Reword Zeitwerk::NameError message again

I am sleeping on this one and trying different options.

The previous revision lacked symmetry for my taste, because if you say
"the top-level constant X", when there is a namespace "M::N", why is
that "M" not qualified as top-level?

The answer is that an error message is not a constant lookup, it is by
convention relative to the top-level namespace. But then, the messages
for simple and compound constant paths lack symmetry.

This alternative is more coherent, and also matches the way you think
about project layouts. You define constants in namespaces represented by
directories.

Let's try this one now.

lib/zeitwerk/loader/callbacks.rb

@@ -18,8 +18,8 @@ module Zeitwerk::Loader::Callbacks
       to_unload[cpath] = [file, cref] if reloading_enabled?
       run_on_load_callbacks(cpath, cget(*cref), file) unless on_load_callbacks.empty?
     else
-      the = cref[0] == Object ? "the top-level" : "the"
-      msg = "expected file #{file} to define #{the} constant #{cpath}"
+      namespace = cref[0] == Object ? "top-level namespace" : "namespace #{real_mod_name(cref[0])}"
+      msg = "expected #{file} to define #{cref[1]} in the #{namespace}"
       log(msg) if logger
 
       # Ruby still keeps the autoload defined, but we remove it because the

test/lib/zeitwerk/test_exceptions.rb

@@ -19,7 +19,7 @@ def assert_error_message(message, error)
     with_setup(files) do
       typo_rb = File.expand_path("typo.rb")
       error = assert_raises(Zeitwerk::NameError) { Typo }
-      assert_error_message "expected file #{typo_rb} to define the top-level constant Typo", error
+      assert_error_message "expected #{typo_rb} to define Typo in the top-level namespace", error
       assert_equal :Typo, error.name
     end
   end
@@ -29,7 +29,7 @@ def assert_error_message(message, error)
     with_setup(files) do
       typo_rb = File.expand_path("m/typo.rb")
       error = assert_raises(Zeitwerk::NameError) { M::Typo }
-      assert_error_message "expected file #{typo_rb} to define the constant M::Typo", error
+      assert_error_message "expected #{typo_rb} to define Typo in the namespace M", error
       assert_equal :Typo, error.name
     end
   end
@@ -39,7 +39,7 @@ def assert_error_message(message, error)
     with_setup(files) do
       x_rb = File.expand_path("x.rb")
       error = assert_raises(Zeitwerk::NameError) { loader.eager_load }
-      assert_error_message "expected file #{x_rb} to define the top-level constant X", error
+      assert_error_message "expected #{x_rb} to define X in the top-level namespace", error
       assert_equal :X, error.name
     end
   end
@@ -49,7 +49,7 @@ def assert_error_message(message, error)
     with_setup(files) do
       x_rb = File.expand_path("m/x.rb")
       error = assert_raises(Zeitwerk::NameError) { loader.eager_load }
-      assert_error_message "expected file #{x_rb} to define the constant M::X", error
+      assert_error_message "expected #{x_rb} to define X in the namespace M", error
       assert_equal :X, error.name
     end
   end
@@ -64,7 +64,7 @@ def assert_error_message(message, error)
     with_setup(files) do
       cli_x_rb = File.expand_path("cli/x.rb")
       error = assert_raises(Zeitwerk::NameError) { loader.eager_load }
-      assert_error_message "expected file #{cli_x_rb} to define the constant Cli::X", error
+      assert_error_message "expected #{cli_x_rb} to define X in the namespace Cli", error
       assert_equal :X, error.name
     end
   end

test/lib/zeitwerk/test_logging.rb

@@ -136,7 +136,7 @@ def logger.debug(message)
   test "logs failed autoloads, provided the require call succeeded" do
     files = [["x.rb", ""]]
     with_files(files) do
-      assert_logged(/expected file #{File.expand_path("x.rb")} to define the top-level constant X/) do
+      assert_logged(/expected #{File.expand_path("x.rb")} to define X in the top-level namespace/) do
         loader.push_dir(".")
         loader.setup
         assert_raises(Zeitwerk::NameError) { X }