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Bug 327051

Summary:	Wrong backtracking in case of keywords with common prefix
Product:	[Modeling] TMF	Reporter:	Dénes Harmath <thsoft>
Component:	Xtext	Assignee:	Project Inbox <tmf.xtext-inbox>
Status:	CLOSED WONTFIX	QA Contact:
Severity:	normal
Priority:	P3	CC:	henrik.lindberg, thsoft
Version:	1.0.1
Target Milestone:	---
Hardware:	Macintosh
OS:	Mac OS X - Carbon (unsup.)
Whiteboard:

Description Dénes Harmath

2010-10-05 19:47:50 EDT

Build Identifier: M20100909-0800

The lexer & parser even when backtracking can't handle the following case (keywords which share the same prefix):

Reproducible: Always

Steps to Reproduce:
Grammar:

grammar org.xtext.example.mydsl.MyDsl with org.eclipse.xtext.common.Terminals

generate myDsl "http://www.xtext.org/example/mydsl/MyDsl"

Model: expressions+=Expression+;

Expression: Bar | Baz | Other;

Bar: {Bar} "\\bar";

Baz: {Baz} "\\baz";

Other hidden(): "\\" id=ID;

Generator options:

fragment = parser.antlr.ex.rt.AntlrGeneratorFragment {
options = {
backtrackLexer = true
backtrack = true
}
}

Input:

\b

Error:

no viable alternative at character '\'

Xtext version: 1.0.1.v201008251220

Comment 1 Henrik Lindberg

2010-11-29 09:45:06 EST

I am having problems with this as well - backtracking lexer and keywords "else" and "elsif" will report problems for the combination of "el" as in "hello" when used elsewhere. Removing the "elsif" from my grammar makes it work.

Comment 2 Sven Efftinge

2012-11-16 05:25:16 EST

I fear that we can't do much about it as it appears to be an Antlr problem.