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;})
    ;

这样做的方法是什么？我试过这个

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

但是使用这个生成的代码会产生编译错误。因为该方法 loactionapth 在方法签名处没有抛出线索。

Answer 1

只有一种方法可以做到这一点：抛出未经检查的异常：

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

如果编译器仍然抱怨（我不记得了，而且我现在无法测试），请if(true)在它前面添加一个：

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