Fix false negative against typical string formatting examples

lib/rubocop/cop/style/format_string.rb

@@ -31,13 +31,13 @@ def offending_node?(node)
         end
 
         def format_method?(name, node)
-          receiver, method_name, args = *node
+          receiver, method_name, *args = *node
 
           # commands have no explicit receiver
           return false unless !receiver && method_name == name
 
           # we do an argument count check to reduce false positives
-          args && args.children.size >= 2
+          args.size >= 2
         end
 
         def format?(node)

spec/rubocop/cop/style/format_string_spec.rb

@@ -54,6 +54,14 @@
       expect(cop.messages)
         .to eq(['Favor `sprintf` over `format`.'])
     end
+
+    it 'registers an offense for format with 2 arguments' do
+      inspect_source(cop,
+                     ['format("%X", 123)'])
+      expect(cop.offenses.size).to eq(1)
+      expect(cop.messages)
+        .to eq(['Favor `sprintf` over `format`.'])
+    end
   end
 
   context 'when enforced style is format' do
@@ -106,6 +114,15 @@
       expect(cop.messages)
         .to eq(['Favor `format` over `sprintf`.'])
     end
+
+    it 'registers an offense for sprintf with 2 arguments' do
+      inspect_source(cop,
+                     ["sprintf('%020d', 123)"])
+      expect(cop.offenses.size).to eq(1)
+      expect(cop.messages)
+        .to eq(['Favor `format` over `sprintf`.'])
+    end
+
   end
 
   context 'when enforced style is percent' do
@@ -127,6 +144,15 @@
         .to eq(['Favor `String#%` over `sprintf`.'])
     end
 
+    it 'registers an offense for sprintf with 3 arguments' do
+      inspect_source(cop,
+                     ['format("%d %04x", 123, 123)'])
+      expect(cop.offenses.size).to eq(1)
+      expect(cop.messages)
+        .to eq(['Favor `String#%` over `format`.'])
+    end
+
+
     it 'accepts format with 1 argument' do
       inspect_source(cop,
                      ['format :xml'])