xtext nested {} Decision 可以使用多个替代项来匹配输入，例如“'}'”

Question

我是 xtext (antlr) 的新手，不明白为什么 IconType '}' 和 WindowType '}' 之间有歧义。
我得到

warning(200): ../org.simsulla.tools.ui.gui/src-gen/org/simsulla/tools/ui/gui/parser/antlr/internal/InternalGui.g:137:1: Decision can match input such as "'windowType'" using multiple alternatives: 1, 2
As a result, alternative(s) 2 were disabled for that input
warning(200): ../org.simsulla.tools.ui.gui.ui/src-gen/org/simsulla/tools/ui/gui/ui/contentassist/antlr/internal/InternalGui.g:117:38: Decision can match input such as "'windowType' '=' '{' 'name' '=' RULE_ID 'iconType' '=' '{' 'name' '=' RULE_ID 'spriteType' '=' RULE_STRING 'Orientation' '=' RULE_STRING '}' '}'" using multiple alternatives: 1, 2
As a result, alternative(s) 2 were disabled for that input

这是我的语法

Ui:
    guiTypes+=GuiTypes+;

GuiTypes:
    windowType+=WindowType+
;

WindowType:
    'windowType' '=' '{'
        'name' '=' name=STRING
        iconType+=IconType* 
    '}'
;

IconType:
    'iconType' '=' '{'
        'name' '=' name=STRING
        'spriteType' '=' spriteType=STRING
        'Orientation' '=' Orientation=STRING
    '}'
;

Answer 1

语法片段有多种重复方式WindowType:

从 Ui 派生到 GuiTypes 到多个 WindowType 实例，或
从 Ui 派生到多个 GuiTypes 实例，其中每个实例派生到 WindowType，或
以上任意组合。

所以一个给定的输入对应于多个不同的解析树。因此语法有歧义。

xtext nested {} Decision 可以使用多个替代项来匹配输入，例如“'}'”

xtext nested {} Decision can match input such as "'}'" using multiple alternatives

nested

grammar

antlr3

xtext