Which is the consensus for button action labels? [duplicate]

Let's say I have a button that varies it's label between Lollipops and Marshmallows. When pressed, it will show a list of one of those.

Like this:

<button id = "showCandies">Lollipops</button>
<!-- After toggle -->
<button id = "showCandies">Marshmallows</button>

What is the consensus, should it show the action it has performed and is therefore being shown, or should show the action that will be executed when pressed?

I've always have this question and I though it could be nice to have it answered. Please, let me know if it is out of place but it applies to programming, since maybe the consensus changes in the context, so I am speaking about buttons/labels etc in programming.