作用域中的java Antlr check返回语句

Question

我想知道如何在语法分析期间检查函数中的所有路径是否都有返回。假设我在Lexer中有以下内容

RETURN: 'return';
PRINT: 'print';
IF:'if';
ELSE: 'else';
THEN:'then';
PLUS: '+';
MINUS:'-';
EQUALS: '==';
DIGIT: '0'..'9';
OPEN:'{';
CLOSE:'}';
STRING: [a..zA..Z]+;
SEMICOLON: ';';

和解析器

function: STRING OPEN statement CLOSE
statement: RETURN expr | PRINT expr | IF expr THEN statement ELSE statement | statement SEMICOLON statement;
expr: DIGIT| expr PLUS expr | expr MINUS expr | expr EQUALS expr;

我的问题是一个有效的函数应该有一个return语句，后面什么都没有。 所以一个有效的是

test { return 2+2 }

或者

test{ if 2 == 2 then return 2 else return 3 }

如果返回后有无法访问的代码，则返回无效代码。例如

test{return 2; print 3}

我该如何检查返回语句后是否没有任何内容

我的主要java方法如下所示：

MyLexer mylexer = new MyLexer(new ANTLRInputStream(System.in));
CommonTokenStream toks = new CommonTokenStream(mylexer);
MyParser parser = new MyParser(tokens);
ParseTree parseTree = parser.program();

Answer 1

我不是专家，直到今天才使用过错误报告，但是如果你只是想要一个错误列表，你可以根据The Definitive ANTLR 4 Reference第9章的启发做以下事情

文件Question.g4：

grammar Question;

/* Detecting invalid input after a return statement. */

question
@init {System.out.println("Question last update 1302");}
    :   function+ EOF
    ;

function
    :   STRING OPEN statement_block CLOSE
    ;

statement_block
    :   statement* if_last? return_statement
    ;

statement
    :   PRINT expr
    |   IF expr THEN statement ELSE statement
    |   statement SEMICOLON statement
    ;

if_last
    :   IF expr THEN statement_block ELSE statement*
    ;

return_statement
    :   RETURN expr
    ;

expr
    :   DIGIT
    |   expr PLUS expr
    |   expr MINUS expr
    |   expr EQUALS expr
    ;

CLOSE  : '}' ;
ELSE   : 'else' ;
EQUALS : '==' ;
IF     : 'if' ;
MINUS  : '-' ;
OPEN   : '{' ;
PLUS   : '+' ;
PRINT  : 'print' ;
RETURN : 'return' ;
THEN   : 'then' ;

DIGIT     : [0-9] ;
STRING    : [a-zA-Z]+ ;
SEMICOLON : ';' ;

WS  : [ \r\n\t] -> channel(HIDDEN) ;

文件MyListener.java：

public class MyListener extends QuestionBaseListener {
    QuestionParser parser;
    public MyListener(QuestionParser parser) { this.parser = parser; }

    public void exitFunction(QuestionParser.FunctionContext ctx) {
        System.out.println(">>> in MyListener for function");
        System.out.println(parser.getTokenStream().getText(ctx));
    }
}

文件test.java：

import org.antlr.v4.runtime.*;

import org.antlr.v4.runtime.tree.*;
import java.io.FileInputStream;
import java.io.InputStream;
import java.io.IOException;
import java.util.*;

public class test {
    public static class UnderlineListener extends BaseErrorListener {
        public void syntaxError(Recognizer<?, ?> recognizer,
                                Object offendingSymbol,
                                int line, int charPositionInLine,
                                String msg,
                                RecognitionException e)
        {
            System.err.println("line " + line + ":" + charPositionInLine + " " + msg);
            underlineError(recognizer,(Token)offendingSymbol,
                line, charPositionInLine);
        }

        protected void underlineError(Recognizer recognizer,
                                      Token offendingToken, int line,
                                      int charPositionInLine) {
            CommonTokenStream tokens =
                (CommonTokenStream)recognizer.getInputStream();
            String input = tokens.getTokenSource().getInputStream().toString();
            String[] lines = input.split("\n");
            String errorLine = lines[line - 1];
            System.err.println(errorLine);
            for (int i=0; i<charPositionInLine; i++) System.err.print(" ");
            int start = offendingToken.getStartIndex();
            int stop = offendingToken.getStopIndex();
            if ( start>=0 && stop>=0 ) {
                for (int i=start; i<=stop; i++) System.err.print("^");
            }
            System.err.println();
        }
    }

    public static void main(String[] args) throws IOException {
        ANTLRInputStream input = new ANTLRFileStream(args[0]);
        QuestionLexer lexer = new QuestionLexer(input);
        CommonTokenStream tokens = new CommonTokenStream(lexer);
        QuestionParser parser = new QuestionParser(tokens);
        parser.removeErrorListeners(); // remove ConsoleErrorListener
        parser.addErrorListener(new UnderlineListener()); // add ours
        ParseTree tree = parser.question();
        System.out.println(" -parsing ended");
        ParseTreeWalker walker = new ParseTreeWalker();
        MyListener my_listener = new MyListener(parser);
        System.out.println(">>>> about to walk");
        walker.walk(my_listener, tree);
    }
}

文件t.text：

test { return 2+2 }
test { if 2 == 2 then return 2 else return 3 }
test { if 2 == 2 then print 2 else print 3 return 4 }
test {return 2; print 3}
test { if 2 == 2 then return 2; abc else return 3; def }
test { if 2 == 2 then if 6 then print 6 else print 3 else if 5 then
print 1; print 2 else print 3 return 4 }

执行：

$ java test t.text 
Question last update 1302
line 4:14 mismatched input ';' expecting {'}', '==', '-', '+'}
test {return 2; print 3}
              ^
line 5:30 mismatched input ';' expecting {'else', '==', '-', '+'}
test { if 2 == 2 then return 2; abc else return 3; def }
                              ^
line 5:49 mismatched input ';' expecting {'}', '==', '-', '+'}
test { if 2 == 2 then return 2; abc else return 3; def }
                                                 ^
 -parsing ended
>>>> about to walk
>>> in MyListener for function
test { return 2+2 }
>>> in MyListener for function
test { if 2 == 2 then return 2 else return 3 }
>>> in MyListener for function
test { if 2 == 2 then print 2 else print 3 return 4 }
>>> in MyListener for function
test {return 2; print 3}
>>> in MyListener for function
test { if 2 == 2 then return 2; abc else return 3; def }
>>> in MyListener for function
test { if 2 == 2 then if 6 then print 6 else print 3 else if 5 then print 1; print 2 else print 3 return 4 }