Hi, 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.
Best regards,
--
Chao Li (Evan)
HighGo Software Co., Ltd.
https://www.highgo.com/
v1-0001-Fix-incorrect-iteration-type-in-extension_file_ex.patch
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