fix(upgrade): check if git is available and working

macOS seems to break dev tools when updating the system. This should
prevent the previous issues. See #11309

Closes #11420

plugins/pipenv/pipenv.plugin.zsh

@@ -1,8 +1,16 @@
-# Pipenv completion
-_pipenv() {
-  eval $(env COMMANDLINE="${words[1,$CURRENT]}" _PIPENV_COMPLETE=complete-zsh pipenv)
-}
-compdef _pipenv pipenv
+if (( ! $+commands[pipenv] )); then
+  return
+fi
+
+# If the completion file doesn't exist yet, we need to autoload it and
+# bind it to `pipenv`. Otherwise, compinit will have already done that.
+if [[ ! -f "$ZSH_CACHE_DIR/completions/_pipenv" ]]; then
+  typeset -g -A _comps
+  autoload -Uz _pipenv
+  _comps[pipenv]=_pipenv
+fi
+
+_PIPENV_COMPLETE=zsh_source pipenv >| "$ZSH_CACHE_DIR/completions/_pipenv" &|
 
 # Automatic pipenv shell activation/deactivation
 _togglePipenvShell() {

tools/check_for_upgrade.sh

@@ -24,7 +24,7 @@ zstyle -s ':omz:update' mode update_mode || {
 # - git is unavailable on the system.
 if [[ "$update_mode" = disabled ]] \
    || [[ ! -w "$ZSH" || ! -O "$ZSH" ]] \
-   || ! command -v git &>/dev/null; then
+   || ! command git --version 2>&1 >/dev/null; then
   unset update_mode
   return
 fi