Improve CLI arg parsing error handling

macos_sign_and_notarize.py

@@ -587,7 +587,7 @@ def validate(*, bundle, binary_names):
 
 def main(args):
     if not args:
-        print("Error: pass binaries to sign as positional arguments", file=sys.stderr)
+        print("Error: pass name of release as first argument", file=sys.stderr)
         return 1
 
     release_name, *args = args
@@ -603,9 +603,21 @@ def main(args):
                 append_next = resources
                 continue
             print(f"Unexpected argument: {arg}", file=sys.stderr)
+            return 1
         append_next.append(Path(arg))
         append_next = None
 
+    if append_next is not None:
+        if append_next is binaries:
+            print("Error: unterminated --binary flag", file=sys.stderr)
+        if append_next is resources:
+            print("Error: unterminated --resource flag", file=sys.stderr)
+        return 1
+
+    if not binaries:
+        print("Error: no binaries passed to be codesigned", file=sys.stderr)
+        return 1
+
     for binary in binaries:
         if not binary.is_file():
             print("Error: {binary} does not exist", file=sys.stderr)