Add more compilers to CI and increase FMT_PEDANTIC warning levels (#736)

* Add a _lot_ more warnings to FMT_PEDANTIC
Fix these warnings

* Add more compilers to CI
Fix (some) of the compiler errors with them

* Enable -Werror on CI
Increase warning level on MSVC when compiling with FMT_PEDANTIC

* Add VS 2013 and 2015 to Appveyor

* Fix Appveyor tests
Formatting

* Implement requested changes
Fix some of the MSVC warnings
Implement C++11 integer_sequence

* Reintroduce appveyor-build.py

* Remove ranges-test from tests

* Remove (some) explicit warning suppressions
Fix C++ standard setting in CI

* Remove (some) explicit warning suppressions
Fix C++ standard setting in CI

* Fix test builds with C++11

* Enable pedantic warnings on tests

* Fix warnings from edits to master

* Cleanups

* Add C++11 support to ranges.h
Re-enable ranges-test
Fix a Visual Studio error about function not returning a value in printf.h
Fix a bug in .travis.yml

support/cmake/cxx14.cmake

@@ -1,67 +1,52 @@
 # C++14 feature support detection
 
-if (NOT FMT_USE_CPP14)
-  return()
-endif ()
-
+include(CheckCXXSourceCompiles)
 include(CheckCXXCompilerFlag)
 
-if (FMT_USE_CPP14)
-  check_cxx_compiler_flag(-std=c++14 HAVE_STD_CPP14_FLAG)
-  if (HAVE_STD_CPP14_FLAG)
-    # Check if including cmath works with -std=c++14 and -O3.
-    # It may not in MinGW due to bug http://ehc.ac/p/mingw/bugs/2250/.
-    set(CMAKE_REQUIRED_FLAGS "-std=c++14 -O3")
-    check_cxx_source_compiles("
-      #include <cmath>
-      int main() {}" FMT_CPP14_CMATH)
-    # Check if including <unistd.h> works with -std=c++14.
-    # It may not in MinGW due to bug http://sourceforge.net/p/mingw/bugs/2024/.
-    check_cxx_source_compiles("
-      #include <unistd.h>
-      int main() {}" FMT_CPP14_UNISTD_H)
-    # Check if snprintf works with -std=c++14. It may not in MinGW.
-    check_cxx_source_compiles("
-      #include <stdio.h>
-      int main() {
-        char buffer[10];
-        snprintf(buffer, 10, \"foo\");
-      }" FMT_CPP14_SNPRINTF)
-    if (FMT_CPP14_CMATH AND FMT_CPP14_UNISTD_H AND FMT_CPP14_SNPRINTF)
-      set(CPP14_FLAG -std=c++14)
-    else ()
-      check_cxx_compiler_flag(-std=gnu++14 HAVE_STD_GNUPP14_FLAG)
-      if (HAVE_STD_CPP14_FLAG)
-        set(CPP14_FLAG -std=gnu++14)
-      endif ()
-    endif ()
-    set(CMAKE_REQUIRED_FLAGS )
-  else ()
-    check_cxx_compiler_flag(-std=c++1y HAVE_STD_CPP1Y_FLAG)
-    if (HAVE_STD_CPP1Y_FLAG)
-      set(CPP14_FLAG -std=c++1y)
-    else ()
-      # Fallback on c++11 if c++14 is not available.
-      check_cxx_compiler_flag(-std=c++11 HAVE_STD_CPP11_FLAG)
-      if (HAVE_STD_CPP11_FLAG)
-        set(CPP14_FLAG -std=c++11)
-      else ()
-        check_cxx_compiler_flag(-std=c++0x HAVE_STD_CPP0X_FLAG)
-        if (HAVE_STD_CPP0X_FLAG)
-          set(CPP14_FLAG -std=c++0x)
-        endif ()
-      endif ()
-    endif ()
+if (NOT CMAKE_CXX_STANDARD)
+  set(CMAKE_CXX_STANDARD 11)
+endif()
+message(STATUS "CXX_STANDARD: ${CMAKE_CXX_STANDARD}")
+
+if (CMAKE_CXX_STANDARD EQUAL 20)
+  check_cxx_compiler_flag(-std=c++20 has_std_20_flag)
+  check_cxx_compiler_flag(-std=c++2a has_std_2a_flag)
+
+  if (has_std_20_flag)
+    set(CXX_STANDARD_FLAG -std=c++20)
+  elseif (has_std_2a_flag)
+    set(CXX_STANDARD_FLAG -std=c++2a)
+  endif ()
+elseif (CMAKE_CXX_STANDARD EQUAL 17)
+  check_cxx_compiler_flag(-std=c++17 has_std_17_flag)
+  check_cxx_compiler_flag(-std=c++1z has_std_1z_flag)
+
+  if (has_std_17_flag)
+    set(CXX_STANDARD_FLAG -std=c++17)
+  elseif (has_std_1z_flag)
+    set(CXX_STANDARD_FLAG -std=c++1z)
+  endif ()
+elseif (CMAKE_CXX_STANDARD EQUAL 14)
+  check_cxx_compiler_flag(-std=c++14 has_std_14_flag)
+  check_cxx_compiler_flag(-std=c++1y has_std_1y_flag)
+
+  if (has_std_14_flag)
+    set(CXX_STANDARD_FLAG -std=c++14)
+  elseif (has_std_1y_flag)
+    set(CXX_STANDARD_FLAG -std=c++1y)
+  endif ()
+elseif (CMAKE_CXX_STANDARD EQUAL 11)
+  check_cxx_compiler_flag(-std=c++11 has_std_11_flag)
+  check_cxx_compiler_flag(-std=c++0x has_std_0x_flag)
+
+  if (has_std_11_flag)
+    set(CXX_STANDARD_FLAG -std=c++11)
+  elseif (has_std_0x_flag)
+    set(CXX_STANDARD_FLAG -std=c++0x)
   endif ()
 endif ()
 
