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Suppress Warnings
15th, Sep. 2019
大阪Ruby会議02
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pp self
● Masataka “Pocke” Kuwabara
● I’m from https://ruby-jp.github.io!
● Works for Bit Journey, Inc. / Kibela
● https://github.com/pocke
● https://twitter.com/p_ck_
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Recently we released Kibela Web API
https://prtimes.jp/main/html/rd/p/000000008.000024220.html
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Goal of this talk
● You can:
○ Find bugs with warnings.
○ Reduce warnings from your applications.
○ Create patches to OSS to suppress warnings.
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Introduce
Warning
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What is the warning?
● Ruby warns code, if
○ It may have a bug.
○ It is deprecated.
● For example:
○ Useless variable: x = 1; p y
○ Deprecated method: File.exists?
■ Use File.exist? instead.
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Warning levels
● Ruby has 3 levels for warning.
● Level 0: All warnings are disabled.
● Level 1: Only important warnings are enabled
(default).
● Level 2: All warnings are enabled.
○ Almost warnings are enabled only with Level 2.
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How to enable all warnings
● `-w` option enables all warnings.
○ The level 2
● $ ruby -e 42
○ Print nothing
● $ ruby -w -e 42
○ -e:1: warning: possibly useless use of a
literal in void context
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Enable warnings without CLI option
● We can also use RUBYOPT environment
variable.
● RUBYOPT is parsed as Ruby’s command line
option.
● RUBYOPT=-w bin/rails s
● $ echo ‘export RUBYOPT=”-w”’ >>
~/.bashrc
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What can we do
with warning?
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With warning, we can:
● We can find bugs with warning.
● We can contribute to OSS easier.
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Find bugs
● Ruby warns possible bug code.
● If you solve a warning, a bug may be solved.
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Contribute to OSS easier
● Warning is easy to fix, in many cases.
● Because
○ The goal is clear.
○ The patch will be small.
● But some warnings is difficult to fix. e.g.
○ Uninitialized instance variable
○ The code has bug(s).
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Why should we
fix warnings?
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Why should we fix warnings?
● We can find bugs with warnings.
● But if application has too many warnings, it is
too difficult.
● Similar with “Broken Windows Theory”.
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Warning
examples
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Warnings examples
● Let’s look warning with real pull requests.
○ Warning meaning.
○ How to fix warning.
○ What problems is found by the warning.
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Deprecated
method
cookpad/rrrspec#76
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Deprecated method
● File.exists?(path)
○ File.exists? is a deprecated name, use File.exist? instead
● Dir.exists?(path)
○ Dir.exists? is a deprecated name, use Dir.exist? instead
Let’s look the pull request!
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●
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Part of the patch
- unless Dir.exists?(packaging_dir)
+ unless Dir.exist?(packaging_dir)
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Overview
● File.exists? and Dir.exists? are
deprecated.
● It should be replaced with File.exist?.
● It does not change any behavior.
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It is one of the easiest warning!
● Good for first step of pull request!
● Because
○ Fixing approach is obvious.
○ It does not change any behavior.
● But it has only small impact.
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Other deprecated methods
● Kernel.#open for URI. (In Ruby 2.7.0-dev)
○ Use URI.open.
■ File.open, IO.open, and IO.popen are also avairable.
● URI.escape
○ Use ERB::Util.#url_encode, CGI.escape, or
URI.encode_www_form_component
○ It depends on the requirement.
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Method
redefined
whitequark/parser#378
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Method Redefined
● def foo; end # It is ignored
def foo; end
○ warning: method redefined; discarding old foo
Let’s look the pull request!
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Patch
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Overview
● Two methods ware accidently redefined in
minitest test file.
● A method has the same content, so I removed
it.
● But the other one has different method body.
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In another case
● If you really want to redefine method,
use remove_method.
○ remove_method :foo
def foo; end
○ e.g. https://github.com/ruby/irb/pull/18
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duplicated
when clause
thoughtbot/capybara-webkit#1068
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Duplicated when clause
● case x
when 1, 2, 1
end
○ duplicated `when' clause with line 2 is ignored
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Part of the patch
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Character
class has
duplicated
range
rouge-ruby/rouge#1197
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Character class has duplicated range
● /[aa]/
○ “a” is duplicated.
● /[\w_]/
○ “\w” includes “_”.
● /[\s\n]/
○ “\s” includes new line.
● /[*+-=]/
○ It means “*” and chars between “+” and “=”.
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Part of the patch (1)
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Part of the patch (2)
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Part of the patch (3)
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Overview
● Ruby also warns Regexp.
● In this pull request, I found and fixed bugs.
○ → It is useful warning to find bug.
● I often find the same warning from validations
in app/models/user.rb.
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instance
variable not
initialized
mizzy/specinfra#685
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Instance variable not initialized
● : def foo
@foo ||= something
end
● : def foo
@foo ? @foo : something
end
○ instance variable @foo not initialized
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Patch
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Other solutions
● Use ||=
○ @foo ||= something # It is OK
● Use defined?
○ defined?(@foo) ? @foo : something
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Conclusion
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Conclusion
● We looked warnings examples.
○ Meanings, how to fix warnings, etc
● With using warnings, we can
○ Find bugs.
○ Contribute to OSS easier.
● Let’s try enabling warnings in your application!
Thank you for listening!