flag: no way to access a FlagSet's output #17628
Description
The FlagSet type has a SetOutput method for setting the destination for
usage messages. This destination is used by the default Usage
function, but it's impossible to use it in custom implementations,
because no accessor for the output exists.
I propose adding a field or method to access the set output.
Relatedly, FlagSet.Usage currently writes the banner to os.Stderr,
ignoring the set output, while PrintDefaults writes to the set output.
What did you do?
https://play.golang.org/p/tDimNWwNwD
What did you expect to see?
This or similar code to compile and write to the set output
What did you see instead?
No way to do so.