plugins/lsp/language-servers/nil_ls: improve settings options

plugins/lsp/language-servers/default.nix

@@ -361,41 +361,8 @@ let
       name = "nil_ls";
       description = "nil for Nix";
       package = pkgs.nil;
-      settingsOptions = {
-        formatting.command = mkOption {
-          type = types.nullOr (types.listOf types.str);
-          default = null;
-          description = ''
-            External formatter command (with arguments).
-            It should accepts file content in stdin and print the formatted code into stdout.
-          '';
-        };
-        diagnostics = {
-          ignored = mkOption {
-            type = types.listOf types.str;
-            default = [ ];
-            description = ''
-              Ignored diagnostic kinds.
-              The kind identifier is a snake_cased_string usually shown together
-              with the diagnostic message.
-            '';
-          };
-          excludedFiles = mkOption {
-            type = types.listOf types.str;
-            default = [ ];
-            description = ''
-              Files to exclude from showing diagnostics. Useful for generated files.
-              It accepts an array of paths. Relative paths are joint to the workspace root.
-              Glob patterns are currently not supported.
-            '';
-          };
-        };
-      };
-      settings = cfg: {
-        nil = {
-          inherit (cfg) formatting diagnostics;
-        };
-      };
+      settingsOptions = import ./nil_ls-settings.nix { inherit lib helpers; };
+      settings = cfg: { nil = cfg; };
     }
     {
       name = "nimls";

plugins/lsp/language-servers/nil_ls-settings.nix

@@ -0,0 +1,63 @@
+{ lib, helpers }:
+# Options:
+#  - https://github.com/oxalica/nil/blob/main/docs/configuration.md?plain=1#
+with lib;
+{
+  formatting = {
+    command = helpers.defaultNullOpts.mkListOf types.str "null" ''
+      External formatter command (with arguments).
+      It should accepts file content in stdin and print the formatted code into stdout.
+    '';
+  };
+
+  diagnostics = {
+    ignored = helpers.defaultNullOpts.mkListOf types.str "[]" ''
+      Ignored diagnostic kinds.
+      The kind identifier is a snake_cased_string usually shown together
+      with the diagnostic message.
+    '';
+
+    excludedFiles = helpers.defaultNullOpts.mkListOf types.str "[]" ''
+      Files to exclude from showing diagnostics. Useful for generated files.
+      It accepts an array of paths. Relative paths are joint to the workspace root.
+      Glob patterns are currently not supported.
+    '';
+  };
+
+  nix = {
+    binary = helpers.defaultNullOpts.mkStr "nix" ''
+      The path to the `nix` binary.
+    '';
+
+    maxMemoryMB = helpers.defaultNullOpts.mkInt 2560 ''
+      The heap memory limit in MiB for `nix` evaluation.
+      Currently it only applies to flake evaluation when `autoEvalInputs` is enabled, and only works
+      for Linux.
+      Other `nix` invocations may be also applied in the future.
+      `null` means no limit.
+      As a reference, `nix flake show --legacy nixpkgs` usually requires about 2GiB memory.
+    '';
+
+    flake = {
+      autoArchive = helpers.defaultNullOpts.mkBool false ''
+        Auto-archiving behavior which may use network.
+         - `null`: Ask every time.
+         - `true`: Automatically run `nix flake archive` when necessary.
+         - `false`: Do not archive. Only load inputs that are already on disk.
+      '';
+
+      autoEvalInputs = helpers.defaultNullOpts.mkBool false ''
+        Whether to auto-eval flake inputs.
+        The evaluation result is used to improve completion, but may cost lots of time and/or memory.
+      '';
+
+      nixpkgsInputName = helpers.defaultNullOpts.mkStr "nixpkgs" ''
+        The input name of nixpkgs for NixOS options evaluation.
+
+        The options hierarchy is used to improve completion, but may cost lots of time and/or memory.
+        If this value is `null` or is not found in the workspace flake's inputs, NixOS options are
+        not evaluated.
+      '';
+    };
+  };
+}

tests/test-sources/plugins/lsp/language-servers/nil-ls.nix

@@ -0,0 +1,33 @@
+{
+  example = {
+    plugins.lsp = {
+      enable = true;
+
+      servers.nil_ls = {
+        enable = true;
+
+        settings = {
+          diagnostics = {
+            ignored = [
+              "unused_binding"
+              "unused_with"
+            ];
+            excludedFiles = [ "Cargo.nix" ];
+          };
+          formatting = {
+            command = [ "nixfmt" ];
+          };
+          nix = {
+            binary = "nix";
+            maxMemoryMB = 2048;
+            flake = {
+              autoArchive = true;
+              autoEvalInputs = false;
+              nixpkgsInputName = "nixpkgs";
+            };
+          };
+        };
+      };
+    };
+  };
+}