I know I have written about this before - and I have used Carrie as the example, too - but a post on io9 spurred me to write it again. The headline is "Well, the new Carrie trailer just showed off the whole damn movie," and it's technically true. It's also super short-sighted, and indicative of the way modern writers have little historical context for this sort of thing. Click on the io9 link to see the 'new' trailer* - the Brian DePalma trailer is embedded above.
You can see it gives the whole prom away. The prom is the selling point, as is the aftermath. And this isn't that unusual; trailers have always given away the best parts because those are the parts that are easiest to sell. Because they're the best parts. You don't sell a movie using the lamest bits. Unless you're Ender's Game, I guess.
So yeah, the Carrie trailer gives away the whole movie. Just like it did in 1976.
* it's actually an older trailer but they added a phone number to it because they're marketing this movie in 1988.