const { SUPPORTED_LOCALES } = require('./src/constants.ts');

const generateAlternateRefs = (path, locales) => {
    console.log('Path:', path);
    console.log('Locales:', locales);

    const alternateRefs = locales.map((locale) => {
        const localePath = path.replace(new RegExp(`^/(${locales.join('|')})`), `/${locale}`);
        return {
            hreflang: locale,
            href: `https://example.com${localePath}`,
        };
    });
    return alternateRefs;
};

/** @type {import('next-sitemap').IConfig} */
module.exports = {
    siteUrl: 'https://example.com',
    changefreq: 'daily',
    priority: 0.7,
    sitemapSize: 5000,
    generateRobotsTxt: true,
    transform: async (config, path) => {
        console.log('Transform Path:', path);

        const alternateRefs = generateAlternateRefs(path, Object.keys(SUPPORTED_LOCALES));
        console.log('Generated Alternate Refs:', alternateRefs);

        return {
            loc: `${config.siteUrl}${path}`,
            changefreq: config.changefreq,
            priority: config.priority,
            lastmod: config.autoLastmod ? new Date().toISOString() : undefined,
            alternateRefs,
        };
    },
    robotsTxtOptions: {
        policies: [
            {
                userAgent: '*',
                allow: '/',
            },
        ],
    },
};

[luukkynda]

I haven't tested this yet, but since hreflang is defined appropriately, did you consider the fact that your regex might be incorrect/returns something different then you'd expect? Since this is a custom transformation, I would assume that something is going wrong in the transformation and that it hasn't got much to do with the package itself