hugolib: Fix alias path for AMP and similar

Fixes #5760

hugolib/alias_test.go

@@ -80,7 +80,7 @@ func TestAliasMultipleOutputFormats(t *testing.T) {
 
 	// the alias redirectors
 	b.AssertFileContent("public/foo/bar/index.html", "<meta http-equiv=\"refresh\" content=\"0; ")
-	b.AssertFileContent("public/foo/bar/amp/index.html", "<meta http-equiv=\"refresh\" content=\"0; ")
+	b.AssertFileContent("public/amp/foo/bar/index.html", "<meta http-equiv=\"refresh\" content=\"0; ")
 	assert.False(b.CheckExists("public/foo/bar/index.json"))
 }
 

hugolib/site_render.go

@@ -305,7 +305,7 @@ func (s *Site) renderAliases() error {
 			for _, a := range p.Aliases() {
 				if f.Path != "" {
 					// Make sure AMP and similar doesn't clash with regular aliases.
-					a = path.Join(a, f.Path)
+					a = path.Join(f.Path, a)
 				}
 
 				lang := p.Language().Lang