Introduce RuboCop Performance (#316)

## What this does

Hello, thanks for your work on this library

This is my first contribution here. I think that adding RuboCop
Performance plugin this can benefit on the long term

Each offense has been fixed in an individual commit, with explanation
and benchmarks, where possible.

Some cops have been temporarily disabled because they can break API

## Type of change

- [ ] Bug fix
- [ ] New feature
- [ ] Breaking change ⚠️ ⚠️ ⚠️  **not at the best of my knowledge**
- [ ] Documentation
- [x] Performance improvement

## Scope check

- [x] I read the [Contributing
Guide](https://github.com/crmne/ruby_llm/blob/main/CONTRIBUTING.md)
- [x] This aligns with RubyLLM's focus on **LLM communication**
- [x] This isn't application-specific logic that belongs in user code
- [x] This benefits most users, not just my specific use case

## Quality check

- [x] I ran `overcommit --install` and all hooks pass
- [x] I tested my changes thoroughly
- [x] ~I updated documentation if needed~
- [x] I didn't modify auto-generated files manually (`models.json`,
`aliases.json`)

## API changes

- [ ] Breaking change
- [ ] New public methods/classes
- [ ] Changed method signatures
- [x] No API changes

## Related issues

<!-- Link issues: "Fixes #123" or "Related to #123" -->

Author: tagliala

.rubocop.yml

@@ -1,4 +1,5 @@
 plugins:
+  - rubocop-performance
   - rubocop-rake
   - rubocop-rspec
 
@@ -21,7 +22,18 @@ Metrics/MethodLength:
   Enabled: false
 Metrics/ModuleLength:
   Enabled: false
+Performance/CollectionLiteralInLoop:
+  Exclude:
+    - spec/**/*
+Performance/RedundantBlockCall:
+  Enabled: false # TODO: temporarily disabled to avoid potential breaking change
+Performance/StringInclude:
+  Exclude:
+    - lib/ruby_llm/providers/**/capabilities.rb
+Performance/UnfreezeString:
+  Exclude:
+    - spec/**/*
 RSpec/ExampleLength:
   Enabled: false
 RSpec/MultipleExpectations:
-  Enabled: false
+  Enabled: false

Gemfile

@@ -22,6 +22,7 @@ group :development do # rubocop:disable Metrics/BlockLength
   gem 'reline'
   gem 'rspec', '~> 3.12'
   gem 'rubocop', '>= 1.0'
+  gem 'rubocop-performance'
   gem 'rubocop-rake', '>= 0.6'
   gem 'rubocop-rspec'
   gem 'ruby_llm-schema', '~> 0.1.0'

lib/ruby_llm/active_record/acts_as.rb

@@ -234,7 +234,7 @@ def setup_persistence_callbacks
       end
 
       def persist_new_message
-        @message = messages.create!(role: :assistant, content: String.new)
+        @message = messages.create!(role: :assistant, content: '')
       end
 
       def persist_message_completion(message)

lib/ruby_llm/content.rb

@@ -43,7 +43,7 @@ def process_attachments_array_or_string(attachments)
     def process_attachments(attachments)
       if attachments.is_a?(Hash)
         # Ignores types (like :image, :audio, :text, :pdf) since we have robust MIME type detection
-        attachments.each_value(&method(:process_attachments_array_or_string))
+        attachments.each_value { |attachment| process_attachments_array_or_string(attachment) }
       else
         process_attachments_array_or_string attachments
       end

lib/ruby_llm/models.rb

@@ -64,7 +64,7 @@ def resolve(model_id, provider: nil, assume_exists: false, config: nil) # ruboco
 
           model = Model::Info.new(
             id: model_id,
-            name: model_id.gsub('-', ' ').capitalize,
+            name: model_id.tr('-', ' ').capitalize,
             provider: provider_instance.slug,
             capabilities: %w[function_calling streaming],
             modalities: { input: %w[text image], output: %w[text] },

lib/ruby_llm/providers/bedrock/streaming/base.rb

@@ -47,7 +47,7 @@ def stream_response(connection, payload, additional_headers = {}, &block)
           end
 
           def handle_stream(&block)
-            buffer = String.new
+            buffer = +''
             proc do |chunk, _bytes, env|
               if env && env.status != 200
                 handle_failed_response(chunk, buffer, env)

lib/ruby_llm/providers/openai/capabilities.rb

@@ -198,11 +198,11 @@ def apply_special_formatting(name)
             .gsub(/(\d{4}) (\d{2}) (\d{2})/, '\1\2\3')
             .gsub(/^(?:Gpt|Chatgpt|Tts|Dall E) /) { |m| special_prefix_format(m.strip) }
             .gsub(/^O([13]) /, 'O\1-')
-            .gsub(/^O[13] Mini/, '\0'.gsub(' ', '-'))
+            .gsub(/^O[13] Mini/, '\0'.tr(' ', '-'))
             .gsub(/\d\.\d /, '\0'.sub(' ', '-'))
             .gsub(/4o (?=Mini|Preview|Turbo|Audio|Realtime|Transcribe|Tts)/, '4o-')
             .gsub(/\bHd\b/, 'HD')
-            .gsub(/(?:Omni|Text) Moderation/, '\0'.gsub(' ', '-'))
+            .gsub(/(?:Omni|Text) Moderation/, '\0'.tr(' ', '-'))
             .gsub('Text Embedding', 'text-embedding-')
         end
 

lib/ruby_llm/stream_accumulator.rb

@@ -8,7 +8,7 @@ class StreamAccumulator
     attr_reader :content, :model_id, :tool_calls
 
     def initialize
-      @content = String.new
+      @content = +''
       @tool_calls = {}
       @input_tokens = 0
       @output_tokens = 0
@@ -66,7 +66,7 @@ def accumulate_tool_calls(new_tool_calls)
       new_tool_calls.each_value do |tool_call|
         if tool_call.id
           tool_call_id = tool_call.id.empty? ? SecureRandom.uuid : tool_call.id
-          tool_call_arguments = tool_call.arguments.empty? ? String.new : tool_call.arguments
+          tool_call_arguments = tool_call.arguments.empty? ? +'' : tool_call.arguments
           @tool_calls[tool_call.id] = ToolCall.new(
             id: tool_call_id,
             name: tool_call.name,

lib/ruby_llm/streaming.rb

@@ -43,7 +43,7 @@ def handle_stream(&block)
     private
 
     def to_json_stream(&)
-      buffer = String.new
+      buffer = +''
       parser = EventStreamParser::Parser.new
 
       create_stream_processor(parser, buffer, &)

lib/tasks/aliases.rake

@@ -65,7 +65,7 @@ namespace :aliases do # rubocop:disable Metrics/BlockLength
 
       base_name = Regexp.last_match(1)
       # Normalize to Anthropic naming convention
-      anthropic_name = base_name.gsub('.', '-')
+      anthropic_name = base_name.tr('.', '-')
 
       # Skip if we already have an alias for this
       next if aliases[anthropic_name]
@@ -91,7 +91,7 @@ namespace :aliases do # rubocop:disable Metrics/BlockLength
       # OpenRouter uses "google/" prefix and sometimes different naming
       openrouter_variants = [
         "google/#{model}",
-        "google/#{model.gsub('gemini-', 'gemini-').gsub('.', '-')}",
+        "google/#{model.gsub('gemini-', 'gemini-').tr('.', '-')}",
         "google/#{model.gsub('gemini-', 'gemini-')}"
       ]