Screenplay: Making `SQLite3` Optional (`target_compile_definitions()`)¶

What If We Know How to Live Without SQLite3?¶

toolcase/data-logger has sink-sqlite3.h and sink-sqlite3.cpp only conditionally
⟶ SQLite3_FOUND (see FindSQLite3)

Optionally Not Depending On SQLite3 ¶

Toplevel: make SQLite3 not required
```
find_package(SQLite3)
```
toolcase/data-logger/ depends on SQLite3 (SQLite::SQLite3)

Library contains sink-sqlite3.h and sink-sqlite3.cpp, depending on SQLite3_FOUND

if (SQLite3_FOUND)
  set(inc_sink_sqlite3 sink-sqlite3.h)
  set(src_sink_sqlite3 sink-sqlite3.cpp)
endif()

… and substitute accordingly

Library depends on SQLite::SQLite3

if (SQLite3_FOUND)
  target_link_libraries(data-logger SQLite::SQLite3)
endif()

Library propagates dependency information to its users (see below); INTERFACE because it does not need that information itself
```
if (SQLite3_FOUND)
  target_compile_definitions(data-logger INTERFACE HAVE_SQLITE3=1)
endif()
```

Optionally Not Depending On Someone Who Depends On SQLite3 ¶

firmware/data-logger.cpp (node app-data-logger) uses/includes <sink-sqlite3.h>
In that node - app-data-logger - it would be nice to have a macro HAVE_SQLITE3 available

Litter #ifdef all across your code

#ifdef HAVE_SQLITE3
#  include <sink-sqlite3.h>
#else
#  include <sink-terminal.h>
#endif

It is a massacre, inevitably!