examples: don't use yysyntax_error_arguments

Suggested by Adrian Vogelsgesang.
https://lists.gnu.org/archive/html/bison-patches/2020-02/msg00069.html

* data/skeletons/lalr1.java (Context.EMPTY, Context.getToken): New.
(Context.yyntokens): Rename as...
(Context.NTOKENS): this.
Because (i) all the Java coding styles recommend upper case for
constants, and (ii) the Java Skeleton exposes Lexer.EOF, not
Lexer.YYEOF.
* data/skeletons/yacc.c (yyparse_context_token): New.
* examples/c/bistromathic/parse.y (yyreport_syntax_error): Don't use
yysyntax_error_arguments.
* examples/java/calc/Calc.y (yyreportSyntaxError): Likewise.

THANKS

@@ -4,6 +4,7 @@ it is today without the invaluable help of these people:
 Aaro Koskinen             aaro.koskinen@iki.fi
 Аскар Сафин               safinaskar@mail.ru
 Adam Sampson              ats@offog.org
+Adrian Vogelsgesang       avogelsgesang@tableau.com
 Ahcheong Lee              dkcjd2000@gmail.com
 Airy Andre                Airy.Andre@edf.fr
 Akim Demaille             akim@gnu.org

data/skeletons/lalr1.java

@@ -867,19 +867,37 @@ b4_dollar_popdef[]dnl
       yytoken = token;]b4_locations_if([[
       yylocation = loc;]])[
     }
+
     private YYStack yystack;
+
+    public int getToken ()
+    {
+      return yytoken;
+    }
+
+    /**
+     * Value returned by getToken when there is no token.
+     */
+    public static final int EMPTY = ]b4_parser_class[.yyempty_;
+
     private int yytoken;]b4_locations_if([[
     public ]b4_location_type[ getLocation ()
     {
       return yylocation;
     }
+
     private ]b4_location_type[ yylocation;]])[
-    static final int yyntokens = ]b4_parser_class[.yyntokens_;
+    static final int NTOKENS = ]b4_parser_class[.yyntokens_;
 
     /* Put in YYARG at most YYARGN of the expected tokens given the
        current YYCTX, and return the number of tokens stored in YYARG.  If
        YYARG is null, return the number of expected tokens (guaranteed to
        be less than YYNTOKENS).  */
+    int yyexpectedTokens (int yyarg[], int yyargn)
+    {
+      return yyexpectedTokens (yyarg, 0, yyargn);
+    }
+
     int yyexpectedTokens (int yyarg[], int yyoffset, int yyargn)
     {
       int yycount = yyoffset;
@@ -893,7 +911,7 @@ b4_dollar_popdef[]dnl
           int yyxbegin = yyn < 0 ? -yyn : 0;
           /* Stay within bounds of both yycheck and yytname.  */
           int yychecklim = yylast_ - yyn + 1;
-          int yyxend = yychecklim < yyntokens ? yychecklim : yyntokens;
+          int yyxend = yychecklim < NTOKENS ? yychecklim : NTOKENS;
           for (int x = yyxbegin; x < yyxend; ++x)
             if (yycheck_[x + yyn] == x && x != yy_error_token_
                 && !yyTableValueIsError (yytable_[x + yyn]))

data/skeletons/yacc.c

@@ -1198,6 +1198,10 @@ yyexpected_tokens (const yyparse_context_t *yyctx,
   return yypstate_expected_tokens (yyctx->yyps, yyarg, yyargn);
 }]])[
 
+static int
+yysyntax_error_arguments (const yyparse_context_t *yyctx,
+                          int yyarg[], int yyargn) YY_ATTRIBUTE_UNUSED;
+
 static int
 yysyntax_error_arguments (const yyparse_context_t *yyctx,
                           int yyarg[], int yyargn)
@@ -1251,7 +1255,17 @@ yysyntax_error_arguments (const yyparse_context_t *yyctx,
 