-if (CMAKE_CXX_STANDARD)
-  # Don't use -std compiler flag if CMAKE_CXX_STANDARD is specified.
-  set(CPP14_FLAG )
-endif ()
-
-message(STATUS "CPP14_FLAG: ${CPP14_FLAG}")
-set(CMAKE_REQUIRED_FLAGS ${CPP14_FLAG})
+set(CMAKE_REQUIRED_FLAGS ${CXX_STANDARD_FLAG})
 
 # Check if variadic templates are working and not affected by GCC bug 39653:
 # https://gcc.gnu.org/bugzilla/show_bug.cgi?id=39653
@@ -69,17 +54,26 @@ check_cxx_source_compiles("
   template <class T, class ...Types>
   struct S { typedef typename S<Types...>::type type; };
   int main() {}" SUPPORTS_VARIADIC_TEMPLATES)
+if (NOT SUPPORTS_VARIADIC_TEMPLATES)
+  set (SUPPORTS_VARIADIC_TEMPLATES OFF)
+endif ()
 
 # Check if initializer lists are supported.
 check_cxx_source_compiles("
   #include <initializer_list>
   int main() {}" SUPPORTS_INITIALIZER_LIST)
+if (NOT SUPPORTS_INITIALIZER_LIST)
+  set (SUPPORTS_INITIALIZER_LIST OFF)
+endif ()
 
 # Check if enum bases are available
 check_cxx_source_compiles("
   enum C : char {A};
   int main() {}"
   SUPPORTS_ENUM_BASE)
+if (NOT SUPPORTS_ENUM_BASE)
+  set (SUPPORTS_ENUM_BASE OFF)
+endif ()
 
 # Check if type traits are available
 check_cxx_source_compiles("
@@ -87,11 +81,17 @@ check_cxx_source_compiles("
   class C { void operator=(const C&); };
   int main() { static_assert(!std::is_copy_assignable<C>::value, \"\"); }"
   SUPPORTS_TYPE_TRAITS)
+if (NOT SUPPORTS_TYPE_TRAITS)
+  set (SUPPORTS_TYPE_TRAITS OFF)
+endif ()
 
 # Check if user-defined literals are available
 check_cxx_source_compiles("
   void operator\"\" _udl(long double);
   int main() {}"
   SUPPORTS_USER_DEFINED_LITERALS)
+if (NOT SUPPORTS_USER_DEFINED_LITERALS)
+  set (SUPPORTS_USER_DEFINED_LITERALS OFF)
+endif ()
 
 set(CMAKE_REQUIRED_FLAGS )