Try this

.woodpecker/.all-checks-complete.yml

@@ -0,0 +1,10 @@
+steps:
+  echo:
+    image: alpine
+    commands:
+      - echo "All required checks complete"
+
+depends_on:
+  - build
+
+skip_clone: true

.woodpecker/.build.yml

@@ -0,0 +1,16 @@
+steps:
+  build:
+    image: nixos/nix
+    commands:
+      - echo 'experimental-features = flakes nix-command' >> /etc/nix/nix.conf
+      # Lint
+      - "nix flake check"
+      # Test
+      - nix develop --command dotnet test
+      - nix develop --command dotnet test --configuration Release
+      - nix develop --command alejandra --check .
+
+    when:
+      - event: "push"
+        evaluate: 'CI_COMMIT_BRANCH == CI_REPO_DEFAULT_BRANCH'
+      - event: "pull_request"

flake.nix

@@ -1,26 +1,45 @@
 {
-    description = "Advent of Code 2023";
+  description = "Advent of Code 2023";
-    inputs = {
+  inputs = {
-        flake-utils.url = "github:numtide/flake-utils";
+    flake-utils.url = "github:numtide/flake-utils";
-        nixpkgs.url = "github:NixOS/nixpkgs/nixos-unstable";
+    nixpkgs.url = "github:NixOS/nixpkgs/nixos-unstable";
-    };
+  };
 
-    outputs = {
+  outputs = {
-        self,
+    self,
-        nixpkgs,
+    nixpkgs,
-        flake-utils,
+    flake-utils,
-    }: flake-utils.lib.eachDefaultSystem (system:
+  }:
-    let pkgs = nixpkgs.legacyPackages.${system}; in
+    flake-utils.lib.eachDefaultSystem (
-    {
+      system: let
-        devShells = { default = pkgs.mkShell {
+        pkgs = nixpkgs.legacyPackages.${system};
-          buildInputs = with pkgs; [
+      in
-            (with dotnetCorePackages;
+        # Conditionally include Swift and Apple SDK for Darwin systems
-              combinePackages [
+        let
-                dotnet-sdk_8
+          darwinDeps =
-                dotnetPackages.Nuget
+            if system == "x86_64-darwin" || system == "aarch64-darwin"
-              ])
+            then [
-          ] ++ [pkgs.swift darwin.apple_sdk.frameworks.Foundation darwin.apple_sdk.frameworks.CryptoKit darwin.apple_sdk.frameworks.GSS pkgs.zlib pkgs.zlib.dev pkgs.openssl pkgs.icu];
+              pkgs.swift
-        };};
+              pkgs.darwin.apple_sdk.frameworks.Foundation
-    }
+              pkgs.darwin.apple_sdk.frameworks.CryptoKit
+              pkgs.darwin.apple_sdk.frameworks.GSS
+            ]
+            else [];
+        in {
+          devShells = {
+            default = pkgs.mkShell {
+              buildInputs = with pkgs;
+                [
+                  (with dotnetCorePackages;
+                    combinePackages [
+                      dotnet-sdk_8
+                      dotnetPackages.Nuget
+                    ])
+                ]
+                ++ darwinDeps
+                ++ [pkgs.zlib pkgs.zlib.dev pkgs.openssl pkgs.icu pkgs.alejandra];
+            };
+          };
+        }
     );
 }