Definite article before generic nouns in constructions with the verb "gustar"

Question

I'm designing a problem based around the generic noun 'el pastel' and I'm wondering which variant of the following two is more acceptable:

1. A ellos les gusta comer el pastel.
2. A ellos les gusta comer pastel.

English translation: 'They like to eat/eating cake.'

From what I gather, the consensus on this is that nouns with a generic reference must be preceded by a definite article, as in 'A ellos les gusta el pastel'. However, the inclusion of the infinitive form of 'comer' before the generic noun seems to make the decision more difficult (maybe something semantic?). To my non-native ear, both variants sound Ok, with Variant 2 sounding a bit more natural.

Answer 1

Number 2 (comer pastel) is the one you want. Number 1, though not ungrammatical, is not natural. That's in short. But why?

These two sentences are basically equivalent, as you said:

1. A ellos les gusta el pastel.
2. A ellos les gusta comer pastel.

The subject (in this unusual construction) goes after the verb. In the first sentence the subject is el pastel. In sentence 2 the subject is comer pastel. In sentence 1, el pastel is a definite noun phrase.

The phrase comer pastel is also (sort of) a definite noun phrase. Inside it there's an infinitive and what in English you'd call a mass noun as its direct object. Pastel in this sense means "cake" in general, as if cake were a substance, although it can of course work as a countable noun (just as English "cake"). But comer pastel is both general and definite as it is, because Spanish infinitives are like that by default.

If you were to use a definite article (comer el pastel) it would sound as if you meant one particular cake that you've already talked about. This is not what you want, because it's not a general statement (it would be right if you said e. g. A ellos les gusta comer el pastel que les hago cada vez que vienen = "They like eating the cake I make for them every time they come").

Things are different if you just want to say les gusta el pastel. You can't say *les gusta pastel because Spanish doesn't work like that; mass nouns in that context do need a definite article.

Note that you can have X + infinitive constructions, where X definite and indefinite articles, demonstratives (ese, aquel), possessives (su, nuestros). At this point the infinitive is already what's called a deverbal noun and it works differently.

Answer 2

There's something a little weird about both of the proposed sentences. What do we do with cake besides eating it? I think your candidates should actually be

1. Les gusta el pastel.

2. Les gusta pastel.

And now the question has a simple answer. #1. Tengo que hacer un pastel de cumpleaños para la fiesta de mi hijo. A sus compañeritos les gusta el pastel / les encanta el pastel.