Fix name resolver for class/module-alias

lib/rbs/environment.rb

@@ -362,7 +362,26 @@ def normalize_module_name?(name)
         when ClassEntry, ModuleEntry
           type_name
         when ClassAliasEntry, ModuleAliasEntry
-          normalize_module_name?(entry.decl.old_name)
+          i = 0
+          outer_paths = entry.outer.map { |outer| outer.name.to_namespace.path }
+          old_name_namespace = entry.decl.old_name.namespace
+          old_name_bottom = entry.decl.old_name.name
+          n = nil #: ::RBS::TypeName | nil | false
+          loop do
+            outer_path = outer_paths[-i, i] or raise
+            t = TypeName.new(
+              namespace: Namespace.new(
+                absolute: false,
+                path: outer_path.flatten
+              ) + old_name_namespace,
+              name: old_name_bottom
+            )
+            n = normalize_module_name?(t)
+            break if n
+            i += 1
+            break if outer_paths.length < i
+          end
+          n
         else
           nil
         end

lib/rbs/validator.rb

@@ -158,11 +158,20 @@ def validate_variable(var)
     def validate_class_alias(entry:)
       case env.normalize_module_name?(entry.decl.new_name)
       when nil
+        # Unreachable?
         raise NoTypeFoundError.new(type_name: entry.decl.old_name, location: entry.decl.location&.[](:old_name))
       when false
         raise CyclicClassAliasDefinitionError.new(entry)
       end
 
+      case env.normalize_module_name?(entry.decl.old_name)
+      when nil
+        raise NoTypeFoundError.new(type_name: entry.decl.old_name, location: entry.decl.location&.[](:old_name))
+      when false
+        # Unreachable?
+        raise CyclicClassAliasDefinitionError.new(entry)
+      end
+
       case entry
       when Environment::ClassAliasEntry
         unless env.class_entry(entry.decl.old_name)

test/rbs/cli_test.rb

@@ -839,6 +839,38 @@ def void: () -> voida
     end
   end
 
+  # https://github.com/ruby/rbs/issues/2293
+  def test_nested_module_alias
+    with_cli do |cli|
+      Dir.mktmpdir do |dir|
+        (Pathname(dir) + 'a.rbs').write(<<~RBS)
+          module Foo
+            module Bar
+              module M
+              end
+              module M2 = M
+            end
+
+            module Baz = Bar
+
+            module Bar::N = Bar::M
+
+            module X = Nothing
+          end
+
+          module Foo::Qux = Foo::Baz
+
+          module Foo::Y = Foo::Nothing
+        RBS
+        assert_raises SystemExit do
+          cli.run(["-I", dir, "validate"])
+        end
+        assert_include stdout.string, "a.rbs:12:13...12:20: Could not find Nothing (RBS::NoTypeFoundError)"
+        assert_include stdout.string, "a.rbs:17:16...17:28: Could not find Foo::Nothing (RBS::NoTypeFoundError)"
+      end
+    end
+  end
+
   def test_constant
     with_cli do |cli|
       cli.run(%w(constant Pathname))

test/validator_test.rb

@@ -277,6 +277,65 @@ class Baz = Baz
     end
   end
 
+  # https://github.com/ruby/rbs/issues/2293
+  def test_validate_class_alias_in_namespace
+    SignatureManager.new do |manager|
+      manager.add_file("foo.rbs", <<-EOF)
+module Foo
+  module Bar
+    module M
+    end
+    module M2 = M
+  end
+
+  module Baz = Bar
+
+  module Bar::N = Bar::M
+
+  module X = Nothing
+end
+
+module Foo::Qux = Foo::Baz
+
+module Foo::Y = Foo::Nothing
+EOF
+
+      manager.build do |env|
+        validator = RBS::Validator.new(env: env)
+        env.class_alias_decls[RBS::TypeName.parse("::Foo::Baz")].tap do |entry|
+          assert_nothing_raised do
+            validator.validate_class_alias(entry: entry)
+          end
+        end
+        env.class_alias_decls[RBS::TypeName.parse("::Foo::Bar::N")].tap do |entry|
+          assert_nothing_raised do
+            validator.validate_class_alias(entry: entry)
+          end
+        end
+        env.class_alias_decls[RBS::TypeName.parse("::Foo::Bar::M2")].tap do |entry|
+          assert_nothing_raised do
+            validator.validate_class_alias(entry: entry)
+          end
+        end
+        env.class_alias_decls[RBS::TypeName.parse("::Foo::Qux")].tap do |entry|
+          assert_nothing_raised do
+            validator.validate_class_alias(entry: entry)
+          end
+        end
+        env.class_alias_decls[RBS::TypeName.parse("::Foo::X")].tap do |entry|
+          assert_raises RBS::NoTypeFoundError do
+            validator.validate_class_alias(entry: entry)
+          end
+        end
+        env.class_alias_decls[RBS::TypeName.parse("::Foo::Y")].tap do |entry|
+          assert_raises RBS::NoTypeFoundError do
+            validator.validate_class_alias(entry: entry)
+          end
+        end
+      end
+    end
+  end
+
   def test_validate_type__presence__module_alias_instance
     SignatureManager.new do |manager|
       manager.add_file("foo.rbs", <<-EOF)