Add a Nix flake (take 2) (#210)

* underpinnings of flake for LSP

* use LSP-lib. specify the same ENV as the compiler is wrapped in for the LSP executable.

* update Idris2 and LSP-lib submodules to latest commits

.gitignore

@@ -18,3 +18,6 @@
 /tests/**/output
 
 src/Server/Generated.idr
+
+#nix build output
+/result

default.nix

@@ -0,0 +1,5 @@
+(import (fetchTarball
+  "https://github.com/edolstra/flake-compat/archive/master.tar.gz") {
+  src = builtins.fetchGit ./.;
+})
+.defaultNix

flake.nix

@@ -0,0 +1,83 @@
+{
+  description = "Idris 2 Language Server";
+
+  inputs = {
+    nixpkgs.url = "github:nixos/nixpkgs";
+
+    idris = {
+      url = "github:idris-lang/Idris2";
+      inputs.nixpkgs.follows = "nixpkgs";
+    };
+
+    lsp-lib = {
+      url = "github:idris-community/LSP-lib";
+      inputs.nixpkgs.follows = "nixpkgs";
+      inputs.idris.follows = "idris";
+    };
+
+    alejandra = {
+      url = "github:kamadorueda/alejandra/3.0.0";
+      inputs.nixpkgs.follows = "nixpkgs";
+    };
+  };
+
+  outputs = {
+    self,
+    nixpkgs,
+    alejandra,
+    idris,
+    lsp-lib,
+  }: let
+    lib = nixpkgs.lib;
+    # support the same systems as Idris2
+    systems = builtins.attrNames idris.packages;
+    forEachSystem = with lib;
+      mkOutputs: let
+        outputsForSystem = system:
+          concatMapAttrs (k: v: {${k}.${system} = v;}) (mkOutputs system);
+      in
+        foldl' recursiveUpdate {} (map outputsForSystem systems);
+  in
+    forEachSystem (
+      system: let
+        pkgs = nixpkgs.legacyPackages.${system};
+        idrisPkgs = idris.packages.${system};
+        buildIdris = idris.buildIdris.${system};
+        lspLib = lsp-lib.packages.${system}.default;
+        supportLibrariesPath = lib.makeLibraryPath [idrisPkgs.support];
+        supportSharePath = lib.makeSearchPath "share" [idrisPkgs.support];
+
+        globalLibraries = let
+          idrName = "idris2-${idris.version}";
+          libSuffix = "lib/${idrName}";
+        in [
+          "\\$HOME/.nix-profile/lib/${idrName}"
+          "/run/current-system/sw/lib/${idrName}"
+          "${idrisPkgs.idris2}/${idrName}"
+        ];
+        globalLibrariesPath = builtins.concatStringsSep ":" globalLibraries;
+
+        lspPkg = buildIdris {
+          projectName = "idris2-lsp";
+          src = ./.;
+          idrisLibraries = [idrisPkgs.idris2-api lspLib];
+          buildInputs = [pkgs.makeWrapper];
+          postInstall = ''
+            wrapProgram $out/bin/idris2-lsp \
+              --run 'export IDRIS2_PREFIX=''${IDRIS2_PREFIX-"$HOME/.idris2"}' \
+              --suffix IDRIS2_LIBS ':' "${supportLibrariesPath}" \
+              --suffix IDRIS2_DATA ':' "${supportSharePath}" \
+              --suffix IDRIS2_PACKAGE_PATH ':' "${globalLibrariesPath}"
+          '';
+        };
+      in rec {
+        packages =
+          idrisPkgs
+          // rec {
+            idris2-lsp = lspPkg.executable;
+            default = idris2-lsp;
+          };
+        formatter = alejandra.packages.${system}.default;
+      }
+    );
+}