sqlite_db_filename returns "" instead of undef

[dboehmer]

The method sqlite_db_filename is documented to return undef for in-memory databases.

DBD-SQLite/lib/DBD/SQLite.pm

Line 1867 in a9c7c51

Retrieve the current (main) database filename. If the database is in-memory or temporary, this returns C<undef>.

But instead it returns an empty string:

$ perl -w -MDBI -E 'say defined ? qq("$_") : "undef" for DBI->connect("dbi:SQLite::memory:")->sqlite_db_filename; say $DBD::SQLite::VERSION'
""
1.62

I'm not confident enough in C to fix this in code. If you'd rather adjust the documentation to the existing behavior I can provide a PR.

[charsbar]

Thanks for spotting this. Until recently, the comment in sqlite3.c has said like this:

If there is no attached database N on the database
** connection D, or if database N is a temporary or in-memory database, then
** a NULL pointer is returned.

However, it has actually been returning an emtpy string or NULL depending on the situation, at least since 2013. And now, the latest version of sqlite3.c has changed its comment as follows.

 If there is no attached database N on the database
** connection D, or if database N is a temporary or in-memory database, then
** this function will return either a NULL pointer or an empty string.

I committed a change in the pod. I'm not going to release this today, but it's about time to release the next stable version, so I think this commit will be in soon.