The shell completion script (`arcanist/resources/shell/bash-completion`) and the corresponding workflow (`ArcanistShellCompleteWorkflow`) can generally be improved. In particular, there are no completions for the following:
- `arc branch --output`
- `arc browse --branch`
- `arc close --status`
- `arc diff --base`
- `arc diff --cc`
- `arc diff --reviewers`
- `arc feature --output`
- `arc get-config`
- `arc help`
- `arc land --onto`
- `arc land --remote`
- `arc lint --engine`
- `arc lint --output`
- `arc lint --severity`
- `arc set-config`
- `arc tasks --order`
- `arc tasks --owner`
- `arc tasks --status`
- `arc unit --engine`
- `arc unit --output`
In addition, the following should //not// provide any completions:
- `arc alias`
- `arc backout`
- `arc close`
- `arc close-revision`
- `arc download`
- `arc flag`
- `arc mark-committed`
- `arc patch`
- `arc revert`
- `arc todo`