[RFA] Change to parse error reporting

[Michael Snyder <msnyder@cygnus.com>]

Folks, 

I've never liked the way in which "parse error" messages in gdb
always point to the token _after_ the error, instead of at the
token _causing_ the error.

This change (implemented for the c/c++ parser only) will make it
point at the error token instead of the following token.  
Extending the change to the other languages will be trivial, 
if you agree with this.

OK to commit?


2002-04-12  Michael Snyder  <msnyder@redhat.com>

	* parser-defs.h (prev_lexptr): New external variable.
	* parse.c (parse_exp_1): Set prev_lexptr to null before
	calling the language-specific parser.
	* c-exp.y (yylex): Set prev_lexptr to start of current token.
	(yyerror): Use prev_lexptr in error reporting.

Index: parse.c
===================================================================
RCS file: /cvs/src/src/gdb/parse.c,v
retrieving revision 1.22
diff -p -r1.22 parse.c
*** parse.c	9 Apr 2002 22:14:39 -0000	1.22
--- parse.c	12 Apr 2002 19:40:35 -0000
*************** int arglist_len;
*** 76,81 ****
--- 76,82 ----
  union type_stack_elt *type_stack;
  int type_stack_depth, type_stack_size;
  char *lexptr;
+ char *prev_lexptr;
  char *namecopy;
  int paren_depth;
  int comma_terminates;
*************** parse_exp_1 (char **stringptr, struct bl
*** 1126,1131 ****
--- 1127,1133 ----
    struct cleanup *old_chain;
  
    lexptr = *stringptr;
+   prev_lexptr = NULL;
  
    paren_depth = 0;
    type_stack_depth = 0;
Index: parser-defs.h
===================================================================
RCS file: /cvs/src/src/gdb/parser-defs.h,v
retrieving revision 1.7
diff -p -r1.7 parser-defs.h
*** parser-defs.h	9 Apr 2002 22:14:39 -0000	1.7
--- parser-defs.h	12 Apr 2002 19:40:35 -0000
*************** extern struct type *follow_types (struct
*** 150,155 ****
--- 150,159 ----
  
  extern char *lexptr;
  
+ /* After a token has been recognized, this variable points to it.  
+    Currently used only for error reporting.  */
+ extern char *prev_lexptr;
+ 
  /* Tokens that refer to names do so with explicit pointer and length,
     so they can share the storage that lexptr is parsing.
  
Index: c-exp.y
===================================================================
RCS file: /cvs/src/src/gdb/c-exp.y,v
retrieving revision 1.7
diff -p -r1.7 c-exp.y
*** c-exp.y	15 Nov 2001 01:55:59 -0000	1.7
--- c-exp.y	12 Apr 2002 19:40:35 -0000
*************** yylex ()
*** 1218,1223 ****
--- 1218,1224 ----
     
   retry:
  
+   prev_lexptr = lexptr;
    unquoted_expr = 1;
  
    tokstart = lexptr;
*************** void
*** 1738,1742 ****
--- 1739,1746 ----
  yyerror (msg)
       char *msg;
  {
+   if (prev_lexptr)
+     lexptr = prev_lexptr;
+ 
    error ("A %s in expression, near `%s'.", (msg ? msg : "error"), lexptr);
  }