Merge branch '42239-fix-mysql-source-installs' into 'master'

Resolve "mysql-only installation from source broken: Gem::LoadError: pg is not part of the bundle"

Closes #42239

See merge request gitlab-org/gitlab-ce!16810

config/initializers/ar5_pg_10_support.rb

 raise "Vendored ActiveRecord 5 code! Delete #{__FILE__}!" if ActiveRecord::VERSION::MAJOR >= 5
 
-require 'active_record/connection_adapters/postgresql_adapter'
-require 'active_record/connection_adapters/postgresql/schema_statements'
-
-#
-# Monkey-patch the refused Rails 4.2 patch at https://github.com/rails/rails/pull/31330
-#
-# Updates sequence logic to support PostgreSQL 10.
-#
-# rubocop:disable all
-module ActiveRecord
-  module ConnectionAdapters
-
-    # We need #postgresql_version to be public as in ActiveRecord 5 for seed_fu
-    # to work. In ActiveRecord 4, it is protected.
-    # https://github.com/mbleigh/seed-fu/issues/123
-    class PostgreSQLAdapter
-      public :postgresql_version
-    end
+if Gitlab::Database.postgresql?
+  require 'active_record/connection_adapters/postgresql_adapter'
+  require 'active_record/connection_adapters/postgresql/schema_statements'
+
+  #
+  # Monkey-patch the refused Rails 4.2 patch at https://github.com/rails/rails/pull/31330
+  #
+  # Updates sequence logic to support PostgreSQL 10.
+  #
+  # rubocop:disable all
+  module ActiveRecord
+    module ConnectionAdapters
+
+      # We need #postgresql_version to be public as in ActiveRecord 5 for seed_fu
+      # to work. In ActiveRecord 4, it is protected.
+      # https://github.com/mbleigh/seed-fu/issues/123
+      class PostgreSQLAdapter
+        public :postgresql_version
+      end
 
-    module PostgreSQL
-      module SchemaStatements
-        # Resets the sequence of a table's primary key to the maximum value.
-        def reset_pk_sequence!(table, pk = nil, sequence = nil) #:nodoc:
-          unless pk and sequence
-            default_pk, default_sequence = pk_and_sequence_for(table)
+      module PostgreSQL
+        module SchemaStatements
+          # Resets the sequence of a table's primary key to the maximum value.
+          def reset_pk_sequence!(table, pk = nil, sequence = nil) #:nodoc:
+            unless pk and sequence
+              default_pk, default_sequence = pk_and_sequence_for(table)
 
-            pk ||= default_pk
-            sequence ||= default_sequence
-          end
+              pk ||= default_pk
+              sequence ||= default_sequence
+            end
 
-          if @logger && pk && !sequence
-            @logger.warn "#{table} has primary key #{pk} with no default sequence"
-          end
+            if @logger && pk && !sequence
+              @logger.warn "#{table} has primary key #{pk} with no default sequence"
+            end
 
-          if pk && sequence
-            quoted_sequence = quote_table_name(sequence)
-            max_pk = select_value("SELECT MAX(#{quote_column_name pk}) FROM #{quote_table_name(table)}")
-            if max_pk.nil?
-              if postgresql_version >= 100000
-                minvalue = select_value("SELECT seqmin FROM pg_sequence WHERE seqrelid = #{quote(quoted_sequence)}::regclass")
-              else
-                minvalue = select_value("SELECT min_value FROM #{quoted_sequence}")
+            if pk && sequence
+              quoted_sequence = quote_table_name(sequence)
+              max_pk = select_value("SELECT MAX(#{quote_column_name pk}) FROM #{quote_table_name(table)}")
+              if max_pk.nil?
+                if postgresql_version >= 100000
+                  minvalue = select_value("SELECT seqmin FROM pg_sequence WHERE seqrelid = #{quote(quoted_sequence)}::regclass")
+                else
+                  minvalue = select_value("SELECT min_value FROM #{quoted_sequence}")
+                end
               end
-            end
 
-            select_value <<-end_sql, 'SCHEMA'
-              SELECT setval(#{quote(quoted_sequence)}, #{max_pk ? max_pk : minvalue}, #{max_pk ? true : false})
-            end_sql
+              select_value <<-end_sql, 'SCHEMA'
+                SELECT setval(#{quote(quoted_sequence)}, #{max_pk ? max_pk : minvalue}, #{max_pk ? true : false})
+              end_sql
+            end
           end
         end
       end
     end
   end
+  # rubocop:enable all
 end
-# rubocop:enable all

config/initializers/peek.rb

@@ -7,10 +7,12 @@ if Gitlab::Database.mysql?
   require 'peek-mysql2'
   PEEK_DB_CLIENT = ::Mysql2::Client
   PEEK_DB_VIEW = Peek::Views::Mysql2
-else
+elsif Gitlab::Database.postgresql?
   require 'peek-pg'
   PEEK_DB_CLIENT = ::PG::Connection
   PEEK_DB_VIEW = Peek::Views::PG
+else
+  raise "Unsupported database adapter for peek!"
 end
 
 Peek.into PEEK_DB_VIEW