refactor(flake): move some code out of flake.in.nix

packages/trash-d/default.nix

@@ -0,0 +1,35 @@
+{
+  dmd,
+  dub,
+  trash-d-src,
+  ronn,
+  stdenv,
+  ...
+}: let
+  inherit (builtins) fromJSON readFile;
+
+  tag = (fromJSON (readFile "${trash-d-src}/dub.json")).version;
+in
+  stdenv.mkDerivation {
+    pname = "trash";
+    version = "${tag}+${trash-d-src.shortRev}";
+
+    src = trash-d-src;
+
+    buildInputs = [dub dmd ronn];
+
+    buildPhase = ''
+      # https://github.com/svanderburg/node2nix/issues/217#issuecomment-751311272
+      export HOME=$(mktemp -d)
+
+      dub build
+    '';
+
+    installPhase = ''
+      mkdir -p $out/bin $out/man/man1
+
+      cp -a ./build/trash $out/bin/
+
+      ronn --roff --pipe MANUAL.md > $out/man/man1/trash.1
+    '';
+  }