Require a space before first argument of a method call (#4265)

Ruby permits a method name to be followed immediately by a string
literal, with no space between them. This change updates the
SpaceBeforeFirstArg cop to register a violation for source code that
does this.

CHANGELOG.md

@@ -12,6 +12,7 @@
 
 ### Bug fixes
 
+* [#4265](https://github.com/bbatsov/rubocop/pull/4265): Require a space before first argument of a method call in `Style/SpaceBeforeFirstArg` cop. ([@cjlarose][])
 * [#4237](https://github.com/bbatsov/rubocop/pull/4237): Fix false positive in `Lint/AmbiguousBlockAssociation` cop for lambdas. ([@smakagon][])
 * [#4242](https://github.com/bbatsov/rubocop/issues/4242): Add `Capfile` to the list of known Ruby filenames. ([@bbatsov][])
 * [#4240](https://github.com/bbatsov/rubocop/issues/4240): Handle `||=` in `Rails/RelativeDateConstant`. ([@bbatsov][])
@@ -2745,3 +2746,4 @@
 [@dpostorivo]: https://github.com/dpostorivo
 [@konto-andrzeja]: https://github.com/konto-andrzeja
 [@sadovnik]: https://github.com/sadovnik
+[@cjlarose]: https://github.com/cjlarose

lib/rubocop/cop/style/space_before_first_arg.rb

@@ -14,10 +14,12 @@ module Style
       #   @bad
       #   something  x
       #   something   y, z
+      #   something'hello'
       #
       #   @good
       #   something x
       #   something y, z
+      #   something 'hello'
       #
       class SpaceBeforeFirstArg < Cop
         include PrecedingFollowingAlignment
@@ -34,7 +36,7 @@ def on_send(node)
           space = range_between(first_arg_with_space.begin_pos,
                                 first_arg.begin_pos)
 
-          add_offense(space, space) if space.length > 1
+          add_offense(space, space) if space.length != 1
         end
 
         def autocorrect(range)

manual/cops_style.md

@@ -5182,10 +5182,12 @@ config parameter is true.
 # bad
 something  x
 something   y, z
+something'hello'
 
 # good
 something x
 something y, z
+something 'hello'
 ```
 
 ### Important attributes

spec/rubocop/cop/style/space_before_first_arg_spec.rb

@@ -28,6 +28,28 @@
       END
     end
 
+    it 'registers an offense for method call with no spaces before the '\
+       'first arg' do
+      inspect_source(cop, <<-END.strip_indent)
+        something'hello'
+        a.something'hello world'
+      END
+      expect(cop.messages)
+        .to eq(['Put one space between the method name and the first ' \
+                'argument.'] * 2)
+    end
+
+    it 'auto-corrects missing space' do
+      new_source = autocorrect_source(cop, <<-END.strip_indent)
+        something'hello'
+        a.something'hello world'
+      END
+      expect(new_source).to eq(<<-END.strip_indent)
+        something 'hello'
+        a.something 'hello world'
+      END
+    end
+
     it 'accepts a method call with one space before the first arg' do
       inspect_source(cop, <<-END.strip_indent)
         something x