Revert "Move hydra-spec to input repository (#1512)"

This reverts commit b391020.

.github/workflows/ci-nix.yaml

@@ -276,14 +276,14 @@ jobs:
 
     - name: ❄ Build specification PDF
       run: |
-        nix build .#spec && cp result/*.pdf .
+        nix build .#spec && cp result/*.pdf spec/
 
     - name: 💾 Upload specification
       uses: actions/upload-artifact@v4
       with:
         name: hydra-spec
         path: |
-          *.pdf
+          ./spec/*.pdf
 
   documentation:
     name: Documentation

flake.nix

@@ -21,7 +21,6 @@
     cardano-node.url = "github:intersectmbo/cardano-node/9.1.0";
     mithril.url = "github:input-output-hk/mithril/2428.0";
     nix-npm-buildpackage.url = "github:serokell/nix-npm-buildpackage";
-    hydra-spec.url = "github:cardano-scaling/hydra-formal-specification";
   };
 
   outputs =
@@ -131,7 +130,9 @@
           packages =
             hydraPackages //
             (if pkgs.stdenv.isLinux then (prefixAttrs "docker-" hydraImages) else { }) // {
-              spec = inputs.hydra-spec.packages.${system}.default;
+              spec = import ./spec {
+                inherit pkgs;
+              };
             };
           process-compose."demo" = import ./nix/hydra/demo.nix {
             inherit system pkgs inputs self;

spec/.envrc

@@ -0,0 +1 @@
+use flake .#spec

spec/.gitignore

@@ -0,0 +1,3 @@
+/main.*
+!/main.tex
+/.auctex-auto/

spec/README.md

@@ -0,0 +1,27 @@
+# Hydra Specification
+
+The Hydra Head protocol is specified in the single document built from this
+directory.
+
+We use LaTeX to write the specification and used to compose this on
+[overleaf](www.overleaf.com). Going forward, any changes to the specification
+should follow the common pull request rules as set out in our [contribution
+guidelines](../CONTRIBUTING.md).
+
+The [Overleaf documentation](https://www.overleaf.com/learn) does provide a good
+introduction to LaTeX syntax and functions to get started.
+
+## Building
+
+You can use `nix` to build a PDF from the LaTeX files using
+
+``` shell
+nix build .#spec
+```
+
+which will write the PDF into `result/hydra-spec.pdf`.
+
+Alternatively, you would need to have a LaTeX distribution installed (e.g.
+`texlive`) and produce a PDF output using `pdflatex` etc. The [LaTeX
+wikibook](https://en.wikibooks.org/wiki/LaTeX/Basics#Building_a_document) might
+be helpful to set things up.