yacc.c: provide the Bison version as an integral macro

Suggested by Balazs Scheidler.
https://github.com/akimd/bison/issues/55

* src/muscle-tab.c (muscle_init): Move/rename `b4_version` to/as...
* src/output.c (prepare): `b4_version_string`.
Also define `b4_version`.
* data/skeletons/bison.m4, data/skeletons/c.m4, data/skeletons/d.m4,
* data/skeletons/java.m4: Adjust.
* doc/bison.texi: Document it.

NEWS

@@ -7,6 +7,12 @@ GNU Bison NEWS
   In Yacc mode, all the tokens are defined twice: once as an enum, and then
   as a macro.  YYEMPTY was missing its macro.
 
+** Changes
+
+  The YYBISON macro in generated "regular C parsers" (from the "yacc.c"
+  skeleton) used to be defined to 1.  It is now defined to the version of
+  Bison as an integer (e.g., 30704 for version 3.7.4).
+
 * Noteworthy changes in release 3.7.3 (2020-10-13) [stable]
 
 ** Bug fixes

data/skeletons/bison.m4

@@ -49,7 +49,7 @@ m4_define([m4_shift4], [m4_shift(m4_shift(m4_shift(m4_shift($@))))])
 # b4_generated_by
 # ---------------
 m4_define([b4_generated_by],
-[b4_comment([A Bison parser, made by GNU Bison b4_version.])
+[b4_comment([A Bison parser, made by GNU Bison b4_version_string.])
 ])
 
 # b4_copyright(TITLE, [YEARS])

data/skeletons/c.m4

@@ -58,11 +58,11 @@ m4_define([b4_cpp_guard_close],
 # b4_pull_flag if they use the values of the %define variables api.pure or
 # api.push-pull.
 m4_define([b4_identification],
-[[/* Identify Bison output.  */
+[[/* Identify Bison output, and Bison version.  */
-#define YYBISON 1
+#define YYBISON ]b4_version[
 
-/* Bison version.  */
+/* Bison version string.  */
-#define YYBISON_VERSION "]b4_version["
+#define YYBISON_VERSION "]b4_version_string["
 
 /* Skeleton name.  */
 #define YYSKELETON_NAME ]b4_skeleton[]m4_ifdef([b4_pure_flag], [[

data/skeletons/d.m4

@@ -103,12 +103,12 @@ m4_define([b4_location_type_if],
 # b4_identification
 # -----------------
 m4_define([b4_identification],
-[/** Version number for the Bison executable that generated this parser.  */
+[[/** Version number for the Bison executable that generated this parser.  */
-  public static immutable string yy_bison_version = "b4_version";
+  public static immutable string yy_bison_version = "]b4_version_string[";
 
   /** Name of the skeleton that generated this parser.  */
-  public static immutable string yy_bison_skeleton = b4_skeleton;
+  public static immutable string yy_bison_skeleton = ]b4_skeleton[;
-])
+]])
 
 
 ## ------------ ##

data/skeletons/java.m4

@@ -71,12 +71,12 @@ m4_define([b4_lexer_if],
 # b4_identification
 # -----------------
 m4_define([b4_identification],
-[  /** Version number for the Bison executable that generated this parser.  */
+[[  /** Version number for the Bison executable that generated this parser.  */
-  public static final String bisonVersion = "b4_version";
+  public static final String bisonVersion = "]b4_version_string[";
 
   /** Name of the skeleton that generated this parser.  */
-  public static final String bisonSkeleton = b4_skeleton;
+  public static final String bisonSkeleton = ]b4_skeleton[;
-])
+]])
 
 
 ## ------------ ##

doc/bison.texi

@@ -15434,6 +15434,12 @@ Macro to discard a value from the parser stack and fake a lookahead
 token.  @xref{Action Features}.
 @end deffn
 
+@deffn {Macro} YYBISON
+The version of Bison as an integer, for instance 30704 for version 3.7.4.
+Defined in @file{yacc.c} only.  Before version 3.7.4, @code{YYBISON} was
+defined to 1.
+@end deffn
+
 @deffn {Variable} yychar
 External integer variable that contains the integer value of the
 lookahead token.  (In a pure parser, it is a local variable within

src/muscle-tab.c

@@ -127,9 +127,6 @@ muscle_init (void)
 
   muscle_table = hash_xinitialize (HT_INITIAL_CAPACITY, NULL, hash_muscle,
                                    hash_compare_muscles, muscle_entry_free);
-
-  /* Version and input file.  */
-  MUSCLE_INSERT_STRING ("version", VERSION);
 }
 
 

src/output.c

@@ -42,6 +42,7 @@
 #include "scan-skel.h"
 #include "symtab.h"
 #include "tables.h"
+#include "strversion.h"
 
 static struct obstack format_obstack;
 
@@ -807,6 +808,9 @@ prepare (void)
   char const *cp = getenv ("BISON_USE_PUSH_FOR_PULL");
   bool use_push_for_pull_flag = cp && *cp && strtol (cp, 0, 10);
 
+  /* Versions.  */
+  MUSCLE_INSERT_STRING ("version_string", VERSION);
+  MUSCLE_INSERT_INT ("version", strversion_to_int (VERSION));
   MUSCLE_INSERT_INT ("required_version", required_version);
 
   /* Flags. */

src/parse-gram.c

@@ -46,7 +46,7 @@
    USER NAME SPACE" below.  */
 
 /* Identify Bison output.  */
-#define YYBISON 1
+#define YYBISON 30703
 
 /* Bison version.  */
 #define YYBISON_VERSION "3.7.3.7-d831b"