nixd/Controller: allow setting initial configuration via CLI

Add a CLI flag `-config` used to set initial configuration.
For editor clients which does not support workspace configuration,
the flag could be used as a fallback.

nixd/include/nixd/CommandLine/Configuration.h

@@ -0,0 +1,11 @@
+/// \file
+/// \brief Allow default configuration being passed via CLI
+
+#include "nixd/Controller/Configuration.h"
+
+namespace nixd {
+
+/// \brief Parse the CLI flag and initialize the config nixd::DefaultConfig
+nixd::Configuration parseCLIConfig();
+
+} // namespace nixd

nixd/lib/CommandLine/Configuration.cpp

@@ -0,0 +1,50 @@
+/// \file
+/// \brief This file implements CLI initialized configuration.
+
+#include "nixd/CommandLine/Configuration.h"
+#include "nixd/CommandLine/Options.h"
+#include "nixd/Controller/Configuration.h"
+
+#include "lspserver/Logger.h"
+
+#include <llvm/Support/CommandLine.h>
+#include <llvm/Support/JSON.h>
+
+#include <iostream>
+#include <string>
+
+using namespace nixd;
+using namespace llvm::cl;
+
+namespace {
+
+opt<std::string> DefaultConfigJSON{"config",
+                                   desc("JSON-encoded initial configuration"),
+                                   init(""), cat(NixdCategory)};
+
+} // namespace
+
+Configuration nixd::parseCLIConfig() {
+  if (DefaultConfigJSON.empty())
+    return {};
+
+  llvm::Expected<llvm::json::Value> V = llvm::json::parse(DefaultConfigJSON);
+
+  if (!V) {
+    llvm::errs()
+        << "The JSON string of default configuration cannot be parsed, reason: "
+        << V.takeError() << "\n";
+    std::exit(-1);
+  }
+
+  llvm::json::Path::Root R;
+  Configuration C;
+  if (!fromJSON(*V, C, R)) {
+    // JSON is valid, but it has incorrect schema
+    llvm::errs()
+        << "The JSON string of default configuration has invalid schema: "
+        << R.getError() << "\n";
+    std::exit(-1);
+  }
+  return C;
+}

nixd/lib/Controller/LifeTime.cpp

@@ -5,6 +5,7 @@
 
 #include "nixd-config.h"
 
+#include "nixd/CommandLine/Configuration.h"
 #include "nixd/CommandLine/Options.h"
 #include "nixd/Controller/Controller.h"
 #include "nixd/Eval/Launch.h"
@@ -183,6 +184,7 @@ void Controller::
       evalExprWithProgress(*Client, getDefaultNixOSOptionsExpr(),
                            "nixos options");
   }
+  Config = parseCLIConfig();
   fetchConfig();
 }
 

nixd/lib/meson.build

@@ -4,6 +4,7 @@ libnixd_deps = [ nixd_lsp_server, nixf, llvm, nixt ]
 
 libnixd_lib = library(
     'nixd',
+    'CommandLine/Configuration.cpp',
     'CommandLine/Options.cpp',
     'Controller/AST.cpp',
     'Controller/CodeAction.cpp',

nixd/tools/nixd/test/format/format.md

@@ -0,0 +1,62 @@
+# RUN: nixd --lit-test -config='{ "formatting": { "command": ["%S/nixfmt"] } }' < %s | FileCheck %s
+
+<-- initialize(0)
+
+```json
+{
+   "jsonrpc":"2.0",
+   "id":0,
+   "method":"initialize",
+   "params":{
+      "processId":123,
+      "rootPath":"",
+      "capabilities":{
+      },
+      "trace":"off"
+   }
+}
+```
+
+```json
+{
+   "jsonrpc":"2.0",
+   "method":"textDocument/didOpen",
+   "params":{
+      "textDocument":{
+         "uri":"file:///format.nix",
+         "languageId":"nix",
+         "version":1,
+         "text":"{ stdenv,\npkgs}: \n let x=1; in { y = x; }"
+      }
+   }
+}
+```
+
+<-- textDocument/formatting
+
+```json
+{
+    "jsonrpc": "2.0",
+    "id": 2,
+    "method": "textDocument/formatting",
+    "params": {
+        "textDocument": {
+            "uri": "file:///format.nix"
+        },
+        "options": {
+            "tabSize": 2,
+            "insertSpaces": true,
+            "trimTrailingWhitespace": true,
+            "insertFinalNewline": true
+        }
+    }
+}
+```
+
+```
+CHECK: "newText": "Hello\n",
+```
+
+```json
+{"jsonrpc":"2.0","method":"exit"}
+```

nixd/tools/nixd/test/format/nixfmt

@@ -0,0 +1,2 @@
+#!/bin/sh
+echo "Hello"