Disallow comments on columns of relation types other than tables, views,

and composite types, which are the only relkinds for which pg_dump support
exists for dumping column comments.  There is no obvious usefulness for
comments on columns of sequences or toast tables; and while comments on
index columns might have some value, it's not worth the risk of compatibility
problems due to possible changes in the algorithm for assigning names to
index columns.  Per discussion.

In consequence, remove now-dead code for copying such comments in CREATE TABLE
LIKE.

src/backend/commands/comment.c

@@ -7,7 +7,7 @@
  * Copyright (c) 1996-2009, PostgreSQL Global Development Group
  *
  * IDENTIFICATION
- *	  $PostgreSQL: pgsql/src/backend/commands/comment.c,v 1.110 2009/12/21 01:34:11 rhaas Exp $
+ *	  $PostgreSQL: pgsql/src/backend/commands/comment.c,v 1.111 2009/12/22 23:54:17 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -627,6 +627,22 @@ CommentAttribute(List *qualname, char *comment)
 		aclcheck_error(ACLCHECK_NOT_OWNER, ACL_KIND_CLASS,
 					   RelationGetRelationName(relation));
 
+	/*
+	 * Allow comments only on columns of tables, views, and composite types
+	 * (which are the only relkinds for which pg_dump will dump per-column
+	 * comments).  In particular we wish to disallow comments on index
+	 * columns, because the naming of an index's columns may change across
+	 * PG versions, so dumping per-column comments could create reload
+	 * failures.
+	 */
+	if (relation->rd_rel->relkind != RELKIND_RELATION &&
+		relation->rd_rel->relkind != RELKIND_VIEW &&
+		relation->rd_rel->relkind != RELKIND_COMPOSITE_TYPE)
+		ereport(ERROR,
+				(errcode(ERRCODE_WRONG_OBJECT_TYPE),
+				 errmsg("\"%s\" is not a table, view, or composite type",
+						RelationGetRelationName(relation))));
+
 	/* Now, fetch the attribute number from the system cache */
 
 	attnum = get_attnum(RelationGetRelid(relation), attrname);

src/backend/parser/parse_utilcmd.c

@@ -19,7 +19,7 @@
  * Portions Copyright (c) 1996-2009, PostgreSQL Global Development Group
  * Portions Copyright (c) 1994, Regents of the University of California
  *
- *	$PostgreSQL: pgsql/src/backend/parser/parse_utilcmd.c,v 2.33 2009/12/20 18:28:14 tgl Exp $
+ *	$PostgreSQL: pgsql/src/backend/parser/parse_utilcmd.c,v 2.34 2009/12/22 23:54:17 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -745,14 +745,12 @@ transformInhRelation(ParseState *pstate, CreateStmtContext *cxt,
 			/* Copy comment on index */
 			if (inhRelation->options & CREATE_TABLE_LIKE_COMMENTS)
 			{
-				Form_pg_attribute *attrs;
-				CommentStmt	   *stmt;
-				int				colno;
-
 				comment = GetComment(parent_index_oid, RelationRelationId, 0);
 
 				if (comment != NULL)
 				{
+					CommentStmt	   *stmt;
+
 					/*
 					 * We have to assign the index a name now, so that we
 					 * can reference it in CommentStmt.
@@ -771,41 +769,6 @@ transformInhRelation(ParseState *pstate, CreateStmtContext *cxt,
 
 					cxt->alist = lappend(cxt->alist, stmt);
 				}
-
-				/* Copy comments on index's columns */
-				attrs = RelationGetDescr(parent_index)->attrs;
-				for (colno = 1;
-					 colno <= RelationGetNumberOfAttributes(parent_index);
-					 colno++)
-				{
-					char	   *attname;
-
-					comment = GetComment(parent_index_oid, RelationRelationId,
-										 colno);
-					if (comment == NULL)
-						continue;
-
-					/*
-					 * We have to assign the index a name now, so that we
-					 * can reference it in CommentStmt.
-					 */
-					if (index_stmt->idxname == NULL)
-						index_stmt->idxname = chooseIndexName(cxt->relation,
-															  index_stmt);
-
-					attname = NameStr(attrs[colno - 1]->attname);
-
-					stmt = makeNode(CommentStmt);
-					stmt->objtype = OBJECT_COLUMN;
-					stmt->objname =
-						list_make3(makeString(cxt->relation->schemaname),
-								   makeString(index_stmt->idxname),
-								   makeString(attname));
-					stmt->objargs = NIL;
-					stmt->comment = comment;
-
-					cxt->alist = lappend(cxt->alist, stmt);
-				}
 			}
 
 			/* Save it in the inh_indexes list for the time being */

src/test/regress/expected/inherit.out

@@ -931,8 +931,6 @@ COMMENT ON COLUMN t1.b IS 'B';
 COMMENT ON CONSTRAINT t1_a_check ON t1 IS 't1_a_check';
 COMMENT ON INDEX t1_pkey IS 'index pkey';
 COMMENT ON INDEX t1_b_key IS 'index b_key';
-COMMENT ON COLUMN t1_pkey.a IS 'index column pkey.a';
-COMMENT ON COLUMN t1_fnidx.pg_expression_1 IS 'index column fnidx';
 ALTER TABLE t1 ALTER COLUMN a SET STORAGE MAIN;
 CREATE TABLE t2 (c text);
 ALTER TABLE t2 ALTER COLUMN c SET STORAGE EXTERNAL;
@@ -1041,12 +1039,10 @@ Has OIDs: no
 
 SELECT c.relname, objsubid, description FROM pg_description, pg_index i, pg_class c WHERE classoid = 'pg_class'::regclass AND objoid = i.indexrelid AND c.oid = i.indexrelid AND i.indrelid = 't_all'::regclass ORDER BY c.relname, objsubid;
    relname   | objsubid | description 
--------------+----------+---------------------
+-------------+----------+-------------
  t_all_b_key |        0 | index b_key
- t_all_key   |        1 | index column fnidx
  t_all_pkey  |        0 | index pkey
- t_all_pkey  |        1 | index column pkey.a
-(4 rows)
+(2 rows)
 
 CREATE TABLE inh_error1 () INHERITS (t1, t4);
 NOTICE:  merging multiple inherited definitions of column "a"

src/test/regress/sql/inherit.sql

@@ -297,8 +297,6 @@ COMMENT ON COLUMN t1.b IS 'B';
 COMMENT ON CONSTRAINT t1_a_check ON t1 IS 't1_a_check';
 COMMENT ON INDEX t1_pkey IS 'index pkey';
 COMMENT ON INDEX t1_b_key IS 'index b_key';
-COMMENT ON COLUMN t1_pkey.a IS 'index column pkey.a';
-COMMENT ON COLUMN t1_fnidx.pg_expression_1 IS 'index column fnidx';
 ALTER TABLE t1 ALTER COLUMN a SET STORAGE MAIN;
 
 CREATE TABLE t2 (c text);