Reject attempts to alter composite types used in indexes.

find_composite_type_dependencies() ignored indexes, which is a poor
decision because an expression index could have a stored column of
a composite (or other container) type even when the underlying table
does not.  Teach it to detect such cases and error out.  We have to
work a bit harder than for other relations because the pg_depend entry
won't identify the specific index column of concern, but it's not much
new code.

This does not address bug #17872's original complaint that dropping
a column in such a type might lead to violations of the uniqueness
property that a unique index is supposed to ensure.  That seems of
much less concern to me because it won't lead to crashes.

Per bug #17872 from Alexander Lakhin.  Back-patch to all supported
branches.

Discussion: https://postgr.es/m/17872-d0fbb799dc3fd85d@postgresql.org

2 files changed, 19 insertions, 2 deletions

diff --git a/src/test/regress/expected/alter_table.out b/src/test/regress/expected/alter_table.out
index d58090baad4..36350ddbb26 100644
--- a/src/test/regress/expected/alter_table.out
+++ b/src/test/regress/expected/alter_table.out
@@ -3093,6 +3093,13 @@ CREATE TYPE test_type1 AS (a int, b text);
 CREATE TABLE test_tbl1 (x int, y test_type1);
 ALTER TYPE test_type1 ALTER ATTRIBUTE b TYPE varchar; -- fails
 ERROR:  cannot alter type "test_type1" because column "test_tbl1.y" uses it
+DROP TABLE test_tbl1;
+CREATE TABLE test_tbl1 (x int, y text);
+CREATE INDEX test_tbl1_idx ON test_tbl1((row(x,y)::test_type1));
+ALTER TYPE test_type1 ALTER ATTRIBUTE b TYPE varchar; -- fails
+ERROR:  cannot alter type "test_type1" because column "test_tbl1_idx.row" uses it
+DROP TABLE test_tbl1;
+DROP TYPE test_type1;
 CREATE TYPE test_type2 AS (a int, b text);
 CREATE TABLE test_tbl2 OF test_type2;
 CREATE TABLE test_tbl2_subclass () INHERITS (test_tbl2);
@@ -3204,7 +3211,8 @@ Typed table of type: test_type2
  c      | text    |           |          | 
 Inherits: test_tbl2
 
-DROP TABLE test_tbl2_subclass;
+DROP TABLE test_tbl2_subclass, test_tbl2;
+DROP TYPE test_type2;
 CREATE TYPE test_typex AS (a int, b text);
 CREATE TABLE test_tblx (x int, y test_typex check ((y).a > 0));
 ALTER TYPE test_typex DROP ATTRIBUTE a; -- fails
diff --git a/src/test/regress/sql/alter_table.sql b/src/test/regress/sql/alter_table.sql
index 1dea671fbe4..eccd1b8e884 100644
--- a/src/test/regress/sql/alter_table.sql
+++ b/src/test/regress/sql/alter_table.sql
@@ -1980,6 +1980,14 @@ CREATE TYPE test_type1 AS (a int, b text);
 CREATE TABLE test_tbl1 (x int, y test_type1);
 ALTER TYPE test_type1 ALTER ATTRIBUTE b TYPE varchar; -- fails
 
+DROP TABLE test_tbl1;
+CREATE TABLE test_tbl1 (x int, y text);
+CREATE INDEX test_tbl1_idx ON test_tbl1((row(x,y)::test_type1));
+ALTER TYPE test_type1 ALTER ATTRIBUTE b TYPE varchar; -- fails
+
+DROP TABLE test_tbl1;
+DROP TYPE test_type1;
+
 CREATE TYPE test_type2 AS (a int, b text);
 CREATE TABLE test_tbl2 OF test_type2;
 CREATE TABLE test_tbl2_subclass () INHERITS (test_tbl2);
@@ -2007,7 +2015,8 @@ ALTER TYPE test_type2 RENAME ATTRIBUTE a TO aa CASCADE;
 \d test_tbl2
 \d test_tbl2_subclass
 
-DROP TABLE test_tbl2_subclass;
+DROP TABLE test_tbl2_subclass, test_tbl2;
+DROP TYPE test_type2;
 
 CREATE TYPE test_typex AS (a int, b text);
 CREATE TABLE test_tblx (x int, y test_typex check ((y).a > 0));