cmd: validate: add --strict mode

[cyphar]

Due to FreeBSD compatibility, we have so far been forced into some unfortunate behaviour with regards to which comparison errors we actually return an error code for. FreeBSD generally does not return errors if a file or keyword only exists in one of the manifests being compared.

Some users do not care about FreeBSD compatibility and just want to get errors if there is any difference between a manifest and directory tree. Commit 9cdd915 ("cmd: gomtree: re-enable errors when there is a Modified entry") added a TODO to implement this, but I've only just got around to implementing it.

This patch adds a new --strict flag to "gomtree validate", which causes it to error out if any changes were detected and also disables the FreeBSD compatibility keyword delta filters. This is more akin to what modern users would expect from a manifest validation tool.

This patch resolves the remaining issues in opencontainers/umoci#620.

Closes #210 Fixes: 21723a3 ("*: fix comparison of missing keywords") Fixes: 9cdd915 ("cmd: gomtree: re-enable errors when there is a Modified entry") Signed-off-by: Aleksa Sarai [email protected]