fix: Eval handler now works correctly even when not tracing

Eval handler relies on specific call stack layout when recovering
original eval call context. Since call hook handler used to
short-circuit over trace_call method when not tracing, the layout
was unexpected when the handlers were loaded but tracing disabled
(eg. when initial code load is performed dynamically after loading
appmap gem).

The fix is to always call trace_call and short-circuit in there,
keeping the call stack the same.

Alternative, rejected solutions:
- check for tracing being disabled in eval handler and use the
  correct (shallower) call stack depth in this case,
- examine all frames sequentially in the eval handler until the
  correct one is found.

Author: dividedmind

lib/appmap/hook/method/ruby2.rb

@@ -8,9 +8,9 @@ class Hook
     # cf. https://eregon.me/blog/2019/11/10/the-delegation-challenge-of-ruby27.html
     class Method
       ruby2_keywords def call(receiver, *args, &block)
-        return do_call(receiver, *args, &block) unless trace?
-
-        call_event = with_disabled_hook { before_hook receiver, *args }
+        call_event = trace? && with_disabled_hook { before_hook receiver, *args }
+        # note we can't short-circuit directly to do_call because then the call stack
+        # depth changes and eval handler doesn't work correctly
         trace_call call_event, receiver, *args, &block
       end
 
@@ -32,7 +32,10 @@ def before_hook(receiver, *args)
         hook_method.bind(receiver).call(*args, &block)
       end
 
+      # rubocop:disable Metrics/MethodLength
       ruby2_keywords def trace_call(call_event, receiver, *args, &block)
+        return do_call(receiver, *args, &block) unless call_event
+
         start_time = gettime
         begin
           return_value = do_call(receiver, *args, &block)
@@ -44,6 +47,7 @@ def before_hook(receiver, *args)
             if call_event
         end
       end
+      # rubocop:enable Metrics/MethodLength
 
       def hook_method_def
         this = self

lib/appmap/hook/method/ruby3.rb

@@ -5,9 +5,9 @@ class Hook
     # Delegation methods for Ruby 3.
     class Method
       def call(receiver, *args, **kwargs, &block)
-        return do_call(receiver, *args, **kwargs, &block) unless trace?
-
-        call_event = with_disabled_hook { before_hook receiver, *args, **kwargs }
+        call_event = trace? && with_disabled_hook { before_hook receiver, *args, **kwargs }
+        # note we can't short-circuit directly to do_call because then the call stack
+        # depth changes and eval handler doesn't work correctly
         trace_call call_event, receiver, *args, **kwargs, &block
       end
 
@@ -34,7 +34,10 @@ def do_call(receiver, *args, **kwargs, &block)
         hook_method.bind_call(receiver, *args, **kwargs, &block)
       end
 
+      # rubocop:disable Metrics/MethodLength
       def trace_call(call_event, receiver, *args, **kwargs, &block)
+        return do_call(receiver, *args, **kwargs, &block) unless call_event
+
         start_time = gettime
         begin
           return_value = do_call(receiver, *args, **kwargs, &block)
@@ -46,6 +49,7 @@ def trace_call(call_event, receiver, *args, **kwargs, &block)
             if call_event
         end
       end
+      # rubocop:enable Metrics/MethodLength
 
       def hook_method_def
         this = self

spec/handler/class_with_eval.rb

@@ -0,0 +1,13 @@
+# frozen_string_literal: true
+
+# rubocop:disable Style/EvalWithLocation
+
+module AppMap
+  class SpecClasses
+    class WithEval
+      eval %(def text; 'text'; end)
+    end
+  end
+end
+
+# rubocop:enable Style/EvalWithLocation

spec/handler/eval_spec.rb

@@ -57,10 +57,17 @@ def record_block
     end
     expect(new_cls.const_get(class_name)).to eq(cls)
   end
+
+  it 'works correctly when loaded even when not tracing' do
+    load "#{__dir__}/class_with_eval.rb"
+    expect { AppMap::SpecClasses::WithEval.new.text }.to_not raise_error(NameError)
+  end
 end
 
 module ClassMaker
   def self.make_class(class_name)
     eval "class #{class_name}; end; #{class_name}"
   end
 end
+
+# rubocop:enable Security/Eval, Style/EvalWithLocation