[Fix #11652] Generate inherit_from correctly also with ERB

The problem with the existing algorithm, for generating the inherit_from line
in --auto-gen-config runs, was that we started by removing the inherit_from
(if present) and then inserted it later.

The things we must deal with in the algorithm are
* there could be a pre-existing inherit_from in .rubocop.yml, or not
* there could be a YAML doc start ---, or not
* there could be inheritance from one or multiple files

A more robust approach to the removing, generating, and re-inserting is to
assume that any pre-existing inherit_from directive is already in the right
place. By replacing it with a placeholder and later replacing the placeholder
with the new inheritance directive, we will get it right without much effort.

changelog/fix_auto_gen_config_with_erb.md

@@ -0,0 +1 @@
+* [#11652](https://github.com/rubocop/rubocop/issues/11652): Make `--auto-gen-config` generate `inherit_from` correctly inside ERB `if`. ([@jonas054][])

lib/rubocop/cli/command/auto_generate_config.rb

@@ -10,6 +10,7 @@ class AutoGenerateConfig < Base
 
         AUTO_GENERATED_FILE = '.rubocop_todo.yml'
         YAML_OPTIONAL_DOC_START = /\A---(\s+#|\s*\z)/.freeze
+        PLACEHOLDER = '###rubocop:inherit_here'
 
         PHASE_1 = 'Phase 1 of 2: run Layout/LineLength cop'
         PHASE_2 = 'Phase 2 of 2: run all cops'
@@ -125,15 +126,19 @@ def add_inheritance_from_auto_generated_file(config_file)
 
         def existing_configuration(config_file)
           File.read(config_file, encoding: Encoding::UTF_8)
-              .sub(/^inherit_from: *[^\n]+/, '')
-              .sub(/^inherit_from: *(\n *- *[^\n]+)+/, '')
+              .sub(/^inherit_from: *[^\n]+/, PLACEHOLDER)
+              .sub(/^inherit_from: *(\n *- *[^\n]+)+/, PLACEHOLDER)
         end
 
         def write_config_file(file_name, file_string, rubocop_yml_contents)
           lines = /\S/.match?(rubocop_yml_contents) ? rubocop_yml_contents.split("\n", -1) : []
-          doc_start_index = lines.index { |line| YAML_OPTIONAL_DOC_START.match?(line) } || -1
-          lines.insert(doc_start_index + 1, "inherit_from:#{file_string}\n")
-          File.write(file_name, lines.join("\n"))
+          unless rubocop_yml_contents&.include?(PLACEHOLDER)
+            doc_start_index = lines.index { |line| YAML_OPTIONAL_DOC_START.match?(line) } || -1
+            lines.insert(doc_start_index + 1, PLACEHOLDER)
+          end
+          File.write(file_name, lines.join("\n")
+                                     .sub(/#{PLACEHOLDER}\n*/o, "inherit_from:#{file_string}\n\n")
+                                     .sub(/\n\n+\Z/, "\n"))
         end
 
