NoMethodError is raised from Rails/UniqueValidationWithoutIndex cop when db/schema.rb is empty

[tk0miya]

Expected behavior

rubocop will be succeeded with no errors.

Actual behavior

Since rubocop-rails-2.20.1, I got the following error on running rubocop:

An error occurred while Rails/UniqueValidationWithoutIndex cop was inspecting /app/.../...rb:NNN:NNN.

Note: I got the same result when I used the latest release; rubocop-rails-2.20.2.

This is the stacktrace when I gave -d option to rubocop:

An error occurred while Rails/UniqueValidationWithoutIndex cop was inspecting /app/.../...rb:NNN:NNN.
undefined method `type' for nil:NilClass
/usr/local/bundle/gems/rubocop-rails-2.20.1/lib/rubocop/rails/schema_loader/schema.rb:47:in `each_table'
/usr/local/bundle/gems/rubocop-rails-2.20.1/lib/rubocop/rails/schema_loader/schema.rb:34:in `build!'
/usr/local/bundle/gems/rubocop-rails-2.20.1/lib/rubocop/rails/schema_loader/schema.rb:14:in `initialize'
/usr/local/bundle/gems/rubocop-rails-2.20.1/lib/rubocop/rails/schema_loader.rb:46:in `new'
/usr/local/bundle/gems/rubocop-rails-2.20.1/lib/rubocop/rails/schema_loader.rb:46:in `load!'
/usr/local/bundle/gems/rubocop-rails-2.20.1/lib/rubocop/rails/schema_loader.rb:18:in `load'
/usr/local/bundle/gems/rubocop-rails-2.20.1/lib/rubocop/cop/mixin/active_record_helper.rb:42:in `schema'
/usr/local/bundle/gems/rubocop-rails-2.20.1/lib/rubocop/cop/rails/unique_validation_without_index.rb:36:in `on_send'
/usr/local/bundle/gems/rubocop-1.52.1/lib/rubocop/cop/commissioner.rb:143:in `public_send'
/usr/local/bundle/gems/rubocop-1.52.1/lib/rubocop/cop/commissioner.rb:143:in `block (2 levels) in trigger_restricted_cops'
/usr/local/bundle/gems/rubocop-1.52.1/lib/rubocop/cop/commissioner.rb:171:in `with_cop_error_handling'
/usr/local/bundle/gems/rubocop-1.52.1/lib/rubocop/cop/commissioner.rb:142:in `block in trigger_restricted_cops'
/usr/local/bundle/gems/rubocop-1.52.1/lib/rubocop/cop/commissioner.rb:141:in `each'
/usr/local/bundle/gems/rubocop-1.52.1/lib/rubocop/cop/commissioner.rb:141:in `trigger_restricted_cops'
/usr/local/bundle/gems/rubocop-1.52.1/lib/rubocop/cop/commissioner.rb:70:in `on_send'
/usr/local/bundle/gems/rubocop-ast-1.29.0/lib/rubocop/ast/traversal.rb:137:in `block in on_dstr'
/usr/local/bundle/gems/rubocop-ast-1.29.0/lib/rubocop/ast/traversal.rb:137:in `each'
/usr/local/bundle/gems/rubocop-ast-1.29.0/lib/rubocop/ast/traversal.rb:137:in `on_dstr'
/usr/local/bundle/gems/rubocop-1.52.1/lib/rubocop/cop/commissioner.rb:71:in `on_begin'
/usr/local/bundle/gems/rubocop-ast-1.29.0/lib/rubocop/ast/traversal.rb:154:in `on_class'
/usr/local/bundle/gems/rubocop-1.52.1/lib/rubocop/cop/commissioner.rb:71:in `on_class'
/usr/local/bundle/gems/rubocop-ast-1.29.0/lib/rubocop/ast/traversal.rb:20:in `walk'
/usr/local/bundle/gems/rubocop-1.52.1/lib/rubocop/cop/commissioner.rb:87:in `investigate'
/usr/local/bundle/gems/rubocop-1.52.1/lib/rubocop/cop/team.rb:156:in `investigate_partial'
/usr/local/bundle/gems/rubocop-1.52.1/lib/rubocop/cop/team.rb:98:in `investigate'
/usr/local/bundle/gems/rubocop-1.52.1/lib/rubocop/runner.rb:345:in `block in inspect_file'
/usr/local/bundle/gems/rubocop-1.52.1/lib/rubocop/runner.rb:344:in `each'
/usr/local/bundle/gems/rubocop-1.52.1/lib/rubocop/runner.rb:344:in `flat_map'
/usr/local/bundle/gems/rubocop-1.52.1/lib/rubocop/runner.rb:344:in `inspect_file'
/usr/local/bundle/gems/rubocop-1.52.1/lib/rubocop/runner.rb:287:in `block in do_inspection_loop'
/usr/local/bundle/gems/rubocop-1.52.1/lib/rubocop/runner.rb:321:in `block in iterate_until_no_changes'
/usr/local/bundle/gems/rubocop-1.52.1/lib/rubocop/runner.rb:314:in `loop'
/usr/local/bundle/gems/rubocop-1.52.1/lib/rubocop/runner.rb:314:in `iterate_until_no_changes'
/usr/local/bundle/gems/rubocop-1.52.1/lib/rubocop/runner.rb:283:in `do_inspection_loop'
/usr/local/bundle/gems/rubocop-1.52.1/lib/rubocop/runner.rb:164:in `block in file_offenses'
/usr/local/bundle/gems/rubocop-1.52.1/lib/rubocop/runner.rb:189:in `file_offense_cache'
/usr/local/bundle/gems/rubocop-1.52.1/lib/rubocop/runner.rb:163:in `file_offenses'
