[plugins/async-prompt] Add async-prompt plugin

Signed-off-by: Olivier Mehani <shtrom@ssji.net>

plugins/async-prompt/async-prompt.plugin.zsh

@@ -0,0 +1,41 @@
+# Asynchronous prompt heavily based on Anish Athalye's [0]
+# [0[ https://www.anishathalye.com/2015/02/07/an-asynchronous-shell-prompt/
+#
+# To use in your theme, define an `rprompt` function that echoes whatever you
+# want to have on the right-hand-side prompt.
+#
+setopt prompt_subst # enable command substition in prompt
+
+ASYNC_PROC=0
+function precmd() {
+    function async() {
+
+        # save to temp file
+	printf "%s" "$(rprompt)" > "/tmp/zsh_prompt_$$"
+
+        # signal parent
+        kill -s USR1 $$
+    }
+
+    # do not clear RPROMPT, let it persist
+
+    # kill child if necessary
+    if [[ "${ASYNC_PROC}" != 0 ]]; then
+        kill -s HUP $ASYNC_PROC >/dev/null 2>&1 || :
+    fi
+
+    # start background computation
+    async &!
+    ASYNC_PROC=$!
+}
+
+function TRAPUSR1() {
+    # read from temp file
+    RPROMPT="$(cat /tmp/zsh_prompt_$$)"
+
+    # reset proc number
+    ASYNC_PROC=0
+
+    # redisplay
+    zle && zle reset-prompt
+}