auto-update: make output more user friendly

The rather raw and scarce output of `podman auto-update` has been a
thorn in my eyes for a longer while.  So far, Podman would only print
updated systemd units, one per line, without further formatting.

Motivated by issue #9949 which is asking for some more useful
information in combination with a dry-run feature, I sat down and
reflected which information may come in handy.

Running `podman auto-update` will now look as follows:

```
$ podman auto-update
Trying to pull [...]

UNIT                    CONTAINER            IMAGE                   POLICY      UPDATED
container-test.service  08fd34e533fd (test)  localhost:5000/busybox  registry    false
```

Also refactor the spaghetti code in the backend a bit to make it easier
to digest and maintain.

For easier testing and for the sake of consistency with other commands
listing output, add a `--format` flag.

The man page will get an overhaul in a follow up commit.

Signed-off-by: Valentin Rothberg <rothberg@redhat.com>

1 files changed, 1 insertions, 1 deletions

diff --git a/pkg/domain/infra/abi/auto-update.go b/pkg/domain/infra/abi/auto-update.go
index b9af4c92c..daa882ecf 100644
--- a/pkg/domain/infra/abi/auto-update.go
+++ b/pkg/domain/infra/abi/auto-update.go
@@ -7,7 +7,7 @@ import (
 	"github.com/containers/podman/v3/pkg/domain/entities"
 )
 
-func (ic *ContainerEngine) AutoUpdate(ctx context.Context, options entities.AutoUpdateOptions) (*entities.AutoUpdateReport, []error) {
+func (ic *ContainerEngine) AutoUpdate(ctx context.Context, options entities.AutoUpdateOptions) ([]*entities.AutoUpdateReport, []error) {
 	// Convert the entities options to the autoupdate ones.  We can't use
 	// them in the entities package as low-level packages must not leak
 	// into the remote client.