Add --v1-compatible flag to commands

[johanfylling]

When applied to commands other than fmt and check, the --rego-v1 flag should enforce that all supplied modules are compatible with OPA v1.0, but not require the rego.v1 or future.keywords imports.
Essentially, using the --rego-v1 flag should make OPA parse, compile, and evaluate policies as if 1.0.

E.g. this is a valid module in OPA 1.0:

package example

# Notice: no imports

allow if {
  count(violations) == 0
}

violations contains msg if {
  ...
}

Commands:

• build
• check
• eval
• fmt
• test

Commands supported at a later date (#6520):

• bench
• deps
• exec
• inspect
• run
• parse

[johanfylling]

It has been decided that we should use the --v1-compatible flag instead of --rego-v1.

[frek818]

@johanfylling, I notice that this issue is closed but the PR (#6520) is still open. Do you know if this feature will make into opa soon.

[johanfylling]

The scope of this issue was redefined to the build, check, fmt, eval, and test commands. I've updated the description to reflect this.

PR #6521 implements #6520; which adds --v1-compatible support to the remaining applicable commands: bench, deps, exec, inspect, run, and parse. This is expected to be included in the next release (0.61.0).

I hope this clarifies things. Thanks for making us aware of the issue 😃.