Add Valgrind memcheck (ruby_memcheck) and run it in CI

.github/workflows/valgrind.yml

@@ -0,0 +1,39 @@
+name: Valgrind
+
+on:
+  push:
+    branches:
+      - main
+  pull_request:
+
+permissions:
+  contents: read
+
+concurrency:
+  group: ${{ github.workflow }}-${{ github.ref }}
+  cancel-in-progress: true
+
+jobs:
+  valgrind:
+    name: memcheck (ubuntu, ruby ${{ matrix.ruby }})
+    runs-on: ubuntu-latest
+    timeout-minutes: 30
+    strategy:
+      fail-fast: false
+      matrix:
+        ruby:
+          - '4.0'
+
+    steps:
+    - uses: actions/checkout@v6
+    - name: Install Valgrind
+      run: |
+        sudo apt-get update
+        sudo apt-get install -y valgrind
+    - name: Set up Ruby
+      uses: ruby/setup-ruby@v1
+      with:
+        ruby-version: ${{ matrix.ruby }}
+        bundler-cache: true
+    - name: Run the spec suite under Valgrind memcheck
+      run: bundle exec rake spec:valgrind

Gemfile

@@ -2,3 +2,7 @@ source 'https://rubygems.org'
 
 # Specify your gem's dependencies in zstd_ruby.gemspec
 gemspec
+
+if RUBY_PLATFORM.include?('linux') && Gem::Version.new(RUBY_VERSION) >= Gem::Version.new('3.0.0')
+  gem 'ruby_memcheck', '~> 3.0'
+end

Rakefile

@@ -15,6 +15,32 @@ end
 
 task :default => [:clobber, :compile, :spec]
 
+begin
+  require 'ruby_memcheck'
+  require 'ruby_memcheck/rspec/rake_task'
+
+  RubyMemcheck.config(
+    binary_name: 'zstdruby',
+    # Valgrind and YJIT interfere with each other, adding noise and slowdown,
+    # so keep YJIT disabled while running under Valgrind.
+    ruby: "#{FileUtils::RUBY} --disable-yjit"
+  )
+
+  namespace :spec do
+    task :check_valgrind do
+      unless system('command -v valgrind > /dev/null 2>&1')
+        abort("\nValgrind is required for `rake spec:valgrind` but was not found.\n" \
+              "Install it first (Linux only), e.g. `sudo apt-get install valgrind`.\n")
+      end
+    end
+
+    RubyMemcheck::RSpec::RakeTask.new(valgrind: [:check_valgrind, :compile])
+  end
+rescue LoadError
+  # ruby_memcheck is an optional development dependency, absent on the platforms
+  # and Ruby versions the Gemfile excludes. Skip the task instead of breaking.
+end
+
 desc 'Sync zstd libs dirs to ext/zstdruby/libzstd'
 task :zstd_update do
   FileUtils.rm_r("ext/zstdruby/libzstd")

spec/zstd-ruby_spec.rb

@@ -34,7 +34,7 @@
     end
 
     it 'should compress large bytes' do
-      large_string = Random.bytes(1<<17 + 15)
+      large_string = Random.bytes((1<<17) + 15)
       compressed = Zstd.compress(large_string)
       expect(Zstd.decompress(compressed)).to eq(large_string)
     end