Why is it "De l' " and not "Des" in this sentence

Question

This is an exercise from Duolingo. So the exercise asks to translate this sentence:

I ate pineapple everyday in Mexico.

And the correct answer is:

J'ai mangé de l'ananas tous les jours au Mexique.

There's two things that I don't understand about this sentence. First, why did we use the partitive article "de l'" instead of the indefinite articles "des" for the word "ananas". Like when we say: Je manges des/un fruit.

Plus, fruit is countable so it doesn't need a partitive article.

And in case if both me and Duolingo are correct, I wonder about the difference in meaning that "des" and "de l'" would make.

Second thing I don't understand is the usage of the passé composé instead of the imparfait; as it's a past habit.

Answer 1

1. First, why did we use the partitive article "de l'" instead of the indefinite articles "des" for the word "ananas".

   You can use either the partitive or the indefinite articles here but it makes more sense to use the partitive if you didn't eat whole ananas but chunks / slices of them, probably the most common case. That would even be no choice for bigger stuff like j'ai mangé du bœuf tous les jours (I ate beef everyday) and never j'ai mangé des bœufs tous les jours (I ate oxen everyday) unless you are a T-Rex ;-). Moreover, the English sentence doesn't use the plural so doesn't read I ate pineapples everyday...

2. I don't understand is the usage of the passé composé instead of the imparfait; as it's a past habit.

   Both the imparfait and the passé composé are valid French. There have been many questions around this choice here.