Disallow whole-row variables in GENERATED expressions.

This was previously allowed, but I think that was just an oversight.
It's a clear violation of the rule that a generated column cannot
depend on itself or other generated columns.  Moreover, because the
code was relying on the assumption that no such cross-references
exist, it was pretty easy to crash ALTER TABLE and perhaps other
places.  Even if you managed not to crash, you got quite unstable,
implementation-dependent results.

Per report from Vitaly Ustinov.
Back-patch to v12 where GENERATED came in.

Discussion: https://postgr.es/m/CAM_DEiWR2DPT6U4xb-Ehigozzd3n3G37ZB1+867zbsEVtYoJww@mail.gmail.com

diff --git a/src/backend/catalog/heap.c b/src/backend/catalog/heap.c
index 431e62e3897269e5fe7af84ab0a9a96f86f722df..ba3e1ecf459bde2b74cf1b6076a6b1504dd0648a 100644 (file)
--- a/src/backend/catalog/heap.c
+++ b/src/backend/catalog/heap.c
@@ -3020,15 +3020,26 @@ check_nested_generated_walker(Node *node, void *context)
        AttrNumber  attnum;
 
        relid = rt_fetch(var->varno, pstate->p_rtable)->relid;
+       if (!OidIsValid(relid))
+           return false;       /* XXX shouldn't we raise an error? */
+
        attnum = var->varattno;
 
-       if (OidIsValid(relid) && AttributeNumberIsValid(attnum) && get_attgenerated(relid, attnum))
+       if (attnum > 0 && get_attgenerated(relid, attnum))
            ereport(ERROR,
-                   (errcode(ERRCODE_SYNTAX_ERROR),
+                   (errcode(ERRCODE_INVALID_OBJECT_DEFINITION),
                     errmsg("cannot use generated column \"%s\" in column generation expression",
                            get_attname(relid, attnum, false)),
                     errdetail("A generated column cannot reference another generated column."),
                     parser_errposition(pstate, var->location)));
+       /* A whole-row Var is necessarily self-referential, so forbid it */
+       if (attnum == 0)
+           ereport(ERROR,
+                   (errcode(ERRCODE_INVALID_OBJECT_DEFINITION),
+                    errmsg("cannot use whole-row variable in column generation expression"),
+                    errdetail("This would cause the generated column to depend on its own value."),
+                    parser_errposition(pstate, var->location)));
+       /* System columns were already checked in the parser */
 
        return false;
    }

diff --git a/src/test/regress/expected/generated.out b/src/test/regress/expected/generated.out
index 71542e95d5f0a6453270ae215bbbee8fb027ce79..c2e5676196b1ab6bdf7e5a5fc1facce42f399fc7 100644 (file)
--- a/src/test/regress/expected/generated.out
+++ b/src/test/regress/expected/generated.out
@@ -46,6 +46,13 @@ ERROR:  cannot use generated column "b" in column generation expression
 LINE 1: ...AYS AS (a * 2) STORED, c int GENERATED ALWAYS AS (b * 3) STO...
                                                              ^
 DETAIL:  A generated column cannot reference another generated column.
+-- a whole-row var is a self-reference on steroids, so disallow that too
+CREATE TABLE gtest_err_2c (a int PRIMARY KEY,
+    b int GENERATED ALWAYS AS (num_nulls(gtest_err_2c)) STORED);
+ERROR:  cannot use whole-row variable in column generation expression
+LINE 2:     b int GENERATED ALWAYS AS (num_nulls(gtest_err_2c)) STOR...
+                                                 ^
+DETAIL:  This would cause the generated column to depend on its own value.
 -- invalid reference
 CREATE TABLE gtest_err_3 (a int PRIMARY KEY, b int GENERATED ALWAYS AS (c * 2) STORED);
 ERROR:  column "c" does not exist

diff --git a/src/test/regress/sql/generated.sql b/src/test/regress/sql/generated.sql
index 914197608b749b39774666a2a8fb4a8e71fd5562..b7eb072671e3cbbd1c218b3d68f2389a8b4ef71f 100644 (file)
--- a/src/test/regress/sql/generated.sql
+++ b/src/test/regress/sql/generated.sql
@@ -17,6 +17,9 @@ CREATE TABLE gtest_err_1 (a int PRIMARY KEY, b int GENERATED ALWAYS AS (a * 2) S
 -- references to other generated columns, including self-references
 CREATE TABLE gtest_err_2a (a int PRIMARY KEY, b int GENERATED ALWAYS AS (b * 2) STORED);
 CREATE TABLE gtest_err_2b (a int PRIMARY KEY, b int GENERATED ALWAYS AS (a * 2) STORED, c int GENERATED ALWAYS AS (b * 3) STORED);
+-- a whole-row var is a self-reference on steroids, so disallow that too
+CREATE TABLE gtest_err_2c (a int PRIMARY KEY,
+    b int GENERATED ALWAYS AS (num_nulls(gtest_err_2c)) STORED);
 
 -- invalid reference
 CREATE TABLE gtest_err_3 (a int PRIMARY KEY, b int GENERATED ALWAYS AS (c * 2) STORED);