Core dump happens when execute sql CREATE VIEW v1(c1) AS (SELECT ('4' COLLATE "C")::INT FROM generate_series(1, 10));

[Yulin PEI]

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