[Fix rubocop#8124] Fix a false positive for `Lint/FormatParameterMism…

…atch`

Fixes rubocop#8124.

This PR fixes a false positive for `Lint/FormatParameterMismatch`
using named parameters with escaped `%`.

CHANGELOG.md

@@ -10,6 +10,7 @@
 ### Bug fixes
 
 * [#8115](https://github.com/rubocop-hq/rubocop/issues/8115): Fix false negative for `Lint::FormatParameterMismatch` when argument contains formatting. ([@andrykonchin][])
+* [#8124](https://github.com/rubocop-hq/rubocop/issues/8124): Fix a false positive for `Lint/FormatParameterMismatch` when using named parameters with escaped `%`. ([@koic][])
 
 ## 0.85.1 (2020-06-07)
 

lib/rubocop/cop/utils/format_string.rb

@@ -120,7 +120,7 @@ def parse
         end
 
         def mixed_formats?
-          formats = format_sequences.map do |seq|
+          formats = format_sequences.reject(&:percent?).map do |seq|
             if seq.name
               :named
             elsif seq.max_digit_dollar_num

spec/rubocop/cop/lint/format_parameter_mismatch_spec.rb

@@ -222,6 +222,10 @@
     expect_no_offenses('"foo %{bar} baz" % { bar: 42 }')
   end
 
+  it 'does not register an offense when using named parameters with escaped `%`' do
+    expect_no_offenses('format("%%%<hex>02X", hex: 10)')
+  end
+
   it 'identifies correctly digits for spacing in format' do
     expect_no_offenses('"duration: %10.fms" % 42')
   end

spec/rubocop/cop/utils/format_string_spec.rb

@@ -97,6 +97,11 @@ def format_sequences(string)
       expect(fs.valid?).to eq true
     end
 
+    it 'returns true when there are only named with escaped `%` formats' do
+      fs = described_class.new('%%%{foo}d')
+      expect(fs.valid?).to eq true
+    end
+
     it 'returns false when there are unnumbered and numbered formats' do
       fs = described_class.new('%s %1$d')
       expect(fs.valid?).to eq false