That's because it's not obvious whether //CommentFoo belongs to the (missing) code for case "a" or whether it's a comment for the next (default) case. There's some heuristics one could employ but there's no clear-cut approach. In fact, if you indent manually, gofmt accepts that as well.

Leaving open for future consideration.

It works well for me.

package test

func foo(a string) {
	switch {
	// if a is "a"
	case a == "a":
		// then call doSomething()
	// not all
	default:
		// then call doOtherThing()
	}
}

That's because it's not obvious whether //CommentFoo belongs to the (missing) code for case "a" or whether it's a comment for the next (default) case. There's some heuristics one could employ but there's no clear-cut approach. In fact, if you indent manually, gofmt accepts that as well.

Thanks for the explanation, that makes sense.

See also #9910, of which this is perhaps a dup.

@josharian Yes, indeed. Closing as duplicate of #9910.