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Subject: Re: Fix a bug in extension_file_exists()
From: Chao Li <li.evan.chao@gmail.com>
In-Reply-To: <6ccbe513-a815-4d2c-a746-abe5de2da86b@iki.fi>
Date: Tue, 10 Feb 2026 08:50:10 +0800
Cc: Postgres hackers <pgsql-hackers@lists.postgresql.org>
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Message-Id: <5FB32F4A-C4CA-400C-9FC8-7AA32CC1020C@gmail.com>
References: <362EA9B3-589B-475A-A16E-F10C30426E28@gmail.com>
 <6ccbe513-a815-4d2c-a746-abe5de2da86b@iki.fi>
To: Heikki Linnakangas <hlinnaka@iki.fi>
Archived-At: <https://www.postgresql.org/message-id/5FB32F4A-C4CA-400C-9FC8-7AA32CC1020C%40gmail.com>
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> On Feb 9, 2026, at 18:02, Heikki Linnakangas <hlinnaka@iki.fi> wrote:
>=20
> On 09/02/2026 11:21, Chao Li wrote:
>> I just noticed a bug in extension_file_exists():
>> ```
>> bool
>> extension_file_exists(const char *extensionName)
>> {
>> bool result =3D false;
>> List   *locations;
>> DIR   *dir;
>> struct dirent *de;
>> locations =3D get_extension_control_directories();
>> foreach_ptr(char, location, locations) // <=3D=3D Here type char is =
wrong
>> {
>> dir =3D AllocateDir(location);
>> ```
>> get_extension_control_directories() returns a list of =
ExtensionLocation, but the loop iterates it as if it contained char *, =
which is incorrect. As a result, AllocateDir() and ReadDir() are called =
with the wrong type.
>> This bug is only triggered on an error path, when PostgreSQL is =
deciding whether to emit a hint. For example:
>> ```
>> evantest=3D# create function f() returns int LANGUAGE plpython3u as =
$$return 1$$;
>> ERROR:  language "plpython3u" does not exist
>> ```
>> No hint is printed.
>> With this patch applied:
>> ```
>> evantest=3D# create function f() returns int LANGUAGE plpython3u as =
$$return 1$$;
>> ERROR:  language "plpython3u" does not exist
>> HINT:  Use CREATE EXTENSION to load the language into the database.
>> ```
>> So the hint is shown as intended.
>> Attached is a patch fixing the iteration to use ExtensionLocation and =
location->loc consistently.
>=20
> Yep, good catch. This went wrong in commit f3c9e341cd, which changed =
the type of objects in the list from "char *" to "ExtensionLocation *". =
So this is master only, stable branches are not affected.
>=20
> I will push the fix shortly, thanks!
>=20
> - Heikki
>=20

Thanks for pushing.

Best regards,
--
Chao Li (Evan)
HighGo Software Co., Ltd.
https://www.highgo.com/