Re: [PATCH 0/7] Deprecate yysyntax_error_arguments

[Akim Demaille]

> Le 26 mars 2020 à 19:09, Akim Demaille <address@hidden> a écrit :
> 
> 
> 
>> Le 21 mars 2020 à 12:53, Akim Demaille <address@hidden> a écrit :
>> 
>> This series of commits explores the removal of
>> yysyntax_error_arguments, as Adrian suggested
>> (https://lists.gnu.org/archive/html/bison-patches/2020-02/msg00069.html).
>> I wanted to see in practice what impact it has on the user code, and
>> here are a few examples.
> 
> I have still not applied these changes, I would be happy to receive
> comments.  But there are a few more patches to add.
> 
> commit f1eb1e197d7453579f7843315a0aca0a2563ca90
> Author: Akim Demaille <address@hidden>
> Date:   Thu Mar 26 08:15:35 2020 +0100
> 
>    skeletons: make yysyntax_error_arguments a private detail

And this one.

commit 8ce89cbc0b7c381a0bb7408d010d0b8fc1926148
Author: Akim Demaille <address@hidden>
Date:   Thu Mar 26 08:35:50 2020 +0100

    java: make yysyntaxErrorArguments a private detail
    
    * data/skeletons/lalr1.java (yysyntaxErrorArguments): Move it from the
    context, to the parser object.
    Generate only for detailed and verbose error messages.
    * tests/local.at (AT_YYERROR_DEFINE(java)): Use yyexpectedTokens
    instead.

diff --git a/data/skeletons/lalr1.java b/data/skeletons/lalr1.java
index c5cbd1be..195fed1a 100644
--- a/data/skeletons/lalr1.java
+++ b/data/skeletons/lalr1.java
@@ -933,46 +933,49 @@ b4_dollar_popdef[]dnl
     {
       return ]b4_parser_class[.yysymbolName (yysymbol);
     }
+  }
 
-    int yysyntaxErrorArguments (int[] yyarg, int yyargn)
-    {
-      /* There are many possibilities here to consider:
-         - If this state is a consistent state with a default action,
-           then the only way this function was invoked is if the
-           default action is an error action.  In that case, don't
-           check for expected tokens because there are none.
-         - The only way there can be no lookahead present (in tok) is
-           if this state is a consistent state with a default action.
-           Thus, detecting the absence of a lookahead is sufficient to
-           determine that there is no unexpected or expected token to
-           report.  In that case, just report a simple "syntax error".
-         - Don't assume there isn't a lookahead just because this
-           state is a consistent state with a default action.  There
-           might have been a previous inconsistent state, consistent
-           state with a non-default action, or user semantic action
-           that manipulated yychar.  (However, yychar is currently out
-           of scope during semantic actions.)
-         - Of course, the expected token list depends on states to
-           have correct lookahead information, and it depends on the
-           parser not to perform extra reductions after fetching a
-           lookahead from the scanner and before detecting a syntax
-           error.  Thus, state merging (from LALR or IELR) and default
-           reductions corrupt the expected token list.  However, the
-           list is correct for canonical LR with one exception: it
-           will still contain any token that will not be accepted due
-           to an error action in a later state.
-      */
-      int yycount = 0;
-      if (this.yytoken != yyempty_)
-        {
-          yyarg[yycount++] = this.yytoken;
-          yycount += this.yyexpectedTokens (yyarg, 1, yyargn);
-        }
-      return yycount;
-    }
+]b4_parse_error_bmatch(
+[detailed\|verbose], [[
+  private int yysyntaxErrorArguments (Context yyctx, int[] yyarg, int yyargn)
+  {
+    /* There are many possibilities here to consider:
+       - If this state is a consistent state with a default action,
+         then the only way this function was invoked is if the
+         default action is an error action.  In that case, don't
+         check for expected tokens because there are none.
+       - The only way there can be no lookahead present (in tok) is
+         if this state is a consistent state with a default action.
+         Thus, detecting the absence of a lookahead is sufficient to
+         determine that there is no unexpected or expected token to
+         report.  In that case, just report a simple "syntax error".
+       - Don't assume there isn't a lookahead just because this
+         state is a consistent state with a default action.  There
+         might have been a previous inconsistent state, consistent
+         state with a non-default action, or user semantic action
+         that manipulated yychar.  (However, yychar is currently out
+         of scope during semantic actions.)
+       - Of course, the expected token list depends on states to
+         have correct lookahead information, and it depends on the
+         parser not to perform extra reductions after fetching a
+         lookahead from the scanner and before detecting a syntax
+         error.  Thus, state merging (from LALR or IELR) and default
+         reductions corrupt the expected token list.  However, the
+         list is correct for canonical LR with one exception: it
+         will still contain any token that will not be accepted due
+         to an error action in a later state.
+    */
+    int yycount = 0;
+    if (yyctx.getToken () != yyempty_)
+      {
+        yyarg[yycount++] = yyctx.getToken ();
+        yycount += yyctx.yyexpectedTokens (yyarg, 1, yyargn);
+      }
+    return yycount;
   }
+]])[
 
- /**
+/**
    * Report a syntax error.
    */
   private void yyreportSyntaxError (Context yyctx)
@@ -984,7 +987,7 @@ b4_dollar_popdef[]dnl
       {
         final int argmax = 5;
         int[] yyarg = new int[argmax];
-        int yycount = yyctx.yysyntaxErrorArguments (yyarg, argmax);
+        int yycount = yysyntaxErrorArguments (yyctx, yyarg, argmax);
         String[] yystr = new String[yycount];
         for (int yyi = 0; yyi < yycount; ++yyi)
           yystr[yyi] = yysymbolName (yyarg[yyi]);
diff --git a/tests/local.at b/tests/local.at
index 5cc51e7e..fdb715c9 100644
--- a/tests/local.at
+++ b/tests/local.at
@@ -972,17 +972,24 @@ m4_define([AT_YYERROR_DEFINE(java)],
 ]AT_ERROR_CUSTOM_IF([[
   public void yyreportSyntaxError (Calc.Context ctx)
   {
-    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)
-      {
-        System.err.print (" (expected:");
-        for (int i = 1; i < n; ++i)
-          System.err.print (" @<:@" + ctx.yysymbolName (arg[i]) + "@:>@");
-        System.err.print (")");
-      }
+                      + )["syntax error");
+    {
+      int token = ctx.getToken ();
+      if (token != ctx.EMPTY)
+        System.err.print (" on token @<:@" + ctx.yysymbolName (token) + 
"@:>@");
+    }
+    {
+      int[] arg = new int[ctx.NTOKENS];
+      int n = ctx.yyexpectedTokens (arg, ctx.NTOKENS);
+      if (0 < n)
+        {
+          System.err.print (" (expected:");
+          for (int i = 0; i < n; ++i)
+            System.err.print (" @<:@" + ctx.yysymbolName (arg[i]) + "@:>@");
+          System.err.print (")");
+        }
+    }
     System.err.println ("");
   }
 ]])