UnmarshalBinary has containers with needCopyOnWrite set to true

[David Wartell]

The below code produces a failure on assert.Equal(t, bitmap, bitmapUnmarshalled) with the following differences:

        	            	Diff:
        	            	--- Expected
        	            	+++ Actual
        	            	@@ -2067,4 +2067,4 @@
        	            	   needCopyOnWrite: ([]bool) (len=2) {
        	            	-   (bool) false,
        	            	-   (bool) false
        	            	+   (bool) true,
        	            	+   (bool) true
        	            	   },

func TestRoaringBitmapMarshalCowBug(t *testing.T) {
	id := uint64(100000)
	bitmap := roaring.NewBitmap()
	for i := uint64(0); i < id; i++ {
		if i%2 == 0 {
			bitmap.Add(uint32(i))
		}
	}

	bitmapBytes, err := bitmap.MarshalBinary()
	require.Nil(t, err)

	bitmapUnmarshalled := roaring.NewBitmap()
	err = bitmapUnmarshalled.UnmarshalBinary(bitmapBytes)
	require.Nil(t, err)

	assert.Equal(t, bitmap, bitmapUnmarshalled)
	assert.True(t, bitmap.Equals(bitmapUnmarshalled))
}

I also noticed a workaround is to Clone() the bitmap after UnmarshalBinary. This seems to clear the true values in needCopyOnWrite []bool

github.com/RoaringBitmap/roaring v1.3.0
go version go1.20.5 darwin/arm64

func TestRoaringBitmapMarshalCowBug(t *testing.T) {
	id := uint64(100000)
	bitmap := roaring.NewBitmap()
	for i := uint64(0); i < id; i++ {
		if i%2 == 0 {
			bitmap.Add(uint32(i))
		}
	}
	bitmapBytes, err := bitmap.MarshalBinary()
	require.Nil(t, err)

	bitmapUnmarshalled := roaring.NewBitmap()
	err = bitmapUnmarshalled.UnmarshalBinary(bitmapBytes)
	require.Nil(t, err)

	// Clone() clears the COW values
	bitmapUnmarshalled = bitmapUnmarshalled.Clone()

	assert.Equal(t, bitmap, bitmapUnmarshalled)
	assert.True(t, bitmap.Equals(bitmapUnmarshalled))
}


=== RUN   TestRoaringBitmapMarshalCowBug
--- PASS: TestRoaringBitmapMarshalCowBug (0.00s)
PASS

[Daniel Lemire]

@davidwartell Please have a look at #397