assertFalse(
        from.getType() + " shouldn't be a subtype of " + to.getType(), from.isSubtypeOf(to));
  }

  private static void assertHasArrayInterfaces(TypeToken<?> arrayType) {
    assertEquals(arrayInterfaces(), ImmutableSet.copyOf(arrayType.getGenericInterfaces()));
  }

  private static ImmutableSet<TypeToken<?>> arrayInterfaces() {
    ImmutableSet.Builder<TypeToken<?>> builder = ImmutableSet.builder();

    assertFalse(
        from.getType() + " shouldn't be a subtype of " + to.getType(), from.isSubtypeOf(to));
  }

  private static void assertHasArrayInterfaces(TypeToken<?> arrayType) {
    assertEquals(arrayInterfaces(), ImmutableSet.copyOf(arrayType.getGenericInterfaces()));
  }

  private static ImmutableSet<TypeToken<?>> arrayInterfaces() {
    ImmutableSet.Builder<TypeToken<?>> builder = ImmutableSet.builder();

// The result is false if x could be a type element OR an ordinary (value) expression.
func isTypeElem(x ast.Expr) bool {
	switch x := x.(type) {
	case *ast.ArrayType, *ast.StructType, *ast.FuncType, *ast.InterfaceType, *ast.MapType, *ast.ChanType:
		return true
	case *ast.UnaryExpr:
		return x.Op == token.TILDE
	case *ast.BinaryExpr:
		return isTypeElem(x.X) || isTypeElem(x.Y)

func (p *Package) cgoType(e ast.Expr) *Type {
	switch t := e.(type) {
	case *ast.StarExpr:
		x := p.cgoType(t.X)
		return &Type{Size: p.PtrSize, Align: p.PtrSize, C: c("%s*", x.C)}
	case *ast.ArrayType:
		if t.Len == nil {
			// Slice: pointer, len, cap.
			return &Type{Size: p.PtrSize * 3, Align: p.PtrSize, C: c("GoSlice")}
		}
		// Non-slice array types are not supported.
	case *ast.StructType:

		"type:runtime.hchan":             nil,
	}

	// Needed by the prettyprinter code for interface inspection.
	for _, typ := range []string{
		"type:internal/abi.Type",
		"type:internal/abi.ArrayType",
		"type:internal/abi.ChanType",
		"type:internal/abi.FuncType",
		"type:internal/abi.MapType",
		"type:internal/abi.PtrType",
		"type:internal/abi.SliceType",
		"type:internal/abi.StructType",