The examples in https://go.googlesource.com/proposal/+/master/design/go2draft-error-handling-overview.md arrange for w.Close() to be called more than once. https://golang.org/pkg/io/#Closer says
The behavior of Close after the first call is undefined. Specific implementations may document their own behavior.

The text before the code, and the problem:

On the other hand, the equivalent actual Go code today would be
Defers w.Close() and then calls w.Close().

For example, the corrected code above shortens to
checks w.Close() but also does that in an above handler.

It's OK for the double-Close to be one of the faults with the 'before', but it would be nice if the improved 'after' version didn't also do it. The more robust version with more helpful errors would be one in between doesn't.

CC: @rsc