         def relative_path_to_todo_from_options_config

spec/rubocop/cli/auto_gen_config_spec.rb

@@ -300,50 +300,77 @@ def f
       end
     end
 
-    it 'overwrites an existing todo file' do
-      create_file('example1.rb', ['# frozen_string_literal: true',
-                                  '',
-                                  'x= 0 ',
-                                  '#' * 125,
-                                  'y ',
-                                  'puts x'])
-      create_file('.rubocop_todo.yml', <<~YAML)
-        Layout/LineLength:
-          Enabled: false
-      YAML
-      create_file('.rubocop.yml', ['inherit_from: .rubocop_todo.yml'])
-      expect(cli.run(['--auto-gen-config'])).to eq(0)
-      expect(File.readlines('.rubocop_todo.yml')[8..].map(&:chomp))
-        .to eq(['# Offense count: 1',
-                '# This cop supports safe autocorrection (--autocorrect).',
-                '# Configuration parameters: AllowForAlignment, ' \
-                'EnforcedStyleForExponentOperator.',
-                '# SupportedStylesForExponentOperator: space, no_space',
-                'Layout/SpaceAroundOperators:',
-                '  Exclude:',
-                "    - 'example1.rb'",
-                '',
-                '# Offense count: 2',
-                '# This cop supports safe autocorrection (--autocorrect).',
-                '# Configuration parameters: AllowInHeredoc.',
-                'Layout/TrailingWhitespace:',
-                '  Exclude:',
-                "    - 'example1.rb'",
-                '',
-                '# Offense count: 1',
-                '# This cop supports safe autocorrection (--autocorrect).',
-                '# Configuration parameters: AllowHeredoc, ' \
-                'AllowURI, URISchemes, IgnoreCopDirectives, ' \
-                'AllowedPatterns.',
-                '# URISchemes: http, https',
-                'Layout/LineLength:',
-                '  Max: 125'])
+    shared_examples 'overwrites todo file' do |description, code|
+      context "when .rubocop.yml contains #{description}" do
+        it 'overwrites an existing todo file' do
+          create_file('example1.rb', ['# frozen_string_literal: true',
+                                      '',
+                                      'x= 0 ',
+                                      '#' * 125,
+                                      'y ',
+                                      'puts x'])
+          create_file('.rubocop_todo.yml', <<~YAML)
+            Layout/LineLength:
+              Enabled: false
+          YAML
+          create_empty_file('other.yml')
+          create_file('.rubocop.yml', code)
+          expect(cli.run(['--auto-gen-config'])).to eq(0)
+          expect(File.readlines('.rubocop_todo.yml')[8..].map(&:chomp))
+            .to eq(['# Offense count: 1',
+                    '# This cop supports safe autocorrection (--autocorrect).',
+                    '# Configuration parameters: AllowForAlignment, ' \
+                    'EnforcedStyleForExponentOperator.',
+                    '# SupportedStylesForExponentOperator: space, no_space',
+                    'Layout/SpaceAroundOperators:',
+                    '  Exclude:',
+                    "    - 'example1.rb'",
+                    '',
+                    '# Offense count: 2',
+                    '# This cop supports safe autocorrection (--autocorrect).',
+                    '# Configuration parameters: AllowInHeredoc.',
+                    'Layout/TrailingWhitespace:',
+                    '  Exclude:',
+                    "    - 'example1.rb'",
+                    '',
+                    '# Offense count: 1',
+                    '# This cop supports safe autocorrection (--autocorrect).',
+                    '# Configuration parameters: AllowHeredoc, ' \
+                    'AllowURI, URISchemes, IgnoreCopDirectives, ' \
+                    'AllowedPatterns.',
+                    '# URISchemes: http, https',
+                    'Layout/LineLength:',
+                    '  Max: 125'])
+          expect(File.readlines('.rubocop.yml').map(&:chomp)).to eq(code)
+
+          # Create new CLI instance to avoid using cached configuration.
+          new_cli = RuboCop::CLI.new
+
+          expect(new_cli.run(['example1.rb'])).to eq(0)
+        end
+      end
+    end
 
-      # Create new CLI instance to avoid using cached configuration.
-      new_cli = RuboCop::CLI.new
+    include_examples 'overwrites todo file',
+                     'only the inherit_from line',
+                     ['inherit_from: .rubocop_todo.yml']
 
-      expect(new_cli.run(['example1.rb'])).to eq(0)
-    end
+    # Makes the shared example work the same with the conditional as without.
+    ENV['HZPKCEAXTFQLOWB'] = 'true'
+
+    include_examples 'overwrites todo file',
+                     'a single line inherit_from in an ERB conditional',
+                     ['<% if ENV["HZPKCEAXTFQLOWB"] %>',
+                      'inherit_from: .rubocop_todo.yml',
+                      '<% end %>']
+
+    include_examples 'overwrites todo file',
+                     'a multiline inherit_from in an ERB conditional',
+                     ['<% if ENV["HZPKCEAXTFQLOWB"] %>',
+                      'inherit_from:',
+                      '  - .rubocop_todo.yml',
+                      '  - other.yml',
+                      '<% end %>']
 
     it 'honors rubocop:disable comments' do
       create_file('example1.rb', ['#' * 121,