DI: report an error when instrumenting a loaded file that is not in registry

Author: p

lib/datadog/di/error.rb

@@ -27,6 +27,11 @@ class AgentCommunicationError < Error
       class DITargetNotDefined < Error
       end
 
+      # Attempting to instrument a line and the file containing the line
+      # was loaded prior to code tracking being enabled.
+      class DITargetNotInRegistry < Error
+      end
+
       # Raised when trying to install a probe whose installation failed
       # earlier in the same process. This exception should contain the
       # original exception report from initial installation attempt.

lib/datadog/di/instrumenter.rb

@@ -224,18 +224,20 @@ def hook_line(probe, &block)
               #
               # If the requested file is not in code tracker's registry,
               # or the code tracker does not exist at all,
-              # do not attempt to instrumnet now.
+              # do not attempt to instrument now.
               # The caller should add the line to the list of pending lines
               # to instrument and install the hook when the file in
               # question is loaded (and hopefully, by then code tracking
               # is active, otherwise the line will never be instrumented.)
+              raise_if_probe_in_loaded_features(probe)
               raise Error::DITargetNotDefined, "File not in code tracker registry: #{probe.file}"
             end
           end
         elsif !permit_untargeted_trace_points
           # Same as previous comment, if untargeted trace points are not
           # explicitly defined, and we do not have code tracking, do not
           # instrument the method.
+          raise_if_probe_in_loaded_features(probe)
           raise Error::DITargetNotDefined, "File not in code tracker registry: #{probe.file}"
         end
 
@@ -352,6 +354,24 @@ def unhook(probe)
 
       attr_reader :lock
 
+      def raise_if_probe_in_loaded_features(probe)
+        # If the probe file is in the list of loaded files
+        # (as per $LOADED_FEATURES, using either exact or suffix match),
+        # raise an error indicating that
+        # code tracker is missing the loaded file because the file
+        # won't be loaded again (DI only works in production environments
+        # that do not normally reload code).
+        if $LOADED_FEATURES.include?(probe.file)
+          raise Error::DITargetNotInRegistry, "File loaded but is not in code tracker registry: #{probe.file}"
+        end
+        # Ths is an expensive check
+        $LOADED_FEATURES.each do |path|
+          if Utils.path_matches_suffix?(path, probe.file)
+            raise Error::DITargetNotInRegistry, "File matching probe path (#{probe.file}) was loaded and is not in code tracker registry: #{path}"
+          end
+        end
+      end
+
       # TODO test that this resolves qualified names e.g. A::B
       def symbolize_class_name(cls_name)
         Object.const_get(cls_name)

spec/datadog/di/instrumenter_spec.rb

@@ -742,6 +742,20 @@
         expect(observed_calls.length).to eq 1
         expect(observed_calls.first).to be_a(Hash)
       end
+
+      context 'when instrumenting a line in loaded but not tracked file' do
+        let(:probe) do
+          Datadog::DI::Probe.new(file: 'hook_line.rb', line_no: 3,
+            id: 1, type: :log)
+        end
+
+        it 'raises DITargetNotInRegistry' do
+          expect do
+            instrumenter.hook_line(probe) do |payload|
+            end
+          end.to raise_error(Datadog::DI::Error::DITargetNotInRegistry, /File matching probe path.*was loaded and is not in code tracker registry/)
+        end
+      end
     end
 
     context 'when method is recursive' do