/usr/local/bundle/gems/rubocop-1.52.1/lib/rubocop/runner.rb:154:in `process_file'
/usr/local/bundle/gems/rubocop-1.52.1/lib/rubocop/runner.rb:135:in `block in each_inspected_file'
/usr/local/bundle/gems/rubocop-1.52.1/lib/rubocop/runner.rb:134:in `each'
/usr/local/bundle/gems/rubocop-1.52.1/lib/rubocop/runner.rb:134:in `reduce'
/usr/local/bundle/gems/rubocop-1.52.1/lib/rubocop/runner.rb:134:in `each_inspected_file'
/usr/local/bundle/gems/rubocop-1.52.1/lib/rubocop/runner.rb:120:in `inspect_files'
/usr/local/bundle/gems/rubocop-1.52.1/lib/rubocop/runner.rb:73:in `run'
/usr/local/bundle/gems/rubocop-1.52.1/lib/rubocop/cli/command/execute_runner.rb:26:in `block in execute_runner'
/usr/local/bundle/gems/rubocop-1.52.1/lib/rubocop/cli/command/execute_runner.rb:52:in `with_redirect'
/usr/local/bundle/gems/rubocop-1.52.1/lib/rubocop/cli/command/execute_runner.rb:25:in `execute_runner'
/usr/local/bundle/gems/rubocop-1.52.1/lib/rubocop/cli/command/execute_runner.rb:17:in `run'
/usr/local/bundle/gems/rubocop-1.52.1/lib/rubocop/cli/command.rb:11:in `run'
/usr/local/bundle/gems/rubocop-1.52.1/lib/rubocop/cli/environment.rb:18:in `run'
/usr/local/bundle/gems/rubocop-1.52.1/lib/rubocop/cli.rb:118:in `run_command'
/usr/local/bundle/gems/rubocop-1.52.1/lib/rubocop/cli.rb:125:in `execute_runners'
/usr/local/bundle/gems/rubocop-1.52.1/lib/rubocop/cli.rb:51:in `block in run'
/usr/local/bundle/gems/rubocop-1.52.1/lib/rubocop/cli.rb:77:in `profile_if_needed'
/usr/local/bundle/gems/rubocop-1.52.1/lib/rubocop/cli.rb:43:in `run'
/usr/local/bundle/gems/rubocop-1.52.1/exe/rubocop:19:in `block in <top (required)>'
/usr/local/bundle/gems/benchmark-0.2.1/lib/benchmark.rb:311:in `realtime'
/usr/local/bundle/gems/rubocop-1.52.1/exe/rubocop:19:in `<top (required)>'
/usr/local/bundle/bin/rubocop:23:in `load'
/usr/local/bundle/bin/rubocop:23:in `<top (required)>'
/usr/local/bundle/gems/bundler-2.2.28/lib/bundler/cli/exec.rb:58:in `load'
/usr/local/bundle/gems/bundler-2.2.28/lib/bundler/cli/exec.rb:58:in `kernel_load'
/usr/local/bundle/gems/bundler-2.2.28/lib/bundler/cli/exec.rb:23:in `run'
/usr/local/bundle/gems/bundler-2.2.28/lib/bundler/cli.rb:478:in `exec'
/usr/local/bundle/gems/bundler-2.2.28/lib/bundler/vendor/thor/lib/thor/command.rb:27:in `run'
/usr/local/bundle/gems/bundler-2.2.28/lib/bundler/vendor/thor/lib/thor/invocation.rb:127:in `invoke_command'
/usr/local/bundle/gems/bundler-2.2.28/lib/bundler/vendor/thor/lib/thor.rb:392:in `dispatch'
/usr/local/bundle/gems/bundler-2.2.28/lib/bundler/cli.rb:31:in `dispatch'
/usr/local/bundle/gems/bundler-2.2.28/lib/bundler/vendor/thor/lib/thor/base.rb:485:in `start'
/usr/local/bundle/gems/bundler-2.2.28/lib/bundler/cli.rb:25:in `start'
/usr/local/bundle/gems/bundler-2.2.28/exe/bundle:49:in `block in <top (required)>'
/usr/local/bundle/gems/bundler-2.2.28/lib/bundler/friendly_errors.rb:128:in `with_friendly_errors'
/usr/local/bundle/gems/bundler-2.2.28/exe/bundle:37:in `<top (required)>'
/usr/local/bin/bundle:23:in `load'
/usr/local/bin/bundle:23:in `<main>'
.

1 file inspected, no offenses detected

Steps to reproduce the problem

Sorry, I can't find a way to reproduce it from scratch.

But it seems the error came from the empty db/scheme.rb.

In my application, it does not have any tables:

ActiveRecord::Schema.define(version: 0) do

end

And, the error will be resolved when I added the following line to rubocop-rails/lib/rubocop/rails/schema_loader/schema.rb:

          def build!(ast)
            raise "Unexpected type: #{ast.type}" unless ast.block_type?
+           return unless ast.body

            each_table(ast) do |table_def|
              next unless table_def.method?(:create_table)

              @tables << Table.new(table_def)
            end

Therefore, I think this is a bug of the schema loader, not Rails/UniqueValidationWithoutIndex cop's.

RuboCop version

root@e26db528aef8> bundle exec rubocop -V
1.52.1 (using Parser 3.2.2.3, rubocop-ast 1.29.0, running on ruby 2.7.5) [x86_64-linux]
  - rubocop-factory_bot 2.23.1
  - rubocop-performance 1.18.0
  - rubocop-rails 2.20.1
  - rubocop-rspec 2.22.0

[tk0miya]

Thanks!