Output files are created even if encryption/decryption failed

[wgslr]

Environment

• OS: Arch Linux 5.4.6-arch3-1 internal/age: add x25519KeySize constant to replace repeated integer literals #1 SMP PREEMPT Tue, 24 Dec 2019 04:36:53 +0000 x86_64
• age version*: 1.0.0beta2-1

What were you trying to do

Decrypt a file without providing the -i argument and subsequently fix the mistake.

What happened

The first decryption attempt already created an empty output file, and a next invocation with fixed argument refused to overwrite it.

$ echo 'Hello age' | age -a -r 'age1fh296r26vut9rpdarl89765z5qh9pavgmlam3w9s69uh5t82darqat8yat' -o encrypted.age.ascii
$ age -d -o decrypted.txt encrypted.age.ascii
Error: no identity matched a recipient
[ Did age not do what you expected? Could an error be more useful? Tell us: https://filippo.io/age/report ]
# fix the mistake
$ age -d -o decrypted.txt -i key.txt encrypted.age.ascii 
Error: failed to open output file "decrypted.txt": open decrypted.txt: file exists
[ Did age not do what you expected? Could an error be more useful? Tell us: https://filippo.io/age/report ]
$ ls -lh
total 8.0K
-rw-r--r-- 1 wojciech wojciech   0 Dec 30 01:52 decrypted.txt

Encryption

Creation of empty files is observed also when encrypting, when given incorrect -r argument:

$ echo 'Hello age' | age -a -o encrypted -r BAD
Error: unknown recipient type: "BAD"
$ ls -l encrypted
-rw-r--r-- 1 wojciech wojciech 0 Dec 30 02:02 encrypted

UX side

Apart from the incorrect, I assume, behaviour of creating empty files, I am not a fan of the no-overwrite policy. I think it would be better to match most unix tools' behaviour of overwriting by default or add an -f/--force flag.

* would be nice to have age --version to properly check that