rubocop: split configuration

 * remove spurious .rubocop.yml override files
 * split the configuration into an enforced and optional
 * run both configurations in jenkins (may result in some duplicate
   comments at different levels)
 * auto-correct the enforced configuration in the pre-commit hook
 * fix comments for Gemfile.d and the root dir; enforced configuration
   is only applied to that directory for now

Change-Id: I8da21073d74e19138b1b580d66c7aae6465348d4
Reviewed-on: https://gerrit.instructure.com/c/canvas-lms/+/273898
Reviewed-by: Simon Williams <[email protected]>
Tested-by: Service Cloud Jenkins <[email protected]>
QA-Review: Cody Cutrer <[email protected]>
Product-Review: Cody Cutrer <[email protected]>

.rubocop.common.yml

@@ -0,0 +1,71 @@
+require:
+  - rubocop-rails
+  - rubocop-rake
+  - rubocop-rspec
+  - rubocop-performance
+  # this odd relative path is so that rubocop works when run without "bundle
+  # exec", such as from most editors/IDEs.
+  - ./gems/rubocop-canvas/lib/rubocop_canvas
+  - outrigger/cops/migration/tagged
+
+AllCops:
+  TargetRubyVersion: 2.7
+
+Bundler/OrderedGems:
+  Enabled: false # this isn't good for us because of how we pin dependencies
+
+Gemspec/OrderedDependencies:
+  Enabled: false # this isn't good for us because of how we pin dependencies
+
+Layout/IndentationConsistency:
+  Exclude:
+    - "**/Gemfile.d/*" # we purposely indent dependent gems
+
+Lint/Debugger:
+  Severity: error
+
+Metrics:
+  Enabled: false # SnR is just too low to have this enabled
+
+Migration/Tagged:
+  Severity: error
+  AllowedTags:
+    - predeploy
+    - postdeploy
+    - cassandra
+    - dynamodb
+
+Naming/FileName:
+  Exclude:
+    - "**/Gemfile.d/~after.rb"
+
+Rails:
+  Exclude:
+    - "**/Gemfile.d/*" # Rails isn't loaded yet, so can't use their helpers in the Gemfile
+
+RSpec/EmptyExampleGroup:
+  Severity: error
+RSpec/ExampleLength:
+  Enabled: false
+RSpec/InstanceVariable:
+  Enabled: false
+RSpec/MultipleExpectations:
+  Enabled: false
+RSpec/NestedGroups:
+  Max: 5
+RSpec/RepeatedDescription:
+  Severity: error
+
+Specs/EnsureSpecExtension:
+  Exclude:
+    - spec/shared_examples/**/*
+Style/AsciiComments:
+  Enabled: false
+Style/Documentation:
+  Enabled: false
+Style/FrozenStringLiteralComment:
+  Severity: error
+Style/SpecialGlobalVars:
+  Enabled: false
+Style/StringLiterals:
+  Enabled: false

.rubocop.enforced.yml

@@ -0,0 +1,85 @@
+inherit_from: .rubocop.common.yml
+
+inherit_mode:
+  merge:
+    - Exclude
+
+AllCops:
+  NewCops: disable
+
+<%=
+
+# keys are cops you want to opt in for (nil being all cops)
+# values are an array of directories to opt in for (nil being all directories)
+OPT_IN = {
+  nil => %w[Gemfile.d].freeze
+}.freeze
+
+# this code generates a configuration that disables all cops for all files
+# _unless_ the cop is already configured in .rubocop.common.yml, OR the file
+# is in one of the OPT_IN directories. It does this by generating an Exclude
+# configuration for every cop (except already configured) that lists all
+# directories (except OPT_IN). AllCops does not support an Include, and
+# even if it did, inheritance to individual cops would not work correctly.
+
+def generate_excludes(opt_in_array)
+  return nil unless opt_in_array
+
+  excludes = []
+  dirs_to_exclude_siblings_of = []
+
+  opt_in_array.each do |dir|
+    components = dir.split("/")
+    (0...components.length).each do |i|
+      ancestor = components[0..i].join("/")
+      exclude = "#{ancestor}/*"
+      excludes << exclude unless excludes.include?(exclude) || opt_in_array.include?(ancestor)
+      dirs_to_exclude_siblings_of << ancestor unless dirs_to_exclude_siblings_of.include?(ancestor)
+    end
+  end
+
+  dirs_to_find_siblings_of = dirs_to_exclude_siblings_of.map do |dir|
+    File.dirname(dir)
+  end.uniq
+
+  dirs_to_find_siblings_of.each do |dir|
+    dirs = Dir["#{dir}/*"]
+      .select { |dir| File.directory?(dir) }
+      .map { |dir| dir.sub(%r{^\./}, "") }
+    dirs -= dirs_to_exclude_siblings_of
+    excludes.concat(dirs.map { |d| "#{d}/**/*" })
+  end
+
+  excludes.sort
+end
+
+resolved_excludes = OPT_IN.transform_values do |dirs|
+  next nil unless dirs
+
+  generate_excludes((Array(dirs) + OPT_IN[nil]).uniq)
+end
+
+require 'yaml'
+
+common_config = YAML.safe_load(File.read(".rubocop.common.yml"))
+common_config["require"].each { |f| require f }
+# already configured cops in common.yml are intended to apply to all files already
+already_configured_cops = common_config.keys.select { |k| k.include?("/") && !common_config[k]['Exclude'] }.to_set
+
+config = {}
+RuboCop::Cop::Registry.all.each do |cop|
+  next if cop.department == :Metrics
+  next if cop.cop_name == 'Lint/Syntax'
+  next if already_configured_cops.include?(cop.cop_name)
+
+  key = [cop.cop_name, cop.department.to_s, nil].find do |key|
+    resolved_excludes.key?(key)
+  end
+  excludes = resolved_excludes[key]
+  next if excludes.nil?
+
+  config[cop.cop_name] = { "Exclude" => excludes }
+end
+
+config.to_yaml.sub(/^---\n/, "")
+%>