revert does not produce errors for unknown files

[zombiezen]

This is an unfortunate consequence of how Git deals with pathspecs as filters. For some definitions of revert, it is technically correct, since it is ensuring that a non-existent file is non-existent in the working copy, but it's almost certainly not what anybody wants and is likely a typo.

This introduced in 1ff07cf. I don't have a good way of fixing this in general without dropping down to calling a Git subprocess for each argument, which does not perform well. I'll note it in the 0.6 release notes and try to figure out the right solution later. At worst, it's a slight annoyance rather than something that behaves radically incorrectly.

Steps to Reproduce

$ gg init
$ gg revert bar.txt

Expected Behavior

gg fails with an error that says that bar.txt is not a known file.

Actual Behavior

gg revert returns success and does nothing.

Version Info

gg built from source at 1ff07cfca9c38805dffd700cb665273f64b62181 on 2018-07-12T22:34:36Z
go: go1.10.3 gc linux/amd64
git version 2.18.0