HI hackers,
I found it could cause a crash when executing sql statement: `CREATE VIEW v1(c1) AS (SELECT ('4' COLLATE "C")::INT FROM generate_series(1, 10)); ` in postgres 13.2 release.
The crash happens at view.c:89 and I did some analysis:
```
ColumnDef *def = makeColumnDef(tle->resname,
exprType((Node *) tle->expr),
exprTypmod((Node *) tle->expr),
exprCollation((Node *) tle->expr));
/*
* It's possible that the column is of a collatable type but the
* collation could not be resolved, so double-check.
*/
// Here is the analysis:
//example : ('4' COLLATE "C")::INT
//exprCollation((Node *) tle->expr) is the oid of collate "COLLATE 'C'" so def->collOid is valid
//exprType((Node *) tle->expr)) is 23 which is the oid of type int4.
//We know that int4 is not collatable by calling type_is_collatable()
if (type_is_collatable(exprType((Node *) tle->expr)))
{
if (!OidIsValid(def->collOid))
ereport(ERROR,
(errcode(ERRCODE_INDETERMINATE_COLLATION),
errmsg("could not determine which collation to use for view column \"%s\"",
def->colname),
errhint("Use the COLLATE clause to set the collation explicitly.")));
}
else
// So we are here! int is not collatable and def->collOid is valid.
Assert(!OidIsValid(def->collOid));
```
I am not sure whether to fix this bug in function DefineVirtualRelation or to fix this bug in parse tree and analyze procedure, so maybe we can discuss.
Best Regard!
Yulin PEI
