Do not register an offense for FormatParameterMismatch on variables

rrosenblum · rrosenblum · commit 12929bc3f967 · 2015-09-10T23:07:28.000-04:00
diff --git a/CHANGELOG.md b/CHANGELOG.md
@@ -13,6 +13,7 @@
 * [#2218](https://github.com/bbatsov/rubocop/issues/2218): Fix loading config error when safe yaml is only partially loaded. ([@maxjacobson][])
 * [#2161](https://github.com/bbatsov/rubocop/issues/2161): Allow an explicit receiver (except `Kernel`) in `Style/SignalException`. ([@lumeet][])
 * [#2237](https://github.com/bbatsov/rubocop/pull/2237): Allow `Lint/FormatParameterMismatch` to be called using `Kernel.format` and `Kernel.sprintf`. ([@rrosenblum][])
+* [#2234](https://github.com/bbatsov/rubocop/issues/2234): Do not register an offense for `Lint/FormatParameterMismatch` when the format string is a variable. ([@rrosenblum][])
 
 ## 0.34.0 (05/09/2015)
 
diff --git a/lib/rubocop/cop/lint/format_parameter_mismatch.rb b/lib/rubocop/cop/lint/format_parameter_mismatch.rb
@@ -30,6 +30,8 @@ def on_send(node)
         private
 
         def offending_node?(node)
+          return false unless called_on_string?(node)
+
           if sprintf?(node) || format?(node) || percent?(node)
             if named_mode?(node)
               false
@@ -42,6 +44,15 @@ def offending_node?(node)
           end
         end
 
+        def called_on_string?(node)
+          receiver_node, _method, format_string, = *node
+          if receiver_node.nil? || receiver_node.const_type?
+            format_string && format_string.str_type?
+          else
+            receiver_node.str_type?
+          end
+        end
+
         def named_mode?(node)
           receiver_node, _method_name, *args = *node
 
diff --git a/spec/rubocop/cop/lint/format_parameter_mismatch_spec.rb b/spec/rubocop/cop/lint/format_parameter_mismatch_spec.rb
@@ -5,6 +5,35 @@
 describe RuboCop::Cop::Lint::FormatParameterMismatch do
   subject(:cop) { described_class.new }
 
+  shared_examples 'variables' do |variable|
+    it 'does not register an offense for % called on a variable' do
+      inspect_source(cop, ["#{variable} = '%s'",
+                           "#{variable} % [foo]"])
+
+      expect(cop.messages).to be_empty
+    end
+
+    it 'does not register an offense for format called on a variable' do
+      inspect_source(cop, ["#{variable} = '%s'",
+                           "format(#{variable}, foo)"])
+
+      expect(cop.messages).to be_empty
+    end
+
+    it 'does not register an offense for format called on a variable' do
+      inspect_source(cop, ["#{variable} = '%s'",
+                           "sprintf(#{variable}, foo)"])
+
+      expect(cop.messages).to be_empty
+    end
+  end
+
+  it_behaves_like 'variables', 'CONST'
+  it_behaves_like 'variables', 'var'
+  it_behaves_like 'variables', '@var'
+  it_behaves_like 'variables', '@@var'
+  it_behaves_like 'variables', '$var'
+
   it 'registers an offense when calling Kernel.format ' \
      'and the fields do not match' do
     inspect_source(cop, 'Kernel.format("%s %s", 1)')
