C++: let %require "3.2" disable the generation of obsolete files

The files stack.hh and position.hh are deprecated.  Rather than
devoting specify %define variables to discard them (api.position.file
and api.stack.file), and rather than having to use special rules when
api.location.file is used, let's simply decide that from %require
"3.2" onwards, these files will not be generated.

The only noticeable thing here is that, in order to be able to check
the behavior of %require "3.2", to have this version (which is still
3.1-*) to accept %require "3.2".

* src/gram.h, src/gram.c (required_version): New.
* src/parse-gram.y (version_check): Set it.
* src/output.c (prepare): Pass it m4.
* data/bison.m4 (b4_required_version_if): Receive it and use it.
* data/location.cc, data/stack.hh: Replace the api.*.file with only
required version comparison.
* tests/input.at: No longer check api.stack.file and api.position.file.
* NEWS, doc/bison.texi: Don't mention them.
Document the %require 3.2 behavior.
* tests/output.at: Use %require 3.2 instead.

src/gram.c

@@ -46,6 +46,8 @@ symbol_number *token_translations = NULL;
 
 int max_user_token_number = 256;
 
+int required_version = 0;
+
 bool
 rule_useful_in_grammar_p (rule const *r)
 {

src/gram.h

@@ -271,4 +271,8 @@ void grammar_rules_useless_report (const char *message);
 /* Free the packed grammar. */
 void grammar_free (void);
 
+/* The version %required by the grammar file, as an int (100 * major +
+   minor).  0 if unspecified.  */
+extern int required_version;
+
 #endif /* !GRAM_H_ */

src/output.c

@@ -625,6 +625,8 @@ prepare (void)
   char const *cp = getenv ("BISON_USE_PUSH_FOR_PULL");
   bool use_push_for_pull_flag = cp && *cp && strtol (cp, 0, 10);
 
+  MUSCLE_INSERT_INT ("required_version", required_version);
+
   /* Flags. */
   MUSCLE_INSERT_BOOL ("defines_flag", defines_flag);
   MUSCLE_INSERT_BOOL ("glr_flag", glr_parser);

src/parse-gram.y

@@ -32,6 +32,7 @@
 %code
 {
   #include "system.h"
+  #include <errno.h>
 
   #include "c-ctype.h"
   #include "complain.h"
@@ -822,10 +823,37 @@ add_param (param_type type, char *decl, location loc)
 static void
 version_check (location const *loc, char const *version)
 {
-  if (strverscmp (version, PACKAGE_VERSION) > 0)
+  /* Changes of behavior are only on minor version changes, so "3.0.5"
+     is the same as "3.0". */
+  errno = 0;
+  char* cp = NULL;
+  unsigned long major = strtoul (version, &cp, 10);
+  if (errno || *cp != '.')
     {
-      complain (loc, complaint, "require bison %s, but have %s",
-                version, PACKAGE_VERSION);
+      complain (loc, complaint, _("invalid version requirement: %s"),
+                version);
+      return;
+    }
+  ++cp;
+  unsigned long minor = strtoul (cp, NULL, 10);
+  if (errno)
+    {
+      complain (loc, complaint, _("invalid version requirement: %s"),
+                version);
+      return;
+    }
+  required_version = major * 100 + minor;
+  /* Pretend to be at least 3.2, even if we are only 3.1-211, as it
+     allows us to check features published in 3.2 while developping
+     3.2.  */
+  const char* api_version = "3.2";
+  const char* package_version =
+    strverscmp (api_version, PACKAGE_VERSION) > 0
+    ? api_version : PACKAGE_VERSION;
+  if (strverscmp (version, package_version) > 0)
+    {
+      complain (loc, complaint, _("require bison %s, but have %s"),
+                version, package_version);
       exit (EX_MISMATCH);
     }
 }