Different / empty output with "opa deps" depending on output format

[anderseknert]

For some queries, the opa deps command show no output at all unless --format json is chosen.

foo.rego

package foo

x := 5

allow {
    is_foo
}

is_foo {
    x == 1
}

❯ opa deps -d foo.rego data.foo.allow
<no output>

❯ opa deps -d foo.rego -f json data.foo.allow
{
  "virtual": [
    [
      {
        "type": "var",
        "value": "data"
      },
      {
        "type": "string",
        "value": "foo"
      },
      {
        "type": "string",
        "value": "allow"
      }
    ],
    [
      {
        "type": "var",
        "value": "data"
      },
      {
        "type": "string",
        "value": "foo"
      },
      {
        "type": "string",
        "value": "is_foo"
      }
    ],
    [
      {
        "type": "var",
        "value": "data"
      },
      {
        "type": "string",
        "value": "foo"
      },
      {
        "type": "string",
        "value": "x"
      }
    ]
  ]
}

If x := 5 is changed to x := input.x then opa deps show output even without JSON formatting.. presumably since a base document is referenced, but I don't know if that's the only determining factor.

❯ opa deps -d foo.rego data.foo.allow
+----------------+-------------------+
| BASE DOCUMENTS | VIRTUAL DOCUMENTS |
+----------------+-------------------+
| input.x        | data.foo.allow    |
|                | data.foo.is_foo   |
|                | data.foo.x        |
+----------------+-------------------+

[anderseknert]

As a side note, the --help output for this command could be improved with an example or two, as it currently says nothing more than "Analyze Rego query dependencies". Also, since it mentions "base documents" and "virtual documents", it would be useful to include an explanation of what that means, or at least link to the docs on the topic.