Fix/implement C++2020 compilation, tests, and CI (#1017)

* Fix C++20 bugs and tests
* Rework CI for C++2020 tests
* Update readme compiler versions

12 files changed, 80 insertions, 67 deletions

diff --git a/README.md b/README.md
index 073517e..34f87f0 100644
--- a/README.md
+++ b/README.md
@@ -86,16 +86,14 @@ This is based on [CppCoreGuidelines semi-specification](https://github.com/isocp
 
 # Quick Start
 ## Supported Compilers
-The GSL officially supports the current and previous major release of MSVC, GCC, Clang, and XCode's Apple-Clang.
-See our latest test results for the most up-to-date list of supported configurations.
+The GSL officially supports the following versions of MSVC, GCC, Clang, and XCode's Apple-Clang.
 
 Compiler |Toolset Versions Currently Tested
 :------- |--:
- XCode |11.4 & 10.3
- GCC |9 & 8
- Clang |11 &  10
- Visual Studio with MSVC | VS2017 (15.9) & VS2019 (16.4) 
- Visual Studio with LLVM | VS2017 (Clang 9) & VS2019 (Clang 10)
+ XCode | 12.4 & 11.3
+ GCC | 9.3.0 & 7.5.0
+ Clang | 11.0.0 & 9.0.0
+ Visual Studio with MSVC | VS2017 (15.9.21) & VS2019 (16.11.2)
 
 ---
 If you successfully port GSL to another platform, we would love to hear from you!
diff --git a/azure-pipelines.yml b/azure-pipelines.yml
index 0d1219a..8ab761e 100644
--- a/azure-pipelines.yml
+++ b/azure-pipelines.yml
@@ -18,10 +18,12 @@ stages:
     parameters:
       jobName: 'Validate GCC latest'
       imageName: ubuntu-20.04
+      CXXVersions: [ 14, 17 ]
   - template: ./pipelines/jobs.yml
     parameters:
       jobName: 'Validate GCC Previous'
       imageName: ubuntu-18.04
+      CXXVersions: [ 14, 17 ]
 
 # Clang
 - stage: Clang
@@ -40,6 +42,7 @@ stages:
     parameters:
       jobName: 'Validate Clang Previous'
       imageName: ubuntu-18.04
+      CXXVersions: [ 14, 17 ]
 
 # MSVC
 - stage: MSVC
@@ -53,6 +56,7 @@ stages:
     parameters:
       jobName: 'Validate MSVC Previous'
       imageName: vs2017-win2016
+      CXXVersions: [ 14, 17 ]
 
 # Apple-Clang
 - stage: Apple_Clang
@@ -62,7 +66,9 @@ stages:
     parameters:
       jobName: 'Validate Apple-Clang latest'
       imageName: macos-10.15
+      CXXVersions: [ 14, 17 ]
   - template: ./pipelines/jobs.yml
     parameters:
       jobName: 'Validate Apple-Clang Previous'
       imageName: macos-10.14
+      CXXVersions: [ 14, 17 ]
diff --git a/include/gsl/util b/include/gsl/util
index 330b996..a215bad 100644
--- a/include/gsl/util
+++ b/include/gsl/util
@@ -143,10 +143,10 @@ GSL_SUPPRESS(bounds.1) // NO-FORMAT: attribute
 
 #if defined(__cpp_lib_span) && __cpp_lib_span >= 202002L
 template <class T, size_t extent = std::dynamic_extent>
-constexpr auto at(std::span<T, extent> sp, const index i)
+constexpr auto at(std::span<T, extent> sp, const index i) -> decltype(sp[sp.size()])
 {
-    Expects(i >= 0 && i < narrow_cast<i>(sp.size()));
-    return sp[i];
+    Expects(i >= 0 && i < narrow_cast<index>(sp.size()));
+    return sp[gsl::narrow_cast<size_t>(i)];
 }
 #endif // __cpp_lib_span >= 202002L
 } // namespace gsl
diff --git a/pipelines/jobs.yml b/pipelines/jobs.yml
index dad2414..783c46d 100644
--- a/pipelines/jobs.yml
+++ b/pipelines/jobs.yml
@@ -1,26 +1,19 @@
 parameters:

   jobName: ''

   imageName: ''

+  CXXVersions: [ 14, 17, 20 ]

+  buildTypes: [ 'Debug', 'Release' ]

 

 jobs:

-- job:

-  displayName: ${{ parameters.imageName }}

-  pool:

-    vmImage: ${{ parameters.imageName }}

-  strategy:

-    matrix:

-      14_debug:

-        GSL_CXX_STANDARD: '14'

-        BUILD_TYPE: 'Debug'

-      14_release:

-        GSL_CXX_STANDARD: '14'

-        BUILD_TYPE: 'Release'

-      17_debug:

-        GSL_CXX_STANDARD: '17'

-        BUILD_TYPE: 'Debug'

-      17_release:

-        GSL_CXX_STANDARD: '17'

