Poll: -od -lib -of and breaking compatibility with build tools

[Nick Sabalausky (Abscissa)]

On 8/12/19 1:59 AM, FeepingCreature wrote:
> I ran into this bug a few days ago.
> 
> DMD, when specifying -od (output directory), -of (output file) and 
> *only* when in -lib mode, treats the output file path as relative to the 
> output directory path. Ie. -odfoo -oflibbar.a results in foo/libbar.a as 
> opposed to ./libbar.a. This is in contradiction to every other mode 
> (-shared, binary output, object output) and every other D compiler (ldc, 
> gdc).

I haven't fully refreshed my memory on this, but looking at the PR, Mr. 
2015 Walter also mentioned that my PR also introduced a discrepancy in 
the meaning of -od for .obj files vs .lib files while fixing the 
original problem.

I only bring this up to point out that any new PR should take extra care 
to fully think through the logic and handling of the relevant flags.

> This issue was raised four years ago. At the time, Walter said he was 
> not fixing it in order to avoid breaking compatibility with existing 
> build setups: see https://github.com/dlang/dmd/pull/4753 .
> 
> People who are using build tools that call dmd: would you rather this be 
> fixed, and have to update your code, or leave it in?
> 
> (Me, I want it fixed. It's a really annoying trap for all the people who 
> are building with dmd but aren't using -od yet, which I was among until 
> a few days ago.)

I can't test right now, but does anyone know whether these flags are 
case-sensitive? I know '-o' and '-O' have different meanings.

If that case sensitivity extends to -of and -od as well, then let's just 
assign the the new, fully rethought and fully orthogonal behaviors to 
'-OF' and '-OD'. That way, we get the best of both worlds: proper 
predictable behavior PLUS absolute unquestionable certainty of not 
breaking anything. We can recommend -OF/-OD as the preferred form, and 
then maybe phase out -of/-od or not.