Cache the completion for a quicker startup

The original idea was by @samjonester in #1210. This version aims to avoid
relying on the stat or date programs because they have different flags depending
on the OS and if it uses BSD or GNU coreutils.

modules/completion/init.zsh

@@ -14,9 +14,6 @@ fi
 # Add zsh-completions to $fpath.
 fpath=("${0:h}/external/src" $fpath)
 
-# Load and initialize the completion system ignoring insecure directories.
-autoload -Uz compinit && compinit -i
-
 #
 # Options
 #
@@ -27,9 +24,21 @@ setopt PATH_DIRS           # Perform path search even on command names with slas
 setopt AUTO_MENU           # Show completion menu on a successive tab press.
 setopt AUTO_LIST           # Automatically list choices on ambiguous completion.
 setopt AUTO_PARAM_SLASH    # If completed parameter is a directory, add a trailing slash.
+setopt EXTENDED_GLOB       # Needed for file modification glob modifiers with compinit
 unsetopt MENU_COMPLETE     # Do not autoselect the first completion entry.
 unsetopt FLOW_CONTROL      # Disable start/stop characters in shell editor.
 
+# Load and initialize the completion system ignoring insecure directories with a
+# cache time of 20 hours, so it should almost always regenerate the first time a
+# shell is opened each day.
+autoload -Uz compinit
+compfiles=(${ZDOTDIR:-$HOME}/.zcompdump(Nm-20))
+if [[ $#compfiles > 0 ]]; then
+  compinit -i -C
+else
+  compinit -i
+fi
+
 #
 # Styles
 #