+ ruby28.y: accept leading args before forward arg.

lib/parser/builders/default.rb

@@ -743,14 +743,18 @@ def numargs(max_numparam)
 
     def forward_only_args(begin_t, dots_t, end_t)
       if self.class.emit_forward_arg
-        forward_arg = n(:forward_arg, [], token_map(dots_t))
-        n(:args, [ forward_arg ],
-          collection_map(begin_t, [ forward_arg ], end_t))
+        arg = forward_arg(dots_t)
+        n(:args, [ arg ],
+          collection_map(begin_t, [ arg ], end_t))
       else
         n(:forward_args, [], collection_map(begin_t, token_map(dots_t), end_t))
       end
     end
 
+    def forward_arg(dots_t)
+      n(:forward_arg, [], token_map(dots_t))
+    end
+
     def arg(name_t)
       n(:arg, [ value(name_t).to_sym ],
         variable_map(name_t))

lib/parser/ruby28.y

@@ -960,6 +960,14 @@ rule
                     {
                       result = val
                     }
+                | tLPAREN2 args tCOMMA args_forward rparen
+                    {
+                      unless @static_env.declared_forward_args?
+                        diagnostic :error, :unexpected_token, { :token => 'tBDOT3' } , val[3]
+                      end
+
+                      result = [val[0], [*val[1], @builder.forwarded_args(val[3])], val[4]]
+                    }
                 | tLPAREN2 args_forward rparen
                     {
                       unless @static_env.declared_forward_args?
@@ -2593,6 +2601,13 @@ keyword_variable: kNIL
 
                       @lexer.state = :expr_value
                     }
+                | tLPAREN2 f_arg tCOMMA args_forward rparen
+                    {
+                      args = [ *val[1], @builder.forward_arg(val[3]) ]
+                      result = @builder.args(val[0], args, val[4])
+
+                      @static_env.declare_forward_args
+                    }
                 | tLPAREN2 args_forward rparen
                     {
                       result = @builder.forward_only_args(val[0], val[1], val[2])

test/test_parser.rb

@@ -7890,6 +7890,12 @@ def test_forward_args_invalid
       %q{                    ^^^ location},
       SINCE_2_7)
 
+    assert_diagnoses(
+      [:error, :unexpected_token, { :token => 'tBDOT3' }],
+      %q{def foo(x,y,z); bar(x, y, z, ...); end},
+      %q{                             ^^^ location},
+      SINCE_2_8)
+
     assert_diagnoses(
       [:error, :unexpected_token, { :token => 'tBDOT3' }],
       %q{def foo(x,y,z); super(...); end},
@@ -7959,6 +7965,26 @@ def test_forward_args_invalid
       SINCE_2_7)
   end
 
+  def test_trailing_forward_arg
+    assert_parses(
+      s(:def, :foo,
+        s(:args,
+          s(:arg, :a),
+          s(:arg, :b),
+          s(:forward_arg)),
+        s(:send, nil, :bar,
+          s(:lvar, :a),
+          s(:int, 42),
+          s(:forwarded_args))),
+      %q{def foo(a, b, ...); bar(a, 42, ...); end},
+      %q{       ~ begin (args)
+        |       ~~~~~~~~~~~ expression (args)
+        |                 ~ end (args)
+        |              ~~~ expression (args.forward_arg)},
+      SINCE_2_8)
+  end
+
+
   def test_erange_without_parentheses_at_eol
     assert_diagnoses(
       [:warning, :triple_dot_at_eol],