fix(_comp_array_filter): adjust error messages for consistency

Author: akinomyoga

bash_completion

@@ -263,10 +263,12 @@ _upvars()
 # Filter the array elements with the specified condition.
 # @param $1 Array name (that is not "value" or other internal variable names)
 # @param $2 When none of the options -EFG are specified, this is used as the
-#   command that tests the array element.  If this is an existing function
-#   name, the function is called with the value of the array element.
-#   Otherwise, this shall be the shell command that tests the array-element
-#   value stored in the shell variable "value".
+#   command that tests the array element.  The command is supposed to exit with
+#   status 0 when the element should be preserved, and 1 when the element
+#   should be removed.  The other exit status will cancel the array filtering.
+#   If this is an existing function name, the function is called with the value
+#   of the array element.  Otherwise, this shall be the shell command that
+#   tests the array-element value stored in the shell variable "value".
 #
 # Options:
 #     -E          $2 is interpreted as a POSIX extended regular expression.
@@ -297,25 +299,26 @@ _comp_array_filter()
             [psm]) _comp_local_anchoring=$_comp_local_opt ;;
             [rC]) _comp_local_flags=$_comp_local_opt$_comp_local_flags ;;
             *)
-                echo "bash_completion: $FUNCNAME: usage error" >&2
+                printf 'bash_completion: %s: %s\n' "$FUNCNAME" 'usage error' >&2
+                printf 'usage: %s %s\n' "$FUNCNAME" "[-EFGpsmrC] ARRAY_NAME CONDITION" >&2
                 return 2
                 ;;
         esac
     done
 
     shift $((OPTIND - 1))
     if (($# != 2)); then
-        printf 'bash_completion: %s: %s\n' "$FUNCNAME" "unexpected number of arguments." >&2
+        printf 'bash_completion: %s: %s\n' "$FUNCNAME" "unexpected number of arguments: $#" >&2
         printf 'usage: %s %s\n' "$FUNCNAME" "[-EFGpsmrC] ARRAY_NAME CONDITION" >&2
         return 2
     elif [[ $1 != [a-zA-Z_]*([a-zA-Z_0-9]) ]]; then
         printf 'bash_completion: %s: %s\n' "$FUNCNAME" "invalid array name '$1'." >&2
         return 2
     elif [[ $1 == @(_comp_local_*|OPTIND|OPTARG|OPTERR) ]]; then
-        printf 'bash_completion: %s: %s\n' "$FUNCNAME" "array name '$1' is reserved for internal uses." >&2
+        printf 'bash_completion: %s: %s\n' "$FUNCNAME" "array name '$1' is reserved for internal uses" >&2
         return 2
     elif [[ ! $_comp_local_pattype && $1 == value ]]; then
-        printf 'bash_completion: %s: %s\n' "$FUNCNAME" "array name '$1' cannot be used for the predicate." >&2
+        printf 'bash_completion: %s: %s\n' "$FUNCNAME" "array name '$1' cannot be used for the predicate" >&2
         return 2
     fi
     # When the array is empty:
@@ -365,15 +368,16 @@ _comp_array_filter()
                 _comp_local_unset=1
                 ;;
             *)
-                printf 'bash_completion: %s: %s\n' "$FUNCNAME" "the filter condition broken." >&2
+                printf 'bash_completion: %s: %s\n' "$FUNCNAME" \
+                    "the filter condition broken '${_comp_local_pattype:+-$_comp_local_pattype }$2'" >&2
                 return 2
                 ;;
         esac
     done
 
     # Compaction of the sparse array
     [[ $_comp_local_flags == *C* ]] ||
-        eval -- "((\${#$1[@]})) && $1=(\"\${$1[@]}\")"
+        eval "((\${#$1[@]})) && $1=(\"\${$1[@]}\")"
 
     [[ ! $_comp_local_unset ]]
 }