explicit begin/rescue & tweaks

We need an explicit begin here because we support Ruby 2.4, and the implicit
begin for blocks was added in 2.5.

Then, some minor tweaks to the error message and tests.

lib/zeitwerk/loader.rb

@@ -474,32 +474,39 @@ def actual_root_dirs
     # @return [void]
     def set_autoloads_in_dir(dir, parent)
       ls(dir) do |basename, abspath|
-        if ruby?(basename)
-          basename.slice!(-3, 3)
-          cname = inflector.camelize(basename, abspath).to_sym
-          autoload_file(parent, cname, abspath)
-        elsif dir?(abspath)
-          # In a Rails application, `app/models/concerns` is a subdirectory of
-          # `app/models`, but both of them are root directories.
-          #
-          # To resolve the ambiguity file name -> constant path this introduces,
-          # the `app/models/concerns` directory is totally ignored as a namespace,
-          # it counts only as root. The guard checks that.
-          unless root_dirs.key?(abspath)
+        begin
+          if ruby?(basename)
+            basename.slice!(-3, 3)
             cname = inflector.camelize(basename, abspath).to_sym
-            autoload_subdir(parent, cname, abspath)
+            autoload_file(parent, cname, abspath)
+          elsif dir?(abspath)
+            # In a Rails application, `app/models/concerns` is a subdirectory of
+            # `app/models`, but both of them are root directories.
+            #
+            # To resolve the ambiguity file name -> constant path this introduces,
+            # the `app/models/concerns` directory is totally ignored as a namespace,
+            # it counts only as root. The guard checks that.
+            unless root_dirs.key?(abspath)
+              cname = inflector.camelize(basename, abspath).to_sym
+              autoload_subdir(parent, cname, abspath)
+            end
           end
+        rescue ::NameError => error
+          path_type = ruby?(abspath) ? "file" : "directory"
+
+          raise NameError, <<~MESSAGE
+            #{error.message} inferred by #{inflector.class} from #{path_type}
+
+              #{abspath}
+
+            Possible ways to address this:
+
+              * Tell Zeitwerk to ignore this particular #{path_type}.
+              * Tell Zeitwerk to ignore one of its parent directories.
+              * Rename the #{path_type} to comply with the naming conventions.
+              * Modify the inflector to handle this case.
+          MESSAGE
         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

@@ -45,19 +45,21 @@ class TestExceptions < LoaderTest
     end
   end
 
-  test "raises NameError if the inflector return an invalid constant name for a file" do
+  test "raises Zeitwerk::NameError if the inflector returns 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"
+    assert_includes error.message, "Tell Zeitwerk to ignore this particular file."
   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
+  test "raises Zeitwerk::NameError if the inflector returns an invalid constant name for a directory" do
+    files = [["foo-bar/baz.rb", "FooBar::Baz = 1"]]
+    error = assert_raises Zeitwerk::NameError do
       with_setup(files) {}
     end
     assert_includes error.message, "wrong constant name Foo-bar"
+    assert_includes error.message, "Tell Zeitwerk to ignore this particular directory."
   end
 end