Support constant assign parsed before class/module definition

Support `Const = RHS` parsed before `class RHS;end` defined in another file.

Author: tompng

lib/rdoc/code_object/constant.rb

@@ -92,10 +92,18 @@ def is_alias_for
       @is_alias_for = found if found
       @is_alias_for
     else
-      @is_alias_for
+      @is_alias_for ||= find_alias_for
     end
   end
 
+  # Find alias constant for a value.
+  # This is used when the constant is parsed before the class or module defined in another file.
+  # Note that module nesting information is lost, so constant lookup is inaccurate.
+
+  def find_alias_for
+    parent.find_module_named(value) if value&.match?(/\A(::)?([A-Z][A-Za-z0-9_]*)(::[A-Z][A-Za-z0-9_]*)*\z/)
+  end
+
   def inspect # :nodoc:
     "#<%s:0x%x %s::%s>" % [
       self.class, object_id,

lib/rdoc/code_object/context.rb

@@ -439,6 +439,7 @@ def add_constant(constant)
       known.value = constant.value if
         known.value.nil? or known.value.strip.empty?
 
+      constant.parent = self
       known.is_alias_for ||= constant.is_alias_for
     else
       @constants_hash[constant.name] = constant

test/rdoc/parser/prism_ruby_test.rb

@@ -1638,6 +1638,50 @@ class Bar; end
     assert_equal 'Foo::C', klass.find_module_named('C').full_name
   end
 
+  def test_constant_alias_reverse_order
+    util_parser <<~RUBY
+      # Parsed first
+      class Foo
+        A = Bar
+        B = Foo::Bar
+        C = Baz
+      end
+
+      # Parsed later
+      class Foo
+        class Bar; end
+      end
+      class Baz; end
+    RUBY
+    klass = @top_level.classes.first
+    assert_equal 'Foo::Bar', klass.find_constant_named('A').is_alias_for.full_name
+    assert_equal 'Foo::Bar', klass.find_constant_named('B').is_alias_for.full_name
+    assert_equal 'Baz', klass.find_constant_named('C').is_alias_for.full_name
+  end
+
+  def test_repeated_constant_alias
+    util_parser <<~RUBY
+      # Parsed first
+      class Foo
+        if cond
+          A = Bar
+          B = Baz
+        else
+          A = Bar
+          B = Baz
+        end
+      end
+
+      # Parsed later
+      class Baz
+      end
+    RUBY
+    klass = @top_level.classes.first
+    assert_equal 'Bar', klass.find_constant_named('A').value
+    assert_nil klass.find_constant_named('A').is_alias_for
+    assert_equal 'Baz', klass.find_constant_named('B').is_alias_for.full_name
+  end
+
   def test_constant_with_singleton_class
     omit if accept_legacy_bug?
     util_parser <<~RUBY