fix: preserve exit code in omp.bash

Other small changes include:

- rename functions to simplify debugging
- quoting some variables and simplifying an expression as suggested by shellcheck
- idempotency when modifying PROMPT_COMMAND.
- check if file exists before trying to remove it in the trap.

src/init/omp.bash

@@ -4,23 +4,27 @@ TIMER_START="/tmp/${USER}.start.$$"
 
 PS0='$(::OMP:: --millis > $TIMER_START)'
 
-function _update_ps1() {
+function _omp_hook() {
+    local ret=$?
+
     omp_elapsed=-1
     if [[ -f $TIMER_START ]]; then
         omp_now=$(::OMP:: --millis)
         omp_start_time=$(cat "$TIMER_START")
-        omp_elapsed=$(($omp_now-$omp_start_time))
-        rm $TIMER_START
+        omp_elapsed=$((omp_now-omp_start_time))
+        rm "$TIMER_START"
     fi
-    PS1="$(::OMP:: --config $POSH_THEME --error $? --execution-time $omp_elapsed --shell bash)"
+    PS1="$(::OMP:: --config $POSH_THEME --shell bash --error $ret --execution-time $omp_elapsed --shell bash)"
+
+    return $ret
 }
 
-if [ "$TERM" != "linux" ] && [ -x "$(command -v ::OMP::)" ]; then
-    PROMPT_COMMAND="_update_ps1; $PROMPT_COMMAND"
+if [ "$TERM" != "linux" ] && [ -x "$(command -v ::OMP::)" ] && ! [[ "$PROMPT_COMMAND" =~ "_omp_hook" ]]; then
+    PROMPT_COMMAND="_omp_hook; $PROMPT_COMMAND"
 fi
 
-function runonexit() {
-  rm $TIMER_START
+function _omp_runonexit() {
+  [[ -f $TIMER_START ]] && rm "$TIMER_START"
 }
 
-trap runonexit EXIT
+trap _omp_runonexit EXIT