To see so much talent gathered around such a weak script, as in “The Big Wedding,” is to wonder whether movie stars are desperate to work, or if they really just enjoy hanging out together so much that they don’t care what they’re doing.

Movie review

2 1/2 (out of five stars)

DIRECTOR: Justin Zackman

CAST: Robert De Niro, Diane Keaton, Susan Sarandon, Amanda Seyfried, Topher Grace, Katherine Heigl, Robin Williams

RATED: R for language, sexual content and brief nudity

Running time: 1 hour, 30 minutes

There are four Academy Award winners in this film — Robert De Niro, Diane Keaton, Susan Sarandon and Robin Williams — plus Katherine Heigl and Amanda Seyfried. Entire films have been built around each one of those people, and yet here they all are, trying to hold up a big tent with holes in it.

And they almost succeed, in that “The Big Wedding” is at no point painful to watch.

Yet neither is it a comedy that ever fully delivers, or even comes close. Writer-director Justin Zackman either doesn’t understand the game he’s in or doesn’t understand the rules of the game, because he creates a farce, then tries to go for sentiment. Writer-director Justin Zackman ends up with a botched, compromised film that either needed to be more real and less nasty or — even better — more nasty and less real.

Farces are precise, mechanical structures. The characters are types, each one usually governed by one particular obsession, and the task of the writer is to set up a situation in which they all collide in hysterical and catastrophic ways. In “The Big Wedding,” Ben Barnes and Seyfried are a young couple about to be married. De Niro is the boy’s adoptive father, Sarandon is his girlfriend, and Diane Keaton is his ex-wife and the mother of his grown children.

Something funny has to happen, right? Something has to be built here. So Zackman comes up with this: Barnes, as Alejandro, was adopted from Colombia, and his birth mother is coming to the wedding. Since he never told his very traditional birth mother that his adoptive parents are divorced, he asks mom (Keaton) and dad (De Niro) to pretend they’re still married. This means that his father’s girlfriend (Sarandon) has to leave or pretend to be someone else.

Sorry, but this doesn’t work on any level.

Two problems with this, one tiny, one huge. The tiny one is that it doesn’t make any sense that Alejandro would bring this up now. If his birth mother is coming to the wedding, he has known this for weeks, so any urgency here is false. But put that one aside. The huge problem is more mechanical in nature: Zackman has set up a situation that, if it goes the other way, it really doesn’t matter, anyway. If the birth mother finds out, who cares? There are small consequences, nothing to be feared, and therefore little or no comic possibility. Moreover, the consequences for the people who will have to act out the deception — mom, dad and the girlfriend — are nonexistent.

Of course, there is only one thing to do when you set up a comic machine that doesn’t fire, and that’s to go sentimental. But if everybody is behaving like a stock comic type, that’s not going to work either. And that’s pretty much the misfire we get in “The Big Wedding,” but elevated to the point of watchability by the presence of some familiar actors.