Insecure completion handler added.

A new "lib/compfix.zsh" script defining a new handle_completion_insecurities()
function has been added, which handles insecure completion directories by
notifying users of said insecurities and moving away all existing completion
caches to a temporary directory. While intended to be called at startup, this
function is generally callable at any time (e.g., for testing).

lib/compfix.zsh

+# Handle completions insecurities (i.e., completion-dependent directories with
+# insecure ownership or permissions) by:
+#
+# * Human-readably notifying the user of these insecurities.
+# * Moving away all existing completion caches to a temporary directory. Since
+#   any of these caches may have been generated from insecure directories, they
+#   are all suspect now. Failing to do so typically causes subsequent compinit()
+#   calls to fail with "command not found: compdef" errors. (That's bad.)
+function handle_completion_insecurities() {
+  # List of the absolute paths of all unique insecure directories, split on
+  # newline from compaudit()'s output resembling:
+  #
+  #     There are insecure directories:
+  #     /usr/share/zsh/site-functions
+  #     /usr/share/zsh/5.0.6/functions
+  #     /usr/share/zsh
+  #     /usr/share/zsh/5.0.6
+  #
+  # Since the ignorable first line is printed to stderr and thus not captured,
+  # stderr is squelched to prevent this output from leaking to the user. 
+  local -aU insecure_dirs
+  insecure_dirs=( ${(f@):-"$(compaudit 2>/dev/null)"} )
+
+  # If no such directories exist, get us out of here.
+  if (( ! ${#insecure_dirs} )); then
+      print "[oh-my-zsh] No insecure completion-dependent directories detected."
+      return
+  fi
+
+  # List ownership and permissions of all insecure directories.
+  print "[oh-my-zsh] Insecure completion-dependent directories detected:"
+  ls -ld "${(@)insecure_dirs}"
+  print "[oh-my-zsh] For safety, completions will be disabled until you manually fix all"
+  print "[oh-my-zsh] insecure directory permissions and ownership and restart oh-my-zsh."
+  print "[oh-my-zsh] See the above list for directories with group or other writability.\n"
+
+  # Locally enable the "NULL_GLOB" option, thus removing unmatched filename
+  # globs from argument lists *AND* printing no warning when doing so. Failing
+  # to do so prints an unreadable warning if no completion caches exist below.
+  setopt local_options null_glob
+
+  # List of the absolute paths of all unique existing completion caches.
+  local -aU zcompdump_files
+  zcompdump_files=( "${ZSH_COMPDUMP}"(.) "${ZDOTDIR:-${HOME}}"/.zcompdump* )
+
+  # Move such caches to a temporary directory.
+  if (( ${#zcompdump_files} )); then
+    # Absolute path of the directory to which such files will be moved.
+    local ZSH_ZCOMPDUMP_BAD_DIR="${ZSH_CACHE_DIR}/zcompdump-bad"
+
+    # List such files first.
+    print "[oh-my-zsh] Insecure completion caches also detected:"
+    ls -l "${(@)zcompdump_files}"
+
+    # For safety, move rather than permanently remove such files.
+    print "[oh-my-zsh] Moving to \"${ZSH_ZCOMPDUMP_BAD_DIR}/\"...\n"
+    mkdir -p "${ZSH_ZCOMPDUMP_BAD_DIR}"
+    mv "${(@)zcompdump_files}" "${ZSH_ZCOMPDUMP_BAD_DIR}/"
+  fi
+}