formatted makefile completion and used helper function

completion/available/makefile.completion.bash

@@ -1,34 +1,37 @@
 # Bash completion for Makefile
 # Loosely adapted from http://stackoverflow.com/a/38415982/1472048
 
-_makecomplete() {
-  COMPREPLY=()
+if _command_exists make || _command_exists gnumake
+then
+    function  __makefile_completions() {
+        COMPREPLY=()
 
-  # https://www.gnu.org/software/make/manual/html_node/Makefile-Names.html
-  local files=()
-  for f in 'GNUmakefile' 'makefile' 'Makefile' ; do
-    [ -f "$f" ] && files+=("$f")
-  done
+        # https://www.gnu.org/software/make/manual/html_node/Makefile-Names.html
+        local files=()
+        for f in 'GNUmakefile' 'makefile' 'Makefile' ; do
+            [ -f "$f" ] && files+=("$f")
+        done
 
-  [ "${#files[@]}" -eq 0 ] && return 0
+        [ "${#files[@]}" -eq 0 ] && return 0
 
-  # collect all targets
-  local targets=()
-  for f in "${files[@]}" ; do
-    while IFS='' read -r line ; do
-      targets+=("$line")
-    done < <(grep -oE '^[a-zA-Z0-9_-]+:([^=]|$)' "$f" | cut -d':' -f1)
-  done
+        # collect all targets
+        local targets=()
+        for f in "${files[@]}" ; do
+            while IFS='' read -r line ; do
+                targets+=("$line")
+            done < <(grep -oE '^[a-zA-Z0-9_-]+:([^=]|$)' "$f" | cut -d':' -f1)
+        done
 
-  [ "${#targets[@]}" -eq 0 ] && return 0
+        [ "${#targets[@]}" -eq 0 ] && return 0
 
-  # use the targets for completion
-  while IFS='' read -r line ; do
-    COMPREPLY+=("$line")
-  done < <(compgen -W "$(tr ' ' '\n' <<<"${targets[@]}" | sort -u)" -- "${COMP_WORDS[COMP_CWORD]}")
+        # use the targets for completion
+        while IFS='' read -r line ; do
+            COMPREPLY+=("$line")
+        done < <(compgen -W "$(tr ' ' '\n' <<<"${targets[@]}" | sort -u)" -- "${COMP_WORDS[COMP_CWORD]}")
 
-  return 0
-}
+        return 0
+    }
 
-complete -o nospace -F _makecomplete make
-complete -o nospace -F _makecomplete gnumake
+    complete -o nospace -F __makefile_completions make
+    complete -o nospace -F __makefile_completions gnumake
+fi