Ensure that the result of evaluating a function during constant-expression

simplification gets detoasted before it is incorporated into a Const node.
Otherwise, if an immutable function were to return a TOAST pointer (an
unlikely case, but it can be made to happen), we would end up with a plan
that depends on the continued existence of the out-of-line toast datum.

src/backend/optimizer/util/clauses.c

@@ -8,7 +8,7 @@
  *
  *
  * IDENTIFICATION
- *	  $PostgreSQL: pgsql/src/backend/optimizer/util/clauses.c,v 1.201.2.4 2007/05/01 18:54:09 tgl Exp $
+ *	  $PostgreSQL: pgsql/src/backend/optimizer/util/clauses.c,v 1.201.2.5 2007/10/11 21:28:12 tgl Exp $
  *
  * HISTORY
  *	  AUTHOR			DATE			MAJOR EVENT
@@ -2662,9 +2662,20 @@ evaluate_expr(Expr *expr, Oid result_type)
 	/* Get back to outer memory context */
 	MemoryContextSwitchTo(oldcontext);
 
-	/* Must copy result out of sub-context used by expression eval */
+	/*
+	 * Must copy result out of sub-context used by expression eval.
+	 *
+	 * Also, if it's varlena, forcibly detoast it.  This protects us against
+	 * storing TOAST pointers into plans that might outlive the referenced
+	 * data.
+	 */
 	if (!const_is_null)
+	{
+		if (resultTypLen == -1)
+			const_val = PointerGetDatum(PG_DETOAST_DATUM_COPY(const_val));
+		else
 			const_val = datumCopy(const_val, resultTypByVal, resultTypLen);
+	}
 
 	/* Release all the junk we just created */
 	FreeExecutorState(estate);