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