flake,CI: add nix build CI support for pulse

Author: jhvst

.envrc

@@ -4,7 +4,7 @@ fi
 
 watch_file flake.nix
 watch_file flake.lock
-if ! use flake . --no-pure-eval
+if ! use flake . --no-pure-eval --accept-flake-config
 then
   echo "devenv could not be built. The devenv environment was not loaded. Make the necessary changes to devenv.nix and hit enter to try again." >&2
 fi

.github/workflows/nix.yaml

@@ -0,0 +1,17 @@
+# This workflow tests the Nix build of pulse. We run it only for PRs (not
+# on every push) and we use Github hosted runners.
+
+name: Nix Build
+
+on:
+  pull_request:
+
+jobs:
+  nix-build:
+    runs-on: ubuntu-latest
+    steps:
+    - uses: actions/checkout@v4
+    - uses: DeterminateSystems/nix-installer-action@main
+    - uses: DeterminateSystems/magic-nix-cache-action@main
+    - name: Build
+      run: nix build -L

flake.nix

@@ -133,6 +133,8 @@
         };
 
         packages = {
+          default = config.packages.pulse;
+
           devenv-up = self.devShells.${system}.default.config.procfileScript;
           devenv-test = self.devShells.${system}.default.config.test;