Add display of eventual result RowDescription (if any) to the output

of Describe on a prepared statement.  This was in the original 3.0
protocol proposal, but I took it out for reasons that seemed good at
the time.  Put it back per yesterday's pghackers discussion.

src/backend/commands/prepare.c

@@ -10,7 +10,7 @@
  * Copyright (c) 2002-2003, PostgreSQL Global Development Group
  *
  * IDENTIFICATION
- *	  $Header: /cvsroot/pgsql/src/backend/commands/prepare.c,v 1.16 2003/05/06 20:26:26 tgl Exp $
+ *	  $Header: /cvsroot/pgsql/src/backend/commands/prepare.c,v 1.17 2003/05/06 21:51:41 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -393,6 +393,34 @@ FetchPreparedStatementParams(const char *stmt_name)
 	return entry->argtype_list;
 }
 
+/*
+ * Given a prepared statement, determine the result tupledesc it will
+ * produce.  Returns NULL if the execution will not return tuples.
+ *
+ * Note: the result is created or copied into current memory context.
+ */
+TupleDesc
+FetchPreparedStatementResultDesc(PreparedStatement *stmt)
+{
+	Query  *query;
+
+	switch (ChoosePortalStrategy(stmt->query_list))
+	{
+		case PORTAL_ONE_SELECT:
+			query = (Query *) lfirst(stmt->query_list);
+			return ExecCleanTypeFromTL(query->targetList, false);
+
+		case PORTAL_UTIL_SELECT:
+			query = (Query *) lfirst(stmt->query_list);
+			return UtilityTupleDescriptor(query->utilityStmt);
+
+		case PORTAL_MULTI_QUERY:
+			/* will not return tuples */
+			break;
+	}
+	return NULL;
+}
+
 /*
  * Implements the 'DEALLOCATE' utility statement: deletes the
  * specified plan from storage.

src/backend/tcop/postgres.c

@@ -8,7 +8,7 @@
  *
  *
  * IDENTIFICATION
- *	  $Header: /cvsroot/pgsql/src/backend/tcop/postgres.c,v 1.336 2003/05/06 20:26:27 tgl Exp $
+ *	  $Header: /cvsroot/pgsql/src/backend/tcop/postgres.c,v 1.337 2003/05/06 21:51:41 tgl Exp $
  *
  * NOTES
  *	  this is the "main" module of the postgres backend and
@@ -1428,6 +1428,7 @@ static void
 exec_describe_statement_message(const char *stmt_name)
 {
 	PreparedStatement *pstmt;
+	TupleDesc	tupdesc;
 	List	   *l;
 	StringInfoData buf;
 
@@ -1445,6 +1446,9 @@ exec_describe_statement_message(const char *stmt_name)
 	if (whereToSendOutput != Remote)
 		return;					/* can't actually do anything... */
 
+	/*
+	 * First describe the parameters...
+	 */
 	pq_beginmessage(&buf, 't');		/* parameter description message type */
 	pq_sendint(&buf, length(pstmt->argtype_list), 4);
 
@@ -1455,6 +1459,24 @@ exec_describe_statement_message(const char *stmt_name)
 		pq_sendint(&buf, (int) ptype, 4);
 	}
 	pq_endmessage(&buf);
+
+	/*
+	 * Next send RowDescription or NoData to describe the result...
+	 */
+	tupdesc = FetchPreparedStatementResultDesc(pstmt);
+	if (tupdesc)
+	{
+		List   *targetlist;
+
+		if (ChoosePortalStrategy(pstmt->query_list) == PORTAL_ONE_SELECT)
+			targetlist = ((Query *) lfirst(pstmt->query_list))->targetList;
+		else
+			targetlist = NIL;
+		SendRowDescriptionMessage(tupdesc, targetlist);
+	}
+	else
+		pq_putemptymessage('n');	/* NoData */
+
 }
 
 /*
@@ -2359,7 +2381,7 @@ PostgresMain(int argc, char *argv[], const char *username)
 	if (!IsUnderPostmaster)
 	{
 		puts("\nPOSTGRES backend interactive interface ");
-		puts("$Revision: 1.336 $ $Date: 2003/05/06 20:26:27 $\n");
+		puts("$Revision: 1.337 $ $Date: 2003/05/06 21:51:41 $\n");
 	}
 
 	/*

src/backend/tcop/utility.c

@@ -10,7 +10,7 @@
  *
  *
  * IDENTIFICATION
- *	  $Header: /cvsroot/pgsql/src/backend/tcop/utility.c,v 1.199 2003/05/06 20:26:27 tgl Exp $
+ *	  $Header: /cvsroot/pgsql/src/backend/tcop/utility.c,v 1.200 2003/05/06 21:51:41 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -1052,11 +1052,6 @@ UtilityReturnsTuples(Node *parsetree)
 				portal = GetPortalByName(stmt->portalname);
 				if (!PortalIsValid(portal))
 					return false; /* not our business to raise error */
-				/*
-				 * Note: if portal contains multiple statements then it's
-				 * possible some of them will return tuples, but we don't
-				 * handle that case here.
-				 */
 				return portal->tupDesc ? true : false;
 			}
 
@@ -1077,7 +1072,7 @@ UtilityReturnsTuples(Node *parsetree)
 					case PORTAL_UTIL_SELECT:
 						return true;
 					case PORTAL_MULTI_QUERY:
-						/* can't figure it out, per note above */
+						/* will not return tuples */
 						break;
 				}
 				return false;
@@ -1124,25 +1119,13 @@ UtilityTupleDescriptor(Node *parsetree)
 			{
 				ExecuteStmt *stmt = (ExecuteStmt *) parsetree;
 				PreparedStatement *entry;
-				Query  *query;
 
 				if (stmt->into)
 					return NULL;
 				entry = FetchPreparedStatement(stmt->name, false);
 				if (!entry)
 					return NULL; /* not our business to raise error */
-				switch (ChoosePortalStrategy(entry->query_list))
-				{
-					case PORTAL_ONE_SELECT:
-						query = (Query *) lfirst(entry->query_list);
-						return ExecCleanTypeFromTL(query->targetList, false);
-					case PORTAL_UTIL_SELECT:
-						query = (Query *) lfirst(entry->query_list);
-						return UtilityTupleDescriptor(query->utilityStmt);
-					case PORTAL_MULTI_QUERY:
-						break;
-				}
-				return NULL;
+				return FetchPreparedStatementResultDesc(entry);
 			}
 
 		case T_ExplainStmt: