[jira] [Closed] (JEXL-346) namespace function syntax leads to strange error for "common case" of ternary operator

["Henri Biestro (Jira)" <ji...@apache.org>]

     [ https://issues.apache.org/jira/browse/JEXL-346?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]

Henri Biestro closed JEXL-346.
------------------------------

> namespace function syntax leads to strange error for "common case" of ternary operator
> --------------------------------------------------------------------------------------
>
>                 Key: JEXL-346
>                 URL: https://issues.apache.org/jira/browse/JEXL-346
>             Project: Commons JEXL
>          Issue Type: Improvement
>    Affects Versions: 3.1
>            Reporter: David Costanzo
>            Assignee: Henri Biestro
>            Priority: Minor
>             Fix For: 3.2
>
>
> The "namespace function call" syntax has precedence over the "ternary operator" syntax, which leads to a strange error message for something that should intuitively work: 
> {code:java}
> x != null ? x : myfunc(y){code}
> Here, {{x}} and {{y}} are String objects and {{myfunc}} is a registered library function that is implemented in JEXL. In JEXL 3.1 this results in the error:
> {{myfile.jexl:211@1:25 parsing error in ''}}
> With the source code that's currently in github the error is a little better but still confusing:
> {{myfile.jexl:211@1:25 parsing error in ')'}}
> The error is because the expression is parsed as:
> {code:java}
> x != null ? (x:myfunc(y)){code}
> That is, the function name is taken to be {{x:myfunc}} despite the spaces and despite the fact that my application doesn't support namespaces.  This swallows up the colon, leaving the ternary operation incomplete when the end of the expression is reached.
> This function name is parsed as {{x:myfunc}} because of the first rule in FunctionCallLookahead in Parser.jjt.
> {code:java}
> void FunctionCallLookahead() #void : {}
> {
> LOOKAHEAD(4) <IDENTIFIER> <COLON> <IDENTIFIER> <LPAREN>
> |
> LOOKAHEAD(2) <IDENTIFIER> <LPAREN>
> |
> LOOKAHEAD(2) <REGISTER> <LPAREN>
> }{code}
> There are many ways to adjust the expression so that it parses as intended. The hard part is for the JEXL programmer to understand what's going on.
> I'd prefer for my application to treat the above JEXL expression as a ternary operation, perhaps by requiring that there is no whitespace between the namespace and the function name, or perhaps by disabling the "namespace function" parsing as a JexlFeature. Failing that, it'd be nice to have a somewhat clearer error message like "unable to locate the : in ternary operation".  With a stronger error message, a web search might explain the problem.
> h4. Impact
> This was encountered by one of our application's JEXL programmers. She was mystified and reported it to a member of the application's development team. After an hour of trial-and-error, he worked out a solution by extra parens and then reported this to me. After several hour of stepping through the JEXL internals, I finally figured out what was going on. That JavaCC-generated code takes some patience!
> The JEXL programmer is not a purist and doesn't care that she had to add some extra parens to get it to work.  Mostly, I would like to save my other JEXL programmers from a similar frustration and associated support cost.
>  



--
This message was sent by Atlassian Jira
(v8.3.4#803005)