feat(debug): Add color to PS4 prompt

Closes kvz#103 kvz#105

example.sh

@@ -72,11 +72,21 @@ __b3bp_err_report() {
 ### Command-line argument switches (like -d for debugmode, -h for showing helppage)
 ##############################################################################
 
+# no color mode
+if [[ "${arg_n:?}" = "1" ]]; then
+  NO_COLOR="true"
+fi
+
 # debug mode
 if [[ "${arg_d:?}" = "1" ]]; then
   set -o xtrace
-  PS4='+(${BASH_SOURCE}:${LINENO}): ${FUNCNAME[0]:+${FUNCNAME[0]}(): }'
   LOG_LEVEL="7"
+  if [[ "${NO_COLOR:-}" = "true" ]]; then
+    # [!] Don't change to double quotes
+    export PS4='+\011 \t ${BASH_SOURCE}:${LINENO} \011 ${FUNCNAME[0]:+${FUNCNAME[0]}:\011 }'
+  else
+    export PS4='+\011 \e[1;30m\t \e[1;34m${BASH_SOURCE}\e[0m:\e[1;36m${LINENO}\e[0m \011 ${FUNCNAME[0]:+\e[0;35m${FUNCNAME[0]}\e[1;30m()\e[0m:\011 }'
+  fi
   # Enable error backtracing
   trap '__b3bp_err_report "${FUNCNAME:-.}" ${LINENO}' ERR
 fi
@@ -86,11 +96,6 @@ if [[ "${arg_v:?}" = "1" ]]; then
   set -o verbose
 fi
 
-# no color mode
-if [[ "${arg_n:?}" = "1" ]]; then
-  NO_COLOR="true"
-fi
-
 # help mode
 if [[ "${arg_h:?}" = "1" ]]; then
   # Help exists with code 1

main.sh

@@ -47,7 +47,8 @@ fi
 __dir="$(cd "$(dirname "${BASH_SOURCE[${__b3bp_tmp_source_idx:-0}]}")" && pwd)"
 __file="${__dir}/$(basename "${BASH_SOURCE[${__b3bp_tmp_source_idx:-0}]}")"
 __base="$(basename "${__file}" .sh)"
-__invocation="$(printf %q "${__file}")$((($#)) && printf ' %q' "$@" || true)"
+# shellcheck disable=SC2034
+__invocation="$( printf %q "${__file}")$( { (($#)) && printf ' %q' "$@"; } || true)"
 
 # Define the environment variables (and their defaults) that this script depends on
 LOG_LEVEL="${LOG_LEVEL:-6}" # 7 = debug -> 0 = emergency
@@ -83,7 +84,7 @@ function __b3bp_log () {
   local color="${!colorvar:-${color_error}}"
   local color_reset="\\x1b[0m"
 
-  if [[ "${NO_COLOR:-}" = "true" ]] || ( [[ "${TERM:-}" != "xterm"* ]] && [[ "${TERM:-}" != "screen"* ]] ) || [[ ! -t 2 ]]; then
+  if [[ "${NO_COLOR:-}" = "true" ]] || { [[ "${TERM:-}" != "xterm"* ]] && [[ "${TERM:-}" != "screen"* ]]; } || [[ ! -t 2 ]]; then
     if [[ "${NO_COLOR:-}" != "false" ]]; then
       # Don't use colors on pipes or non-recognized terminals
       color=""; color_reset=""
@@ -336,11 +337,37 @@ __b3bp_err_report() {
 ### Command-line argument switches (like -d for debugmode, -h for showing helppage)
 ##############################################################################
 
+# no color mode
+if [[ "${arg_n:?}" = "1" ]]; then
+  NO_COLOR="true"
+fi
+
 # debug mode
 if [[ "${arg_d:?}" = "1" ]]; then
   set -o xtrace
-  PS4='+(${BASH_SOURCE}:${LINENO}): ${FUNCNAME[0]:+${FUNCNAME[0]}(): }'
   LOG_LEVEL="7"
+
+  ### PS4 - Debug prompt string  (when using `set -o xtrace`)
+  ##############################################################################
+
+  # When debugging a shell script via `set -x` or `set -o xtrace`
+  # this tricked-out prompt is used.
+  #
+  # The first character (+) is used and repeated for stack depth (subshells).
+  # Then insert a tab (\011), and log the current time (\t), (source)filename,
+  # line number and function name
+  # And finally, the actual line of code.
+
+  #+       15:09:25  ./main.sh:299         main():         help 'Option -f (--file) requires an argument'
+  #+       15:09:25  ./main.sh:116         help():         echo ''
+
+  if [[ "${NO_COLOR:-}" = "true" ]]; then
+    # [!] Don't change to double quotes
+    export PS4='+\011 \t ${BASH_SOURCE}:${LINENO} \011 ${FUNCNAME[0]:+${FUNCNAME[0]}:\011 }'
+  else
+    # the 'debug-so-fancy' coloured version. no double quotes here either
+    export PS4='+\011 \e[1;30m\t \e[1;34m${BASH_SOURCE}\e[0m:\e[1;36m${LINENO}\e[0m \011 ${FUNCNAME[0]:+\e[0;35m${FUNCNAME[0]}\e[1;30m()\e[0m:\011 }'
+  fi
   # Enable error backtracing
   trap '__b3bp_err_report "${FUNCNAME:-.}" ${LINENO}' ERR
 fi
@@ -350,11 +377,6 @@ if [[ "${arg_v:?}" = "1" ]]; then
   set -o verbose
 fi
 
-# no color mode
-if [[ "${arg_n:?}" = "1" ]]; then
-  NO_COLOR="true"
-fi
-
 # help mode
 if [[ "${arg_h:?}" = "1" ]]; then
   # Help exists with code 1