switch build to flake

Author: chris-martin

.gitignore

@@ -0,0 +1,70 @@
+{
+  inputs = {
+    "nixos-23.05".url = "github:NixOS/nixpkgs/nixos-23.05";
+    flake-utils.url = "github:numtide/flake-utils";
+  };
+  outputs = inputs@{ self, ... }:
+    let packageName = "lazy-async";
+    in inputs.flake-utils.lib.eachDefaultSystem (system:
+      let
+        nixpkgs = {
+          "nixos-23.05" = import inputs."nixos-23.05" { inherit system; };
+        };
+        pkgs = nixpkgs."nixos-23.05";
+        project = pkgs.haskellPackages.developPackage {
+          root = ./lazy-async;
+          name = packageName;
+        };
+        inherit (pkgs.lib) fold composeExtensions concatMap attrValues;
+
+        combineOverrides = old:
+          fold composeExtensions (old.overrides or (_: _: { }));
+
+      in
+      {
+        defaultPackage = self.packages.${system}.${packageName};
+
+        packages = {
+          "${packageName}" = project;
+
+          testConfigurations =
+            let
+
+              inherit (pkgs.haskell.lib) dontCheck;
+
+              makeTestConfiguration =
+                let defaultPkgs = pkgs;
+                in { pkgs ? defaultPkgs, ghcVersion, overrides ? new: old: { } }:
+                  let inherit (pkgs.haskell.lib) dontCheck packageSourceOverrides;
+                  in (pkgs.haskell.packages.${ghcVersion}.override (old: {
+                    overrides = combineOverrides old [
+                      (packageSourceOverrides {
+                        lazy-async = ./lazy-async;
+                      })
+                      overrides
+                    ];
+
+                  })).lazy-async;
+
+            in
+            rec {
+              ghc-9-0 = makeTestConfiguration {
+                pkgs = nixpkgs."nixos-23.05";
+                ghcVersion = "ghc90";
+              };
+              ghc-9-2 = makeTestConfiguration {
+                pkgs = nixpkgs."nixos-23.05";
+                ghcVersion = "ghc92";
+              };
+              ghc-9-4 = makeTestConfiguration {
+                pkgs = nixpkgs."nixos-23.05";
+                ghcVersion = "ghc94";
+              };
+              all = pkgs.symlinkJoin {
+                name = packageName;
+                paths = [ ghc-9-0 ghc-9-2 ghc-9-4 ];
+              };
+            };
+        };
+      });
+}

flake.lock

@@ -42,7 +42,7 @@ common language
 
 common dependencies
     build-depends:
-      , base ^>= 4.14 || ^>= 4.15 || ^>= 4.16 || ^>= 4.17
+      , base ^>= 4.15 || ^>= 4.16 || ^>= 4.17
       , exceptions ^>= 0.10.4
       , lifted-async ^>= 0.10.2
       , monad-control ^>= 1.0.3