Re: Fix a bug in extension_file_exists()

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 = false;
> List *locations;
> DIR *dir;
> struct dirent *de;
>
> locations = get_extension_control_directories();
>
> foreach_ptr(char, location, locations) // <== Here type char is wrong
> {
> dir = 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=# 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=# 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.

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.

I will push the fix shortly, thanks!

- Heikki