Add draft of ZSH completion plugin

It's quite basic and I cannot really do what I would like, but it's
good enough.

Author: dbaty

MANIFEST.in

@@ -7,6 +7,7 @@ include README.rst
 graft src/cogite
 
 prune docs
+prune extra
 prune tests
 exclude .pylintrc
 exclude .readthedocs.yaml

docs/features.rst

@@ -36,3 +36,11 @@ Conflict resolution
 -------------------
 
 FIXME
+
+
+.. _shell_completion:
+
+Shell completion
+----------------
+
+FIXME: document ZSH completion

extra/completion.zsh

@@ -0,0 +1,67 @@
+#compdef cogite
+
+_cogite() {
+    if [[ ${CURRENT} -eq 2 ]]; then
+        COMPREPLY=($(compgen -W "auth ci pr status" -- ${cur}))
+    elif [[ ${CURRENT} -eq 3 ]]; then
+        local cmd=${COMP_WORDS[1]}
+        case ${cmd} in
+            auth)
+                COMPREPLY=($(compgen -W "add delete" -- ${cur}))
+                ;;
+            ci)
+                COMPREPLY=($(compgen -W "browse" -- ${cur}))
+                ;;
+            pr)
+                COMPREPLY=($(compgen -W "add browse draft merge ready rebase reqreview" -- ${cur}))
+                ;;
+            status)
+                COMPREPLY=($(compgen -W "--poll" -- ${cur}))
+                ;;
+        esac
+    elif [[ ${CURRENT} -gt 3 ]]; then
+        local cmd="${COMP_WORDS[1]} ${COMP_WORDS[2]}"
+        case ${cmd} in
+            "auth add")
+                COMPREPLY=($(compgen -W "--help" -- ${cur}))
+                ;;
+            "auth delete")
+                COMPREPLY=($(compgen -W "--help" -- ${cur}))
+                ;;
+            "ci browse")
+                COMPREPLY=($(compgen -W "--help" -- ${cur}))
+                ;;
+            "pr add")
+                COMPREPLY=($(compgen -W "--help --base --draft" -- ${cur}))
+                # FIXME (dbaty, 2021-12-04) : I would like to use `_arguments`
+                # to have more detailed auto-completion, with this:
+                #     _arguments \
+                #         '--base[branch where changes should be applied]' \
+                #         '--draft[mark as a draft pull request]'
+                # ... but I get the following error:
+                #    _arguments:34: bad output format specification
+                #    _arguments:366: bad math expression: operator expected at `descrs'
+                ;;
+            "pr browse")
+                COMPREPLY=($(compgen -W "--help --browse" -- ${cur}))
+                ;;
+            "pr draft")
+                COMPREPLY=($(compgen -W "--help --base" -- ${cur}))
+                ;;
+            "pr merge")
+                COMPREPLY=($(compgen -W "--help" -- ${cur}))
+                ;;
+            "pr ready")
+                COMPREPLY=($(compgen -W "--help" -- ${cur}))
+                ;;
+            "pr rebase")
+                COMPREPLY=($(compgen -W "--help" -- ${cur}))
+                ;;
+            "pr reqreview")
+                COMPREPLY=($(compgen -W "--help" -- ${cur}))
+                ;;
+        esac
+    fi
+}
+
+complete -F _cogite cogite