Add Rails/AddColumnIndex rubocop rule

The `column` method in ActiveRecord::ConnectionAdapters::TableDefinition
supports adding the `index:` option. The documentation says:

> Instantiates a new column for the table. See connection.add_column for
> available options.
>
> Additional options are:
>
> :index - Create an index for the column. Can be either true or an
> options hash.

So basically the `connection.add_column` method silently ignores the
`index:` option, and whenever we intended to create an index this way,
we didn't.

We're creating a new migration where we properly add the indexes that
weren't added when we intended to.

Thanks to the rubocop-rails team, who added this cop in version 2.11.0
and helped us notice this bug.

.rubocop.yml

@@ -208,6 +208,9 @@ Performance/Sum:
 Rails/ActiveRecordCallbacksOrder:
   Enabled: true
 
+Rails/AddColumnIndex:
+  Enabled: true
+
 Rails/CreateTableWithTimestamps:
   Enabled: true
   Exclude:

db/migrate/20151028145921_add_confidence_score_to_comments.rb

@@ -1,5 +1,5 @@
 class AddConfidenceScoreToComments < ActiveRecord::Migration[4.2]
   def change
-    add_column :comments, :confidence_score, :integer, index: true
+    add_column :comments, :confidence_score, :integer
   end
 end

db/migrate/20160411161531_add_genre_and_dob_to_users.rb

@@ -1,6 +1,6 @@
 class AddGenreAndDobToUsers < ActiveRecord::Migration[4.2]
   def change
-    add_column :users, :genre, :string, index: true, limit: 10
+    add_column :users, :genre, :string, limit: 10
-    add_column :users, :date_of_birth, :datetime, index: true
+    add_column :users, :date_of_birth, :datetime
   end
 end

db/migrate/20160610094658_desnormalize_ballot_line.rb

@@ -1,7 +1,7 @@
 class DesnormalizeBallotLine < ActiveRecord::Migration[4.2]
   def change
-    add_column :budget_ballot_lines, :budget_id, :integer, index: true
+    add_column :budget_ballot_lines, :budget_id, :integer
-    add_column :budget_ballot_lines, :group_id, :integer, index: true
+    add_column :budget_ballot_lines, :group_id, :integer
-    add_column :budget_ballot_lines, :heading_id, :integer, index: true
+    add_column :budget_ballot_lines, :heading_id, :integer
   end
 end

db/migrate/20160905092539_denormalize_investments.rb

@@ -1,6 +1,6 @@
 class DenormalizeInvestments < ActiveRecord::Migration[4.2]
   def change
-    add_column :budget_investments, :budget_id, :integer, index: true
+    add_column :budget_investments, :budget_id, :integer
-    add_column :budget_investments, :group_id, :integer, index: true
+    add_column :budget_investments, :group_id, :integer
   end
 end

db/migrate/20161221172447_add_selected_to_budget_investment.rb

@@ -1,5 +1,5 @@
 class AddSelectedToBudgetInvestment < ActiveRecord::Migration[4.2]
   def change
-    add_column :budget_investments, :selected, :bool, default: false, index: true
+    add_column :budget_investments, :selected, :bool, default: false
   end
 end

db/migrate/20170120161058_add_geozone_restricted_to_polls.rb

@@ -1,5 +1,5 @@
 class AddGeozoneRestrictedToPolls < ActiveRecord::Migration[4.2]
   def change
-    add_column :polls, :geozone_restricted, :boolean, default: false, index: true
+    add_column :polls, :geozone_restricted, :boolean, default: false
   end
 end

db/migrate/20170208110146_add_officer_id_to_failed_census_calls.rb

@@ -1,6 +1,6 @@
 class AddOfficerIdToFailedCensusCalls < ActiveRecord::Migration[4.2]
   def change
-    add_column :failed_census_calls, :poll_officer_id, :integer, index: true
+    add_column :failed_census_calls, :poll_officer_id, :integer
     add_foreign_key :failed_census_calls, :poll_officers
   end
 end

db/migrate/20170703120055_add_incompatible_to_budget_investments.rb

@@ -1,5 +1,5 @@
 class AddIncompatibleToBudgetInvestments < ActiveRecord::Migration[4.2]
   def change
-    add_column :budget_investments, :incompatible, :bool, default: false, index: true
+    add_column :budget_investments, :incompatible, :bool, default: false
   end
 end

db/migrate/20190410132842_add_selected_to_proposal.rb

@@ -1,5 +1,5 @@
 class AddSelectedToProposal < ActiveRecord::Migration[4.2]
   def change
-    add_column :proposals, :selected, :bool, default: false, index: true
+    add_column :proposals, :selected, :bool, default: false
   end
 end

db/migrate/20210811195800_add_missing_indexes.rb

@@ -0,0 +1,17 @@
+class AddMissingIndexes < ActiveRecord::Migration[5.2]
+  def change
+    add_index :comments, :confidence_score
+    add_index :users, :gender
+    add_index :users, :date_of_birth
+    add_index :budget_ballot_lines, :budget_id
+    add_index :budget_ballot_lines, :group_id
+    add_index :budget_ballot_lines, :heading_id
+    add_index :budget_investments, :budget_id
+    add_index :budget_investments, :group_id
+    add_index :budget_investments, :selected
+    add_index :polls, :geozone_restricted
+    add_index :failed_census_calls, :poll_officer_id
+    add_index :budget_investments, :incompatible
+    add_index :proposals, :selected
+  end
+end

db/schema.rb

@@ -10,7 +10,7 @@
 #
 # It's strongly recommended that you check this file into your version control system.
 
