Use receiver #name rather than #inspect to build NameError message

Merged: https://github.com/ruby/ruby/pull/3080

error.c

@@ -1761,6 +1761,17 @@ name_err_mesg_equal(VALUE obj1, VALUE obj2)
     return Qtrue;
 }
 
+/* :nodoc: */
+static VALUE
+name_err_mesg_receiver_name(VALUE obj)
+{
+    if (RB_SPECIAL_CONST_P(obj)) return Qundef;
+    if (RB_BUILTIN_TYPE(obj) == T_MODULE || RB_BUILTIN_TYPE(obj) == T_CLASS) {
+        return rb_check_funcall(obj, rb_intern("name"), 0, 0);
+    }
+    return Qundef;
+}
+
 /* :nodoc: */
 static VALUE
 name_err_mesg_to_str(VALUE obj)
@@ -1789,7 +1800,9 @@ name_err_mesg_to_str(VALUE obj)
 	    d = FAKE_CSTR(&d_str, "false");
 	    break;
 	  default:
-	    d = rb_protect(rb_inspect, obj, &state);
+	    d = rb_protect(name_err_mesg_receiver_name, obj, &state);
+	    if (state || d == Qundef || d == Qnil)
+		d = rb_protect(rb_inspect, obj, &state);
 	    if (state)
 		rb_set_errinfo(Qnil);
 	    if (NIL_P(d)) {

spec/ruby/language/constants_spec.rb

@@ -154,6 +154,36 @@ describe "Literal (A::X) constant resolution" do
     -> { ConstantSpecs::ParentA::CS_CONSTX }.should raise_error(NameError)
   end
 
+  ruby_version_is "2.8" do
+    it "uses the module or class #name to craft the error message" do
+      mod = Module.new do
+        def self.name
+          "ModuleName"
+        end
+
+        def self.inspect
+          "<unusable info>"
+        end
+      end
+
+      -> { mod::DOES_NOT_EXIST }.should raise_error(NameError, /uninitialized constant ModuleName::DOES_NOT_EXIST/)
+    end
+
+    it "uses the module or class #inspect to craft the error message if they are anonymous" do
+      mod = Module.new do
+        def self.name
+          nil
+        end
+
+        def self.inspect
+          "<unusable info>"
+        end
+      end
+
+      -> { mod::DOES_NOT_EXIST }.should raise_error(NameError, /uninitialized constant <unusable info>::DOES_NOT_EXIST/)
+    end
+  end
+
   it "sends #const_missing to the original class or module scope" do
     ConstantSpecs::ClassA::CS_CONSTX.should == :CS_CONSTX
   end