antlr - 如何在 Antlr 语法中抛出异常

Question

我有这种语法，

locationPath returns [CustomParser xpathParser]  
    :^(LOCATION_PATH relativeLocationPath {**Want to throw a exception if this condition matches**})
    |^(LOCATION_PATH absoluteLocationPath {$xpathParser=$absoluteLocationPath.xpathParser;})
    ;

有什么方法可以做到？我试过这个

locationPath returns [CustomParser xpathParser]  
    :^(LOCATION_PATH relativeLocationPath {throw new Exception})
    |^(LOCATION_PATH absoluteLocationPath {$xpathParser=$absoluteLocationPath.xpathParser;})

但是有了这个，生成的代码会给出编译错误。因为该方法 loactionapth 在方法签名中没有抛出线索。

Answer 1

只有一种方法可以做到这一点:抛出一个未经检查的异常:

locationPath returns [CustomParser xpathParser]  
 : ^(LOCATION_PATH relativeLocationPath) {throw new RuntimeException("No way!");}
 | ^(LOCATION_PATH absoluteLocationPath {$xpathParser=$absoluteLocationPath.xpathParser;})
 ;

如果编译器仍然提示(我不记得了，我现在无法测试)，添加一个 if(true)在它面前:

locationPath returns [CustomParser xpathParser]  
 : ^(LOCATION_PATH relativeLocationPath) {if(true) throw new RuntimeException("No way!");}
 | ^(LOCATION_PATH absoluteLocationPath {$xpathParser=$absoluteLocationPath.xpathParser;})
 ;