allow method definition in cmdarg

save cmdarg_stack and isolate command argument state from outer scope
to allow method definition in cmdarg

import from ruby/ruby@04bb9d6b75a55d4000700769eead5a5cb942c25b

src/parse.y

@@ -2226,6 +2226,8 @@ primary         : literal
                     {
                       p->in_def++;
                       $<nd>$ = local_switch(p);
+                      $<stack>1 = p->cmdarg_stack;
+                      p->cmdarg_stack = 0;
                     }
                   f_arglist
                   bodystmt
@@ -2234,12 +2236,15 @@ primary         : literal
                       $$ = new_def(p, $2, $4, $5);
                       local_resume(p, $<nd>3);
                       p->in_def--;
+                      p->cmdarg_stack = $<stack>1;
                     }
                 | keyword_def singleton dot_or_colon {p->lstate = EXPR_FNAME;} fname
                     {
                       p->in_single++;
                       p->lstate = EXPR_ENDFN; /* force for args */
                       $<nd>$ = local_switch(p);
+                      $<stack>1 = p->cmdarg_stack;
+                      p->cmdarg_stack = 0;
                     }
                   f_arglist
                   bodystmt
@@ -2248,6 +2253,7 @@ primary         : literal
                       $$ = new_sdef(p, $2, $5, $7, $8);
                       local_resume(p, $<nd>6);
                       p->in_single--;
+                      p->cmdarg_stack = $<stack>1;
                     }
                 | keyword_break
                     {

test/t/syntax.rb

@@ -265,3 +265,10 @@ assert('parenthesed do-block in cmdarg') do
   result = x.test (proc do :ok; end)
   assert_equal :ok, result
 end
+
+assert('method definition in cmdarg') do
+  if false
+    bar def foo; self.each do end end
+  end
+  true
+end