Moved the check for `exception` to rb_execarg_addopt

Check for `exception` option in rb_execarg_addopt, as well as
other options.  And then raise a particular ArgumentError if it is
not allowed.

internal.h

@@ -1977,6 +1977,7 @@ struct rb_execarg {
     unsigned uid_given : 1;
     unsigned gid_given : 1;
     unsigned exception : 1;
+    unsigned exception_given : 1;
     struct waitpid_state *waitpid_state; /* for async process management */
     rb_pid_t pgroup_pgid; /* asis(-1), new pgroup(0), specified pgroup (0<V). */
     VALUE rlimit_limits; /* Qfalse or [[rtype, softlim, hardlim], ...] */

process.c

@@ -2116,6 +2116,13 @@ rb_execarg_addopt(VALUE execarg_obj, VALUE key, VALUE val)
 		     "gid option is unimplemented on this machine");
 #endif
 	}
+        else if (id == id_exception) {
+            if (eargp->exception_given) {
+                rb_raise(rb_eArgError, "exception option specified twice");
+            }
+            eargp->exception = RTEST(val);
+            eargp->exception_given = 1;
+        }
         else {
 	    return ST_STOP;
         }
@@ -2592,23 +2599,16 @@ rb_execarg_get(VALUE execarg_obj)
 }
 
 static VALUE
-rb_execarg_init(int argc, const VALUE *orig_argv, int accept_shell, VALUE execarg_obj, int allow_exc_opt)
+rb_execarg_init(int argc, const VALUE *orig_argv, int accept_shell, VALUE execarg_obj)
 {
     struct rb_execarg *eargp = rb_execarg_get(execarg_obj);
-    VALUE prog, ret, exception = Qnil;
+    VALUE prog, ret;
     VALUE env = Qnil, opthash = Qnil;
     VALUE argv_buf;
     VALUE *argv = ALLOCV_N(VALUE, argv_buf, argc);
     MEMCPY(argv, orig_argv, VALUE, argc);
     prog = rb_exec_getargs(&argc, &argv, accept_shell, &env, &opthash);
-    if (allow_exc_opt && !NIL_P(opthash) && rb_hash_has_key(opthash, ID2SYM(id_exception))) {
-        opthash = rb_hash_dup(opthash);
-        exception = rb_hash_delete(opthash, ID2SYM(id_exception));
-    }
     rb_exec_fillarg(prog, argc, argv, env, opthash, execarg_obj);
-    if (RTEST(exception)) {
-        eargp->exception = 1;
-    }
     ALLOCV_END(argv_buf);
     ret = eargp->use_shell ? eargp->invoke.sh.shell_script : eargp->invoke.cmd.command_name;
     RB_GC_GUARD(execarg_obj);
@@ -2621,7 +2621,10 @@ rb_execarg_new(int argc, const VALUE *argv, int accept_shell, int allow_exc_opt)
     VALUE execarg_obj;
     struct rb_execarg *eargp;
     execarg_obj = TypedData_Make_Struct(0, struct rb_execarg, &exec_arg_data_type, eargp);
-    rb_execarg_init(argc, argv, accept_shell, execarg_obj, allow_exc_opt);
+    rb_execarg_init(argc, argv, accept_shell, execarg_obj);
+    if (!allow_exc_opt && eargp->exception_given) {
+        rb_raise(rb_eArgError, "exception option is not allowed");
+    }
     return execarg_obj;
 }