Xtext 语法错误“Decision can match input ... using multiple alternatives: 1, 3, 4, 5”

Question

我的 xtext 语法定义卡住了。基本上我喜欢为一个组件定义多个参数。组件应包含至少一个参数定义 paramA OR paramB OR paramC OR (paramA AND paramB) OR (paramB AND paramC) OR (paramA AND paramB AND paramC)。

总共有 6 种情况，你可以在我的语法定义中看到：

Component:
    'Define available parameters:' (
        (newParamA = ParamA | newParamB = ParamB | newParamC = ParamC)
        | (newParamA = ParamA & newParamB = ParamB)
        | (newParamA = ParamA & newParamC = ParamC)
        | (newParamB = ParamB & newParamC = ParamC)
        | (newParamA = ParamA & newParamB = ParamB & newParamC = ParamC)
    )
;

ParamA: ('paramA = ' paramA=Integer ';');
ParamB: ('paramB = ' paramB=Integer ';');
ParamC: ('paramC = ' paramC=Integer ';');

// Datatype
Integer returns ecore::EIntegerObject: '-'? INT;

当我减少语法以仅使用 (newParamA = ParamA | newParamB = ParamB | newParamC = ParamC) 时，这是有效的，这意味着在第一个代码 sn-p 中没有其他情况：

Define available parameters:
    paramA = 1;
...
Define available parameters:
    paramB = 2;
...
Define available parameters:
    paramC = 3;

但我希望能够在我的 dsl 中定义多个可用参数，例如

Define available parameters:
    paramA = 1; paramB = 2;
...
Define available parameters:
    paramB = 2; paramC = 3;
...
Define available parameters:
    paramA = 1; paramB = 2; paramC = 3;

知道如何解决这个问题吗？希望您能帮助我，我将不胜感激！

这是我从代码 sn-p #1 生成语法时遇到的错误：

warning(200): ../my.packagename/src-gen/my/packagename/projectname/parser/antlr/internal/InternalMyDSL.g:722:1: Decision can match input such as "'paramC = ' '-' RULE_INT ';'" using multiple alternatives: 1, 3, 4, 5
As a result, alternative(s) 3,5,4 were disabled for that input
Semantic predicates were present but were hidden by actions.

...

4514 [main] ERROR enerator.CompositeGeneratorFragment  - java.io.FileNotFoundException: ..\my.packagename.ui\src-gen\my\packagename\projectname\ui\contentassist\antlr\internal\InternalMyDSLParser.java (The system cannot find the file specified)
org.eclipse.emf.common.util.WrappedException: java.io.FileNotFoundException: ..\my.packagename.ui\src-gen\my\packagename\projectname\ui\contentassist\antlr\internal\InternalMyDSLParser.java (The system cannot find the file specified)
    at org.eclipse.xtext.util.Files.readFileIntoString(Files.java:129)
    at org.eclipse.xtext.generator.parser.antlr.AbstractAntlrGeneratorFragment.simplifyUnorderedGroupPredicates(AbstractAntlrGeneratorFragment.java:130)
    at org.eclipse.xtext.generator.parser.antlr.AbstractAntlrGeneratorFragment.simplifyUnorderedGroupPredicatesIfRequired(AbstractAntlrGeneratorFragment.java:118)
    at org.eclipse.xtext.generator.parser.antlr.XtextAntlrUiGeneratorFragment.generate(XtextAntlrUiGeneratorFragment.java:86)

这是我尝试过的解决方法（可行），但这不是解决方案，因为语言中的关键字正在更改以避免解析器错误：

('newParamA1 = ' paramA1=Integer ';')
| ('newParamB1 = ' paramB1=Integer ';')
| ('newParamC1 = ' paramC1=Integer ';')
| (('newParamA2 = ' paramA2=Integer ';') & ('newParamB2 = ' paramB2=Integer ';'))
| (('newParamA3 = ' paramA3=Integer ';') & ('newParamC2 = ' paramC2=Integer ';'))
| (('newParamB3 = ' paramB3=Integer ';') & ('newParamC3 = ' paramC3=Integer ';'))
| (('newParamA4 = ' paramA4=Integer ';') & ('newParamB4 = ' paramB4=Integer ';') & ('newParamC4 = ' paramC4=Integer ';'))

Answer 1

我认为您真正想要的是一种验证，以确保在语义级别而不是在句法级别上给出至少一个参数。这将大大简化您的语法，例如您可以使用

(newParamA = ParamA)? & (newParamB = ParamB)? & (newParamC = ParamC)?

（括号。为清楚起见添加）

另请注意，避免关键字中的空格通常是个好主意。你应该更喜欢'paramA' '=' 而不是'paramA ='。这将大大改善词法分析器/解析器中的错误处理。

Answer 2

你想做的是这样的：

你想要一个简单的语法（正如 Sebastian 所描述的那样）：

(newParamA = ParamA)? & (newParamB = ParamB)? & (newParamC = ParamC)?

为确保至少需要一个参数，您可以编写自己的验证器，如下所示：

class MyDSLValidator extends AbstractMyDSLValidator {
    @Check
    def void atLeastOneParameter(Component component) {
        if (component.newParamA == null && component.newParamB == null && component.newParamC == null) {
            error('requires at least one parameter definition', MyDSLPackage.Literals.COMPONENT__PARAMA);
        }
    }
}