Prevent write queries for `exec_query`

Follow up #34505.

activerecord/lib/active_record/connection_adapters/postgresql_adapter.rb

@@ -609,6 +609,10 @@ def load_additional_types(oids = nil)
         FEATURE_NOT_SUPPORTED = "0A000" #:nodoc:
 
         def execute_and_clear(sql, name, binds, prepare: false)
+          if preventing_writes? && write_query?(sql)
+            raise ActiveRecord::ReadOnlyError, "Write query attempted while in readonly mode: #{sql}"
+          end
+
           if without_prepared_statement?(binds)
             result = exec_no_cache(sql, name, [])
           elsif !prepare

activerecord/lib/active_record/connection_adapters/sqlite3_adapter.rb

@@ -209,7 +209,7 @@ def disable_referential_integrity # :nodoc:
       # DATABASE STATEMENTS ======================================
       #++
 
-      READ_QUERY = ActiveRecord::ConnectionAdapters::AbstractAdapter.build_read_query_regexp(:select) # :nodoc:
+      READ_QUERY = ActiveRecord::ConnectionAdapters::AbstractAdapter.build_read_query_regexp(:select, :pragma) # :nodoc:
       private_constant :READ_QUERY
 
       def write_query?(sql) # :nodoc:
@@ -222,6 +222,10 @@ def explain(arel, binds = [])
       end
 
       def exec_query(sql, name = nil, binds = [], prepare: false)
+        if preventing_writes? && write_query?(sql)
+          raise ActiveRecord::ReadOnlyError, "Write query attempted while in readonly mode: #{sql}"
+        end
+
         materialize_transactions
 
         type_casted_binds = type_casted_binds(binds)

activerecord/test/cases/adapter_test.rb

@@ -165,6 +165,43 @@ class << @connection
       end
     end
 
+    def test_errors_when_an_insert_query_is_called_while_preventing_writes
+      assert_raises(ActiveRecord::ReadOnlyError) do
+        @connection.while_preventing_writes do
+          @connection.insert("INSERT INTO subscribers(nick) VALUES ('138853948594')")
+        end
+      end
+    end
+
+    def test_errors_when_an_update_query_is_called_while_preventing_writes
+      @connection.insert("INSERT INTO subscribers(nick) VALUES ('138853948594')")
+
+      assert_raises(ActiveRecord::ReadOnlyError) do
+        @connection.while_preventing_writes do
+          @connection.update("UPDATE subscribers SET nick = '9989' WHERE nick = '138853948594'")
+        end
+      end
+    end
+
+    def test_errors_when_a_delete_query_is_called_while_preventing_writes
+      @connection.insert("INSERT INTO subscribers(nick) VALUES ('138853948594')")
+
+      assert_raises(ActiveRecord::ReadOnlyError) do
+        @connection.while_preventing_writes do
+          @connection.delete("DELETE FROM subscribers WHERE nick = '138853948594'")
+        end
+      end
+    end
+
+    def test_doesnt_error_when_a_select_query_is_called_while_preventing_writes
+      @connection.insert("INSERT INTO subscribers(nick) VALUES ('138853948594')")
+
+      @connection.while_preventing_writes do
+        result = @connection.select_all("SELECT subscribers.* FROM subscribers WHERE nick = '138853948594'")
+        assert_equal 1, result.length
+      end
+    end
+
     def test_uniqueness_violations_are_translated_to_specific_exception
       @connection.execute "INSERT INTO subscribers(nick) VALUES('me')"
       error = assert_raises(ActiveRecord::RecordNotUnique) do