Cannot "unregister" a function, collation or aggregate in SQLite3 extension

[Danack]

Description

aka php#10726

[Danack]

https://www.sqlite.org/c3ref/create_function.html

Sounds like PDOSqlite::destroyFunction is needed...

The sixth, seventh and eighth parameters passed to the three "sqlite3_create_function*" functions, xFunc, xStep and xFinal, are pointers to C-language functions that implement the SQL function or aggregate. A scalar SQL function requires an implementation of the xFunc callback only; NULL pointers must be passed as the xStep and xFinal parameters. An aggregate SQL function requires an implementation of xStep and xFinal and NULL pointer must be passed for xFunc. To delete an existing SQL function or aggregate, pass NULL pointers for all three function callbacks.

The sixth, seventh, eighth and ninth parameters (xStep, xFinal, xValue and xInverse) passed to sqlite3_create_window_function are pointers to C-language callbacks that implement the new function. xStep and xFinal must both be non-NULL. xValue and xInverse may either both be NULL, in which case a regular aggregate function is created, or must both be non-NULL, in which case the new function may be used as either an aggregate or aggregate window function. More details regarding the implementation of aggregate window functions are available here.

If the final parameter to sqlite3_create_function_v2() or sqlite3_create_window_function() is not NULL, then it is destructor for the application data pointer. The destructor is invoked when the function is deleted, either by being overloaded or when the database connection closes. The destructor is also invoked if the call to sqlite3_create_function_v2() fails. When the destructor callback is invoked, it is passed a single argument which is a copy of the application data pointer which was the fifth parameter to sqlite3_create_function_v2().

It is permitted to register multiple implementations of the same functions with the same name but with either differing numbers of arguments or differing preferred text encodings. SQLite will use the implementation that most closely matches the way in which the SQL function is used. A function implementation with a non-negative nArg parameter is a better match than a function implementation with a negative nArg. A function where the preferred text encoding matches the database encoding is a better match than a function where the encoding is different. A function where the encoding difference is between UTF16le and UTF16be is a closer match than a function where the encoding difference is between UTF8 and UTF16.

[Danack]

I implemented the deleteFunction (and placeholder code for the other two) in branch: https://github.com/Imagick/php-src/tree/pdo_sub_classing_sqlite_delete_function

But I think this probably needs an RFC of it's own, as the API is "not great":
php#10726 (comment)