has_duplicates() doesn't build in CPP11 mode

[dkogan]

Hi. New code was added in 20.39 that doesn't build, as opposed to 20.37. I discovered this as I was updating the Debian package. It produces errors like this:

$ g++ \
   -DETL_DEBUG \
   -I../../test/../include \
   -isystem ../../test/UnitTest++/.. \
   -Wno-aggressive-loop-optimizations \
   -Wno-pessimizing-move \
   -std=gnu++20 \
   -fno-omit-frame-pointer \
   -fno-common \
   -Wall \
   -Wextra \
   -Werror \
   -Wfloat-equal \
   -Wuseless-cast \
   -Wshadow \
   -Wnull-dereference \
   -o /tmp/tst.o \
   -c ../../test/test_observer.cpp


In file included from ../../test/../include/etl/algorithm.h:42,
                 from ../../test/../include/etl/observer.h:54,
                 from ../../test/test_observer.cpp:31:
../../test/../include/etl/type_traits.h: In instantiation of ‘struct etl::has_duplicates<const {anonymous}::Notification3&>’:
../../test/../include/etl/type_traits.h:2310:10:   required from ‘struct etl::has_duplicates<{anonymous}::Notification2&, const {anonymous}::Notification3&>’
 2310 |   struct has_duplicates<TFirst, TRest...> : etl::conditional_t<etl::is_one_of<TFirst, TRest...>::value,
      |          ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
../../test/../include/etl/observer.h:308:5:   required from ‘class etl::observer<{anonymous}::Notification2&, const {anonymous}::Notification3&>’
  308 |     ETL_STATIC_ASSERT((!etl::has_duplicates<T1, TRest...>::value), "Observer has duplicate notification types");
      |                                                            ^~~~~
../../test/../include/etl/observer.h:304:9:   required from ‘class etl::observer<{anonymous}::Notification1, {anonymous}::Notification2&, const {anonymous}::Notification3&>’
  304 |   class observer<T1, TRest...> : public observer<T1>, public observer<TRest...>
      |         ^~~~~~~~~~~~~~~~~~~~~~
../../test/test_observer.cpp:147:26:   required from here
  147 | class Observer1 : public ObserverType
      |                          ^~~~~~~~~~~~
../../test/../include/etl/type_traits.h:2310:98: error: wrong number of template arguments (1, should be at least 2)
 2310 |   struct has_duplicates<TFirst, TRest...> : etl::conditional_t<etl::is_one_of<TFirst, TRest...>::value,
      |                                                                                                  ^~~~~
../../test/../include/etl/type_traits.h:1355:10: note: provided for ‘template<class T, class T1, class ... TRest> struct etl::is_one_of’
 1355 |   struct is_one_of
      |          ^~~~~~~~~


