[Bug #20474] Keep spaces in leading blank line

parse.y

@@ -8578,6 +8578,10 @@ parser_update_heredoc_indent(struct parser_params *p, int c)
             }
             p->heredoc_line_indent = -1;
         }
+        else {
+            /* Whitespace only line has no indentation */
+            p->heredoc_line_indent = 0;
+        }
     }
     return FALSE;
 }

test/ruby/test_syntax.rb

@@ -889,6 +889,16 @@ e"
     assert_dedented_heredoc(expect, result)
   end
 
+  def test_dedented_heredoc_with_leading_blank_line
+    # the blank line has six leading spaces
+    result = "      \n" \
+             "    b\n"
+    expect = "  \n" \
+             "b\n"
+    assert_dedented_heredoc(expect, result)
+  end
+
+
   def test_dedented_heredoc_with_blank_more_indented_line_escaped
     result = "    a\n" \
              "\\ \\ \\ \\ \\ \\ \n" \
@@ -996,7 +1006,7 @@ eom
   end
 
   def test_dedented_heredoc_concatenation
-    assert_equal("\n0\n1", eval("<<~0 '1'\n \n0\#{}\n0"))
+    assert_equal(" \n0\n1", eval("<<~0 '1'\n \n0\#{}\n0"))
   end
 
   def test_heredoc_mixed_encoding