This is Fennel 1.5.1 on Lua 5.4.

(fennel.view math.maxinteger)
runtime error: invalid conversion specification: '%.100e'

I've also stumbled across this bug, in the following context:

struct dirent {
    char d_name[256];
};

int sel(const struct dirent *d) {
    return d->d_name[0] != '.';
}

Assertion failed: tq == QUALNONE (expr.c: decay: 101)
cproc: compile: process signaled: Aborted

Removing const works.