Remove psql's ancient hack that suppressed functions taking or returning

cstring from the output of \df.  Now that the default behavior is to
exclude all system functions, the de-cluttering rationale for this behavior
seems pretty weak; and it was always quite confusing/unhelpful if you were
actually looking for I/O functions.  (Not to mention if you were looking
for encoding converters or other cases that might take or return cstring.)

doc/src/sgml/ref/psql-ref.sgml

 <!--
-$PostgreSQL: pgsql/doc/src/sgml/ref/psql-ref.sgml,v 1.222 2009/04/04 00:39:14 tgl Exp $
+$PostgreSQL: pgsql/doc/src/sgml/ref/psql-ref.sgml,v 1.223 2009/04/08 22:29:30 tgl Exp $
 PostgreSQL documentation
 -->
 
@@ -1055,16 +1055,10 @@ testdb=&gt;
 
         <note>
         <para>
-        To look up functions taking argument or returning values of a specific
+        To look up functions taking arguments or returning values of a specific
         type, use your pager's search capability to scroll through the <literal>\df</>
         output.
         </para>
-
-        <para>
-        To reduce clutter, <literal>\df</> does not show data type I/O
-        functions.  This is implemented by ignoring functions that accept
-        or return type <type>cstring</>.
-        </para>
         </note>
 
         </listitem>

src/bin/psql/describe.c

@@ -8,7 +8,7 @@
  *
  * Copyright (c) 2000-2009, PostgreSQL Global Development Group
  *
- * $PostgreSQL: pgsql/src/bin/psql/describe.c,v 1.207 2009/04/04 00:44:30 tgl Exp $
+ * $PostgreSQL: pgsql/src/bin/psql/describe.c,v 1.208 2009/04/08 22:29:30 tgl Exp $
  */
 #include "postgres_fe.h"
 
@@ -274,13 +274,7 @@ describeFunctions(const char *pattern, bool verbose, bool showSystem)
 		appendPQExpBuffer(&buf,
 						  "     LEFT JOIN pg_catalog.pg_language l ON l.oid = p.prolang\n");
 
-	/*
-	 * we skip in/out funcs by excluding functions that take or return cstring
-	 */
-	appendPQExpBuffer(&buf,
-		   "WHERE p.prorettype <> 'pg_catalog.cstring'::pg_catalog.regtype\n"
-					  "      AND p.proargtypes[0] IS DISTINCT FROM 'pg_catalog.cstring'::pg_catalog.regtype\n"
-					  "      AND NOT p.proisagg\n");
+	appendPQExpBuffer(&buf, "WHERE NOT p.proisagg\n");
 
  	if (!showSystem && !pattern)
  		appendPQExpBuffer(&buf, "      AND n.nspname <> 'pg_catalog'\n"
@@ -643,7 +637,7 @@ objectDescription(const char *pattern, bool showSystem)
 						  "n.nspname", "p.proname", NULL,
 						  "pg_catalog.pg_function_is_visible(p.oid)");
 
-	/* Function descriptions (except in/outs for datatypes) */
+	/* Function descriptions */
 	appendPQExpBuffer(&buf,
 					  "UNION ALL\n"
 					  "  SELECT p.oid as oid, p.tableoid as tableoid,\n"
@@ -652,11 +646,7 @@ objectDescription(const char *pattern, bool showSystem)
 					  "  CAST('%s' AS pg_catalog.text) as object\n"
 					  "  FROM pg_catalog.pg_proc p\n"
 	 "       LEFT JOIN pg_catalog.pg_namespace n ON n.oid = p.pronamespace\n"
-
-		 "  WHERE p.prorettype <> 'pg_catalog.cstring'::pg_catalog.regtype\n"
-					  "      AND (p.proargtypes[0] IS NULL\n"
-					  "      OR   p.proargtypes[0] <> 'pg_catalog.cstring'::pg_catalog.regtype)\n"
-					  "      AND NOT p.proisagg\n",
+					  "  WHERE NOT p.proisagg\n",
 					  gettext_noop("function"));
 
  	if (!showSystem && !pattern)