避免尖括号的反语法 [英] antlr grammar avoiding angle brackets

问题描述

在这个问题中，我问过从任意文本中提取标签的问题.提供的解决方案效果很好，但是我想处理一种边缘情况.回顾一下，我正在解析任意用户输入的文本，并希望出现<或>的任何内容以符合有效的标记语法.如果尖括号不是有效标签的一部分，则应将其转为<或>.我要查找的语法是<foo#123>，其中foo是固定条目列表中的文本，而123是数字[0-9]+.解析器:

In this question I asked about extracting tags from arbitrary text. The solution provided worked well, but there's one edge case I'd like to handle. To recap, I'm parsing arbitrary user-entered text and would like to have any occurrence of < or > to conform to valid tag syntax. Where an angle bracket isn't part of a valid tag, it should be escaped as < or >. The syntax I'm looking for is <foo#123> where foo is text from a fixed list of entries and 123 is a number [0-9]+. The parser:

parser grammar TagsParser;

options {
    tokenVocab = TagsLexer;
}

parse: (tag | text)* EOF;
tag: LANGLE fixedlist GRIDLET ID RANGLE;
text: NOANGLE;
fixedlist: FOO | BAR | BAZ;

词法分析器:

lexer grammar TagsLexer;

LANGLE: '<' -> pushMode(tag);
NOANGLE: ~[<>]+;

mode tag:

RANGLE: '>' -> popMode;
GRIDLET: '#';
FOO: 'foo';
BAR: 'bar';
BAZ: 'baz';
ID: [0-9]+;
OTHERTEXT: . ;

这很好并且可以成功解析以下文本:

This works well and successfully parses text such as:

<foo#123>
Hi <bar#987>!
<baz#1><foo#2>anythinghere<baz#3>
if 1 &lt; 2

当我使用BailErrorStrategy时，它也成功失败了以下操作:

It also successfully fails the following when I use the BailErrorStrategy:

<foo123>
<bar#a>
<foo#123H>
<unsupported#123>
if 1 < 2

最后一个成功失败，因为<进入tag模式并且与支持的标记格式不匹配.但是，我也想避免在文本中使用>的实例，因此以下内容也应该失败:

The last one successfully fails because < enters the tag mode and it doesn't match a supported tag format. However, I would also like to avoid instances of > in the text as well, so the following should fail as well:

if 2 > 1

该文本应指定为if 2 > 1，而不要使用原始尖括号.

That text should be specified as if 2 > 1 instead of having the raw angle bracket.

如何修改语法，以使不是有效标签一部分的>出现都无法解析?

How can I modify the grammar so that occurrences of > which aren't part of a valid tag fail to parse?

推荐答案

按照您现在的语法，它会在标记之外的标记之外的>失败，因为>不会出现在词法分析器语法中在tag模式之外.没错，这是一个失败.但是，如果您坚持在 parse 期间失败，则只需为词法分析器的默认模式添加直角即可:

As your grammar stands now, it will fail > outside of a tag with token recognition error, because > doesn't appear in the lexer grammar outside of the tag mode. That's a failure all right as it is. But if you insist on failing during parse, then just add right angle to the lexer's default mode:

lexer grammar TagsLexer;

LANGLE: '<' -> pushMode(tag);
NOANGLE: ~[<>]+;
BADRANGLE: '>';

mode tag;

RANGLE: '>' -> popMode;
...

然后，标签外的>在解析期间将失败.

Then > outside of a tag will fail during parse.

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