module T::Private::Methods::SignatureValidation

def self.base_override_loc_str(signature, super_signature)
ignature.mode == Modes.abstract ? 'Implementation' : 'Override'
on: in #{method_loc_str(super_signature.method)}" \
 in #{method_loc_str(signature.method)}"

def self.method_loc_str(method)
rce_location
ation.join(':')
n>"
 #{loc}"

def self.pretty_mode(signature)
= Modes.overridable_override
rride'
e}"

def self.validate(signature)
  # Constructors in any language are always a bit weird: they're called in a
  # static context, but their bodies are implemented by instance methods. So
  # a mix of the rules that apply to instance methods and class methods
  # apply.
  #
  # In languages like Java and Scala, static methods/companion object methods
  # are never inherited. (In Java it almost looks like you can inherit them,
  # because `Child.static_parent_method` works, but this method is simply
  # resolved statically to `Parent.static_parent_method`). Even though most
  # instance methods overrides have variance checking done, constructors are
  # not treated like this, because static methods are never
  # inherited/overridden, and the constructor can only ever be called
  # indirectly by way of the static method. (Note: this is only a mental
  # model--there's not actually a static method for the constructor in Java,
  # there's an `invokespecial` JVM instruction that handles this).
  #
  # But Ruby is not like Java: singleton class methods in Ruby *are*
  # inherited, unlike static methods in Java. In fact, this is similar to how
  # JavaScript works. TypeScript simply then sidesteps the issue with
  # structural typing: `typeof Parent` is not compatible with `typeof Child`
  # if their constructors are different. (In a nominal type system, simply
  # having Child descend from Parent should be the only factor in determining
  # whether those types are compatible).
  #
  # Flow has nominal subtyping for classes. When overriding (static and
  # instance) methods in a child class, the overrides must satisfy variance
  # constraints. But it still carves out an exception for constructors,
  # because then literally every class would have to have the same
  # constructor. This is simply unsound. Hack does a similar thing--static
  # method overrides are checked, but not constructors. Though what Hack
  # *does* have is a way to opt into override checking for constructors with
  # a special annotation.
  #
  # It turns out, Sorbet already has this special annotation: either
  # `abstract` or `overridable`. At time of writing, *no* static override
  # checking happens unless marked with these keywords (though at runtime, it
  # always happens). Getting the static system to parity with the runtime by
  # always checking overrides would be a great place to get to one day, but
  # for now we can take advantage of it by only doing override checks for
  # constructors if they've opted in.
  #
  # (When we get around to more widely checking overrides statically, we will
  # need to build a matching special case for constructors statically.)
  #
  # Note that this breaks with tradition: normally, constructors are not
  # allowed to be abstract. But that's kind of a side-effect of everything
  # above: in Java/Scala, singleton class methods are never abstract because
  # they're not inherited, and this extends to constructors. TypeScript
  # simply rejects `new klass()` entirely if `klass` is
  # `typeof AbstractClass`, requiring instead that you write
  # `{ new(): AbstractClass }`. We may want to consider building some
  # analogue to `T.class_of` in the future that works like this `{new():
  # ...}` type.
  if signature.method_name == :initialize && signature.method.owner.is_a?(Class) &&
      signature.mode == Modes.standard
    return
  end
  super_method = signature.method.super_method
  if super_method && super_method.owner != signature.method.owner
    Methods.maybe_run_sig_block_for_method(super_method)
    super_signature = Methods.signature_for_method(super_method)
    # If the super_method has any kwargs we can't build a
    # Signature for it, so we'll just skip validation in that case.
    if !super_signature && !super_method.parameters.select {|kind, _| kind == :rest || kind == :kwrest}.empty?
      nil
    else
      # super_signature can be nil when we're overriding a method (perhaps a builtin) that didn't use
      # one of the method signature helpers. Use an untyped signature so we can still validate
      # everything but types.
      #
      # We treat these signatures as overridable, that way people can use `.override` with
      # overrides of builtins. In the future we could try to distinguish when the method is a
      # builtin and treat non-builtins as non-overridable (so you'd be forced to declare them with
      # `.overridable`).
      #
      super_signature ||= Methods::Signature.new_untyped(method: super_method)
      validate_override_mode(signature, super_signature)
      validate_override_shape(signature, super_signature)
      validate_override_types(signature, super_signature)
    end
  else
    validate_non_override_mode(signature)
  end
end

