Fix broken sidebar links for chained class aliases

When Ruby defines chained aliases like `A = B = C` (e.g.,
`HTTPRequestURITooLarge = HTTPRequestURITooLong = HTTPURITooLong`
in net/http), the sidebar link for the outermost alias pointed to
the intermediate alias's HTML file, which is never generated.

The root cause: `update_aliases` creates ClassModule objects whose
`is_alias_for` references stale intermediate objects from
`add_module_alias` that don't know they are aliases. Resolve through
the store to follow already-processed aliases back to the real class.

Also make `name_for_path` follow the alias chain recursively as a
defensive measure.

Fixes #1664.

Author: st0012

lib/rdoc/code_object/class_module.rb

@@ -673,7 +673,7 @@ def path
   # module or class return the name of the latter.
 
   def name_for_path
-    is_alias_for ? is_alias_for.full_name : full_name
+    is_alias_for ? is_alias_for.name_for_path : full_name
   end
 
   ##
@@ -848,6 +848,13 @@ def type
   def update_aliases
     constants.each do |const|
       next unless cm = const.is_alias_for
+
+      # Resolve chained aliases (A = B = C) to the real class/module.
+      cm = @store.find_class_or_module(cm.full_name) || cm
+      while (target = cm.is_alias_for)
+        cm = target
+      end
+
       cm_alias = cm.dup
       cm_alias.name = const.name
 

test/rdoc/generator/darkfish_test.rb

@@ -610,6 +610,43 @@ def test_canonical_url_for_classes
     assert_include(content, '<link rel="canonical" href="https://docs.ruby-lang.org/en/master/Klass/Inner.html">')
   end
 
+  def test_generate_chained_alias_sidebar_links
+    # Reproduces ruby/rdoc#1664:
+    #   class Original < Base
+    #   DirectAlias = Original           # alias of real class
+    #   ChainedAlias = DirectAlias       # alias of an alias
+    #
+    # ChainedAlias's sidebar link must point to Original.html, not DirectAlias.html
+    # (which is never generated because aliases don't get their own files).
+    parent = @top_level.add_module RDoc::NormalModule, 'Parent'
+    original = parent.add_class RDoc::NormalClass, 'Original'
+
+    direct_alias_const = RDoc::Constant.new 'DirectAlias', nil, ''
+    direct_alias_const.record_location @top_level
+    direct_alias_const.is_alias_for = original
+    parent.add_constant direct_alias_const
+    parent.update_aliases
+
+    direct_alias = @store.find_class_or_module 'Parent::DirectAlias'
+
+    chained_alias_const = RDoc::Constant.new 'ChainedAlias', nil, ''
+    chained_alias_const.record_location @top_level
+    chained_alias_const.is_alias_for = direct_alias
+    parent.add_constant chained_alias_const
+    parent.update_aliases
+
+    @store.complete :private
+    @g.generate
+
+    assert_file 'Parent/Original.html'
+    refute File.exist?('Parent/DirectAlias.html'), 'alias should not get its own file'
+    refute File.exist?('Parent/ChainedAlias.html'), 'chained alias should not get its own file'
+
+    index_html = File.binread('index.html')
+    assert_match %r{href="\./Parent/Original\.html">DirectAlias<}, index_html
+    assert_match %r{href="\./Parent/Original\.html">ChainedAlias<}, index_html
+  end
+
   def test_canonical_url_for_rdoc_files
     @store.add_file("CONTRIBUTING.rdoc", parser: RDoc::Parser::Simple)