[rubygems/rubygems] Fix gemspec require_paths type validation

It was not properly being detected as an Array attribute, and thus not
properly validated.

Fixing this allows us to remove a strange `rescue` clause in Bundler.

https://github.com/rubygems/rubygems/commit/4121a32408

lib/bundler/installer/standalone.rb

@@ -58,9 +58,6 @@ module Bundler
       else
         SharedHelpers.relative_path_to(full_path, from: Bundler.root.join(bundler_path))
       end
-    rescue TypeError
-      error_message = "#{spec.name} #{spec.version} has an invalid gemspec"
-      raise Gem::InvalidSpecificationException.new(error_message)
     end
 
     def prevent_gem_activation

lib/bundler/rubygems_ext.rb

@@ -60,6 +60,12 @@ module Gem
   FLATTENS_REQUIRED_PATHS = Specification.new.respond_to?(:flatten_require_paths).freeze
 
   class Specification
+    # Can be removed once RubyGems 3.5.15 support is dropped
+    correct_array_attributes = @@default_value.select {|_k,v| v.is_a?(Array) }.keys
+    unless @@array_attributes == correct_array_attributes
+      @@array_attributes = correct_array_attributes # rubocop:disable Style/ClassVars
+    end
+
     require_relative "match_metadata"
     require_relative "match_platform"
 

lib/rubygems/specification.rb

@@ -175,7 +175,7 @@ class Gem::Specification < Gem::BasicSpecification
   end
 
   @@attributes = @@default_value.keys.sort_by(&:to_s)
-  @@array_attributes = @@default_value.reject {|_k,v| v != [] }.keys
+  @@array_attributes = @@default_value.select {|_k,v| v.is_a?(Array) }.keys
   @@nil_attributes, @@non_nil_attributes = @@default_value.keys.partition do |k|
     @@default_value[k].nil?
   end

spec/bundler/install/gems/standalone_spec.rb

@@ -295,7 +295,7 @@ RSpec.shared_examples "bundle install --standalone" do
 
     it "outputs a helpful error message" do
       expect(err).to include("You have one or more invalid gemspecs that need to be fixed.")
-      expect(err).to include("bar 1.0 has an invalid gemspec")
+      expect(err).to include("bar.gemspec is not valid")
     end
   end
 

test/rubygems/test_gem_specification.rb

@@ -2989,6 +2989,18 @@ duplicate dependency on c (>= 1.2.3, development), (~> 1.2) use:
                  e.message
   end
 
+  def test_validate_require_paths_with_invalid_types
+    util_setup_validate
+
+    @a1.require_paths = [1, 2]
+    e = assert_raise Gem::InvalidSpecificationException do
+      @a1.validate
+    end
+
+    assert_equal "require_paths must be an Array of String",
+                 e.message
+  end
+
   def test_validate_files
     pend "test_validate_files skipped on MS Windows (symlink)" if Gem.win_platform?
     util_setup_validate