main: Handle command line argument parsing errors

Add an error handler that just prints the error messages from
'unix-opts' to standard error and exits with EX_USAGE.

Inspired by:
- http://lispcookbook.github.io/cl-cookbook/scripting.html#handling-malformed-or-missing-arguments
- https://github.com/libre-man/unix-opts/blob/0e61f34b2ecf62288437810d4abb31e572048b04/example/example.lisp

2 files changed, 14 insertions, 1 deletions

diff --git a/l/src/main.lisp b/l/src/main.lisp
index 99a60d0..9701d5f 100644
--- a/l/src/main.lisp
+++ b/l/src/main.lisp
@@ -20,7 +20,15 @@
          :long "version"))
 
 (defun main ()
-  (multiple-value-bind (options free-args) (opts:get-opts)
+  (multiple-value-bind (options free-args)
+    (handler-bind
+      ((opts:unknown-option #'handle-option-error)
+       (opts:missing-arg #'handle-option-error)
+       (opts:arg-parser-failed #'handle-option-error)
+       (opts:missing-required-option #'handle-option-error))
+
+      (opts:get-opts))
+
     (when-option (options :help)
       (opts:describe
         :usage-of "extreload"
diff --git a/l/src/option.lisp b/l/src/option.lisp
index d828230..11f7f98 100644
--- a/l/src/option.lisp
+++ b/l/src/option.lisp
@@ -4,3 +4,8 @@
   `(let ((value (getf ,options ,option)))
      (when value
        ,@body)))
+
+(defun handle-option-error (condition)
+  (format *error-output* "error: ~a~%" condition)
+
+  (opts:exit 64))