glr2.cc: add an example

Currently this example crashes on input such as "T (x) + y;".
The same example with glr.c works properly.

* examples/c++/glr/Makefile, examples/c++/glr/README.md,
* examples/c++/glr/c++-types.test, examples/c++/glr/c++-types.yy,
* examples/c++/glr/local.mk, examples/c++/local.mk: New.
Based on examples/c/glr/c++-types.y.

data/skeletons/glr2.cc

@@ -2092,7 +2092,7 @@ class glr_stack
               {
                 state_set_index yynewStack = yystateStack.yysplitStack (yyk);
                 YY_DEBUG_STREAM << "Splitting off stack " << yynewStack.get()
-                                << " from " << yyk.get();
+                                << " from " << yyk.get() << '\n';
                 YYRESULTTAG yyflag =
                   yyglrReduce (yynewStack, *yyconflicts,
                                yyimmediate[*yyconflicts]);

examples/c++/calc++/local.mk

@@ -18,14 +18,14 @@
 ## Parser generation.  ##
 ## ------------------- ##
 
-%D%/parser.stamp: $(dependencies)
 SUFFIXES += .yy .stamp
 .yy.stamp:
 	$(AM_V_YACC)rm -f $@
 	$(AM_V_at)touch $@.tmp
 	$(AM_V_at)$(YACCCOMPILE) -o $*.cc $<
 	$(AM_V_at)mv -f $@.tmp $@
 
+%D%/parser.stamp: $(dependencies)
 $(calcxx_sources_generated): %D%/parser.stamp
 	@test -f $@ || rm -f %D%/parser.stamp
 	@test -f $@ || $(MAKE) $(AM_MAKEFLAGS) %D%/parser.stamp

examples/c++/glr/Makefile

@@ -0,0 +1,28 @@
+# This Makefile is designed to be simple and readable.  It does not
+# aim at portability.  It requires GNU Make.
+
+BASE = c++-types
+BISON = bison
+XSLTPROC = xsltproc
+
+all: $(BASE)
+
+%.c %.h %.xml %.gv: %.y
+	$(BISON) $(BISONFLAGS) --defines --xml --graph=$*.gv -o $*.c $<
+
+$(BASE): $(BASE).o
+	$(CC) $(CFLAGS) -o $@ $^
+
+run: $(BASE)
+	@echo "Type C++ declarations or expressions.  Quit with ctrl-d."
+	./$<
+
+html: $(BASE).html
+%.html: %.xml
+	$(XSLTPROC) $(XSLTPROCFLAGS) -o $@ $$($(BISON) --print-datadir)/xslt/xml2xhtml.xsl $<
+
+CLEANFILES =									\
+  $(BASE) *.o $(BASE).[ch] $(BASE).output $(BASE).xml $(BASE).html $(BASE).gv
+
+clean:
+	rm -f $(CLEANFILES)

examples/c++/glr/README.md

@@ -0,0 +1,24 @@
+# glr
+
+This example demonstrates the use of GLR parsers to handle (local)
+ambiguities in the C++ language.  See the node "Merging GLR Parses" in
+Bison's documentation.
+
+<!---
+Local Variables:
+fill-column: 76
+ispell-dictionary: "american"
+End:
+
+Copyright (C) 2020 Free Software Foundation, Inc.
+
+This file is part of Bison, the GNU Compiler Compiler.
+
+Permission is granted to copy, distribute and/or modify this document
+under the terms of the GNU Free Documentation License, Version 1.3 or
+any later version published by the Free Software Foundation; with no
+Invariant Sections, with no Front-Cover Texts, and with no Back-Cover
+Texts.  A copy of the license is included in the "GNU Free
+Documentation License" file as part of this distribution.
+
+--->

