Here is a program with some invalid inline assembly:

void main() {
    asm {
        "a";
    }
}

I compile with

$ ldc2 asm.d
asm.d(3):1:2: error: invalid instruction mnemonic 'a'
        a
        ^

It correctly shows an error, but also produces an executable (it seems like it just removed the inline asm statement and compiled everything else), and the return code from compiling is 0 (success). This could go unnoticed if checking for success is automated based on the shell command's return code. I think the problem is that this error occurs during codegen, and there is no code to handle a codegen error in driver/toobj.cpp (that I could find).