def self.validate_non_override_mode(signature)
  case signature.mode
  when Modes.override
    if signature.method_name == :each && signature.method.owner < Enumerable
      # Enumerable#each is the only method in Sorbet's RBI payload that defines an abstract method.
      # Enumerable#each does not actually exist at runtime, but it is required to be implemented by
      # any class which includes Enumerable. We want to declare Enumerable#each as abstract so that
      # people can call it anything which implements the Enumerable interface, and so that it's a
      # static error to forget to implement it.
      #
      # This is a one-off hack, and we should think carefully before adding more methods here.
      nil
    else
      raise "You marked `#{signature.method_name}` as #{pretty_mode(signature)}, but that method doesn't already exist in this class/module to be overridden.\n" \
        "  Either check for typos and for missing includes or super classes to make the parent method shows up\n" \
        "  ... or remove #{pretty_mode(signature)} here: #{method_loc_str(signature.method)}\n"
    end
  when Modes.standard, *Modes::NON_OVERRIDE_MODES
    # Peaceful
    nil
  else
    raise "Unexpected mode: #{signature.mode}. Please report this bug at https://github.com/sorbet/sorbet/issues"
  end
  # Given a singleton class, we can check if it belongs to a
  # module by looking at its superclass; given `module M`,
  # `M.singleton_class.superclass == Module`, which is not true
  # for any class.
  owner = signature.method.owner
  if (signature.mode == Modes.abstract || Modes::OVERRIDABLE_MODES.include?(signature.mode)) &&
      owner.singleton_class? && owner.superclass == Module
    raise "Defining an overridable class method (via #{pretty_mode(signature)}) " \
          "on a module is not allowed. Class methods on " \
          "modules do not get inherited and thus cannot be overridden."
  end
end

def self.validate_override_mode(signature, super_signature)
  case signature.mode
  when *Modes::OVERRIDE_MODES
    # Peaceful
  when Modes.abstract
    # Either the parent method is abstract, or it's not.
    #
    # If it's abstract, we want to allow overriding abstract with abstract to
    # possibly narrow the type or provide more specific documentation.
    #
    # If it's not, then marking this method `abstract` will silently be a no-op.
    # That's bad and we probably want to report an error, but fixing that
    # will have to be a separate fix (that bad behavior predates this current
    # comment, introduced when we fixed the abstract/abstract case).
    #
    # Therefore:
    # Peaceful (mostly)
  when *Modes::NON_OVERRIDE_MODES
    if super_signature.mode == Modes.standard
      # Peaceful
    elsif super_signature.mode == Modes.abstract
      raise "You must use `.override` when overriding the abstract method `#{signature.method_name}`.\n" \
            "  Abstract definition: #{method_loc_str(super_signature.method)}\n" \
            "  Implementation definition: #{method_loc_str(signature.method)}\n"
    elsif super_signature.mode != Modes.untyped
      raise "You must use `.override` when overriding the existing method `#{signature.method_name}`.\n" \
            "  Parent definition: #{method_loc_str(super_signature.method)}\n" \
            "  Child definition:  #{method_loc_str(signature.method)}\n"
    end
  else
    raise "Unexpected mode: #{signature.mode}. Please report this bug at https://github.com/sorbet/sorbet/issues"
  end
end

