Change how migrations duplicated between glitch and upstream are handled (#2878)

config/initializers/0_duplicate_migrations.rb

@@ -1,56 +0,0 @@
-# frozen_string_literal: true
-
-# Some migrations have been present in glitch-soc for a long time and have then
-# been merged in upstream Mastodon, under a different version number.
-#
-# This puts us in an uneasy situation in which if we remove upstream's
-# migration file, people migrating from upstream will end up having a conflict
-# with their already-ran migration.
-#
-# On the other hand, if we keep upstream's migration and remove our own,
-# any current glitch-soc user will have a conflict during migration.
-#
-# For lack of a better solution, as those migrations are indeed identical,
-# we decided monkey-patching Rails' Migrator to completely ignore the duplicate,
-# keeping only the one that has run, or an arbitrary one.
-
-ALLOWED_DUPLICATES = [2018_04_10_220657, 2018_08_31_171112].freeze
-
-module ActiveRecord
-  class Migrator
-    def self.new(direction, migrations, schema_migration, internal_metadata, target_version = nil)
-      migrated = Set.new(Base.connection.migration_context.get_all_versions)
-
-      migrations.group_by(&:name).each_value do |duplicates|
-        next unless duplicates.length > 1 && duplicates.all? { |m| ALLOWED_DUPLICATES.include?(m.version) }
-
-        # We have a set of allowed duplicates. Keep the migrated one, if any.
-        non_migrated = duplicates.reject { |m| migrated.include?(m.version.to_i) }
-
-        migrations = begin
-          if duplicates.length == non_migrated.length || non_migrated.empty?
-            # There weren't any migrated one, so we have to pick one “canonical” migration
-            migrations - duplicates[1..]
-          else
-            # Just reject every duplicate which hasn't been migrated yet
-            migrations - non_migrated
-          end
-        end
-      end
-
-      super
-    end
-  end
-
-  class MigrationContext
-    def needs_migration?
-      # A set of duplicated migrations is considered migrated if at least one of
-      # them is migrated.
-      migrated = get_all_versions
-      migrations.group_by(&:name).each_value do |duplicates|
-        return true unless duplicates.any? { |m| migrated.include?(m.version.to_i) }
-      end
-      false
-    end
-  end
-end

db/migrate/20180410220657_glitch_create_bookmarks.rb

@@ -1,10 +1,11 @@
 # frozen_string_literal: true
 
-# This migration is a duplicate of 20180831171112 and may get ignored, see
-# config/initializers/0_duplicate_migrations.rb
+# This migration is a duplicate of 20180831171112
+
+class GlitchCreateBookmarks < ActiveRecord::Migration[5.1]
+  def up
+    return if table_exists?(:bookmarks)
 
-class CreateBookmarks < ActiveRecord::Migration[5.1]
-  def change
     create_table :bookmarks do |t|
       t.references :account, null: false
       t.references :status, null: false
@@ -19,4 +20,6 @@ class CreateBookmarks < ActiveRecord::Migration[5.1]
 
     add_index :bookmarks, [:account_id, :status_id], unique: true
   end
+
+  def down; end
 end

db/migrate/20180831171112_create_bookmarks.rb

@@ -1,10 +1,11 @@
 # frozen_string_literal: true
 
-# This migration is a duplicate of 20180410220657 and may get ignored, see
-# config/initializers/0_duplicate_migrations.rb
+# This migration is a duplicate of 20180410220657
 
 class CreateBookmarks < ActiveRecord::Migration[5.2]
-  def change
+  def up
+    return if table_exists?(:bookmarks)
+
     create_table :bookmarks do |t|
       t.references :account, null: false
       t.references :status, null: false
@@ -19,4 +20,8 @@ class CreateBookmarks < ActiveRecord::Migration[5.2]
 
     add_index :bookmarks, [:account_id, :status_id], unique: true
   end
+
+  def down
+    drop_table :bookmarks
+  end
 end