Ensure the thread local state is always set up.

lib/pp.rb

@@ -183,6 +183,24 @@ def pop_inspect_key(id)
       Thread.current[:__recursive_key__][:inspect].delete id
     end
 
+    private def guard_inspect(object)
+      recursive_state = Thread.current[:__recursive_key__]
+
+      if recursive_state && recursive_state.key?(:inspect)
+        begin
+          push_inspect_key(object)
+          yield
+        ensure
+          pop_inspect_key(object) unless PP.sharing_detection
+        end
+      else
+        guard_inspect_key do
+          push_inspect_key(object)
+          yield
+        end
+      end
+    end
+
     # Adds +obj+ to the pretty printing buffer
     # using Object#pretty_print or Object#pretty_print_cycle.
     #
@@ -198,15 +216,12 @@ def pp(obj)
         return
       end
 
-      begin
-        push_inspect_key(obj)
+      guard_inspect(obj) do
         group do
           obj.pretty_print self
         rescue NoMethodError
           text Kernel.instance_method(:inspect).bind_call(obj)
         end
-      ensure
-        pop_inspect_key(obj) unless PP.sharing_detection
       end
     end
 

test/test_pp.rb

@@ -243,6 +243,22 @@ def test_hash_in_array
     assert_equal("[{}]", PP.singleline_pp([->(*a){a.last.clear}.ruby2_keywords.call(a: 1)], ''.dup))
     assert_equal("[{}]", PP.singleline_pp([Hash.ruby2_keywords_hash({})], ''.dup))
   end
+
+  def test_direct_pp
+    buffer = String.new
+
+    a = []
+    a << a
+
+    # Isolate the test from any existing Thread.current[:__recursive_key__][:inspect].
+    Thread.new do
+      q = PP::SingleLine.new(buffer)
+      q.pp(a)
+      q.flush
+    end.join
+
+    assert_equal("[[...]]", buffer)
+  end
 end
 
 class PPDelegateTest < Test::Unit::TestCase