The first vector returned by ChunkGenerator is size 1 when chunk-size is 0

[sommd]

Describe the bug
When using ChunkGenerator with a chunk-size of 0, the first vector returned is size 1. Following vectors are size 0.

Expected behavior
The first (and all following) vectors should be size 0.

Reproduction steps

TEST_CASE("chunks") {
  auto vector = GENERATE(take(5, chunk(0, value(1))));
  REQUIRE(vector.size() == 0);
}

Platform information:

• OS: Linux 5.1.15-arch1-1-ARCH
• Compiler+version: g++ (GCC) 9.1.0
• Catch version: Catch v2.7.2 (it looks like the bug still exists though)

Additional context
My specific use-case in which I ran into this is a test like this:

TEST_CASE("my function") {
  auto size = GENERATE(0, 1, 2, 3);
  auto vector = GENERATE_COPY(take(1, chunk(size, random(-100, 100))));

  auto list = VectorToList(vector);
  
  REQUIRE(list.size() == size);
}

It's possible that the intended behaviour was to return a minimum chunk-size of 1 for all chunks, but I think it would make much more sense to return empty vectors, otherwise the use-case above would be more annoying to write.

[horenmar]

I am honestly surprised that I didn't make the ChunkGenerator assert on chunk_size == 0.

Anyway, I will have to think about it for a bit -- I am not sure what I think about making the generator potentially infinite even when given a finite generator as an input.