in reviewing #7085 I noticed the output of running mne.compute_covariance(epochs, ...) yields the info message

Computing data rank from raw with rank=None

Looks like mne.compute_covariance converts epochs to a numpy array (let's call it "data"), and then _compute_covariance_auto(data, ...) calls compute_rank(RawArray(data.T, ...), ...). So the message will always say you're computing from "raw" regardless of whether you pass in Raw or Epochs