Prevent symbolic links from themes

hugolib/filesystems/basefs.go

@@ -718,6 +718,7 @@ func createThemesOverlayFs(p *paths.Paths) (afero.Fs, []string, error) {
 	}
 
 	fs, err := createOverlayFs(p.Fs.Source, absPaths)
+	fs = hugofs.NewNoLstatFs(fs)
 
 	return fs, absPaths, err
 

hugolib/filesystems/basefs_test.go

@@ -218,6 +218,12 @@ func TestRealDirs(t *testing.T) {
 
 	checkFileCount(bfs.Resources.Fs, "", assert, 3)
 
+	assert.NotNil(bfs.themeFs)
+	fi, b, err := bfs.themeFs.(afero.Lstater).LstatIfPossible(filepath.Join("resources", "t1.txt"))
+	assert.NoError(err)
+	assert.False(b)
+	assert.Equal("t1.txt", fi.Name())
+
 }
 
 func TestStaticFs(t *testing.T) {