convert to flake

Author: abathur

.github/workflows/ci.yml

@@ -17,7 +17,7 @@ jobs:
       uses: actions/checkout@v2
       with:
         path: lilgit
-    - uses: cachix/install-nix-action@v16
+    - uses: cachix/install-nix-action@v18
       with:
         nix_path: nixpkgs=channel:nixpkgs-unstable
     - run: nix-build lilgit/default.nix
@@ -28,10 +28,10 @@ jobs:
         os: [ ubuntu-latest, macos-latest ]
       fail-fast: false
     steps:
-    - uses: cachix/install-nix-action@v16
+    - uses: cachix/install-nix-action@v18
       with:
         nix_path: nixpkgs=channel:nixpkgs-unstable
-    - run: echo declare -p __lilgit | nix-shell -E 'import (fetchGit { url="https://github.com/abathur/lilgit"; ref="main"; } + "/shell.nix")'
+    - run: echo declare -p __lilgit | nix-shell -E 'import (fetchGit { url="https://github.com/abathur/lilgit"; rev="'${GITHUB_SHA}'"; allRefs = true; } + "/shell.nix")'
   # macOS only because it depends on bsd 'footprint' for
   # easy measuring of RAM footprint...
   performance:
@@ -51,7 +51,7 @@ jobs:
         repository: nixos/nixpkgs
         path: nixpkgs
         fetch-depth: 0
-    - uses: cachix/install-nix-action@v16
+    - uses: cachix/install-nix-action@v18
       with:
         nix_path: nixpkgs=channel:nixpkgs-unstable
     - name: benchmark