Generic diagram generator from markup language

I’m looking for diagram generator (using some markup language as the input) capable of generating generic block-and-arrow diagrams. I would have labeled blocks containing other labeled blocks, and sometimes-labeled lines/arrows between the blocks. I want to list the blocks and let the generator automatically size and place them on a canvas.

I’ve looked at common diagram generators but they all seem focused on other types of diagrams. Has anyone used something capable of generating this type of diagram?