Track new Ruby 3.2 VM cache metrics

In Ruby 3.2 the `class_serial` and `global_constant_state` VM metrics
were removed in favor of the new `constant_cache_invalidations` and
`constant_cache_misses` metrics.

Report these new metrics when available. This does not require an update
to the "Ruby (VM) metrics" magic dashboard definition.

ruby/ruby@13bd617
ruby/ruby@6068da8

.changesets/track-new-ruby-3-2-vm-cache-metrics.md

@@ -0,0 +1,6 @@
+---
+bump: "patch"
+type: "change"
+---
+
+Track new Ruby 3.2 VM cache metrics. In Ruby 3.2 the `class_serial` and `global_constant_state` metrics are no longer reported for the "Ruby (VM) metrics" magic dashboard, because Ruby 3.2 removed these metrics. Instead we will now report the new `constant_cache_invalidations` and `constant_cache_misses` metrics reported by Ruby 3.2.

lib/appsignal/probes/mri.rb

@@ -18,17 +18,38 @@ def initialize(appsignal: Appsignal, gc_profiler: Appsignal::GarbageCollection.p
       def call
         stat = RubyVM.stat
 
-        set_gauge(
-          "ruby_vm",
-          stat[:class_serial],
-          :metric => :class_serial
-        )
-
-        set_gauge(
-          "ruby_vm",
-          stat[:constant_cache] ? stat[:constant_cache].values.sum : stat[:global_constant_state],
-          :metric => :global_constant_state
-        )
+        constant_cache_invalidations = stat[:constant_cache_invalidations]
+        if constant_cache_invalidations
+          set_gauge(
+            "ruby_vm",
+            constant_cache_invalidations,
+            :metric => :constant_cache_invalidations
+          )
+        end
+
+        constant_cache_misses = stat[:constant_cache_misses]
+        if constant_cache_misses
+          set_gauge(
+            "ruby_vm",
+            constant_cache_misses,
+            :metric => :constant_cache_misses
+          )
+        end
+
+        class_serial = stat[:class_serial]
+        if class_serial
+          set_gauge("ruby_vm", class_serial, :metric => :class_serial)
+        end
+
+        global_constant_state =
+          stat[:constant_cache] ? stat[:constant_cache].values.sum : stat[:global_constant_state]
+        if global_constant_state
+          set_gauge(
+            "ruby_vm",
+            global_constant_state,
+            :metric => :global_constant_state
+          )
+        end
 
         set_gauge("thread_count", Thread.list.size)
         if Appsignal::GarbageCollection.enabled?

spec/lib/appsignal/probes/mri_spec.rb

@@ -42,10 +42,15 @@ def set_gauge(*args) # rubocop:disable Naming/AccessorMethodName
         allow(GC::Profiler).to receive(:enabled?).and_return(true)
       end
 
-      it "should track vm metrics" do
+      it "should track vm cache metrics" do
         probe.call
-        expect_gauge_value("ruby_vm", :tags => { :metric => :class_serial })
-        expect_gauge_value("ruby_vm", :tags => { :metric => :global_constant_state })
+        if DependencyHelper.ruby_3_2_or_newer?
+          expect_gauge_value("ruby_vm", :tags => { :metric => :constant_cache_invalidations })
+          expect_gauge_value("ruby_vm", :tags => { :metric => :constant_cache_misses })
+        else
+          expect_gauge_value("ruby_vm", :tags => { :metric => :class_serial })
+          expect_gauge_value("ruby_vm", :tags => { :metric => :global_constant_state })
+        end
       end
 
       it "tracks thread counts" do

spec/support/helpers/dependency_helper.rb

@@ -13,6 +13,10 @@ def ruby_3_1_or_newer?
     ruby_version >= Gem::Version.new("3.1.0")
   end
 
+  def ruby_3_2_or_newer?
+    ruby_version >= Gem::Version.new("3.2.0")
+  end
+
   def running_jruby?
     Appsignal::System.jruby?
   end