Target rules in dashboard linter

[mshahzeb]

• Dont allow unused targets to be present in the dashboard
• Check for targets with empty expressions

[rgeyer]

• Check for targets with empty expressions

target-promql-rule already checks this, since an empty expression can not be parsed as promql. We could add this test case to the test suite, just to cover it.

Related, I just found on the awx mixin, which uses a panel reference as it's target, that the linter does not support this case. Explicitly because, the target-promql-rule attempts to parse the expr, but there isn't one.

[target-promql-rule] 'AWX': Dashboard 'AWX', panel 'License Type' invalid PromQL query '': 1:1: parse error: no expression found in input

The linter should permit these type of targets, and should validate that the referenced panel/query exists.

"targets": [
            {
               "panelId": 3,
               "refId": "A"
            }
         ],

[mshahzeb]

This is fixed and merged in the PR referenced above^