use exceptions

nixd/include/nixd/CommandLine/Configuration.h

@@ -3,6 +3,8 @@
 
 #include "nixd/Controller/Configuration.h"
 
+#include <exception>
+
 namespace nixd {
 
 /// \brief Parse the CLI flag and initialize the config nixd::DefaultConfig

nixd/include/nixd/Support/Exception.h

@@ -0,0 +1,18 @@
+#pragma once
+
+#include <llvm/Support/Error.h>
+
+#include <exception>
+
+namespace nixd {
+
+class LLVMErrorException : public std::exception {
+  llvm::Error E;
+
+public:
+  LLVMErrorException(llvm::Error E) : E(std::move(E)) {}
+
+  llvm::Error takeError() { return std::move(E); }
+};
+
+} // namespace nixd

nixd/include/nixd/Support/JSON.h

@@ -0,0 +1,38 @@
+#include "Exception.h"
+
+#include <llvm/ADT/StringRef.h>
+#include <llvm/Support/JSON.h>
+
+#include <exception>
+
+namespace nixd {
+
+class JSONParseException : public LLVMErrorException {
+public:
+  JSONParseException(llvm::Error E) : LLVMErrorException(std::move(E)) {}
+
+  [[nodiscard]] const char *what() const noexcept override {
+    return "JSON result cannot be parsed";
+  }
+};
+
+class JSONSchemaException : public LLVMErrorException {
+public:
+  JSONSchemaException(llvm::Error E) : LLVMErrorException(std::move(E)) {}
+
+  [[nodiscard]] const char *what() const noexcept override {
+    return "JSON schema mismatch";
+  }
+};
+
+llvm::json::Value parse(llvm::StringRef JSON);
+
+template <class T> T fromJSON(const llvm::json::Value &V) {
+  llvm::json::Path::Root R;
+  T Result;
+  if (!fromJSON(V, Result, R))
+    throw JSONSchemaException(R.getError());
+  return Result;
+}
+
+} // namespace nixd

nixd/lib/CommandLine/Configuration.cpp

@@ -4,6 +4,7 @@
 #include "nixd/CommandLine/Configuration.h"
 #include "nixd/CommandLine/Options.h"
 #include "nixd/Controller/Configuration.h"
+#include "nixd/Support/JSON.h"
 
 #include "lspserver/Logger.h"
 
@@ -28,23 +29,5 @@ 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;
+  return nixd::fromJSON<Configuration>(nixd::parse(DefaultConfigJSON));
 }

nixd/lib/Controller/LifeTime.cpp

@@ -11,6 +11,7 @@
 #include "nixd/Eval/Launch.h"
 
 #include "lspserver/Protocol.h"
+#include "nixd/Support/Exception.h"
 
 #include <llvm/Support/CommandLine.h>
 
@@ -184,7 +185,12 @@ void Controller::
       evalExprWithProgress(*Client, getDefaultNixOSOptionsExpr(),
                            "nixos options");
   }
-  Config = parseCLIConfig();
+  try {
+    Config = parseCLIConfig();
+  } catch (LLVMErrorException &Err) {
+    lspserver::elog("{0}, reason: {1}", Err.what(), Err.takeError());
+    std::exit(-1);
+  }
   fetchConfig();
 }
 

nixd/lib/Support/JSON.cpp

@@ -0,0 +1,10 @@
+#include "nixd/Support/JSON.h"
+
+#include <llvm/ADT/StringRef.h>
+
+llvm::json::Value nixd::parse(llvm::StringRef JSON) {
+  llvm::Expected<llvm::json::Value> E = llvm::json::parse(JSON);
+  if (!E)
+    throw JSONParseException(E.takeError());
+  return *E;
+}

nixd/lib/meson.build

@@ -34,6 +34,7 @@ libnixd_lib = library(
     'Support/AutoCloseFD.cpp',
     'Support/AutoRemoveShm.cpp',
     'Support/ForkPiped.cpp',
+    'Support/JSON.cpp',
     'Support/StreamProc.cpp',
     dependencies: libnixd_deps,
     include_directories: libnixd_include,