prune: Add JSON support and separate code

[aawsome]

What does this PR change? What problem does it solve?

Separates the pruning code in three functions:

• Find out what to do
• Print statistcs (+ added JSON output here)
• do the actual pruning work

In a next step, unit tests can be added for all three parts (not included here)

This PR conflicts with #2881 - I'll fix this depending on what PR is tackled first.

Was the change discussed in an issue or in the forum before?

Refactoring the code: discussion with @fd0
Also closes #3129

Checklist

• I have read the Contribution Guidelines
• I have enabled maintainer edits for this PR
• I have added tests for all changes in this PR
• I have added documentation for the changes (in the manual)
• There's a new file in changelog/unreleased/ that describes the changes for our users (template here)
• I have run gofmt on the code in all commits
• All commit messages are formatted in the same style as the other commits in the repo
• I'm done, this Pull Request is ready for review

[aawsome]

rebased after #3148 was merged.

[MichaelEischer]

I was wondering how the JSON should look like to make it easier to extend it to a streaming output as with the backup command in the future. The most important part is probably to add a message type and a comment that this may change in the future.

restic prune --json still prints a lot of non-JSON text.

[aawsome]

@MichaelEischer I included your proposals and also rebased as #3139 is merged now. The prunePlan struct was quite handy ;-)

restic prune --json still prints a lot of non-JSON text.

Yes, so far --json can be only used in combination with --quiet. I was hoping for #3009 which IMO include the json checks for the various print functions...

[MichaelEischer]

Yes, so far --json can be only used in combination with --quiet. I was hoping for #3009 which IMO include the json checks for the various print functions...

Unfortunately, it is not possible to let --json imply --quiet. For example the backup command allows for different levels of verbosity for its JSON output.

[aawsome]

rebased.

[MichaelEischer]

Unfortunately, it is not possible to let --json imply --quiet. For example the backup command allows for different levels of verbosity for its JSON output.

#3009 won't be able to let --json imply --quiet as that would break the backup command output (the format must not force a certain log level). So this has to be handled locally.

[aawsome]

#3009 won't be able to let --json imply --quiet as that would break the backup command output (the format must not force a certain log level). So this has to be handled locally.

Actually I was thinking of something like the last commit I added. IMO this works and doesn't break anything except removing the output for some command that don't support --json if it is given.
Also makes many checks for gopts.JSON obsolete, but this would be an independent follow-up.

I also rebased to current master.

[aawsome]

IMO this works and doesn't break anything

Ok, it breaks find which uses the Print and Printf functions to manually generate JSON output 😩

I'll add some more checks for gopts.JSON and leave this cleanup to #3009 or a separate PR.

[MichaelEischer]

I've rebased to PR to fix the merge conflicts.

[darkdragon-001]

Thanks for your great work so far!
Are there any updates? I am specifically interested in the JSON output.

[darkdragon-001]

@aawsome has this been implemented somewhere else or why was it closed?