From: David Unric <dunric29a@...>
Date: 2010-11-10T03:55:20+09:00
Subject: Re: Analyzer for errors in code ?

Robert Klemme wrote in post #960353:
> On Tue, Nov 9, 2010 at 5:00 PM, David Unric <dunric29a@gmail.com> wrote:
>> I would like to check a source code for common errors like use of unused
>> variables. The "ruby -c" only checks for syntax errors.
>>
>> Is there some tool for Ruby like pylint or pyflakes for Python ?
>> It has to _not_ run the code to do analysis. At least mistypos of method
>> and variable names would be enough.
>
> Unused local variables would be doable, but detection of typos of
> variable and method names is almost impossible without running the
> code.  The reason is that the set of valid method names may change at
> will during the course of a programs execution.  Plus, with
> #method_missing you can properly handle methods that are never ever
> defined.  The usability of such a tool might be very limited.
>
> Having said that you may want to try ruby's command line option -w.
>
> See also
> 
http://stackoverflow.com/questions/1805146/where-can-i-find-an-actively-developed-lint-tool-for-ruby
>
> Kind regards
>
> robert

I understand it is difficult because the dynamic nature of Ruby, but 
Python is in the same league and PyLint tool does "wonders" at detecting 
possible errors without code execution 
(http://www.logilab.org/card/pylintfeatures). It uses Abstract Syntax 
Tree parser and Ruby also has its own AST so it would be possible.

But I asked for something more simplistic, like revealing trivial errors 
like mentioned variable name typo.

See the following example:

Running with 'ruby -c' returns 'Syntax OK'.
Running with 'ruby -w' also doesn't warn about undefined 'mymsg' 
variable.

Only when the condition becomes true, execution aborts with `<main>': 
undefined local variable or method `mymsg' for main:Object (NameError)

if __FILE__ == $0
    my_msg = 'Hello'
    if ARGV[0] == 'doit'
        puts mymsg
    else
        puts 'Nope'
    end
end


How to avoid such pitfalls with writing more complex ruby code ? I can't 
believe there is no other way how to verify the code without 'waiting 
for exception at proper conditions' and then solve the bug.

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