[antlr-interest] gUnit freezing when choking on invalid input

[Thomas Vial]

Wow that was quick :-)
I'll give it a try and post the results here. Thanks a lot for your
reactivity!

What I love with gUnit is the clean syntax: input --> expected result,
especially with ASTs. It's just what unit testing is for: testing code of
course AND documenting it with examples.

Thomas

PS : hope you don't mind my replying to the mailing list, so that everybody
can try too


On Sat, Jun 28, 2008 at 5:17 AM, Leon Su <leonsu at mac.com> wrote:

> Hi, I've  updated the gunit-1.0.1.jar on the wiki download page.
> Please let me know if there's any other issue.
> Thanks.
>
> Leon
>
> On Jun 27, 2008, at 2:55 AM, Thomas Vial wrote:
>
>  Hi all,
>>
>>
>> I am experiencing an annoying issue with gUnit freezing when parsing
>> of test input fails. Here is my test case, with ANTLR v3.0 and gUnit
>> 1.0.1.
>>
>> ----------[Expr.g]----------------------
>> grammar Expr;
>>
>> options {
>>        output=AST;
>> }
>>
>> tokens {
>>        PROG;
>> }
>>
>> @header {
>> package com.expr;
>> }
>>
>> @lexer::header {
>> package com.expr;
>> }
>>
>> program:
>>        (expr ';')*                                                     ->
>> ^(PROG expr*)
>> ;
>>
>> // The following rules are deliberately incorrect
>> // Should be expr1 ('+' expr1)* and expr2 ('*' expr2)*
>> // for a real expression parser :-)
>> expr:
>>        expr1 '+' expr1                                         -> ^('+'
>> expr1 expr1)
>> ;
>>
>> expr1:
>>        expr2 '*' expr2                                         -> ^('*'
>> expr2 expr2)
>> ;
>>
>> expr2:
>>        INTEGER                                                         ->
>> INTEGER
>> |       '(' expr ')'                                            -> expr
>> ;
>>
>>
>> INTEGER:
>>        ('0'..'9')+
>> ;
>> -------------------------------------------
>>
>>
>> ----------[Expr.testsuite]-----------
>> gunit Expr;
>>
>> @header {
>> package com.expr;
>> }
>>
>> expr:
>>        "1+2"                           -> (+ 1 2)
>> -------------------------------------------
>>
>>
>> With this input, gUnit freezes indefinitely. When feeding the parser
>> directly, I get "line 0:-1 mismatched input '<EOF>' expecting '*'",
>> which is correct wrt the badly written grammar (see comments above
>> rules expr and expr1). However gUnit does not see the error and gets
>> stuck. I have noticed, by looking at the JUnit code that gUnit
>> generates with the -o option (the JUnit version of the test freezes,
>> too), that it internally uses threads to pass input to the parser and
>> retrieve its output. The issue might have something to do some thread
>> starving on a reader.
>>
>> This is annoying when run from the command line: the whole test suite
>> freezes, so you have to execute the parser against every test by hand
>> to track the actual error. This also makes gUnit unusable in
>> continuous integration scenarii.
>>
>> Another oddity is that gUnit behaves as expected, i.e. reporting the
>> error, when the AST construction is done inline:
>> -------------------------------------------
>> expr:
>>        expr1 '+'^ expr1
>> ;
>>
>> expr1:
>>        expr2 '*'^ expr2
>> ;
>> -------------------------------------------
>>
>> Shouldn't both construction methods be equivalent?
>>
>>
>>
>>
>> Any insights on these issues?
>>
>> Thanks!
>>
>> Thomas
>>
>
>


-- 
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Thomas VIAL
OCTO Technology
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