examples/c++/glr/c++-types.test

@@ -0,0 +1,52 @@
+#! /bin/sh
+
+# Copyright (C) 2020 Free Software Foundation, Inc.
+#
+# This program is free software: you can redistribute it and/or modify
+# it under the terms of the GNU General Public License as published by
+# the Free Software Foundation, either version 3 of the License, or
+# (at your option) any later version.
+#
+# This program is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+# GNU General Public License for more details.
+#
+# You should have received a copy of the GNU General Public License
+# along with this program.  If not, see <http://www.gnu.org/licenses/>.
+
+cat >input <<EOF
+z + q;
+
+T x;
+
+T x = y;
+
+x = y;
+EOF
+run 0 "\
+1.0-4: +(z, q)
+3.0-2: <declare>(T, x)
+5.0-6: <init-declare>(T, x, y)
+7.0-4: =(x, y)"
+
+exit 77
+
+cat >input <<EOF
+T (x) + y;
+
+T (x);
+
+T (y) = z + q;
+
+T (y y) = z + q;
+
+z + q;
+EOF
+run 0 "\
+1.0-8: +(<cast>(x, T), y)
+3.0-4: <OR>(<declare>(T, x), <cast>(x, T))
+5.0-12: <OR>(<init-declare>(T, y, +(z, q)), =(<cast>(y, T), +(z, q)))
+7.0-14: <error>
+9.0-4: +(z, q)
+err: 7.5: syntax error, unexpected identifier, expecting '=' or '+' or ')'"

