feat: support --gen-suppressions

When valgrind is run with `--gen-suppressions`, it will write the
error's suppression to XML as something like:

    <suppression>
      <sname>insert_a_suppression_name_here</sname>
      <skind>Memcheck:Leak</skind>
      <skaux>match-leak-kinds: definite</skaux>
      <sframe> <fun>malloc</fun> </sframe>
      <sframe> <fun>objspace_xmalloc0</fun> </sframe>
      <sframe> <fun>ruby_xmalloc0</fun> </sframe>
      <sframe> <fun>ruby_xmalloc_body</fun> </sframe>
      <sframe> <fun>ruby_xmalloc</fun> </sframe>
    </suppression>

If this data is present, then ValgrindError will stream it in the
right format for copy-pasting into a suppressions file.

See https://wiki.wxwidgets.org/Valgrind_Suppression_File_Howto for more.

lib/ruby_memcheck.rb

@@ -8,6 +8,7 @@
 require "ruby_memcheck/stack"
 require "ruby_memcheck/test_task"
 require "ruby_memcheck/valgrind_error"
+require "ruby_memcheck/suppression"
 require "ruby_memcheck/version"
 
 module RubyMemcheck

lib/ruby_memcheck/suppression.rb

@@ -0,0 +1,25 @@
+# frozen_string_literal: true
+
+module RubyMemcheck
+  class Suppression
+    attr_reader :root
+
+    def initialize(configuration, suppression_node)
+      @root = suppression_node
+    end
+
+    def to_s
+      return "" if root.nil?
+
+      str = StringIO.new
+      str << "{\n"
+      str << "  #{root.at_xpath("sname").content}\n"
+      str << "  #{root.at_xpath("skind").content}\n"
+      root.xpath("./sframe/fun | ./sframe/obj").each do |frame|
+        str << "  #{frame.name}:#{frame.content}\n"
+      end
+      str << "}\n"
+      str.string
+    end
+  end
+end

lib/ruby_memcheck/valgrind_error.rb

@@ -2,7 +2,7 @@
 
 module RubyMemcheck
   class ValgrindError
-    attr_reader :kind, :msg, :stack
+    attr_reader :kind, :msg, :stack, :suppression
 
     def initialize(configuration, error)
       @kind = error.at_xpath("kind").content
@@ -14,6 +14,7 @@ def initialize(configuration, error)
         end
       @stack = Stack.new(configuration, error.at_xpath("stack"))
       @configuration = configuration
+      @suppression = Suppression.new(configuration, error.at_xpath("suppression"))
     end
 
     def skip?
@@ -34,6 +35,7 @@ def to_s
           "  #{frame}\n"
         end
       end
+      str << suppression.to_s
       str.string
     end
 

test/ruby_memcheck/ruby_memcheck_suppression_test.rb

@@ -0,0 +1,53 @@
+# frozen_string_literal: true
+
+require "test_helper"
+require "nokogiri"
+
+module RubyMemcheck
+  class RubyMemcheckSuppressionTest < Minitest::Test
+    def setup
+      @configuration = Configuration.new(
+        binary_name: "ruby_memcheck_c_test",
+        output_io: @output_io,
+      )
+    end
+
+    def test_given_nil
+      assert_equal("", RubyMemcheck::Suppression.new(@configuration, nil).to_s)
+    end
+
+    def test_given_a_suppression_node
+      suppression = ::Nokogiri::XML(<<~EOF).at_xpath("//suppression")
+        <foo>
+          <suppression>
+            <sname>insert_a_suppression_name_here</sname>
+            <skind>Memcheck:Leak</skind>
+            <skaux>match-leak-kinds: definite</skaux>
+            <sframe> <fun>malloc</fun> </sframe>
+            <sframe> <fun>objspace_xmalloc0</fun> </sframe>
+            <sframe> <fun>ruby_xmalloc0</fun> </sframe>
+            <sframe> <obj>/usr/lib/libX11.so.6.3.0</fun> </sframe>
+            <sframe> <fun>ruby_xmalloc_body</fun> </sframe>
+            <sframe> <fun>ruby_xmalloc</fun> </sframe>
+          </suppression>
+        </foo>
+      EOF
+      expected = <<~EOF
+        {
+          insert_a_suppression_name_here
+          Memcheck:Leak
+          fun:malloc
+          fun:objspace_xmalloc0
+          fun:ruby_xmalloc0
+          obj:/usr/lib/libX11.so.6.3.0
+          fun:ruby_xmalloc_body
+          fun:ruby_xmalloc
+        }
+      EOF
+      assert_equal(
+        expected,
+        RubyMemcheck::Suppression.new(@configuration, suppression).to_s,
+      )
+    end
+  end
+end

test/ruby_memcheck/ruby_memcheck_test.rb

@@ -97,6 +97,28 @@ def test_suppressions
       assert_empty(@output_io.string)
     end
 
+    def test_generation_of_suppressions
+      valgrind_options = RubyMemcheck::Configuration::DEFAULT_VALGRIND_OPTIONS.dup
+      valgrind_options << "--gen-suppressions=all"
+      build_configuration(valgrind_options: valgrind_options)
+
+      assert_raises(RubyMemcheck::TestTask::VALGRIND_REPORT_MSG) do
+        run_with_memcheck(<<~RUBY)
+          RubyMemcheck::CTest.new.memory_leak
+        RUBY
+      end
+
+      assert_equal(1, @test_task.errors.length)
+
+      output = @output_io.string
+      refute_empty(output)
+      assert_match(/^100 bytes in 1 blocks are definitely lost in loss record/, output)
+      assert_match(/^ \*memory_leak \(ruby_memcheck_c_test\.c:\d+\)$/, output)
+      assert_match(/^  insert_a_suppression_name_here/, output)
+      assert_match(/^  Memcheck:Leak/, output)
+      assert_match(/^  fun:allocate_memory_leak/, output)
+    end
+
     def test_reports_multiple_errors
       assert_raises(RubyMemcheck::TestTask::VALGRIND_REPORT_MSG) do
         run_with_memcheck(<<~RUBY)