[CF 5992] v3 - Fix ALTER TABLE DROP EXPRESSION with ONLY option

This branch was automatically generated by a robot using patches from an
email thread registered at:

https://commitfest.postgresql.org/patch/5992

The branch will be overwritten each time a new patch version is posted to
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on the master branch.

Patch(es): https://www.postgresql.org/message-id/CALdSSPigTFDUAsEmGtt3RdXYpbzWFpDcmwKasuxNDdXswDf19A@mail.gmail.com
Author(s): Jian He

Author: Commitfest Bot

src/backend/commands/tablecmds.c

@@ -8733,11 +8733,12 @@ ATPrepDropExpression(Relation rel, AlterTableCmd *cmd, bool recurse, bool recurs
 	 * tables, somewhat similar to how DROP COLUMN does it, so that the
 	 * resulting state can be properly dumped and restored.
 	 */
-	if (!recurse &&
+	if (!recurse && !recursing &&
 		find_inheritance_children(RelationGetRelid(rel), lockmode))
 		ereport(ERROR,
-				(errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
-				 errmsg("ALTER TABLE / DROP EXPRESSION must be applied to child tables too")));
+				errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
+				errmsg("ALTER TABLE / DROP EXPRESSION must be applied to child tables too"),
+				errhint("Do not specify the ONLY keyword."));
 
 	/*
 	 * Cannot drop generation expression from inherited columns.

src/test/regress/expected/generated_stored.out

@@ -1264,6 +1264,7 @@ CREATE TABLE gtest30 (
     b int GENERATED ALWAYS AS (a * 2) STORED
 );
 CREATE TABLE gtest30_1 () INHERITS (gtest30);
+CREATE TABLE gtest30_1_1 () INHERITS (gtest30_1);
 ALTER TABLE gtest30 ALTER COLUMN b DROP EXPRESSION;
 \d gtest30
       Table "generated_stored_tests.gtest30"
@@ -1280,16 +1281,28 @@ Number of child tables: 1 (Use \d+ to list them.)
  a      | integer |           |          | 
  b      | integer |           |          | 
 Inherits: gtest30
+Number of child tables: 1 (Use \d+ to list them.)
+
+\d gtest30_1_1
+    Table "generated_stored_tests.gtest30_1_1"
+ Column |  Type   | Collation | Nullable | Default 
+--------+---------+-----------+----------+---------
+ a      | integer |           |          | 
+ b      | integer |           |          | 
+Inherits: gtest30_1
 
 DROP TABLE gtest30 CASCADE;
-NOTICE:  drop cascades to table gtest30_1
+NOTICE:  drop cascades to 2 other objects
+DETAIL:  drop cascades to table gtest30_1
+drop cascades to table gtest30_1_1
 CREATE TABLE gtest30 (
     a int,
     b int GENERATED ALWAYS AS (a * 2) STORED
 );
 CREATE TABLE gtest30_1 () INHERITS (gtest30);
 ALTER TABLE ONLY gtest30 ALTER COLUMN b DROP EXPRESSION;  -- error
 ERROR:  ALTER TABLE / DROP EXPRESSION must be applied to child tables too
+HINT:  Do not specify the ONLY keyword.
 \d gtest30
                     Table "generated_stored_tests.gtest30"
  Column |  Type   | Collation | Nullable |              Default               

src/test/regress/expected/generated_virtual.out

@@ -1232,6 +1232,7 @@ CREATE TABLE gtest30 (
     b int GENERATED ALWAYS AS (a * 2) VIRTUAL
 );
 CREATE TABLE gtest30_1 () INHERITS (gtest30);
+CREATE TABLE gtest30_1_1 () INHERITS (gtest30_1);
 ALTER TABLE gtest30 ALTER COLUMN b DROP EXPRESSION;
 ERROR:  ALTER TABLE / DROP EXPRESSION is not supported for virtual generated columns
 DETAIL:  Column "b" of relation "gtest30" is a virtual generated column.
@@ -1250,16 +1251,28 @@ Number of child tables: 1 (Use \d+ to list them.)
  a      | integer |           |          | 
  b      | integer |           |          | generated always as (a * 2)
 Inherits: gtest30
+Number of child tables: 1 (Use \d+ to list them.)
+
+\d gtest30_1_1
+              Table "generated_virtual_tests.gtest30_1_1"
+ Column |  Type   | Collation | Nullable |           Default           
+--------+---------+-----------+----------+-----------------------------
+ a      | integer |           |          | 
+ b      | integer |           |          | generated always as (a * 2)
+Inherits: gtest30_1
 
 DROP TABLE gtest30 CASCADE;
-NOTICE:  drop cascades to table gtest30_1
+NOTICE:  drop cascades to 2 other objects
+DETAIL:  drop cascades to table gtest30_1
+drop cascades to table gtest30_1_1
 CREATE TABLE gtest30 (
     a int,
     b int GENERATED ALWAYS AS (a * 2) VIRTUAL
 );
 CREATE TABLE gtest30_1 () INHERITS (gtest30);
 ALTER TABLE ONLY gtest30 ALTER COLUMN b DROP EXPRESSION;  -- error
 ERROR:  ALTER TABLE / DROP EXPRESSION must be applied to child tables too
+HINT:  Do not specify the ONLY keyword.
 \d gtest30
                 Table "generated_virtual_tests.gtest30"
  Column |  Type   | Collation | Nullable |           Default           

src/test/regress/sql/generated_stored.sql

@@ -577,9 +577,11 @@ CREATE TABLE gtest30 (
     b int GENERATED ALWAYS AS (a * 2) STORED
 );
 CREATE TABLE gtest30_1 () INHERITS (gtest30);
+CREATE TABLE gtest30_1_1 () INHERITS (gtest30_1);
 ALTER TABLE gtest30 ALTER COLUMN b DROP EXPRESSION;
 \d gtest30
 \d gtest30_1
+\d gtest30_1_1
 DROP TABLE gtest30 CASCADE;
 CREATE TABLE gtest30 (
     a int,

src/test/regress/sql/generated_virtual.sql

@@ -628,9 +628,11 @@ CREATE TABLE gtest30 (
     b int GENERATED ALWAYS AS (a * 2) VIRTUAL
 );
 CREATE TABLE gtest30_1 () INHERITS (gtest30);
+CREATE TABLE gtest30_1_1 () INHERITS (gtest30_1);
 ALTER TABLE gtest30 ALTER COLUMN b DROP EXPRESSION;
 \d gtest30
 \d gtest30_1
+\d gtest30_1_1
 DROP TABLE gtest30 CASCADE;
 CREATE TABLE gtest30 (
     a int,