[erlang-bugs] [erlang-patches] Compiler/linter bug breaking unused variable warnings

[Anthony Ramine]

Hello,

I've added a commit that fixes variable usage tracking when reporting the redefinition of a record field, e.g. X is not reported as unused in:

	t() -> X = 1, #r{a=foo,a=bar}.

Please refetch.

Regards,

-- 
Anthony Ramine

Le 23 juil. 2013 à 09:27, Anthony Ramine a écrit :

> Hello,
> 
> I've added a commit to the branch that fix the bug discovered with Paul Davis where used variables in try expressions aren't properly marked as unsafe.
> 
> Please refetch.
> 
> -- 
> Anthony Ramine
> 
> Le 1 juil. 2013 à 19:30, Anthony Ramine a écrit :
> 
>> Hi Fredrik,
>> 
>> I've amended the commit message and gave an example of a simpler expression triggering the bug, e.g.:
>> 
>> t(X, Y) ->
>> {A=X,A=Y}.
>> 
>> As for the vt_no_unused/1 call in expr_list/1, it is a mistake as Vt1 comes from the variable tables returned by expr/3 in the lists:foldl/3 call, which means it can't contain any old variable which was unused anyway.
>> 
>> Regards,
>> 
>> -- 
>> Anthony Ramine
>> 
>> Le 1 juil. 2013 à 11:23, Fredrik a écrit :
>> 
>>> On 06/06/2013 01:47 AM, Anthony Ramine wrote:
>>>> Hello,
>>>> 
>>>> When analyzing complex expressions (i.e. comprehensions, cases, tries, ifs and receives), erl_lint does not forget about old unused variables when returning the updated variable table. This causes a bug where old
>>>> unused variables are not recorded as such:
>>>> 
>>>> t(X, Y) ->
>>>> #r{a=[ K || K <- Y ],b=[ K || K <- Y ].
>>>> 
>>>> As erl_lint uses vtmerge_pat/2 to merge the results of the analysis of the two list comprehensions, X is marked as used and the warning is not emitted.
>>>> 
>>>> The function vtmerge_pat/2 is used instead of the similar vtmerge/2 which does not mark multiple occurrences of a variable as usage to handle cases like the following one:
>>>> 
>>>> t(X, Y) ->
>>>> #r{a=A=X,b=A=Y}.
>>>> 
>>>> Other simpler expressions like conses, tuples and external fun references does not correctly follow this behaviour.
>>>> 
>>>> This patch fixes both issues and makes erl_lint not return old unused variables in updated tables and makes all compound expressions use vtmerge_pat/2.
>>>> 
>>>> 	git fetch 
>>>> https://github.com/nox/otp.git
>>>> fix-erl_lint-variable-usage
>>>> 
>>>> 	
>>>> https://github.com/nox/otp/compare/erlang:maint...fix-erl_lint-variable-usage
>>>> 
>>>> 	
>>>> https://github.com/nox/otp/compare/erlang:maint...fix-erl_lint-variable-usage.patch
>>>> 
>>>> 
>>>> Regards,
>>>> 
>>>> 
>>> Hi Anthony,
>>> Your patch has been reviewed and the feedback was:
>>> 
>>> "
>>> Hi,
>>> 
>>> The first example of the commit messages lacks a '}' before the dot.
>>> 
>>> I'm not sure I understand exactly what the paragraph starting with "Other simpler expressions..." means. Could you clarify, please? (And substitute "do" for "does"...)
>>> 
>>> I noticed that if the call to vt_no_unused() in the last line of expr_list/3 is removed the test suite still passes; there is no case where the call actually removes anything. Would it be possible to include a test that covers this particular call?
>>> 
>>> Best regards,
>>> 
>>> "
>>> 
>>> -- 
>>> 
>>> BR Fredrik Gustafsson
>>> Erlang OTP Team
>>> 
>> 
>