modules: add env option

modules/output.nix

@@ -28,6 +28,26 @@ let
 in
 {
   options = {
+    env = mkOption {
+      type =
+        with types;
+        lazyAttrsOf (oneOf [
+          str
+          path
+          int
+          float
+        ]);
+      description = "Environment variables to set in the neovim wrapper.";
+      default = { };
+      example = {
+        FOO = 1;
+        PI = 3.14;
+        BAR_PATH = "/home/me/.local/share/bar";
+        INFER_MODE = "local";
+        BAZ_MAX_COUNT = 1000;
+      };
+    };
+
     extraPlugins = mkOption {
       type = with types; listOf (nullOr (either package pluginWithConfigType));
       default = [ ];

modules/top-level/output.nix

@@ -339,7 +339,16 @@ in
           initSource;
 
       extraWrapperArgs = builtins.concatStringsSep " " (
-        (optional (
+        # Setting environment variables in the wrapper
+        (lib.mapAttrsToList (
+          name: value:
+          lib.escapeShellArgs [
+            "--set"
+            name
+            value
+          ]
+        ) config.env)
+        ++ (optional (
           config.extraPackages != [ ]
         ) ''--prefix PATH : "${lib.makeBinPath config.extraPackages}"'')
         ++ (optional config.wrapRc ''--add-flags -u --add-flags "${initFile}"'')