Add diagnostic support forgotten in last commit

src/Diagnostic.cpp

@@ -0,0 +1,15 @@
+#include <sstream>
+using namespace std;
+#include "Diagnostic.h"
+
+namespace sysy {
+
+Diagnostic error(antlr4::ParserRuleContext *ctx, const std::string &msg) {
+  auto line = ctx->start->getLine();
+  auto col = ctx->start->getCharPositionInLine();
+  ostringstream ss;
+  ss << line << ':' << col << ": error " << msg << '\n';
+  return Diagnostic(ss.str());
+}
+
+} // namespace sysy

src/Diagnostic.h

@@ -0,0 +1,31 @@
+#pragma once
+
+#include "antlr4-runtime.h"
+#include <cstdlib>
+#include <iostream>
+#include <string>
+
+namespace sysy {
+
+class Diagnostic {
+private:
+  const std::string message;
+
+public:
+  Diagnostic(const std::string &message) : message(message) {}
+  Diagnostic(std::string &&message) : message(std::move(message)) {}
+  Diagnostic(const Diagnostic &) = default;
+  Diagnostic(Diagnostic &&) = default;
+
+public:
+  ~Diagnostic() {
+    if (not message.empty()) {
+      std::cerr << message << '\n';
+      exit(EXIT_FAILURE);
+    }
+  }
+}; // class Diagnostic
+
+Diagnostic error(antlr4::ParserRuleContext *ctx, const std::string &msg);
+
+} // namespace sysy

test/11_add2.sy

@@ -0,0 +1,7 @@
+//test add
+int main(){
+    int a, b;
+    a = 10;
+    b = 0;
+    return a + b;
+}