FFI Sync Engine changes

[abrassel]

Change list

Add sync engine cfg option to the ffi. This will allow us to build with local file paths only (mostly useful for testing).

How is this tested?

Changed ffi-test.c to build both a sync and default engine. It should pass both.

Note This is a draft because I can't get the test to build right. For some reason, the codegenned c code isn't defining the SYNC-ENGINE flag. Any ideas @nicklan

Issue

This addresses #199

[abrassel]

@scovich do you happen to know why the C define is missing in the codegen for SYNC-ENGINE?

[scovich]

@scovich do you happen to know why the C define is missing in the codegen for SYNC-ENGINE?

I believe cbindgen tries to emit a single header that works no matter which features were selected (and uses #if defined checks to strip out unneeded bits of code if a specific feature isn't enabled). But cbindgen has no way to guess which features the downstream user actually enabled, so it's up to the library user to pass an appropriate -D to the compiler. In case of cffi-test, the Makefile currently sets the default engine:

CFLAGS=-c -Wall -DDEFINE_DEFAULT_ENGINE #`pkg-config --cflags arrow-glib`

Most likely you just need to add -DDEFINE_SYNC_ENGINE there and all will be well?

[abrassel]

@scovich ready for re-review!

[nicklan]

nice thanks. just a couple small things

[nicklan]

one last small thing please!

[nicklan]

thanks for iterating! lgtm!

[scovich]

Nice work, thanks!

[abrassel]

@nicklan @scovich can one of y'all merge this!

[nicklan]

Merged! Thanks for the contribution!