The when defined(enable_libbacktrace): is evaluated at compile time and is false by default. When Nim loads this config.nims as a parent config during the testutils build, the libbacktrace block is silently skipped. Nothing is passed as --import.
Why the old guard (not defined(disable_libbacktrace)) wasn't enough: it required someone to explicitly opt out, but disable_libbacktrace is never passed during nimble's internal dependency build invocations. The opt-in approach is safe by default.
If any build in this project genuinely uses libbacktrace, you'd need to both add it to waku.nimble requires and pass -d:enable_libbacktrace explicitly.
