Standard compliant DEFAULT clause

Hi,

here's a fix for a _very_ longstanding bug in PostgreSQL.

According to SQL:2003 DEFAULT may only contain
certain functional expressions and constant literals.
Please, note the year of the standard. Or I know a better one,
PostgreSQL is not even SQL92 compliant in this regard, after 14 years!
http://www.contrib.andrew.cmu.edu/~shadow/sql/sql1992.txt

Please review and apply immediately.
Or not, it's just a bitter and late (because of my bitterness) response
to the rejection of my IDENTITY/GENERATED patches.
Where's the much praised standard behaviour on standard syntax?
So much for hypocrisy.

--
----------------------------------
Zoltán Böszörményi
Cybertec Geschwinde & Schönig GmbH
http://www.postgresql.at/

--- pgsql.orig/src/backend/catalog/heap.c    2007-05-15 09:34:25.000000000 +0200
+++ pgsql/src/backend/catalog/heap.c    2007-05-18 21:33:04.000000000 +0200
@@ -1935,6 +1935,43 @@
               errmsg("cannot use column references in default expression")));

     /*
+     * Make sure default expr may contain only
+     * standard compliant functions as of SQL:2003:
+     * - CURRENT_DATE
+     * - CURRENT_TIME[ ( precision ) ]
+     * - CURRENT_TIMESTAMP[ ( precision ) ]
+     * - LOCALTIME[ ( precision ) ]
+     * - LOCALTIMESTAMP[ ( precision ) ]
+     * - as a PostgreSQL extension,
+     *   all others that call now() implicitely or explicitely
+     * - USER
+     * - CURRENT_USER
+     * - CURRENT_ROLE
+     * - SESSION_USER
+     * with two other PostgreSQL extensions:
+     * - nextval() so SERIALs work
+     * - any immutable functions to pave the way for GENERATED columns
+     * Please note that PostgreSQL lacks SYSTEM_USER and CURRENT_PATH.
+     */
+    if (is_opclause(expr)) {
+        OpExpr *clause = (OpExpr *)expr;
+
+        switch (clause->opfuncid)
+        {
+            case 745:    /* current_user */
+            case 746:    /* session_user */
+            case 1299:    /* now() */
+            case 1574:    /* nextval() */
+                break;
+            default:
+                if (contain_mutable_functions(expr))
+                    ereport(ERROR,
+                        (errcode(ERRCODE_INVALID_OBJECT_DEFINITION),
+                          errmsg("cannot use non-IMMUTABLE functions in default expression")));
+        }
+    }
+
+    /*
      * It can't return a set either.
      */
     if (expression_returns_set(expr))