emit UnreachableBranch to the "void" condition

lib/steep/ast/types/factory.rb

@@ -409,6 +409,8 @@ def partition_union(type)
             ]
           when AST::Types::Any, AST::Types::Boolean, AST::Types::Top, AST::Types::Logic::Base
             [type, type]
+          when AST::Types::Bot, AST::Types::Void
+            [nil, nil]
           when AST::Types::Nil
             [nil, type]
           when AST::Types::Literal

test/logic_type_interpreter_test.rb

@@ -377,6 +377,40 @@ def test_type_case_select
     end
   end
 
+  def test_call_void
+    with_checker(<<-RBS) do |checker|
+      RBS
+      source = parse_ruby("email = foo; email.void!")
+
+      node = source.node.children[1]
+
+      call = TypeInference::MethodCall::Typed.new(
+        node: node,
+        context: TypeInference::MethodCall::TopLevelContext.new,
+        method_name: :void!,
+        receiver_type: parse_type("::String"),
+        actual_method_type: parse_method_type("() -> void"),
+        method_decls: [],
+        return_type: AST::Types::Void.new()
+      )
+
+      typing = Typing.new(source: source, root_context: nil, cursor: nil)
+      typing.add_typing(dig(node), AST::Types::Void.new(), nil)
+      typing.add_typing(dig(node, 0), parse_type("::String"), nil)
+
+      env = type_env
+        .assign_local_variable(:email, parse_type("::String"), nil)
+
+      interpreter = LogicTypeInterpreter.new(subtyping: checker, typing: typing, config: config)
+      truthy_result, falsy_result = interpreter.eval(env: env, node: node)
+
+      assert_equal parse_type("bot"), truthy_result.type
+      assert_equal parse_type("bot"), falsy_result.type
+      assert_equal true, truthy_result.unreachable
+      assert_equal true, falsy_result.unreachable
+    end
+  end
+
   def test_type_case_select_untyped
     with_checker do |checker|
       interpreter = LogicTypeInterpreter.new(subtyping: checker, typing: nil, config: config)

test/type_check_test.rb

@@ -583,6 +583,99 @@ def test_if_unreachable__unless_else
     )
   end
 
+  def test_if_unreachable__if_void
+    run_type_check_test(
+      signatures: {
+        "a.rbs" => <<~RBS
+          class Foo
+            def void: () -> void
+          end
+        RBS
+      },
+      code: {
+        "a.rb" => <<~RUBY
+          # Both branches are unreachable
+          if Foo.new.void
+            123
+          else
+            123
+          end
+        RUBY
+      },
+      expectations: <<~YAML
+        ---
+        - file: a.rb
+          diagnostics:
+          - range:
+              start:
+                line: 2
+                character: 0
+              end:
+                line: 2
+                character: 2
+            severity: ERROR
+            message: The branch is unreachable
+            code: Ruby::UnreachableBranch
+          - range:
+              start:
+                line: 4
+                character: 0
+              end:
+                line: 4
+                character: 4
+            severity: ERROR
+            message: The branch is unreachable
+            code: Ruby::UnreachableBranch
+      YAML
+    )
+  end
+  def test_if_unreachable__if_bot
+    run_type_check_test(
+      signatures: {
+        "a.rbs" => <<~RBS
+          class Foo
+            def bot: () -> bot
+          end
+        RBS
+      },
+      code: {
+        "a.rb" => <<~RUBY
+          # Both branches are unreachable
+          if Foo.new.bot
+            123
+          else
+            123
+          end
+        RUBY
+      },
+      expectations: <<~YAML
+        ---
+        - file: a.rb
+          diagnostics:
+          - range:
+              start:
+                line: 2
+                character: 0
+              end:
+                line: 2
+                character: 2
+            severity: ERROR
+            message: The branch is unreachable
+            code: Ruby::UnreachableBranch
+          - range:
+              start:
+                line: 4
+                character: 0
+              end:
+                line: 4
+                character: 4
+            severity: ERROR
+            message: The branch is unreachable
+            code: Ruby::UnreachableBranch
+      YAML
+    )
+  end
+
   def test_case_unreachable_1
     run_type_check_test(
       signatures: {

test/type_factory_test.rb

@@ -430,4 +430,13 @@ def test_partition_union__bool_union
       end
     end
   end
+
+  def test_partition_union__void
+    with_factory() do |factory|
+      factory.partition_union(factory.type(parse_type("void"))).tap do |truthy, falsy|
+        assert_equal nil, truthy
+        assert_equal nil, falsy
+      end
+    end
+  end
 end