Style/CaseLikeIf false positive

[noraj]

Related issues

#8541, #7736 (comment), and mostly #8508

Expected behavior

No offense when there is a something else than a comparison with a string/int, etc.
This is the same as #8508 where there was a comparison with a class but here it's is_a? method rather than the equal operator.

Actual behavior

False positive when using a method, eg. is_a? with a class.

if arg_feeds[0].is_a?(String)
 #
elsif arg_feeds[0].is_a?(Array)
 #
else
 #
end

Steps to reproduce the problem

$ git clone https://gitlab.com/noraj/nvd_api.git && cd nvd_api
$ gem install bundle
$ ./bin/nvd_feed_api_setup
$ rake install
$ rubocop

RuboCop version

$ bundle exec rubocop -V
0.92.0 (using Parser 2.7.1.5, rubocop-ast 0.7.1, running on ruby 2.7.1 x86_64-linux)

[koic]

case statement uses === so it does not look like a false positive to is_a?.
https://ruby-doc.org/core-2.7.0/Module.html#method-i-3D-3D-3D

[noraj]

is_a? always return true or false.

irb(main):002:0> 1.is_a?(Numeric)
=> true
irb(main):003:0> 1.is_a?(Integer)
=> true

So if you have:

case var
when is_a?(Numeric)
 # command
when is_a?(Integer)
  # command
end

And you pass var = 1, both when statement will in fact be when true, I don't know if both will be executed or if a case-witch always execute only one statement.

I don't exactly understand why but when I switch from if/elsif to switch-case it broke all my unit test when it was using is_a?.

[noraj]

Take an example like here https://gitlab.com/noraj/nvd_api/-/blob/master/lib/nvd_feed_api.rb#L94-100

and change

if arg_feeds[0].is_a?(String)
elsif arg_feeds[0].is_a?(Array)

into

case arg_feeds[0]
when is_a?(String)
whenis_a?(Array)

And run bundle exec rake install before and after and you'll see before all is good and after nothing work.

[koic]

When auto-correction (rubocop --only Style/CaseLikeIf -A) is executed, it will be as follows.

diff --git a/lib/nvd_feed_api.rb b/lib/nvd_feed_api.rb
index 0c145f5..addbe2e 100644
--- a/lib/nvd_feed_api.rb
+++ b/lib/nvd_feed_api.rb
@@ -91,12 +91,13 @@ class NVDFeedScraper
     if arg_feeds.empty?
       return_value = @feeds
     elsif arg_feeds.length == 1
-      if arg_feeds[0].is_a?(String)
+      case arg_feeds[0]
+      when String
         @feeds.each do |feed| # feed is an object
           return_value = feed if arg_feeds.include?(feed.name)
         end
         # if nothing found return nil
-      elsif arg_feeds[0].is_a?(Array)
+      when Array
         raise 'one of the provided arguments is not a String' unless arg_feeds[0].all? { |x| x.is_a?(String) }

         # Sorting CVE can allow us to parse quicker
@@ -165,7 +166,8 @@ class NVDFeedScraper
     raise 'no argument provided, 1 or more expected' if arg_cve.empty?

     if arg_cve.length == 1
-      if arg_cve[0].is_a?(String)
+      case arg_cve[0]
+      when String
         raise 'bad CVE name' unless /^CVE-[0-9]{4}-[0-9]{4,}$/i.match?(arg_cve[0])

         year = /^CVE-([0-9]{4})-[0-9]{4,}$/i.match(arg_cve[0]).captures[0]
@@ -186,7 +188,7 @@ class NVDFeedScraper
         f = feeds(matched_feed)
         f.json_pull
         return_value = f.cve(arg_cve[0])
-      elsif arg_cve[0].is_a?(Array)
+      when Array
(snip)

So, the expected syntax is:

case var
when Numeric
 # command
when Integer
  # command
end

How about it?
(Maybe it can be improved to the warning message.)

[fatkodima]

Correction:
The autocorrected code will be

case var
when Numeric
 # command
when Integer
  # command
end

case-when executes the body of the first (and only one) truthy condition, like with if-elsif.
So, this is not a false positive.

[noraj]

So the idea is that arg_feeds[0].is_a?(Array) == true is equivalent to arg_feeds[0].class == Array so we can write when String in both cases. I applied with rubocop --only Style/CaseLikeIf -A and it doesn't break my code, thanks for the clarification.

[marcandre]

So the idea is that arg_feeds[0].is_a?(Array) == true is equivalent to arg_feeds[0].class == Array

is equivalent to Array === arg_feeds[0], and when Array is equivalent to Array ===