lib/helpers: new functions _bash_it_history_auto_*()

Two new functions `_bash_it_history_auto_save()` and `_bash_it_history_auto_load()`, which append new history to disk and load new history from disk, respectively.

See Bash-it#1595 for discussion.

lib/helpers.bash

@@ -837,3 +837,39 @@ then
     fi
   }
 fi
+
+function _bash_it_history_auto_save()
+{
+	case $HISTCONTROL in
+	*'noauto'*|*'autoload'*)
+		: # Do nothing, as configured.
+		;;
+	*'auto'*)
+		# Append new history from this session to the $HISTFILE
+		history -a
+		;;
+	*)
+		: # Do nothing, default.
+		;;
+	esac
+}
+
+function _bash_it_history_auto_load()
+{
+	case $HISTCONTROL in
+	*'noauto'*|*'autosave'*)
+		: # Do nothing, as configured.
+		;;
+	*'autoloadnew'*)
+		# Read new entries from $HISTFILE
+		history -n
+		;;
+	*'auto'*)
+		# Blank in-memory history, then read entire $HISTFILE fresh from disk.
+		history -c && history -r
+		;;
+	*)
+		: # Do nothing, default.
+		;;
+	esac
+}

themes/base.theme.bash

@@ -611,7 +611,8 @@ function safe_append_prompt_command {
 	fi
 }
 
-function _save-and-reload-history() {
-	local autosave=${1:-0}
-	[[ $autosave -eq 1 ]] && history -a && history -c && history -r
+function _save-and-reload-history()
+{
+	[[ ${1:-${autosave:-${HISTORY_AUTOSAVE:-0}}} -eq 1 ]] && local HISTCONTROL="${HISTCONTROL:-}${HISTCONTROL:+:}autoshare"
+	_bash_it_history_auto_save && _bash_it_history_auto_load
 }