nix: example of local package overrides during development (#2607)

flake.nix

@@ -37,6 +37,7 @@
           overlays = [
             rust-overlay.overlays.default
             tgi-nix.overlays.default
+            (import nix/overlay.nix)
           ];
         };
         crateOverrides = import ./nix/crate-overrides.nix { inherit pkgs nix-filter; };

nix/overlay.nix

@@ -0,0 +1,41 @@
+final: prev: {
+  # You can use this overlay to temporarily override packages for
+  # development. For permanent overrides, it's better to do this in
+  # our package flake:
+  #
+  # https://github.com/huggingface/text-generation-inference-nix
+  #
+  # Note that overriding packages that are in the transitive closure
+  # of many other packages (e.g. transformers) will require a large
+  # rebuild.
+
+  pythonPackagesExtensions = prev.pythonPackagesExtensions ++ [
+    (
+      python-self: python-super: with python-self; {
+        # Python package override example:
+        #   transformers = python-super.transformers.overrideAttrs (
+        #     _: _: {
+        #       src = final.fetchFromGitHub {
+        #         owner = "huggingface";
+        #         repo = "transformers";
+        #         rev = "2bd4d5897dc73e8b172832070a6f9e567a0df017";
+        #         hash = "sha256-JOIpKH9ssDEfI2Tf15e0iPKtThJwQ9GxMvRAnm+M2Pg=";
+        #       };
+        #    }
+        # );
+      }
+    )
+  ];
+
+  # Non-python package override example:
+  #
+  # ripgrep = prev.ripgrep.overrideAttrs (
+  #    _: _: {
+  #      src = final.fetchFromGitHub {
+  #      owner = "BurntSushi";
+  #      repo = "ripgrep";
+  #      rev = "79cbe89deb1151e703f4d91b19af9cdcc128b765";
+  #      hash = "sha256-JPTM2KNmGMb+/jOfK3X7OM1wnN+3TU35SJOIcqmp3mg=";
+  #   };
+  # });
+}