Handle invalid text field appearance streams posing as other PDF objects

There seem to be PDFs in the wild that have appearance streams with a
valid '/Subtype /Form' entry but invalid /Type entry. Such invalid
objects are not correctly recognized by HexaPDF and thus not assigned
the correct class.

This change amends the previous fix to handle this additional case.

CHANGELOG.md

@@ -27,6 +27,8 @@
 * [HexaPDF::Type::AcroForm::SignatureField#field_value] to always return a
   correctly wrapped object
 * [HexaPDF::Writer] to remove /Type entry from trailer
+* [HexaPDF::Type::AcroForm::AppearanceGenerator#create_text_appearances] to
+  handle invalid appearance streams that are not correct Form XObjects
 
 
 ## 0.46.0 - 2024-08-11

lib/hexapdf/type/acro_form/appearance_generator.rb

@@ -227,8 +227,11 @@ def create_text_appearances
 
           form = (@widget[:AP] ||= {})[:N] ||= @document.add({Type: :XObject, Subtype: :Form})
           # Wrap existing object in Form class in case the PDF writer didn't include the /Subtype
-          # key; we can do this since we know this has to be a Form object
-          form = @document.wrap(form, type: :XObject, subtype: :Form) unless form[:Subtype] == :Form
+          # key or the type of the object is wrong; we can do this since we know this has to be a
+          # Form object
+          unless form.type == :XObject && form[:Subtype] == :Form
+            form = @document.wrap(form, type: :XObject, subtype: :Form)
+          end
           form.value.replace({Type: :XObject, Subtype: :Form, BBox: [0, 0, width, height],
                               Matrix: matrix, Resources: HexaPDF::Object.deep_copy(default_resources)})
           form.contents = ''

test/hexapdf/type/acro_form/test_appearance_generator.rb

@@ -452,6 +452,12 @@ def check_rotation(angle, width, height, matrix)
       assert_equal(form, @widget[:AP][:N])
       refute(form.key?(:key))
       assert_match(/test1/, form.contents)
+
+      form.delete(:Type)
+      @widget[:AP][:N] = @doc.wrap(form, type: HexaPDF::Type::Annotation)
+      @field[:V] = 'test2'
+      @generator.create_appearances
+      assert_match(/test2/, form.contents)
     end
 
     describe "takes the rotation into account" do