Give an optional type hint to lhs of ||

lib/steep/type_construction.rb

@@ -1778,7 +1778,10 @@ def synthesize(node, hint: nil, condition: false)
           yield_self do
             left_node, right_node = node.children
 
-            left_type, constr, left_context = synthesize(left_node, hint: hint, condition: true).to_ary
+            if hint
+              left_hint = union_type_unify(hint, AST::Builtin.nil_type, AST::Builtin.false_type)
+            end
+            left_type, constr, left_context = synthesize(left_node, hint: left_hint, condition: true).to_ary
 
             interpreter = TypeInference::LogicTypeInterpreter.new(subtyping: checker, typing: typing, config: builder_config)
             left_truthy, left_falsy = interpreter.eval(env: left_context.type_env, node: left_node)

sample/lib/conference.rb

@@ -32,3 +32,8 @@ def foo(...)
     bar(self, ...).to_s
   end
 end
+
+
+
+conference = nil #: Conference?
+

test/type_check_test.rb

@@ -1507,4 +1507,30 @@ def test_lambda__hint_is_untyped
       YAML
     )
   end
+
+  def test_safe_navigation_operator__or_hint
+    run_type_check_test(
+      signatures: {
+        "a.rbs" => <<~RBS
+          class Hello
+            def foo: (Integer?) -> Integer
+          end
+        RBS
+      },
+      code: {
+        "a.rb" => <<~RUBY
+          class Hello
+            def foo(a)
+              a&.then {|x| x.infinite? } || -1
+            end
+          end
+        RUBY
+      },
+      expectations: <<~YAML
+        ---
+        - file: a.rb
+          diagnostics: []
+      YAML
+    )
+  end
 end