The question is on this sentence from L'Étranger by Camus. It is describing a scorching summer sky.
Il m'a semblé que le ciel s'ouvrait sur toute son étendue pour laisser pleuvoir du feu.
Which way of understanding du feu is correct?
du is a partitive article. du feu is the subject of pleuvoir, i.e. it is what rains. laisser pleuvoir du feu means "letting fire rain."
du is a partitive article. du feu is the object of pleuvoir, which is a transitive verb here; i.e. du feu is what gets poured. laisser pleuvoir du feu means "allowing the pouring of fire" or "allowing fire to be poured." We don't find out who or what is doing the pouring.
du is a contraction of de le. du feu is a prepositional complement of pleuvoir and describes the manner of raining or pouring. (de feu can be compared to de toute la respiration in this other post or to "with love" in "loving someone with the love of a brother.")
A related question would be: how one says, "Then God let it rain." Can we say Alors le Dieu le laisser pleuvoir?