How can one reliably run unittests

[deadalnix]

On Thursday, 26 August 2021 at 11:32:06 UTC, jfondren wrote:
> On Thursday, 26 August 2021 at 09:38:54 UTC, deadalnix wrote:
>> The root of the problem, really, is that I don't cares about 
>> main when running unit tests. I don't want to know if it is 
>> there or not, I don't want it to run, nothing. If the compiler 
>> needs one to link under the hood, then good for it, but this 
>> is an implementation detail.
>
> OK. Create a bugzilla issue. There are some related bugs that 
> someone might want to fix at the same time (#20340 it doesn't 
> use a betterC main when -betterC is passed, #16440 it breaks 
> with -c and -of).
>
> This is about the extent of the current support, in 
> src/dmd/mars.d's tryMain:
>
> ```d
>     if (params.addMain)
>         files.push("__main.d");
>     // Create Modules
>     Modules modules = createModules(files, libmodules);
>     // Read files
>     // Start by "reading" the special files (__main.d, 
> __stdin.d)
>     foreach (m; modules)
>     {
>         if (params.addMain && m.srcfile.toString() == 
> "__main.d")
>         {
>             auto data = arraydup("int main(){return 
> 0;}\0\0\0\0"); // need 2 trailing nulls for sentinel and 2 for 
> lexer
>             m.srcBuffer = new FileBuffer(cast(ubyte[]) data[0 
> .. $-4]);
>         }
> ```
>
> and src/dmd/glue.d:
>
> ```d
> private bool onlyOneMain(Loc loc)
> {
>     __gshared Loc lastLoc;
>     __gshared bool hasMain = false;
>     if (hasMain)
>     {
>         const(char)* msg = "";
>         if (global.params.addMain)
>             msg = ", -main switch added another `main()`";
> ```
>
> It's not surprising that such a lightweight implementation 
> doesn't result in world-class ergonomics. It's something I use 
> all the time to test individual modules at the CLI, and I'd 
> much rather have this than nothing. But for bells and whistles 
> I'd look to dub.
>
> In a pinch you could write a dmd wrapper that calls dmd, sees 
> if it gets a linker complaint about main, and if so calls dmd 
> again with -main. An obvious performance hit, probably not that 
> bad in most cases where you would consider this, but now you 
> don't have care about main.
>
> [...]

Congratulations, you just wrote the embryo of a test framework. 
It will work, and indeed, most projects ou there get one past a 
certain size.

It' very unfortunate though, because the compiler has all the 
info it needs to do the right thing, and yet refuses to do it.

Note that you could likely get better perfs out of this by 
linking in a weak definition of _Dmain, so it won't clash, but 
the general problem remains.