Motivation for this change

Adding a D Programming Language Compiler Wrapper tool that runs and caches D programs.

This is an alternative to the existing rdmd tool. It's a rewrite that leverages a new compiler feature that allows it to run the compiler once instead of having to run it twice like rdmd does. This is a big change to how the cache logic works so I decided to fork the tool rather than trying to update rdmd to support both the old and new logic in the same tool.

It also introduces new features like "Source Compiler Directives" which allow D Language source files to contain compiler configuration. It addresses the same problem described here:

http://chriswarbo.net/projects/nixos/nix_shell_shebangs.html

By using /usr/bin/env, we lose the ability to pass arguments to the nix-shell command. To work around this, nix-shell will look at that second line to get its options.

D programs can use this tool by adding the shebang line #!/usr/bin/env rund to the top of their main source file allowing them to be executed with ./myprogram.d.

i.e.

#!/usr/bin/env rund
//!debugSymbols
//     ^ this is an example of a source compiler directive
import std.stdio;void main() { writeln("Hello World!"); }

Things done

• Tested using sandboxing (nix.useSandbox on NixOS, or option sandbox in nix.conf on non-NixOS)
• Built on platform(s)
  • NixOS
  • macOS
  • other Linux distributions
• Tested via one or more NixOS test(s) if existing and applicable for the change (look inside nixos/tests)
• [N/A] Tested compilation of all pkgs that depend on this change using nix-shell -p nix-review --run "nix-review wip"
• Tested execution of all binary files (usually in ./result/bin/)
• [N/A] Determined the impact on package closure size (by running nix path-info -S before and after)
• Assured whether relevant documentation is up to date
• Fits CONTRIBUTING.md.