Implement generating thin-edge binariespost-merge/nix-thin-edge-builder

The flake now exports a working `lib.mkThinEdge` function with which
users can generate a working binary with only the components they wish
to include.

It works as follows:

- It pulls in all the dependencies required for the thin-edge CLI
- It then pulls in and patches the sources given. Any path references to
  tedge_api/lib are patched to their nix-store equivalencies.
- The Cargo.lock is generated by downloading the cargo index and
  overriding its location to be effectively offline
- A temporary Rust project is created, where all the different
  components are then referenced and pulled in.
- This Rust project is then compiled using `crane` (currently a private
  fork with some hacks due to a deficiency in Nix relating to importing
  store paths in the TOML reader)
- crane automatically copies the resulting binary to the output

Signed-off-by: Marcel Müller <m.mueller@ifm.com>

1 files changed, 20 insertions, 0 deletions

diff --git a/lib/nix-thin-edge-builder/writeCargoRegistry.nix b/lib/nix-thin-edge-builder/writeCargoRegistry.nix
new file mode 100644
index 00000000..d536b2ab
--- /dev/null
+++ b/lib/nix-thin-edge-builder/writeCargoRegistry.nix
@@ -0,0 +1,20 @@
+{ craneLib, pkgs }:
+
+let
+  cratesIoRegistry = fetchGit {
+    url = "https://github.com/rust-lang/crates.io-index.git";
+    ref = "master";
+    rev = "e9936adc4a5f03f929c3d19a8d3bcc73479ccc9a";
+  };
+  localCrateRegistry = pkgs.linkFarm "local-crate-registry" [
+    { name = "index"; path = cratesIoRegistry; }
+  ];
+  config = {
+    source = {
+      crates-io = { 
+        local-registry = localCrateRegistry;
+      };
+    };
+  };
+in
+craneLib.writeTOML "Cargo.toml" config