tests: check variants and typed mid-rule actions

See
http://lists.gnu.org/archive/html/bison-patches/2018-08/msg00013.html

* tests/c++.at (Variants and Typed Mid-rule Actions): New.

tests/c++.at

@@ -386,6 +386,132 @@ AT_TEST([[%skeleton "lalr1.cc" %define parse.assert %define api.token.constructo
 m4_popdef([AT_TEST])
 
 
+
+## ------------------------------------- ##
+## Variants and Typed Mid-rule Actions.  ##
+## ------------------------------------- ##
+
+AT_SETUP([Variants and Typed Mid-rule Actions])
+
+# See http://lists.gnu.org/archive/html/bug-bison/2017-06/msg00000.html.
+#
+# Check that typed mid-rule actions behave properly (pre-construction
+# of $$ before the user action, support of %printer and %destructor,
+# etc.).
+
+AT_BISON_OPTION_PUSHDEFS([%skeleton "lalr1.cc"])
+
+AT_DATA_GRAMMAR([[input.y]],
+[[%skeleton "lalr1.cc"
+%defines
+
+%debug
+%define parse.assert
+%define api.value.type variant
+%define api.token.constructor
+%error-verbose
+
+%code
+{
+  #include <iostream>
+  namespace yy
+  {
+    static yy::parser::symbol_type yylex();
+  }
+}
+
+%token <int> NUMBER;
+%nterm <int> expr;
+%token EOI 0;
+%printer { yyo << $$; } <int>;
+%destructor { std::cerr << "destroy: " << $$ << '\n'; } <int>
+%%
+expr:
+  NUMBER { $$ = $1 * 10; }
+| expr <int>{ $$ = 20; } NUMBER
+  {
+    std::cerr << "expr: " << $1 << ' ' << $2 << ' ' << $3 << '\n';
+    $$ = 40;
+  }
+;
+
+%%
+namespace yy
+{
+  parser::symbol_type yylex()
+  {
+    static int loc = 0;
+    switch (loc++)
+      {
+      case 0:
+        return parser::make_NUMBER (1);
+      case 1:
+        return parser::make_NUMBER (30);
+      default:
+        return parser::make_EOI ();
+      }
+  }
+
+  void parser::error(const std::string& message)
+  {
+    std::cerr << message << '\n';
+  }
+}
+
+int main()
+{
+  yy::parser p;
+  p.set_debug_level (1);
+  return p.parse();
+}
+]])
+
+
+AT_FULL_COMPILE([[input]])
+# This used to print "Discarding 'a'." again at the end.
+AT_PARSER_CHECK([[./input]], [[0]], [[]],
+[[Starting parse
+Entering state 0
+Reading a token: Next token is token NUMBER (1)
+Shifting token NUMBER (1)
+Entering state 1
+Reducing stack by rule 1 (line 34):
+   $1 = token NUMBER (1)
+-> $$ = nterm expr (10)
+destroy: 1
+Stack now 0
+Entering state 2
+Reading a token: Next token is token NUMBER (30)
+Reducing stack by rule 2 (line 35):
+-> $$ = nterm @1 (20)
+Stack now 2 0
+Entering state 4
+Next token is token NUMBER (30)
+Shifting token NUMBER (30)
+Entering state 5
+Reducing stack by rule 3 (line 35):
+   $1 = nterm expr (10)
+   $2 = nterm @1 (20)
+   $3 = token NUMBER (30)
+expr: 10 20 30
+-> $$ = nterm expr (40)
+destroy: 30
+destroy: 20
+destroy: 10
+Stack now 0
+Entering state 2
+Reading a token: Next token is token EOI ()
+Shifting token EOI ()
+Entering state 3
+Cleanup: popping token EOI ()
+Cleanup: popping nterm expr (40)
+destroy: 40
+]])
+
+AT_BISON_OPTION_POPDEFS
+AT_CLEANUP
+
+
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