refactor(frontend): 添加对只编译前端的支持

src/CMakeLists.txt

@@ -3,17 +3,27 @@
 add_subdirectory(utils)
 add_subdirectory(ir)
 add_subdirectory(frontend)
-add_subdirectory(sem)
-add_subdirectory(irgen)
-add_subdirectory(mir)
+if(NOT COMPILER_PARSE_ONLY)
+  add_subdirectory(sem)
+  add_subdirectory(irgen)
+  add_subdirectory(mir)
+endif()
 
 add_executable(compiler
   main.cpp
 )
 target_link_libraries(compiler PRIVATE
   frontend
-  sem
-  irgen
-  mir
   utils
 )
+
+if(NOT COMPILER_PARSE_ONLY)
+  target_link_libraries(compiler PRIVATE
+    sem
+    irgen
+    mir
+  )
+  target_compile_definitions(compiler PRIVATE COMPILER_PARSE_ONLY=0)
+else()
+  target_compile_definitions(compiler PRIVATE COMPILER_PARSE_ONLY=1)
+endif()

src/antlr4/SysY.g4

@@ -3,18 +3,66 @@
 // 的最小返回表达式编译。
 
 // 后续需要自行添加
+
 grammar SysY;
 
+/*===-------------------------------------------===*/
+/* Lexer rules                                     */
+/*===-------------------------------------------===*/
+
+INT: 'int';
+RETURN: 'return';
+
+ASSIGN: '=';
+ADD: '+';
+
+LPAREN: '(';
+RPAREN: ')';
+LBRACE: '{';
+RBRACE: '}';
+SEMICOLON: ';';
+
+ID: [a-zA-Z_][a-zA-Z_0-9]*;
+ILITERAL: [0-9]+;
+
+WS: [ \t\r\n] -> skip;
+LINECOMMENT: '//' ~[\r\n]* -> skip;
+BLOCKCOMMENT: '/*' .*? '*/' -> skip;
+
+/*===-------------------------------------------===*/
+/* Syntax rules                                    */
+/*===-------------------------------------------===*/
+
 compUnit
     : funcDef EOF
     ;
 
-funcDef
-    : Int Ident L_PAREN R_PAREN block
+decl
+    : btype varDef SEMICOLON
     ;
 
-block
-    : L_BRACE blockItem* R_BRACE
+btype
+    : INT
+    ;
+
+varDef
+    : lValue (ASSIGN initValue)?
+    ;
+
+initValue
+    : exp
+    ;
+
+funcDef
+    : funcType ID LPAREN RPAREN blockStmt
+    ;
+
+funcType
+    : INT
+    ;
+
+blockStmt
+    : LBRACE blockItem* RBRACE
     ;
 
 blockItem
@@ -22,63 +70,29 @@ blockItem
     | stmt
     ;
 
-decl
-    : varDecl
-    ;
-
 stmt
     : returnStmt
     ;
 
-varDecl
-    : Int Ident (Assign exp)? Semi
-    ;
-
 returnStmt
-    : Return exp Semi
+    : RETURN exp SEMICOLON
     ;
 
 exp
-    : addExp
+    : LPAREN exp RPAREN          # parenExp
+    | var                        # varExp
+    | number                     # numberExp
+    | exp ADD exp                # additiveExp
     ;
 
-addExp
-    : primary (AddOp primary)*
+var
+    : ID
     ;
 
-primary
-    : Number
-    | Ident
-    | L_PAREN exp R_PAREN
+lValue
+    : ID
     ;
 
-Int     : 'int';
-Return  : 'return';
-
-AddOp   : '+';
-Assign  : '=';
-Semi    : ';';
-L_PAREN : '(';
-R_PAREN : ')';
-L_BRACE : '{';
-R_BRACE : '}';
-
-Ident
-    : [a-zA-Z_][a-zA-Z_0-9]*
-    ;
-
-Number
-    : [0-9]+
-    ;
-
-WS
-    : [ \t\r\n]+ -> skip
-    ;
-
-COMMENT
-    : '//' ~[\r\n]* -> skip
-    ;
-
-BLOCK_COMMENT
-    : '/*' .*? '*/' -> skip
+number
+    : ILITERAL
     ;

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;