Add plugin for Gb completion (http://getgb.io)

plugins/getgb/getgb.plugin.zsh

+function _gb_commands() {
+    local ret=1 state
+    _arguments -C ':command:->command' '*::options:->options' && ret=0
+
+    case $state in
+      (command)
+
+        local -a subcommands
+        subcommands=(
+          "build:build a package"
+          "doc:show documentation for a package or symbol"
+          "env:print project environment variables"
+          "generate:generate Go files by processing source"
+          "help:displays the help"
+          "info:info returns information about this project"
+          "list:list the packages named by the importpaths"
+          "test:test packages"
+          "vendor:manage your vendored dependencies"
+        )
+        _describe -t subcommands 'gb subcommands' subcommands && ret=0
+      ;;
+
+      (options)
+        case $line[1] in
+          (build)
+            _arguments \
+              -f'[ignore cached packages]' \
+              -F'[do not cache packages]' \
+              -q'[decreases verbosity]' \
+              -P'[the number of build jobs to run in parallel]' \
+              -R'[sets the base of the project root search path]' \
+              -dotfile'[output a dot formatted file of the build steps]' \
+              -ldflags'["flag list" arguments to pass to the linker]' \
+              -gcflags'["arg list" arguments to pass to the compiler]' \
+              -race'[enable data race detection]' \
+              -tags'["tag list" additional build tags]'
+            ;;
+          (list)
+            _arguments \
+              -f'[alternate format for the list, using the syntax of package template]' \
+              -s'[read format template from STDIN]' \
+              -json'[prints output in structured JSON format]'
+            ;;
+          (test)
+            _arguments \
+              -v'[print output from test subprocess]' \
+              -ldflags'["flag list" arguments to pass to the linker]' \
+              -gcflags'["arg list" arguments to pass to the compiler]' \
+              -race'[enable data race detection]' \
+              -tags'["tag list" additional build tags]'
+            ;;
+          (vendor)
+            __gb-vendor
+        esac
+      ;;
+    esac
+
+    return ret
+}
+
+compdef _gb_commands gb
+
+__gb-vendor ()
+{
+  local curcontext="$curcontext" state line
+
+  _arguments -C ':command:->command' '*::options:->options'
+
+	case $state in
+		(command)
+
+			local -a subcommands
+			subcommands=(
+				'delete:deletes a local dependency'
+				'fetch:fetch a remote dependency'
+				'list:lists dependencies, one per line'
+        'purge:remove all unreferenced dependencies'
+				'restore:restore dependencies from the manifest'
+				'update:update a local dependency'
+			)
+			_describe -t subcommands 'gb vendor subcommands' subcommands && ret=0
+		;;
+
+		(options)
+			case $line[1] in
+				(delete)
+					_arguments \
+						-all'[remove all dependencies]'
+				  ;;
+        (fetch)
+          _arguments \
+            -branch'[fetch from a particular branch]' \
+            -no-recurse'[do not fetch recursively]' \
+            -tag'[fetch the specified tag]' \
+            -revision'[fetch the specific revision from the branch (if supplied)]' \
+            -precaire'[allow the use of insecure protocols]' \
+          ;;
+        (list)
+          _arguments \
+            -f'[controls the template used for printing each manifest entry]'
+          ;;
+        (restore)
+          _arguments \
+            -precaire'[allow the use of insecure protocols]'
+          ;;
+        (update)
+          _arguments \
+            -all'[update all dependencies in the manifest or supply a given dependency]' \
+            -precaire'[allow the use of insecure protocols]'
+          ;;
+			esac
+		;;
+	esac
+}