ANTLR输入不匹配'< EOF>' [英] ANTLR mismatched input '<EOF>'

问题描述

给出以下ANTLR 4.1语法，其中一行故意注释掉了...

Given the following ANTLR 4.1 grammar, with one line intentionally commented out ...

grammar Foobar;

//whyDoesThisRuleHelp : expression ;
expression : operand | binaryOperation ;
binaryOperation : operand WS BINARY_OPERATOR WS expression ;
operand : LETTER ;

BINARY_OPERATOR : 'EQ' ;
LETTER : [a-z] ;
WS : [ \n]+ ;

..为什么echo -n "a EQ b" | grun Foobar expression产生

line 1:6 mismatched input '<EOF>' expecting WS

.. 但是如果我们取消注释，在上方的block : expression ;行中，grun 不会产生任何错误?

.. but if we uncomment the block : expression ; line above then grun produces no errors?

推荐答案

您正在看到一个罕见但已知的错误的影响:
在没有明确的EOF的情况下，没有可行的替代方法可以错误地引发启动规则

You are seeing the effects of a rare but known bug:
No viable alternative can be incorrectly thrown for start rules without explicit EOF

正确解决此问题对性能的影响目前令人吃惊，因此我们无意在可预见的将来应用此补丁.解决方法是创建一个以显式EOF结尾的规则，然后在此处开始解析.

The performance implications of properly fixing this are currently staggering, so we have no intention of applying the patch for the foreseeable future. The workaround is to create a rule that ends with an explicit EOF, and start parsing there.

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