Happy to answer questions! Let's do it in Discussions, though, and not Issues.

In the extconf (ext/sqlite3/extconf.rb), which is where the C extension is configured, you'll see this line:

        have_func('sqlite3_column_database_name')

The method have_func comes from Ruby's mkmf.rb or MakeMakefile module, and is documented here:

https://docs.ruby-lang.org/en/master/MakeMakefile.html#method-i-have_func

Relevant:

Returns whether or not the function func can be found in the common header files, or within any headers that you provide. If found, a macro is passed as a preprocessor constant to the compiler using the function name, in uppercase, prepended with HAVE_.

For example, if have_func('foo') returned true, then the HAVE_FOO preprocessor macro would be passed to the compiler.

Make sense?