-ActiveRecord::Schema.define(version: 2021_05_19_115700) do
+ActiveRecord::Schema.define(version: 2021_08_11_195800) do
 
   # These are extensions that must be enabled in order to support this database
   enable_extension "pg_trgm"
@@ -155,6 +155,9 @@ ActiveRecord::Schema.define(version: 2021_05_19_115700) do
     t.integer "heading_id"
     t.index ["ballot_id", "investment_id"], name: "index_budget_ballot_lines_on_ballot_id_and_investment_id", unique: true
     t.index ["ballot_id"], name: "index_budget_ballot_lines_on_ballot_id"
+    t.index ["budget_id"], name: "index_budget_ballot_lines_on_budget_id"
+    t.index ["group_id"], name: "index_budget_ballot_lines_on_group_id"
+    t.index ["heading_id"], name: "index_budget_ballot_lines_on_heading_id"
     t.index ["investment_id"], name: "index_budget_ballot_lines_on_investment_id"
   end
 
@@ -274,8 +277,12 @@ ActiveRecord::Schema.define(version: 2021_05_19_115700) do
     t.integer "original_heading_id"
     t.index ["administrator_id"], name: "index_budget_investments_on_administrator_id"
     t.index ["author_id"], name: "index_budget_investments_on_author_id"
+    t.index ["budget_id"], name: "index_budget_investments_on_budget_id"
     t.index ["community_id"], name: "index_budget_investments_on_community_id"
+    t.index ["group_id"], name: "index_budget_investments_on_group_id"
     t.index ["heading_id"], name: "index_budget_investments_on_heading_id"
+    t.index ["incompatible"], name: "index_budget_investments_on_incompatible"
+    t.index ["selected"], name: "index_budget_investments_on_selected"
     t.index ["tsv"], name: "index_budget_investments_on_tsv", using: :gin
   end
 
@@ -424,6 +431,7 @@ ActiveRecord::Schema.define(version: 2021_05_19_115700) do
     t.index ["cached_votes_total"], name: "index_comments_on_cached_votes_total"
     t.index ["cached_votes_up"], name: "index_comments_on_cached_votes_up"
     t.index ["commentable_id", "commentable_type"], name: "index_comments_on_commentable_id_and_commentable_type"
+    t.index ["confidence_score"], name: "index_comments_on_confidence_score"
     t.index ["hidden_at"], name: "index_comments_on_hidden_at"
     t.index ["user_id"], name: "index_comments_on_user_id"
     t.index ["valuation"], name: "index_comments_on_valuation"
@@ -570,6 +578,7 @@ ActiveRecord::Schema.define(version: 2021_05_19_115700) do
     t.string "district_code"
     t.integer "poll_officer_id"
     t.integer "year_of_birth"
+    t.index ["poll_officer_id"], name: "index_failed_census_calls_on_poll_officer_id"
     t.index ["user_id"], name: "index_failed_census_calls_on_user_id"
   end
 
@@ -1203,6 +1212,7 @@ ActiveRecord::Schema.define(version: 2021_05_19_115700) do
     t.integer "related_id"
     t.tsvector "tsv"
     t.index ["budget_id"], name: "index_polls_on_budget_id", unique: true
+    t.index ["geozone_restricted"], name: "index_polls_on_geozone_restricted"
     t.index ["related_type", "related_id"], name: "index_polls_on_related_type_and_related_id"
     t.index ["starts_at", "ends_at"], name: "index_polls_on_starts_at_and_ends_at"
   end
@@ -1283,6 +1293,7 @@ ActiveRecord::Schema.define(version: 2021_05_19_115700) do
     t.index ["geozone_id"], name: "index_proposals_on_geozone_id"
     t.index ["hidden_at"], name: "index_proposals_on_hidden_at"
     t.index ["hot_score"], name: "index_proposals_on_hot_score"
+    t.index ["selected"], name: "index_proposals_on_selected"
     t.index ["tsv"], name: "index_proposals_on_tsv", using: :gin
   end
 
@@ -1595,7 +1606,9 @@ ActiveRecord::Schema.define(version: 2021_05_19_115700) do
     t.boolean "recommended_debates", default: true
     t.boolean "recommended_proposals", default: true
     t.index ["confirmation_token"], name: "index_users_on_confirmation_token", unique: true
+    t.index ["date_of_birth"], name: "index_users_on_date_of_birth"
     t.index ["email"], name: "index_users_on_email", unique: true
+    t.index ["gender"], name: "index_users_on_gender"
     t.index ["geozone_id"], name: "index_users_on_geozone_id"
     t.index ["hidden_at"], name: "index_users_on_hidden_at"
     t.index ["password_changed_at"], name: "index_users_on_password_changed_at"