Fix an old problem in decompilation of CASE constructs: the ruleutils.c code

looks for a CaseTestExpr to figure out what the parser did, but it failed to
consider the possibility that an implicit coercion might be inserted above
the CaseTestExpr.  This could result in an Assert failure in some cases
(but correct results if Asserts weren't enabled), or an "unexpected CASE WHEN
clause" error in other cases.  Per report from Alan Li.

Back-patch to 8.1; problem doesn't exist before that because CASE was
implemented differently.

src/backend/utils/adt/ruleutils.c

@@ -9,7 +9,7 @@
  *
  *
  * IDENTIFICATION
- *	  $PostgreSQL: pgsql/src/backend/utils/adt/ruleutils.c,v 1.295 2009/01/07 13:44:36 tgl Exp $
+ *	  $PostgreSQL: pgsql/src/backend/utils/adt/ruleutils.c,v 1.296 2009/02/25 18:00:01 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -4575,24 +4575,29 @@ get_rule_expr(Node *node, deparse_context *context,
 						 * which we have to show "TRUE" or "FALSE".  Also,
 						 * depending on context the original CaseTestExpr
 						 * might have been reduced to a Const (but we won't
-						 * see "WHEN Const").
+						 * see "WHEN Const").  We have also to consider the
+						 * possibility that an implicit coercion was inserted
+						 * between the CaseTestExpr and the operator.
 						 */
 						if (IsA(w, OpExpr))
 						{
+							List	   *args = ((OpExpr *) w)->args;
+							Node	   *lhs;
 							Node	   *rhs;
 
-							Assert(IsA(linitial(((OpExpr *) w)->args),
-									   CaseTestExpr) ||
-								   IsA(linitial(((OpExpr *) w)->args),
-									   Const));
-							rhs = (Node *) lsecond(((OpExpr *) w)->args);
+							Assert(list_length(args) == 2);
+							lhs = strip_implicit_coercions(linitial(args));
+							Assert(IsA(lhs, CaseTestExpr) ||
+								   IsA(lhs, Const));
+							rhs = (Node *) lsecond(args);
 							get_rule_expr(rhs, context, false);
 						}
-						else if (IsA(w, CaseTestExpr))
+						else if (IsA(strip_implicit_coercions(w),
+									 CaseTestExpr))
 							appendStringInfo(buf, "TRUE");
 						else if (not_clause(w))
 						{
-							Assert(IsA(get_notclausearg((Expr *) w),
+							Assert(IsA(strip_implicit_coercions((Node *) get_notclausearg((Expr *) w)),
 									   CaseTestExpr));
 							appendStringInfo(buf, "FALSE");
 						}