In file included from ../../test/../include/etl/type_traits.h:58:
../../test/../include/etl/observer.h: In instantiation of ‘class etl::observer<{anonymous}::Notification2&, const {anonymous}::Notification3&>’:
../../test/../include/etl/observer.h:304:9:   required from ‘class etl::observer<{anonymous}::Notification1, {anonymous}::Notification2&, const {anonymous}::Notification3&>’
  304 |   class observer<T1, TRest...> : public observer<T1>, public observer<TRest...>
      |         ^~~~~~~~~~~~~~~~~~~~~~
../../test/test_observer.cpp:147:26:   required from here
  147 | class Observer1 : public ObserverType
      |                          ^~~~~~~~~~~~
../../test/../include/etl/observer.h:308:60: error: ‘value’ is not a member of ‘etl::has_duplicates<{anonymous}::Notification2&, const {anonymous}::Notification3&>’
  308 |     ETL_STATIC_ASSERT((!etl::has_duplicates<T1, TRest...>::value), "Observer has duplicate notification types");
      |                                                            ^~~~~
../../test/../include/etl/static_assert.h:35:63: note: in definition of macro ‘ETL_STATIC_ASSERT’
   35 |   #define ETL_STATIC_ASSERT(Condition, Message) static_assert(Condition, Message)
      |                                                               ^~~~~~~~~
../../test/../include/etl/observer.h: In instantiation of ‘class etl::observer<{anonymous}::Notification1, {anonymous}::Notification2&, const {anonymous}::Notification3&>’:
../../test/test_observer.cpp:147:26:   required from here
  147 | class Observer1 : public ObserverType
      |                          ^~~~~~~~~~~~
../../test/../include/etl/observer.h:308:60: error: ‘value’ is not a member of ‘etl::has_duplicates<{anonymous}::Notification1, {anonymous}::Notification2&, const {anonymous}::Notification3&>’
  308 |     ETL_STATIC_ASSERT((!etl::has_duplicates<T1, TRest...>::value), "Observer has duplicate notification types");
      |                                                            ^~~~~
../../test/../include/etl/static_assert.h:35:63: note: in definition of macro ‘ETL_STATIC_ASSERT’
   35 |   #define ETL_STATIC_ASSERT(Condition, Message) static_assert(Condition, Message)
      |                                                               ^~~~~~~~~
../../test/../include/etl/type_traits.h: In instantiation of ‘struct etl::has_duplicates<int>’:
../../test/../include/etl/type_traits.h:2310:10:   required from ‘struct etl::has_duplicates<void, int>’
 2310 |   struct has_duplicates<TFirst, TRest...> : etl::conditional_t<etl::is_one_of<TFirst, TRest...>::value,
      |          ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
../../test/../include/etl/observer.h:308:5:   required from ‘class etl::observer<void, int>’
  308 |     ETL_STATIC_ASSERT((!etl::has_duplicates<T1, TRest...>::value), "Observer has duplicate notification types");
      |                                                            ^~~~~
../../test/test_observer.cpp:237:32:   required from here
  237 | class ObserverVoidInt : public ObserverVoidIntType
      |                                ^~~~~~~~~~~~~~~~~~~
../../test/../include/etl/type_traits.h:2310:98: error: wrong number of template arguments (1, should be at least 2)
 2310 |   struct has_duplicates<TFirst, TRest...> : etl::conditional_t<etl::is_one_of<TFirst, TRest...>::value,
      |                                                                                                  ^~~~~
../../test/../include/etl/type_traits.h:1355:10: note: provided for ‘template<class T, class T1, class ... TRest> struct etl::is_one_of’
 1355 |   struct is_one_of
      |          ^~~~~~~~~
../../test/../include/etl/observer.h: In instantiation of ‘class etl::observer<void, int>’:
../../test/test_observer.cpp:237:32:   required from here
  237 | class ObserverVoidInt : public ObserverVoidIntType
      |                                ^~~~~~~~~~~~~~~~~~~
../../test/../include/etl/observer.h:308:60: error: ‘value’ is not a member of ‘etl::has_duplicates<void, int>’
  308 |     ETL_STATIC_ASSERT((!etl::has_duplicates<T1, TRest...>::value), "Observer has duplicate notification types");
      |                                                            ^~~~~
../../test/../include/etl/static_assert.h:35:63: note: in definition of macro ‘ETL_STATIC_ASSERT’
   35 |   #define ETL_STATIC_ASSERT(Condition, Message) static_assert(Condition, Message)
      |                                                               ^~~~~~~~~

has_duplicates() is intended to take any number of templated types, and recursively wittles them down one by one. The problem is that the CPP11 path has matching calls for 0 arguments and >=2 arguments, but not for ` argument. A patch to add that path:

diff --git a/include/etl/generators/type_traits_generator.h b/include/etl/generators/type_traits_generator.h
index f086b84..8833a2a 100644
--- a/include/etl/generators/type_traits_generator.h
+++ b/include/etl/generators/type_traits_generator.h
@@ -2314,13 +2314,14 @@ typedef integral_constant<bool, true>  true_type;
   struct has_duplicates;
 
   template <typename TFirst, typename... TRest>
   struct has_duplicates<TFirst, TRest...> : etl::conditional_t<etl::is_one_of<TFirst, TRest...>::value,
                                                                etl::true_type,
                                                                has_duplicates<TRest...>> {};
-
+  template <typename TFirst>
+  struct has_duplicates<TFirst> : etl::false_type {};
   template <>
   struct has_duplicates<> : etl::false_type {};
 #endif
 
 #if ETL_USING_CPP17
   template <typename... TTypes>

I'm building the new Debian package with this patch. Thanks.