output: Fix permalink in sitemap etc. when multiple permalinkable output formats

In Hugo 0.55.0 we made AMP `permalinkable`. We also render the output formats in their natural sort order, meaning `AMP` will be rendered before `HTML`. References in the sitemap would then point to the AMP version, and this is normally not what you'd want.

This commit fixes that by making `HTML` by default sort before the others.

If this is not you want, you can set `weight` on the output format configuration.

Fixes #5910

hugolib/sitemap_test.go

@@ -100,3 +100,22 @@ func TestParseSitemap(t *testing.T) {
 	}
 
 }
+
+// https://github.com/gohugoio/hugo/issues/5910
+func TestSitemapOutputFormats(t *testing.T) {
+
+	b := newTestSitesBuilder(t).WithSimpleConfigFile()
+
+	b.WithContent("blog/html-amp.md", `
+---
+Title: AMP and HTML
+outputs: [ "html", "amp" ]
+---
+
+`)
+
+	b.Build(BuildCfg{})
+
+	// Should link to the HTML version.
+	b.AssertFileContent("public/sitemap.xml", " <loc>http://example.com/blog/html-amp/</loc>")
+}