Improve parser so that we can show an error cursor position for errors

during parse analysis, not only errors detected in the flex/bison stages.
This is per my earlier proposal.  This commit includes all the basic
infrastructure, but locations are only tracked and reported for errors
involving column references, function calls, and operators.  More could
be done later but this seems like a good set to start with.  I've also
moved the ReportSyntaxErrorPosition logic out of psql and into libpq,
which should make it available to more people --- even within psql this
is an improvement because warnings weren't handled by ReportSyntaxErrorPosition.

src/include/parser/parse_node.h

@@ -7,7 +7,7 @@
  * Portions Copyright (c) 1996-2006, PostgreSQL Global Development Group
  * Portions Copyright (c) 1994, Regents of the University of California
  *
- * $PostgreSQL: pgsql/src/include/parser/parse_node.h,v 1.47 2006/03/05 15:58:57 momjian Exp $
+ * $PostgreSQL: pgsql/src/include/parser/parse_node.h,v 1.48 2006/03/14 22:48:22 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -20,6 +20,15 @@
 /*
  * State information used during parse analysis
  *
+ * parentParseState: NULL in a top-level ParseState.  When parsing a subquery,
+ * links to current parse state of outer query.
+ *
+ * p_sourcetext: source string that generated the raw parsetree being
+ * analyzed, or NULL if not available.  (The string is used only to
+ * generate cursor positions in error messages: we need it to convert
+ * byte-wise locations in parse structures to character-wise cursor
+ * positions.)
+ *
  * p_rtable: list of RTEs that will become the rangetable of the query.
  * Note that neither relname nor refname of these entries are necessarily
  * unique; searching the rtable by name is a bad idea.
@@ -53,6 +62,7 @@
 typedef struct ParseState
 {
 	struct ParseState *parentParseState;		/* stack link */
+	const char *p_sourcetext;	/* source text, or NULL if not available */
 	List	   *p_rtable;		/* range table so far */
 	List	   *p_joinlist;		/* join items so far (will become FromExpr
 								 * node's fromlist) */
@@ -73,6 +83,8 @@ typedef struct ParseState
 } ParseState;
 
 extern ParseState *make_parsestate(ParseState *parentParseState);
+extern int	parser_errposition(ParseState *pstate, int location);
+
 extern Var *make_var(ParseState *pstate, RangeTblEntry *rte, int attrno);
 extern Oid	transformArrayType(Oid arrayType);
 extern ArrayRef *transformArraySubscripts(ParseState *pstate,