While using roaring/v2 in my project, I encountered unexpected error interval had zero length from .Validate() at the end of operations similar to those in TestValidate. Please note that bmap is not empty while calling .Validate().

Version: v2.4.3

import (
	"testing"

	"github.com/RoaringBitmap/roaring/v2"
	"github.com/stretchr/testify/require"
)

func TestValidate(t *testing.T) {
	b := roaring.New()
	b.RemoveRange(0, 180)
	b.AddRange(0, 180)
	b.RemoveRange(180, 217)
	b.AddRange(180, 217)
	b.RemoveRange(217, 2394)
	b.RemoveRange(2394, 2427)
	b.AddRange(2394, 2427)
	b.RemoveRange(2427, 2428)
	b.AddRange(2427, 2428)
	b.RemoveRange(2428, 3345)
	b.RemoveRange(3345, 3346)
	b.RemoveRange(3346, 3597)
	b.RemoveRange(3597, 3815)
	b.RemoveRange(3815, 3816)
	b.AddRange(3815, 3816)
	b.RemoveRange(3816, 3856)
	b.RemoveRange(3856, 4067)
	b.RemoveRange(4067, 4069)
	b.RemoveRange(4069, 4071)
	b.RemoveRange(4071, 4095)
	b.RemoveRange(4095, 4096)
	b.RunOptimize()
	require.False(t, b.IsEmpty())
	require.NoError(t, b.Validate())
}

Question: by the way, I’ve discovered that an empty bitmap doesn’t pass validation. Is that intentional? For example, in my project, bitmaps can be empty, and that’s a valid state. However, if I want to perform validation, I have to handle these two cases separately

func TestValidateEmpty(t *testing.T) {
	require.NoError(t, roaring.New().Validate())
}

Question: in my project, I store bitmaps in storage in binary format using .MarshalBinary. I started storing data when the bitmap version was v1 (from the package github.com/RoaringBitmap/roaring). Before saving a v1 bitmap to storage, I also called v1.RunOptimize().

Now, since the v2 binary format is backward-compatible with v1, when reading data from storage, I simply use v2.UnmarshalBinary(..v1 bytes...). Additionally, from time to time, I call v2.Validate() afterward to ensure everything is correct.

However, I’ve discovered that even though v1.RunOptimize() was applied before serialization, v2.Validate() can still fail (see the example below). To prevent this, I have to explicitly call v2.RunOptimize() after deserialization before running v2.Validate().

Is this behavior intentional?

v1 version: v1.9.4.
v2 version: v2.4.3.

import (
	"testing"

	v1 "github.com/RoaringBitmap/roaring"
	v2 "github.com/RoaringBitmap/roaring/v2"
	"github.com/stretchr/testify/require"
)

func TestValidateFromV1(t *testing.T) {
	v1 := v1.NewBitmap()
	for i := 0; i <= 2; i++ {
		v1.Add(uint32(i))
	}
	v1.RunOptimize()
	b, err := v1.MarshalBinary()
	require.NoError(t, err)
	v2 := v2.New()
	require.NoError(t, v2.UnmarshalBinary(b))
	// v2.RunOptimize() <- if uncomment this line, .Validate will pass
	require.NoError(t, v2.Validate())
}

Question: which are gurantees for .Validate if i from origin use v2 bitmap, but don't do any .RunOptimize(). Could it fail ?