refactor(frontend): 添加对只编译前端的支持

src/main.cpp

@@ -4,10 +4,12 @@
 
 #include "frontend/AntlrDriver.h"
 #include "frontend/SyntaxTreePrinter.h"
+#if !COMPILER_PARSE_ONLY
 #include "ir/IR.h"
 #include "irgen/IRGen.h"
 #include "mir/MIR.h"
 #include "sem/Sema.h"
+#endif
 #include "utils/CLI.h"
 #include "utils/Log.h"
 
@@ -26,6 +28,7 @@ int main(int argc, char** argv) {
       need_blank_line = true;
     }
 
+#if !COMPILER_PARSE_ONLY
     auto* comp_unit = dynamic_cast<SysYParser::CompUnitContext*>(antlr.tree);
     if (!comp_unit) {
       throw std::runtime_error(FormatError("main", "语法树根节点不是 compUnit"));
@@ -51,6 +54,12 @@ int main(int argc, char** argv) {
       }
       mir::PrintAsm(*machine_func, std::cout);
     }
+#else
+    if (opts.emit_ir || opts.emit_asm) {
+      throw std::runtime_error(
+          FormatError("main", "当前为 parse-only 构建；IR/汇编输出已禁用"));
+    }
+#endif
   } catch (const std::exception& ex) {
     PrintException(std::cerr, ex);
     return 1;