+ ruby28.y: add right hand assignment

doc/AST_FORMAT.md

@@ -730,6 +730,28 @@ Format:
 
 ~~~
 
+### Right-hand assignment
+
+Format:
+
+~~~
+(rasgn (int 1) (lvasgn :a))
+"1 => a"
+ ~~~~~~ expression
+   ~~ operator
+~~~
+
+#### Multiple right-hand assignment
+
+Format:
+
+~~~
+(mrasgn (send (int 13) :divmod (int 5)) (mlhs (lvasgn :a) (lvasgn :b)))
+"13.divmod(5) => a,b"
+ ~~~~~~~~~~~~~~~~~~~ expression
+              ^^ operator
+~~~
+
 ## Class and module definition
 
 ### Module

lib/parser/ast/processor.rb

@@ -75,6 +75,9 @@ def on_op_asgn(node)
       alias on_mlhs     process_regular_node
       alias on_masgn    process_regular_node
 
+      alias on_rasgn    process_regular_node
+      alias on_mrasgn   process_regular_node
+
       def on_const(node)
         scope_node, name = *node
 

lib/parser/builders/default.rb

@@ -619,6 +619,15 @@ def multi_assign(lhs, eql_t, rhs)
         binary_op_map(lhs, eql_t, rhs))
     end
 
+    def rassign(lhs, assoc_t, rhs)
+      n(:rasgn, [lhs, rhs], binary_op_map(lhs, assoc_t, rhs))
+    end
+
+    def multi_rassign(lhs, assoc_t, rhs)
+      n(:mrasgn, [ lhs, rhs ],
+        binary_op_map(lhs, assoc_t, rhs))
+    end
+
     #
     # Class and module definition
     #

lib/parser/meta.rb

@@ -12,7 +12,7 @@ module Meta
         sym dsym xstr regopt regexp array splat
         pair kwsplat hash irange erange self
         lvar ivar cvar gvar const defined? lvasgn
-        ivasgn cvasgn gvasgn casgn mlhs masgn
+        ivasgn cvasgn gvasgn casgn mlhs masgn rasgn mrasgn
         op_asgn and_asgn ensure rescue arg_expr
         or_asgn back_ref nth_ref
         match_with_lvasgn match_current_line

lib/parser/ruby28.y

@@ -206,8 +206,26 @@ rule
                     {
                       result = @builder.multi_assign(val[0], val[1], val[2])
                     }
+                | rassign
                 | expr
 
+        rassign: arg_value tASSOC lhs
+                    {
+                      result = @builder.rassign(val[0], val[1], val[2])
+                    }
+                | arg_value tASSOC mlhs
+                    {
+                      result = @builder.multi_rassign(val[0], val[1], val[2])
+                    }
+                | rassign tASSOC lhs
+                    {
+                      result = @builder.rassign(val[0], val[1], val[2])
+                    }
+                | rassign tASSOC mlhs
+                    {
+                      result = @builder.multi_rassign(val[0], val[1], val[2])
+                    }
+
     command_asgn: lhs tEQL command_rhs
                     {
                       result = @builder.assign(val[0], val[1], val[2])

test/test_parser.rb

@@ -9520,6 +9520,56 @@ def test_endless_method_without_brackets
       [:error, :unexpected_token, { :token => 'tEQL' }],
       %Q{def obj.foo = 42},
       %q{            ^ location},
+      SINCE_2_8
+    )
+  end
+
+  def test_rasgn
+    assert_parses(
+      s(:rasgn,
+        s(:int, 1), s(:lvasgn, :a)),
+      %q{1 => a},
+      %q{~~~~~~ expression
+        |  ^^ operator},
+      SINCE_2_8)
+
+    assert_parses(
+      s(:rasgn,
+        s(:send, s(:int, 1), :+, s(:int, 2)),
+        s(:gvasgn, :$a)),
+      %q{1 + 2 => $a},
+      %q{~~~~~~~~~~~ expression
+        |      ^^ operator},
+      SINCE_2_8)
+  end
+
+  def test_mrasgn
+    assert_parses(
+      s(:mrasgn,
+        s(:send, s(:int, 13), :divmod, s(:int, 5)),
+        s(:mlhs, s(:lvasgn, :a), s(:lvasgn, :b))),
+      %q{13.divmod(5) => a,b},
+      %q{~~~~~~~~~~~~~~~~~~~ expression
+        |             ^^ operator},
+      SINCE_2_8)
+
+    assert_parses(
+      s(:mrasgn,
+        s(:mrasgn,
+          s(:send, s(:int, 13), :divmod, s(:int, 5)),
+          s(:mlhs, s(:lvasgn, :a), s(:lvasgn, :b))),
+        s(:mlhs, s(:lvasgn, :c), s(:lvasgn, :d))),
+      %q{13.divmod(5) => a,b => c, d},
+      %q{~~~~~~~~~~~~~~~~~~~ expression (mrasgn)
+        |~~~~~~~~~~~~~~~~~~~~~~~~~~~ expression},
+      SINCE_2_8)
+  end
+
+  def test_rasgn_line_continuation
+    assert_diagnoses(
+      [:error, :unexpected_token, { :token => 'tASSOC' }],
+      %Q{13.divmod(5)\n=> a,b; [a, b]},
+      %{             ^^ location},
       SINCE_2_8)
   end
 end