feat(scripts/fetch_binary.d): Fetching dmd source and misc improvement.

[dukc]

Along with ability to fetch dmd sources, the largest improvement is a better help page.

ping @PetarKirov

[dukc]

I just used this to actually fetch some DMD sources. It turns out the hashing needs to be done differently, since dmd sources are NAR hashed in unpacked form as opposed to content hash of the .tar.gz as in other downloads. I've adapted the hashing command and it now works. Unfortunately this means using vanilla Nix commands as the new-gen equivalents either don't have the necessary flags for this scenario or are documented really badly.

ping @PetarKirov .

[dukc]

Ping @PetarKirov

Any issues with this? I'm going to merge at 15th or later if no answer, as the CI is passing.

[github-actions[bot]]

Thanks for your Pull Request!

Below you will find a summary of the cachix status of each package, for each supported platform.

package	x86_64-linux	x86_64-darwin	aarch64-darwin
dmd	✅ cached	✅ cached	🚫 not supported
dmd-2_092_1	✅ cached	✅ cached	🚫 not supported
dmd-2_096_1	✅ cached	✅ cached	🚫 not supported
dmd-2_098_1	✅ cached	✅ cached	🚫 not supported
dmd-2_100_2	✅ cached	✅ cached	🚫 not supported
dmd-2_102_2	✅ cached	✅ cached	🚫 not supported
dmd-2_103_1	✅ cached	✅ cached	🚫 not supported
dmd-2_104_2	✅ cached	✅ cached	🚫 not supported
dmd-2_105_2	✅ cached	✅ cached	🚫 not supported
dmd-binary-2_079_1	✅ cached	✅ cached	🚫 not supported
dmd-binary-2_080_1	✅ cached	✅ cached	🚫 not supported
dmd-binary-2_081_2	✅ cached	✅ cached	🚫 not supported
dmd-binary-2_082_1	✅ cached	✅ cached	🚫 not supported
dmd-binary-2_083_1	✅ cached	✅ cached	🚫 not supported
dmd-binary-2_084_1	✅ cached	✅ cached	🚫 not supported
dmd-binary-2_085_1	✅ cached	✅ cached	🚫 not supported
dmd-binary-2_086_1	✅ cached	✅ cached	🚫 not supported
dmd-binary-2_087_1	✅ cached	✅ cached	🚫 not supported
dmd-binary-2_088_1	✅ cached	✅ cached	🚫 not supported
dmd-binary-2_089_1	✅ cached	✅ cached	🚫 not supported
dmd-binary-2_090_1	✅ cached	✅ cached	🚫 not supported
dmd-binary-2_098_0	✅ cached	✅ cached	🚫 not supported
dmd-bootstrap	✅ cached	✅ cached	🚫 not supported
dub	✅ cached	✅ cached	✅ cached
dub-1_30_0	✅ cached	✅ cached	✅ cached
ldc	✅ cached	🚧 known to fail (disabled)	🚧 known to fail (disabled)
ldc-1_30_0	✅ cached	🚧 known to fail (disabled)	🚧 known to fail (disabled)
ldc-binary-1_19_0	✅ cached	✅ cached	🚫 not supported
ldc-binary-1_25_0	✅ cached	✅ cached	✅ cached
ldc-binary-1_28_0	✅ cached	✅ cached	✅ cached
ldc-binary-1_32_1	✅ cached	✅ cached	✅ cached
ldc-binary-1_34_0	✅ cached	✅ cached	✅ cached
ldc-bootstrap	✅ cached	✅ cached	✅ cached

[PetarKirov]

@dukc Sorry for delay! In addition to the lack of available time on my side, I had started a large refactoring that of this script (all the way back in Jan-Feb) and I was hoping I could finish it before merging your code to avoid conflicts, but I think at this point it would be better if I merge your PR and redo my stuff, to avoid any additional delays.

[dukc]

Thanks!