def self.validate_override_shape(signature, super_signature)
  return if signature.override_allow_incompatible
  return if super_signature.mode == Modes.untyped
  method_name = signature.method_name
  mode_verb = super_signature.mode == Modes.abstract ? 'implements' : 'overrides'
  if !signature.has_rest && signature.arg_count < super_signature.arg_count
    raise "Your definition of `#{method_name}` must accept at least #{super_signature.arg_count} " \
          "positional arguments to be compatible with the method it #{mode_verb}: " \
          "#{base_override_loc_str(signature, super_signature)}"
  end
  if !signature.has_rest && super_signature.has_rest
    raise "Your definition of `#{method_name}` must have `*#{super_signature.rest_name}` " \
          "to be compatible with the method it #{mode_verb}: " \
          "#{base_override_loc_str(signature, super_signature)}"
  end
  if signature.req_arg_count > super_signature.req_arg_count
    raise "Your definition of `#{method_name}` must have no more than #{super_signature.req_arg_count} " \
          "required argument(s) to be compatible with the method it #{mode_verb}: " \
          "#{base_override_loc_str(signature, super_signature)}"
  end
  if !signature.has_keyrest
    # O(nm), but n and m are tiny here
    missing_kwargs = super_signature.kwarg_names - signature.kwarg_names
    if !missing_kwargs.empty?
      raise "Your definition of `#{method_name}` is missing these keyword arg(s): #{missing_kwargs} " \
            "which are defined in the method it #{mode_verb}: " \
            "#{base_override_loc_str(signature, super_signature)}"
    end
  end
  if !signature.has_keyrest && super_signature.has_keyrest
    raise "Your definition of `#{method_name}` must have `**#{super_signature.keyrest_name}` " \
          "to be compatible with the method it #{mode_verb}: " \
          "#{base_override_loc_str(signature, super_signature)}"
  end
  # O(nm), but n and m are tiny here
  extra_req_kwargs = signature.req_kwarg_names - super_signature.req_kwarg_names
  if !extra_req_kwargs.empty?
    raise "Your definition of `#{method_name}` has extra required keyword arg(s) " \
          "#{extra_req_kwargs} relative to the method it #{mode_verb}, making it incompatible: " \
          "#{base_override_loc_str(signature, super_signature)}"
  end
  if super_signature.block_name && !signature.block_name
    raise "Your definition of `#{method_name}` must accept a block parameter to be compatible " \
          "with the method it #{mode_verb}: " \
          "#{base_override_loc_str(signature, super_signature)}"
  end
end

def self.validate_override_types(signature, super_signature)
  return if signature.override_allow_incompatible
  return if super_signature.mode == Modes.untyped
  return unless [signature, super_signature].all? do |sig|
    sig.check_level == :always || (sig.check_level == :tests && T::Private::RuntimeLevels.check_tests?)
  end
  mode_noun = super_signature.mode == Modes.abstract ? 'implementation' : 'override'
  # arg types must be contravariant
  super_signature.arg_types.zip(signature.arg_types).each_with_index do |((_super_name, super_type), (name, type)), index|
    if !super_type.subtype_of?(type)
      raise "Incompatible type for arg ##{index + 1} (`#{name}`) in signature for #{mode_noun} of method " \
            "`#{signature.method_name}`:\n" \
            "* Base: `#{super_type}` (in #{method_loc_str(super_signature.method)})\n" \
            "* #{mode_noun.capitalize}: `#{type}` (in #{method_loc_str(signature.method)})\n" \
            "(The types must be contravariant.)"
    end
  end
  # kwarg types must be contravariant
  super_signature.kwarg_types.each do |name, super_type|
    type = signature.kwarg_types[name]
    if !super_type.subtype_of?(type)
      raise "Incompatible type for arg `#{name}` in signature for #{mode_noun} of method `#{signature.method_name}`:\n" \
            "* Base: `#{super_type}` (in #{method_loc_str(super_signature.method)})\n" \
            "* #{mode_noun.capitalize}: `#{type}` (in #{method_loc_str(signature.method)})\n" \
            "(The types must be contravariant.)"
    end
  end
  # return types must be covariant
  super_signature_return_type = super_signature.return_type
  if super_signature_return_type == T::Private::Types::Void::Private::INSTANCE
    # Treat `.void` as `T.anything` (see corresponding comment in definition_valitor for more)
    super_signature_return_type = T::Types::Anything::Private::INSTANCE
  end
  if !signature.return_type.subtype_of?(super_signature_return_type)
    raise "Incompatible return type in signature for #{mode_noun} of method `#{signature.method_name}`:\n" \
          "* Base: `#{super_signature.return_type}` (in #{method_loc_str(super_signature.method)})\n" \
          "* #{mode_noun.capitalize}: `#{signature.return_type}` (in #{method_loc_str(signature.method)})\n" \
          "(The types must be covariant.)"
  end
end