Warm the olive oil in a large soup pot over medium-low heat, and add the garlic and rosemary.
Cook for a minute or two, and then add the tomatoes, sugar, salt, a few grinds of pepper, roughly half of the chickpeas, and the stock. Bring to a boil over high heat; then reduce the heat to low and simmer, partially covered, for 20 minutes.
Remove the soup from the heat to purée. If using an immersion blender, purée the soup directly in the pot. Otherwise, wait a few minutes, until the soup cools; then purée it in batches in a blender or food processor and return it to the pot.
Add the remaining chickpeas, and warm the soup over medium heat. Serve warm.