Fix infinite loop for Style/IfUnlessModifier

Closes rubocop#8006 & rubocop#8025

CHANGELOG.md

@@ -19,6 +19,7 @@
 * [#8035](https://github.com/rubocop-hq/rubocop/issues/8035): Fix a false positive for `Lint/DeprecatedOpenSSLConstant` when using double quoted string argument. ([@koic][])
 * [#7971](https://github.com/rubocop-hq/rubocop/issues/7971): Fix an issue where `--disable-uncorrectable` would not update uncorrected code with `rubocop:todo`. ([@rrosenblum][])
 * [#8035](https://github.com/rubocop-hq/rubocop/issues/8035): Fix a false positive for `Lint/DeprecatedOpenSSLConstant` when argument is a variable, method, or consntant. ([@koic][])
+* [#8006](https://github.com/rubocop-hq/rubocop/issues/8006): Fix infinite loop for `Style/IfUnlessModifier`. ([@tejasbubane][])
 
 ### Changes
 

lib/rubocop/cop/mixin/statement_modifier.rb

@@ -41,9 +41,10 @@ def modifier_fits_on_single_line?(node)
 
       def length_in_modifier_form(node, cond)
         keyword = node.loc.keyword
-        indentation = keyword.source_line[/^\s*/]
-        line_length("#{indentation}#{node.body.source} #{keyword.source} " \
-                    "#{cond.source}")
+        line_before_condition, = keyword.source_line.split(keyword.source)
+        condition_source = "#{node.body.source} #{keyword.source} #{cond.source}"
+        source = line_before_condition + condition_source
+        line_length(source)
       end
 
       def max_line_length

spec/rubocop/cop/style/if_unless_modifier_spec.rb

@@ -421,6 +421,26 @@ def f
     expect(corrected).to eq "a = (1 if b)\n"
   end
 
+  context 'when the code before condition pushes inline length over limit' do
+    let(:line_length_config) { { 'Enabled' => true, 'Max' => 100 } }
+
+    it 'does not result in infinite loop with assignment' do
+      expect_no_offenses(<<~RUBY)
+        timespan = if params[:timespan] && POSSIBLE_TIMESPANS.include?(params[:timespan])
+                     params[:timespan].to_sym
+                   end
+      RUBY
+    end
+
+    it 'does not result in infinite loop with any other statement' do
+      expect_no_offenses(<<~RUBY)
+        puts 'ab'; if params[:timespan] && POSSIBLE_TIMESPANS.include?(params[:timespan])
+                     params[:timespan].to_sym
+                   end
+      RUBY
+    end
+  end
+
   it "doesn't break if-end when used as RHS of instance var assignment" do
     corrected = autocorrect_source(<<~RUBY)
       @a = if b