Nightly and beta cut-off at 2023-01-01 to shrink repository size (#172)

.github/workflows/ci.yaml

@@ -16,7 +16,21 @@ permissions:
   contents: read
 
 jobs:
-  # TODO: `nix flake check` costs too much time and memory for GitHub Actions machines.
+  flake-check:
+    name: Flake check
+    runs-on: ubuntu-latest
+
+    steps:
+    - name: Checkout
+      uses: actions/checkout@v4
+
+    - name: Install Nix
+      uses: cachix/install-nix-action@v25
+      with:
+        nix_path: nixpkgs=channel:nixos-unstable
+
+    - name: Check flake
+      run: nix flake check -v --show-trace --no-update-lock-file
 
   check-sync-script:
     name: Check sync script is deterministic

.gitignore

@@ -2,5 +2,6 @@ target
 result
 result-*
 *.tmp
+__pycache__
 
 examples/cross-aarch64/flake.lock

README.md

@@ -18,8 +18,16 @@ Features:
 
 - These hashes are auto-updated daily using GitHub Actions.
 
-- Current oldest supported version is stable 1.29.0 and beta/nightly 2018-09-13
-  (which are randomly picked and may change over time).
+- Current oldest supported stable version is 1.29.0 which are randomly picked.
+
+  Stable versions will not be purged currently.
+
+- Current oldest supported nightly version is 2023-01-01.
+
+  To prevent significant repository size bloating, our current strategy is keep
+  only nightly and beta versions not earlier than `{current_year - 1}-01-01`.
+  Earlier versions may be accessed via
+  [old snapshot tags](https://github.com/oxalica/rust-overlay/tags).
 
 - We targets nixos-unstable and supported releases of NixOS, on x86\_64-linux.
   They are tested on CI. Other platforms and nixpkgs channels may also work but