-        BUILD_TYPE: 'Release'

-  continueOnError: false

-  steps:

-  - template: ./steps.yml

+- ${{ each CXXVersion in parameters.CXXVersions }}:

+  - ${{ each buildType in parameters.buildTypes }}:

+    - job:

+      displayName: ${{ format('{0} {1} C++{2}', parameters.imageName, buildType, CXXVersion) }}

+      pool:

+        vmImage: ${{ parameters.imageName }}

+      continueOnError: false

+      steps:

+      - template: ./steps.yml

+        parameters:

+          buildType: ${{ buildType }}

+          CXXVersion: ${{ CXXVersion }}

diff --git a/pipelines/steps.yml b/pipelines/steps.yml
index 41a7fca..2e80713 100644
--- a/pipelines/steps.yml
+++ b/pipelines/steps.yml
@@ -1,9 +1,13 @@
+parameters:

+    buildType: ''

+    CXXVersion: ''

+

 steps:

   - task: CMake@1

     name: Configure

     inputs:

       workingDirectory: build

-      cmakeArgs: '-DCMAKE_CXX_STANDARD=$(GSL_CXX_STANDARD) -DCMAKE_BUILD_TYPE=$(BUILD_TYPE) -Werror=dev .. '

+      cmakeArgs: '-DGSL_CXX_STANDARD=${{ parameters.CXXVersion }} -DCMAKE_BUILD_TYPE=${{ parameters.buildType }} -DCI_TESTING:BOOL=ON -DCMAKE_VERBOSE_MAKEFILE:BOOL=ON -Werror=dev .. '

 

   - task: CMake@1

     name: Build

diff --git a/tests/CMakeLists.txt b/tests/CMakeLists.txt
index c05aaa7..dd71105 100644
--- a/tests/CMakeLists.txt
+++ b/tests/CMakeLists.txt
@@ -9,6 +9,10 @@ include(ExternalProject)
 # will make visual studio generated project group files
 set_property(GLOBAL PROPERTY USE_FOLDERS ON)
 
+if(CI_TESTING AND GSL_CXX_STANDARD EQUAL 20)
+    add_compile_definitions(FORCE_STD_SPAN_TESTS=1)
+endif()
+
 if(IOS)
     add_compile_definitions(GTEST_HAS_DEATH_TEST=1 IOS_PROCESS_DELAY_WORKAROUND=1)
 endif()
@@ -54,7 +58,7 @@ if (CMAKE_CURRENT_SOURCE_DIR STREQUAL CMAKE_SOURCE_DIR)
     find_package(Microsoft.GSL REQUIRED)
 endif()
 
-if (MSVC AND (GSL_CXX_STANDARD EQUAL 17))
+if (MSVC AND (GSL_CXX_STANDARD GREATER_EQUAL 17))
     set(GSL_CPLUSPLUS_OPT -Zc:__cplusplus -permissive-)
 endif()
 
@@ -135,6 +139,11 @@ else()
           $<$<AND:$<VERSION_GREATER:$<CXX_COMPILER_VERSION>,4.99>,$<VERSION_LESS:$<CXX_COMPILER_VERSION>,6>>:
             $<$<EQUAL:${GSL_CXX_STANDARD},17>:-Wno-undefined-func-template>
           >
+          $<$<AND:$<EQUAL:${GSL_CXX_STANDARD},20>,$<CXX_COMPILER_VERSION:11.0.0>>:
+              -Wno-zero-as-null-pointer-constant  # failing Clang Ubuntu 20.04 tests, seems to be a bug with clang 11.0.0
+                                                  # (operator< is being re-written by the compiler as operator<=> and
+                                                  # raising the warning)
+          >
         >
         $<$<CXX_COMPILER_ID:AppleClang>:
           $<$<AND:$<VERSION_GREATER:$<CXX_COMPILER_VERSION>,9.1>,$<VERSION_LESS:$<CXX_COMPILER_VERSION>,10>>:
diff --git a/tests/algorithm_tests.cpp b/tests/algorithm_tests.cpp
index 16746b4..e369be0 100644
--- a/tests/algorithm_tests.cpp
+++ b/tests/algorithm_tests.cpp
@@ -27,7 +27,6 @@ namespace gsl
 struct fail_fast;
 } // namespace gsl
 
-using namespace std;
 using namespace gsl;
 
 TEST(algorithm_tests, same_type)
@@ -73,8 +72,8 @@ TEST(algorithm_tests, same_type)
         std::array<int, 5> src{1, 2, 3, 4, 5};
         std::array<int, 10> dst{};
 
-        const span<int> src_span(src);
-        const span<int, 10> dst_span(dst);
+        const gsl::span<int> src_span(src);
+        const gsl::span<int, 10> dst_span(dst);
 
         copy(src_span, dst_span);
         copy(src_span, dst_span.subspan(src_span.size()));
diff --git a/tests/at_tests.cpp b/tests/at_tests.cpp
index 92a8e4d..93e6b7b 100644
--- a/tests/at_tests.cpp
+++ b/tests/at_tests.cpp
@@ -119,7 +119,7 @@ TEST(at_tests, InitializerList)
     EXPECT_DEATH(gsl::at({1, 2, 3, 4}, 4), expected);
 }
 
