[Fix rubocop#4740] Make Lint/RescueWithoutErrorClass aware of modif…

…ier form `rescue`

The cop would miss cases of `rescue` without error class when used in
modifier form.

This change fixes that.

CHANGELOG.md

@@ -2,6 +2,10 @@
 
 ## master (unreleased)
 
+### Bug fixes
+
+* [#4740](https://github.com/bbatsov/rubocop/issues/4740): Make `Lint/RescueWithoutErrorClass` aware of modifier form `rescue`. ([@drenmi][])
+
 ## 0.50.0 (2017-09-14)
 
 ### New features

lib/rubocop/cop/lint/rescue_without_error_class.rb

@@ -20,11 +20,19 @@ module Lint
       #   rescue
       #     bar
       #   end
+      #
+      # @example
+      #
+      #   # good
+      #   foo rescue BarError; "baz"
+      #
+      #   # bad
+      #   foo rescue "baz"
       class RescueWithoutErrorClass < Cop
         MSG = 'Avoid rescuing without specifying an error class.'.freeze
 
         def_node_matcher :rescue_without_error_class?, <<-PATTERN
-          (resbody nil ...)
+          (resbody nil _ !(const ...))
         PATTERN
 
         def on_resbody(node)

manual/cops_lint.md

@@ -1592,6 +1592,13 @@ rescue
   bar
 end
 ```
+```ruby
+# good
+foo rescue BarError; "baz"
+
+# bad
+foo rescue "baz"
+```
 
 ### References
 

spec/rubocop/cop/lint/rescue_without_error_class_spec.rb

@@ -15,6 +15,17 @@
       RUBY
     end
 
+    it 'registers an offense without an error class, assigning to variable' do
+      expect_offense(<<-RUBY.strip_indent)
+        begin
+          foo
+        rescue => e
+        ^^^^^^ Avoid rescuing without specifying an error class.
+          bar
+        end
+      RUBY
+    end
+
     it 'does not register an offense with an error class' do
       expect_no_offenses(<<-RUBY.strip_indent)
         begin
@@ -24,6 +35,17 @@
         end
       RUBY
     end
+
+    it 'does not register an offense with an error class, ' \
+       'assigning to variable' do
+      expect_no_offenses(<<-RUBY.strip_indent)
+        begin
+          foo
+        rescue BarError => e
+          bar
+        end
+      RUBY
+    end
   end
 
   context 'when rescuing in a method definition' do
@@ -38,6 +60,17 @@ def baz
       RUBY
     end
 
+    it 'registers an offense without an error class, assigning to variable' do
+      expect_offense(<<-RUBY.strip_indent)
+        def baz
+          foo
+        rescue => e
+        ^^^^^^ Avoid rescuing without specifying an error class.
+          bar
+        end
+      RUBY
+    end
+
     it 'does not register an offense with an error class' do
       expect_no_offenses(<<-RUBY.strip_indent)
         def baz
@@ -47,5 +80,31 @@ def baz
         end
       RUBY
     end
+
+    it 'does not register an offense with an error class, ' \
+       'assigning to variable' do
+      expect_no_offenses(<<-RUBY.strip_indent)
+        def baz
+          foo
+        rescue BarError => e
+          bar
+        end
+      RUBY
+    end
+  end
+
+  context 'when rescuing as a modifier' do
+    it 'registers an offense with something besides an an error class' do
+      expect_offense(<<-RUBY.strip_indent)
+        foo rescue 42
+            ^^^^^^ Avoid rescuing without specifying an error class.
+      RUBY
+    end
+
+    it 'does not register an offense with an error class' do
+      expect_no_offenses(<<-RUBY.strip_indent)
+        foo rescue BarError
+      RUBY
+    end
   end
 end