Il manque "de" or "du"?

Question

In the "Manquer de" section it says that we don't use an article so we'd use either "de" or "d'", but in the next section with impersonal structure the example given is: "Il manque du sel dans cette soupe." Since the soup "is lacking of" salt, wouldn't it just be "de sel"? Why would we use an article here?

Christian Huter · Accepted Answer

The comment about not using the partitive article only applies to the case of "manquer de". It does not apply to the impersonal structure (Il manque [quelque chose] à [quelqu'un/quelque chose]). The impersonal structure does not include the preposition "de" so that you can use the normal partitive articles.
On the other hand, if you did not use the impersonal structure, it would be:
"Cette soupe manque de sel."
 
The rule that you do not have a partitive article "manquer de" is not a particularity of "manquer", it applies to all forms of "verb + preposition de": avoir besoin de, avoir envie de, ...
"J'ai besoin de sel." (Not: "besoin de du sel" or "besoin du sel")