Prevent RDoc from polluting in_files

There is currently a bug in RDoc v6.5.0 that causes the value of
`RDoc::ClassModule#in_files` to become polluted when referring to a
constant nested in a module where the module has been previously seen
but the constant has not.  For example, if RDoc sees a core extension
like:

  ```ruby
  class Float
    def as_json(*)
      # ...
    end
  end
  ```

and later sees a reference to `Float::INFINITY` in a file `foo.rb`, then
it will add `foo.rb` to `in_files` for `Float`.  That will cause
`foo.rb` to appear in `public/classes/Float.html` and `Float` to appear
in `public/files/foo.rb`.

This commit monkey patches RDoc to prevent such pollution.  The monkey
patch has been tested with the test suites of RDoc v6.5.0 and RDoc
`master` as of ruby/rdoc@9e75bf6, and
all tests pass.

Author: jonathanhefner

lib/sdoc/rdoc_monkey_patches.rb

@@ -22,3 +22,19 @@ def cross_reference(name, text = nil, code = true)
     super
   end
 end)
+
+
+RDoc::Parser::Ruby.prepend(Module.new do
+  def get_class_or_module(container, ignore_constants = false)
+    @ignoring_constants ||= nil
+    original_ignoring_constants, @ignoring_constants = @ignoring_constants, ignore_constants
+    super
+  ensure
+    @ignoring_constants = original_ignoring_constants
+  end
+
+  def record_location(*)
+    @ignoring_constants ||= nil
+    super unless @ignoring_constants
+  end
+end)

spec/rdoc_monkey_patches_spec.rb

@@ -47,4 +47,32 @@ def qux; end
       _(description).must_match %r"and <a href=.+?>qux \(also\) cannot</a>"
     end
   end
+
+  describe RDoc::Parser::Ruby do
+    it "does not pollute RDoc::ClassModule#in_files when parsing constants" do
+      Dir.mktmpdir do |dir|
+        Dir.chdir(dir) do
+          File.write("float_ext.rb", <<~RUBY)
+            class Float
+              def ext; end
+            end
+          RUBY
+
+          File.write("foo.rb", <<~RUBY)
+            class Foo
+              def foo; Float::INFINITY; end
+            end
+          RUBY
+
+          rdoc_store = rdoc_dry_run("--files", "float_ext.rb", "foo.rb").store
+
+          _(rdoc_store.find_class_or_module("Float").in_files).
+            must_equal [rdoc_store.find_file_named("float_ext.rb")]
+
+          _(rdoc_store.find_file_named("foo.rb").classes_and_modules).
+            must_equal [rdoc_store.find_class_or_module("Foo")]
+        end
+      end
+    end
+  end
 end