I'm wondering if it inlines it (and thus eliminates it). But this would come with a performance penalty: it makes the function you assert() in no longer a leaf

I'm wondering if it inlines it (and thus eliminates it). But this would come with a performance penalty: it makes the function you assert() in no longer a leaf function (it calls assert()) and AFAIK, Go only inlines leaf functions. (So, any function in which you call assert() is no longer eligible for inlining.)