Given a LGPL'ed grammar file, is the source generated by a compiler-compiler for the grammar a derivative works? What about if the grammar file was modified before it was given as input to the compiler-compiler? There isn't any linking, at least not in the conventional sense.
If the output is a derivitive work, must I then simply provide the (modified) grammer sources making any best efforts to ensure the grammar will function without dependencies imposed by the program/library using it? Or are there more restrictions which must be resolved?
1) Since the grammar contains the essence of the resulting code, it definitely belongs to "all the source code needed to generate, install, and (for an executable work) run the object code and to modify the work, including scripts to control those activities" and is not a part of "the work's System Libraries, or general-purpose tools or generally available free programs which are used unmodified in performing those activities but which are not part of the work". In brief, LGPLv3 applies.
So, you need to convey the "Minimal Corresponding Source" (the one used to build the version in the Combined Work) according to sec.4 d) 0) or GPLv3 sec.6, mark it as modified if it is and possibly include custom tools if required by GPL's definition of "Corresponding Source". (In general, as sec.0 says, LGPLv3 is effectively GPLv3 with a few additional provisions.)
2) It might be a derivative work of the generator used as well if the latter inserts parts of itself into the code (see FSF FAQ#Can I use GPL-covered tools... to compile...?) - check the generator's workings and licensing terms if necessary. If it is, you'll have to satisfy both LGPLv3 and the generator's terms that apply to the results of its work.