feat: Add Config/build/never-clean option to never clean during build

[krlmlr]

Is this something you would support? Happy to add documentation. Do we need a test?

My use cases are duckdb and igraph -- if I need a clean rebuild, I clean, otherwise I'm happy with incremental compiles. The auto-clean gets triggered too frequently, I'm frustrated by it more often than not. The bootstrap.R script doesn't seem to get run with load_all() .

[gaborcsardi]

Thanks! I am not even sure why needs_clean() is needed, ideally make would handle the dependencies and rebuild only the object files that need rebuilding.

Maybe we could remove needs_clean() entirely?

[gaborcsardi]

OK, I see now that changing a header file does not trigger recompilation of the objects that use it, so that's why we have needs_clean(). Maybe we can do better with gcc -MM?

I am still not sure why a missing DLL would need a cleanup.

[gaborcsardi]

In the meanwhile I don't mind adding this flag.

[krlmlr]

Thanks. Added NEWS and docs in e4e5fb8 .

R has a .c|.cpp -> .d rule built in, all we need (in theory) is include file.d for each file.c or file.cpp . In duckdb, I'm doing more:

• Excluding system and vendored headers
• Version-controlling the generated files

Let's see.