examples/c++/glr/c++-types.yy

@@ -0,0 +1,258 @@
+/* Simplified -*- C++ -*- Type and Expression Grammar.  */
+
+%glr-parser
+%skeleton "glr2.cc"
+%header
+%locations
+%debug
+
+/* Nice error messages with details. */
+%define parse.error detailed
+
+%code requires
+{
+  union Node {
+    struct {
+      int isNterm;
+      int parents;
+    } nodeInfo;
+    struct {
+      int isNterm; /* 1 */
+      int parents;
+      char const *form;
+      union Node *children[3];
+    } nterm;
+    struct {
+      int isNterm; /* 0 */
+      int parents;
+      char *text;
+    } term;
+  };
+  typedef union Node Node;
+}
+
+%define api.value.type {Node *}
+
+%code
+{
+
+#include <cassert>
+#include <cctype>
+#include <cstdio>
+#include <cstdlib>
+#include <cstring>
+
+#if __cplusplus < 201103L
+# define nullptr 0
+#endif
+
+  static Node *new_nterm (char const *form, Node *child0 = nullptr, Node *child1 = nullptr, Node *child2 = nullptr);
+  static Node *new_term (char *);
+  static void free_node (Node *);
+  static std::ostream& operator<< (std::ostream& o, const Node &node);
+  static YYSTYPE stmtMerge (YYSTYPE x0, YYSTYPE x1);
+
+  static int yylex (YYSTYPE *lvalp, YYLTYPE *llocp);
+}
+
+%expect-rr 1
+
+%token
+  TYPENAME "typename"
+  ID "identifier"
+
+%right '='
+%left '+'
+
+%destructor { free_node ($$); } stmt expr decl declarator TYPENAME ID
+
+%%
+
+prog : %empty
+     | prog stmt   { std::cout << @2 << ": " << *$2 << '\n'; free_node ($2); }
+     ;
+
+stmt : expr ';'  %merge <stmtMerge>     { $$ = $1; }
+     | decl      %merge <stmtMerge>
+     | error ';'        { $$ = new_nterm ("<error>"); }
+     | '@'              { $$ = $1; YYACCEPT; }
+     ;
+
+expr : ID
+     | TYPENAME '(' expr ')'
+                        { $$ = new_nterm ("<cast>", $3, $1); }
+     | expr '+' expr    { $$ = new_nterm ("+", $1, $3); }
+     | expr '=' expr    { $$ = new_nterm ("=", $1, $3); }
+     ;
+
+decl : TYPENAME declarator ';'
+                        { $$ = new_nterm ("<declare>", $1, $2); }
+     | TYPENAME declarator '=' expr ';'
+                        { $$ = new_nterm ("<init-declare>", $1,
+                                          $2, $4); }
+     ;
+
+declarator
+     : ID
+     | '(' declarator ')' { $$ = $2; }
+     ;
+
+%%
+
+int
+main (int argc, char **argv)
+{
+  // Enable parse traces on option -p.
+  if (1 < argc && strcmp (argv[1], "-p") == 0)
+    yydebug = 1;
+  yy::parser parser;
+  return !!parser.parse ();
+}
+
+
+/* A C error reporting function.  */
+void yy::parser::error (const location_type& l, const std::string& m)
+{
+  std::cerr << l << ": " << m << '\n';
+}
+
+int yylex (YYSTYPE *lvalp, YYLTYPE *llocp)
+{
+  static int lineNum = 1;
+  static int colNum = 0;
+
+  while (1)
+    {
+      int c;
+      assert (!feof (stdin));
+      c = getchar ();
+      switch (c)
+        {
+        case EOF:
+          return 0;
+        case '\t':
+          colNum = (colNum + 7) & ~7;
+          break;
+        case ' ': case '\f':
+          colNum += 1;
+          break;
+        case '\n':
+          lineNum += 1;
+          colNum = 0;
+          break;
+        default:
+          {
+            int tok;
+            llocp->begin.line = llocp->end.line = lineNum;
+            llocp->begin.column = colNum;
+            if (isalpha (c))
+              {
+                char buffer[256];
+                unsigned i = 0;
+
+                do
+                  {
+                    buffer[i++] = static_cast<char> (c);
+                    colNum += 1;
+                    assert (i != sizeof buffer - 1);
+                    c = getchar ();
+                  }
+                while (isalnum (c) || c == '_');
+
+                ungetc (c, stdin);
+                buffer[i++] = 0;
+                tok
+                  = isupper (static_cast <unsigned char> (buffer[0]))
+                  ? yy::parser::token::TYPENAME
+                  : yy::parser::token::ID;
+                *lvalp = new_term (strcpy (static_cast<char*> (malloc (i)), buffer));
+              }
+            else
+              {
+                colNum += 1;
+                tok = c;
+                *lvalp = nullptr;
+              }
+            llocp->end.column = colNum-1;
+            return tok;
+          }
+        }
+    }
+}
+
+static Node *
+new_nterm (char const *form, Node *child0, Node *child1, Node *child2)
+{
+  Node *res = new Node;
+  res->nterm.isNterm = 1;
+  res->nterm.parents = 0;
+  res->nterm.form = form;
+  res->nterm.children[0] = child0;
+  if (child0)
+    child0->nodeInfo.parents += 1;
+  res->nterm.children[1] = child1;
+  if (child1)
+    child1->nodeInfo.parents += 1;
+  res->nterm.children[2] = child2;
+  if (child2)
+    child2->nodeInfo.parents += 1;
+  return res;
+}
+
+static Node *
+new_term (char *text)
+{
+  Node *res = new Node;
+  res->term.isNterm = 0;
+  res->term.parents = 0;
+  res->term.text = text;
+  return res;
+}
+
+static void
+free_node (Node *node)
+{
+  if (!node)
+    return;
+  node->nodeInfo.parents -= 1;
+  /* Free only if 0 (last parent) or -1 (no parents).  */
+  if (node->nodeInfo.parents > 0)
+    return;
+  if (node->nodeInfo.isNterm == 1)
+    {
+      free_node (node->nterm.children[0]);
+      free_node (node->nterm.children[1]);
+      free_node (node->nterm.children[2]);
+    }
+  else
+    free (node->term.text);
+  delete node;
+}
+
+static std::ostream&
+operator<< (std::ostream& o, const Node &node)
+{
+  if (node.nodeInfo.isNterm == 1)
+    {
+      o << node.nterm.form;
+      if (node.nterm.children[0])
+        {
+          o << '(' << *node.nterm.children[0];
+          if (node.nterm.children[1])
+            o << ", " << *node.nterm.children[1];
+          if (node.nterm.children[2])
+            o << ", " << *node.nterm.children[2];
+          o << ")";
+        }
+    }
+  else
+    o << node.term.text;
+  return o;
+}
+
+
+static YYSTYPE
+stmtMerge (YYSTYPE x0, YYSTYPE x1)
+{
+  return new_nterm ("<OR>", x0, x1);
+}