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From "Knut Anders Hatlen (JIRA)" <j...@apache.org>
Subject [jira] Commented: (DERBY-4879) Lookahead warning from ij.jj
Date Sun, 31 Oct 2010 11:35:23 GMT

    [ https://issues.apache.org/jira/browse/DERBY-4879?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12926695#action_12926695
] 

Knut Anders Hatlen commented on DERBY-4879:
-------------------------------------------

If we do as the warning says, and set FORCE_LA_CHECK to true, we get even more warnings, since
it then warns us about everything that would have been a problem if LOOKAHEAD had been 1 (it
is 2). But I think it should be fairly straightforward to massage the grammar into a shape
in which it's safe to lower the lookahead to 1.

Getting rid of the warning isn't just about reducing noise in the build. If we'd had lookahead
adequacy checking, which the warning says was disabled, we would for example have been warned
about mistakes like this one in ij.jj -> ijStatement(), where FirstStatement appears twice
in the grammar:

|       r=ExecuteStatement()    
|       r=FirstStatement()      
|       r=FirstStatement()      
|       r=JBMSPreparedStatementExec()   

> Lookahead warning from ij.jj
> ----------------------------
>
>                 Key: DERBY-4879
>                 URL: https://issues.apache.org/jira/browse/DERBY-4879
>             Project: Derby
>          Issue Type: Improvement
>          Components: Tools
>    Affects Versions: 10.7.1.0
>            Reporter: Knut Anders Hatlen
>            Assignee: Knut Anders Hatlen
>            Priority: Minor
>
> When building with "ant -q", I see this warning when JavaCC processes ij.jj:
>      [java] Warning: Lookahead adequacy checking not being performed since option LOOKAHEAD
is more than 1.  Set option FORCE_LA_CHECK to true to force checking.

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