perf: cache RuboCop team and filter cop registry to enabled cops

[ryanquanz]

Summary

Cache the RuboCop cop team and registry in initialize instead of rebuilding them for every ERB tag. Filter the registry to only enabled cops. Memoize target_ruby_version, the version check, and the global registry.

Problem

The old code called build_team (which calls cop_classes → Team.mobilize) inside inspect_content, which runs per ERB node. This created ~500 cop instances and a new Team for every <%= %> tag. The team and config are immutable across a single linter instance's lifetime — there was never a reason to rebuild per node.

Also, cop_classes included all registered cops (~569) regardless of whether they were enabled in the merged config. Now only enabled cops (~510 in a typical config) are included.

Impact

The improvement depends on ERB tag density — more tags per file means more avoided rebuilds.

ERB tags/file	Before	After	Reduction
2	0.64s	0.47s	−27%
10	3.25s	2.42s	−26%
15	5.35s	3.49s	−35%
25	8.94s	5.56s	−38%

(50 synthetic files, all default linters enabled)

Changes

1 file changed, +21 −11. No new tests needed — existing rubocop_spec.rb covers all offense detection and autocorrect paths. The behavioral contract is identical.

Reproducible benchmark

# Save anywhere, run with: bundle exec ruby /tmp/erblint_benchmark.rb
require "erb_lint/all"; require "benchmark"; require "fileutils"
WORKDIR = Dir.mktmpdir("erblint_bench")
50.times do |i|
  lines = ['<div class="container">']
  15.times do |j|
    lines.concat(["  <div>", "    <%= helper_method_#{j}(arg1, arg2) %>",
      "    <% if condition_#{j} %>", "      <span><%= object_#{j}.name %></span>",
      "    <% end %>", "  </div>"])
  end
  File.write(File.join(WORKDIR, "template_#{i}.html.erb"), lines.push("</div>").join("\n"))
end
files = Dir.glob(File.join(WORKDIR, "*.html.erb"))
fl = ERBLint::FileLoader.new(WORKDIR)
cfg = ERBLint::RunnerConfig.default_for(ERBLint::RunnerConfig.new({
  "EnableDefaultLinters" => true, "linters" => { "ErbSafety" => { "enabled" => false },
  "Rubocop" => { "enabled" => true, "rubocop_config" => {
    "Layout/InitialIndentation" => { "Enabled" => false },
    "Layout/TrailingEmptyLines" => { "Enabled" => false },
    "Layout/TrailingWhitespace" => { "Enabled" => false },
    "Naming/FileName" => { "Enabled" => false },
    "Style/FrozenStringLiteralComment" => { "Enabled" => false },
    "Layout/LineLength" => { "Enabled" => false },
    "Lint/UselessAssignment" => { "Enabled" => false }}}}}, fl))
run = -> {
  r = ERBLint::Runner.new(fl, cfg)
  files.each { |f| r.clear_offenses; r.run(ERBLint::ProcessedSource.new(f, File.read(f, encoding: Encoding::UTF_8))) }
}
run.call # warmup
times = 3.times.map { GC.start; Benchmark.realtime { run.call } }.sort
puts "#{files.size} files, median: #{format("%.3f", times[1])}s"
FileUtils.rm_rf(WORKDIR)