 ]b4_parse_error_case(
          [custom],
-[b4_locations_if([[/*  The location of this context.  */
+[[/* The token type of the lookahead of this context.  */
+static int
+yyparse_context_token (const yyparse_context_t *yyctx) YY_ATTRIBUTE_UNUSED;
+
+static int
+yyparse_context_token (const yyparse_context_t *yyctx)
+{
+  return yyctx->yytoken;
+}
+
+]b4_locations_if([[/* The location of the lookahead of this context.  */
 static YYLTYPE *
 yyparse_context_location (const yyparse_context_t *yyctx) YY_ATTRIBUTE_UNUSED;
 

examples/c/bistromathic/parse.y

@@ -284,22 +284,25 @@ yylex (const char **line, YYSTYPE *yylval, YYLTYPE *yylloc)
 int
 yyreport_syntax_error (const yyparse_context_t *ctx)
 {
-  enum { ARGMAX = 10 };
   int res = 0;
-  int arg[ARGMAX];
-  int n = yysyntax_error_arguments (ctx, arg, ARGMAX);
+  YY_LOCATION_PRINT (stderr, *yyparse_context_location (ctx));
+  fprintf (stderr, ": syntax error");
+  {
+    enum { TOKENMAX = 10 };
+    int expected[TOKENMAX];
+    int n = yyexpected_tokens (ctx, expected, TOKENMAX);
     if (n < 0)
       // Forward errors to yyparse.
       res = n;
-  YY_LOCATION_PRINT (stderr, *yyparse_context_location (ctx));
-  fprintf (stderr, ": syntax error");
-  if (n >= 0)
-    {
-      for (int i = 1; i < n; ++i)
+    else
+      for (int i = 0; i < n; ++i)
         fprintf (stderr, "%s %s",
-                 i == 1 ? ": expected" : " or", yysymbol_name (arg[i]));
-      if (n)
-        fprintf (stderr, " before %s", yysymbol_name (arg[0]));
+                 i == 0 ? ": expected" : " or", yysymbol_name (expected[i]));
+  }
+  {
+    int lookahead = yyparse_context_token (ctx);
+    if (lookahead != YYEMPTY)
+      fprintf (stderr, " before %s", yysymbol_name (lookahead));
   }
   fprintf (stderr, "\n");
   return res;

examples/java/calc/Calc.y

@@ -108,15 +108,20 @@ class CalcLexer implements Calc.Lexer {
 
   public void yyreportSyntaxError (Calc.Context ctx)
   {
-    final int ARGMAX = 10;
-    int[] arg = new int[ARGMAX];
-    int n = ctx.yysyntaxErrorArguments (arg, ARGMAX);
     System.err.print (ctx.getLocation () + ": syntax error");
-    for (int i = 1; i < n; ++i)
-      System.err.print ((i == 1 ? ": expected " : " or ")
+    {
+      final int TOKENMAX = 10;
+      int[] arg = new int[TOKENMAX];
+      int n = ctx.yyexpectedTokens (arg, TOKENMAX);
+      for (int i = 0; i < n; ++i)
+        System.err.print ((i == 0 ? ": expected " : " or ")
                           + ctx.yysymbolName (arg[i]));
-    if (n != 0)
-      System.err.print (" before " + ctx.yysymbolName (arg[0]));
+    }
+    {
+      int lookahead = ctx.getToken ();
+      if (lookahead != ctx.EMPTY)
+        System.err.print (" before " + ctx.yysymbolName (lookahead));
+    }
     System.err.println ("");
   }
 

tests/local.at

@@ -964,8 +964,8 @@ m4_define([AT_YYERROR_DEFINE(java)],
 ]AT_ERROR_CUSTOM_IF([[
   public void yyreportSyntaxError (Calc.Context ctx)
   {
-    int[] arg = new int[ctx.yyntokens];
-    int n = ctx.yysyntaxErrorArguments (arg, ctx.yyntokens);
+    int[] arg = new int[ctx.NTOKENS];
+    int n = ctx.yysyntaxErrorArguments (arg, ctx.NTOKENS);
     System.err.print (]AT_LOCATION_IF([[ctx.getLocation () + ": "]]
                       + )["syntax error on token @<:@" + ctx.yysymbolName (arg[0]) + "@:>@");
     if (1 < n)