if r != 0 {
			return r
		}
		iname := importName(a)
		jname := importName(b)
		r = cmp.Compare(iname, jname)
		if r != 0 {
			return r
		}
		return cmp.Compare(importComment(a), importComment(b))
	})

	// Dedup. Thanks to our sorting, we can just consider
	// adjacent pairs of imports.
	deduped := specs[:0]
	for i, s := range specs {
		if i == len(specs)-1 || !collapse(s, specs[i+1]) {

	checkPkg := func(t *testing.T, m *Module, pkg string, data []byte) {
		p := m.Package(pkg)
		bp, err := p.Import(build.Default, build.ImportComment)
		if err != nil {
			t.Fatal(err)
		}
		bp1, err := build.Default.Import(".", filepath.Join(src, pkg), build.ImportComment)
		if err != nil {
			t.Fatal(err)
		}

		if !reflect.DeepEqual(bp, bp1) {
			t.Errorf("mismatch")
			t.Logf("index:\n%s", hex.Dump(data))