Better error for invalid constant names

lib/zeitwerk/error.rb

@@ -4,4 +4,7 @@ class Error < StandardError
 
   class ReloadingDisabledError < Error
   end
+
+  class NameError < ::NameError
+  end
 end

lib/zeitwerk/loader.rb

@@ -490,6 +490,16 @@ def set_autoloads_in_dir(dir, parent)
             autoload_subdir(parent, cname, abspath)
           end
         end
+      rescue ::NameError => error
+        raise NameError, <<~MESSAGE
+          #{error.message}
+          This invalid constant name was inferred by #{inflector.class} from #{abspath}.
+
+          You can either:
+            - Mark this path to be ignored.
+            - Rename the file to respect the general convention.
+            - Modify the inflector to handle this case better.
+        MESSAGE
       end
     end
 

test/lib/zeitwerk/test_exceptions.rb

@@ -44,4 +44,20 @@ class TestExceptions < LoaderTest
       assert_raises(RuntimeError, "foo") { Raises }
     end
   end
+
+  test "raises NameError if the inflector return an invalid constant name for a file" do
+    files = [["foo-bar.rb", "FooBar = 1"]]
+    error = assert_raises Zeitwerk::NameError do
+      with_setup(files) {}
+    end
+    assert_includes error.message, "wrong constant name Foo-bar"
+  end
+
+  test "raises NameError if the inflector return an invalid constant name for a directory" do
+    files = [["foo-bar/baz.rb", "FooBar = 1"]]
+    error = assert_raises NameError do
+      with_setup(files) {}
+    end
+    assert_includes error.message, "wrong constant name Foo-bar"
+  end
 end