extra_flags in boards.txt prevents user adding flags?

[dmcomm]

If I understand correctly, the normal way for the user to add flags is via compiler.cpp.extra_flags etc. But build.extra_flags overrides this so it doesn't do anything. And overriding build.extra_flags is not an option either because this would delete the values that MiniCore is using.

Edit: Sorry, I'm confused, they do seem to be separate things. But boards.txt does also set compiler.cpp.extra_flags in some cases.

[dmcomm]

OK, it seems that setting compiler.cpp.extra_flags in platform.local.txt does nothing in MiniCore because it's set in boards.txt. Setting it via --build-property does apply, but this presumably overrides the values in boards.txt. And this doesn't conflict provided that LTO is disabled?