[Feature #19370] Prohibit nesting anonymous parameter forwarding

parse.y

@@ -15009,6 +15009,8 @@ add_forwarding_args(struct parser_params *p)
 static void
 forwarding_arg_check(struct parser_params *p, ID arg, ID all, const char *var)
 {
+    bool conflict = false;
+
     struct vtable *vars, *args;
 
     vars = p->lvtbl->vars;
@@ -15017,6 +15019,7 @@ forwarding_arg_check(struct parser_params *p, ID arg, ID all, const char *var)
     while (vars && !DVARS_TERMINAL_P(vars->prev)) {
         vars = vars->prev;
         args = args->prev;
+        conflict |= (vtable_included(args, arg) && !(all && vtable_included(args, all)));
     }
 
     bool found = false;
@@ -15032,6 +15035,9 @@ forwarding_arg_check(struct parser_params *p, ID arg, ID all, const char *var)
     if (!found) {
         compile_error(p, "no anonymous %s parameter", var);
     }
+    else if (conflict) {
+        compile_error(p, "anonymous %s parameter is also used within block", var);
+    }
 }
 
 #ifndef RIPPER

test/ruby/test_syntax.rb

@@ -76,6 +76,7 @@ class TestSyntax < Test::Unit::TestCase
 
   def test_anonymous_block_forwarding
     assert_syntax_error("def b; c(&); end", /no anonymous block parameter/)
+    assert_syntax_error("def b(&) ->(&) {c(&)} end", /anonymous block parameter is also used/)
     assert_separately([], "#{<<-"begin;"}\n#{<<-'end;'}")
     begin;
       def b(&); c(&) end
@@ -143,6 +144,9 @@ class TestSyntax < Test::Unit::TestCase
   def test_anonymous_rest_forwarding
     assert_syntax_error("def b; c(*); end", /no anonymous rest parameter/)
     assert_syntax_error("def b; c(1, *); end", /no anonymous rest parameter/)
+    assert_syntax_error("def b(*) ->(*) {c(*)} end", /anonymous rest parameter is also used/)
+    assert_syntax_error("def b(a, *) ->(*) {c(1, *)} end", /anonymous rest parameter is also used/)
+    assert_syntax_error("def b(*) ->(a, *) {c(*)} end", /anonymous rest parameter is also used/)
     assert_separately([], "#{<<-"begin;"}\n#{<<-'end;'}")
     begin;
       def b(*); c(*) end
@@ -156,6 +160,9 @@ class TestSyntax < Test::Unit::TestCase
   def test_anonymous_keyword_rest_forwarding
     assert_syntax_error("def b; c(**); end", /no anonymous keyword rest parameter/)
     assert_syntax_error("def b; c(k: 1, **); end", /no anonymous keyword rest parameter/)
+    assert_syntax_error("def b(**) ->(**) {c(**)} end", /anonymous keyword rest parameter is also used/)
+    assert_syntax_error("def b(k:, **) ->(**) {c(k: 1, **)} end", /anonymous keyword rest parameter is also used/)
+    assert_syntax_error("def b(**) ->(k:, **) {c(**)} end", /anonymous keyword rest parameter is also used/)
     assert_separately([], "#{<<-"begin;"}\n#{<<-'end;'}")
     begin;
       def b(**); c(**) end