Omit "#class" for simple values

lib/debug/variable_inspector.rb

@@ -42,14 +42,25 @@ def named_members_of(obj)
         Variable.new(name: iv, value: M_INSTANCE_VARIABLE_GET.bind_call(obj, iv))
       end
 
-      members.unshift Variable.internal(name: '#class', value: M_CLASS.bind_call(obj))
       members.concat(ivars_members)
 
+      unless simple_value?(obj)
+        members.unshift Variable.internal(name: '#class', value: M_CLASS.bind_call(obj))
+      end
+
       members
     end
 
     private
 
+    SIMPLE_VALUE_TYPES = [NilClass, FalseClass, TrueClass, Symbol, String, Integer, Float, Class, Module, Array, Hash]
+
+    # A "simple" value is one that does not need its `#class` to be shown.
+    def simple_value?(o)
+      # Check `#instance_of?` instead of `#is_a?` so objects of subclasses show their `#class` for added clarity.
+      SIMPLE_VALUE_TYPES.any? { |t| M_INSTANCE_OF.bind_call(o, t) }
+    end
+
     def value_inspect(obj, short: true)
       self.class.value_inspect(obj, short: short)
     end
@@ -69,6 +80,7 @@ def self.value_inspect(obj, short: true)
 
     # TODO: Replace with Reflection helpers once they are merged
     # https://github.com/ruby/debug/pull/1002
+    M_INSTANCE_OF = method(:instance_of?).unbind
     M_INSTANCE_VARIABLES = method(:instance_variables).unbind
     M_INSTANCE_VARIABLE_GET = method(:instance_variable_get).unbind
     M_CLASS = method(:class).unbind

test/debug/variable_inspector_test.rb

@@ -47,7 +47,6 @@ def test_named_members_of_hash
       )
 
       expected = [
-        Variable.internal(name: '#class', value: Hash),
         Variable.new(name: ':sym', value: "has Symbol key"),
         Variable.new(name: '"str"', value: "has String key"),
         Variable.new(name: '1', value: "has Integer key"),
@@ -73,7 +72,6 @@ def test_named_members_of_struct
 
     def test_named_members_of_string
       expected = [
-        Variable.internal(name: '#class', value: String),
         Variable.internal(name: '#length', value: 5),
         Variable.internal(name: '#encoding', value: Encoding::UTF_8),
         # skip #dump member for short strings
@@ -85,7 +83,6 @@ def test_named_members_of_string
       long_string = "A long string " + ('*' * 1000)
 
       expected = [
-        Variable.internal(name: '#class', value: String),
         Variable.internal(name: '#length', value: long_string.length),
         Variable.internal(name: '#encoding', value: Encoding::UTF_8),
         Variable.internal(name: '#dump', value: VariableInspector::NaiveString.new(long_string)),
@@ -95,10 +92,7 @@ def test_named_members_of_string
     end
 
     def test_named_members_of_class
-      expected = [
-        Variable.internal(name: '#class', value: Class),
-        Variable.internal(name: '%ancestors', value: PointStruct.ancestors.drop(1)),
-      ]
+      expected = [Variable.internal(name: '%ancestors', value: PointStruct.ancestors.drop(1)),]
 
       assert_equal expected, @inspector.named_members_of(PointStruct)
     end
@@ -109,10 +103,7 @@ def test_named_members_of_module
         include *ancestors
       end
 
-      expected = [
-        Variable.internal(name: '#class', value: Module),
-        Variable.internal(name: '%ancestors', value: ancestors),
-      ]
+      expected = [Variable.internal(name: '%ancestors', value: ancestors)]
 
       assert_equal expected, @inspector.named_members_of(mod)
     end
@@ -196,6 +187,31 @@ def test_named_members_of_other_objects
       assert_equal expected, @inspector.named_members_of(point)
     end
 
+    def test_hide_class_of_simple_values
+      assert_not_includes @inspector.named_members_of(nil).map(&:name), "#class"
+      assert_not_includes @inspector.named_members_of(true), "#class"
+      assert_not_includes @inspector.named_members_of(false), "#class"
+      assert_not_includes @inspector.named_members_of(:symbol), "#class"
+      assert_not_includes @inspector.named_members_of("string"), "#class"
+      assert_not_includes @inspector.named_members_of(123), "#class"
+      assert_not_includes @inspector.named_members_of(123.4), "#class"
+      assert_not_includes @inspector.named_members_of(Class.new), "#class"
+      assert_not_includes @inspector.named_members_of(Module.new), "#class"
+      assert_not_includes @inspector.named_members_of(Array.new), "#class"
+      assert_not_includes @inspector.named_members_of(Hash.new), "#class"
+    end
+
+    def test_show_class_of_subclasses_of_simple_types
+      # Skipping these classes, which can't be subclassed meaningfully (or at all):
+      # NilClass, TrueClass, FalseClass, Symbol, Integer, Float, Class, Module
+      string_subclass = Class.new(String)
+      array_subclass = Class.new(Array)
+      hash_subclass = Class.new(Hash) # E.g. HashWithIndifferentAccess would behave this way
+      assert_includes @inspector.named_members_of(string_subclass.new), Variable.internal(name: "#class", value: string_subclass)
+      assert_includes @inspector.named_members_of(array_subclass.new), Variable.internal(name: "#class", value: array_subclass)
+      assert_includes @inspector.named_members_of(hash_subclass.new), Variable.internal(name: "#class", value: hash_subclass)
+    end
+
     private
 
     class PointStruct < Struct.new(:x, :y, keyword_init: true)