Unknown flag -j when using identity encryption

[devonhk]

I was trying to encrypt a string with an identity file and got an error about an undocumented flag (-j).

Repro steps

❯ echo  'foo' | age  -i ~/age.tmp --armor
age: error: -i/--identity and -j can't be used in encryption mode unless symmetric encryption is explicitly selected with -e/--encrypt
age: hint: did you forget to specify -d/--decrypt?
age: report unexpected or unhelpful errors at https://filippo.io/age/report

Expected behaviour

-j flag is documented if it's actually used or it's excluded from the error message.

At least 1 other individual seems confused about the flag

[FiloSottile]

-j is documented along with all other flags in the man page. https://htmlpreview.github.io/?https://github.com/FiloSottile/age/blob/main/doc/age.1.html

What do you mean undocumented?

(#548 is about how to make a plugin that works with -j which is a more advanced topic.)

[str4d]

I think what they mean by "undocumented" is that the error message refers to ("documents") -j when the user's command does not use it.

It's clear to me that the error message is speaking generally (the same error applies to both -i and -j), but I can see how some users might find it unclear. A more precise error would be to only reference each kind of flag if it appears in the error message. This would likely mean two error messages (one for each flag) that are otherwise identical, and the error message references whichever flag appears first.