-#if defined(__cplusplus) && __cplusplus >= 202002L
+#if defined(FORCE_STD_SPAN_TESTS) || defined(__cpp_lib_span) && __cpp_lib_span >= 202002L
 TEST(at_tests, std_span)
 {
     std::vector<int> vec{1, 2, 3, 4, 5};
@@ -128,18 +128,24 @@ TEST(at_tests, std_span)
     std::vector<int> cvec{1, 2, 3, 4, 5};
     std::span csp{cvec};
 
-    for (size_t i = 0, i < vec.size(); ++i)
+    for (gsl::index i = 0; i < gsl::narrow_cast<gsl::index>(vec.size()); ++i)
     {
-        EXPECT_TRUE(&gsl::at(sp, i) == &vec[i]);
-        EXPECT_TRUE(&gsl::at(csp, i) == &cvec[i]);
+        EXPECT_TRUE(&gsl::at(sp, i) == &vec[gsl::narrow_cast<size_t>(i)]);
+        EXPECT_TRUE(&gsl::at(csp, i) == &cvec[gsl::narrow_cast<size_t>(i)]);
     }
 
+    const auto terminateHandler = std::set_terminate([] {
+        std::cerr << "Expected Death. std_span";
+        std::abort();
+    });
+    const auto expected = GetExpectedDeathString(terminateHandler);
+
     EXPECT_DEATH(gsl::at(sp, -1), expected);
-    EXPECT_DEATH(gsl::at(sp, sp.size()), expected);
+    EXPECT_DEATH(gsl::at(sp, gsl::narrow_cast<gsl::index>(sp.size())), expected);
     EXPECT_DEATH(gsl::at(csp, -1), expected);
-    EXPECT_DEATH(gsl::at(csp, sp.size()), expected);
+    EXPECT_DEATH(gsl::at(csp, gsl::narrow_cast<gsl::index>(sp.size())), expected);
 }
-#endif // __cplusplus >= 202002L
+#endif // defined(FORCE_STD_SPAN_TESTS) || defined(__cpp_lib_span) && __cpp_lib_span >= 202002L
 
 #if !defined(_MSC_VER) || defined(__clang__) || _MSC_VER >= 1910
 static constexpr bool test_constexpr()
diff --git a/tests/span_compatibility_tests.cpp b/tests/span_compatibility_tests.cpp
index 56bd385..95d8223 100644
--- a/tests/span_compatibility_tests.cpp
+++ b/tests/span_compatibility_tests.cpp
@@ -55,14 +55,14 @@ void ArrayConvertibilityCheck()
         EXPECT_TRUE(sp_const_nullptr_1.data() == stl_nullptr.data());
         EXPECT_TRUE(sp_const_nullptr_1.size() == 3);
 
-        span<const T* const> sp_const_nullptr_2{std::as_const(stl_nullptr)};
+        gsl::span<const T* const> sp_const_nullptr_2{std::as_const(stl_nullptr)};
         EXPECT_TRUE(sp_const_nullptr_2.data() == stl_nullptr.data());
         EXPECT_TRUE(sp_const_nullptr_2.size() == 3);
 
-        static_assert(std::is_same<decltype(span{stl_nullptr}), span<T*, 3>>::value,
+        static_assert(std::is_same<decltype(gsl::span{stl_nullptr}), gsl::span<T*, 3>>::value,
                       "std::is_same< decltype(span{stl_nullptr}), span<T*, 3>>::value");
         static_assert(
-            std::is_same<decltype(span{std::as_const(stl_nullptr)}), span<T* const, 3>>::value,
+            std::is_same<decltype(gsl::span{std::as_const(stl_nullptr)}), gsl::span<T* const, 3>>::value,
             "std::is_same< decltype(span{std::as_const(stl_nullptr)}), span<T* const, "
             "3>>::value");
     }
diff --git a/tests/span_ext_tests.cpp b/tests/span_ext_tests.cpp
index 7ce4e51..3d35f8f 100644
--- a/tests/span_ext_tests.cpp
+++ b/tests/span_ext_tests.cpp
@@ -48,7 +48,7 @@ TEST(span_ext_test, make_span_from_pointer_length_constructor)
 

     {

         int* p = nullptr;

-        auto s = make_span(p, narrow_cast<span<int>::size_type>(0));

+        auto s = make_span(p, narrow_cast<gsl::span<int>::size_type>(0));

         EXPECT_TRUE(s.size() == 0);

         EXPECT_TRUE(s.data() == nullptr);

     }

@@ -136,9 +136,9 @@ TEST(span_ext_test, make_span_from_std_array_constructor)
 

     // This test checks for the bug found in gcc 6.1, 6.2, 6.3, 6.4, 6.5 7.1, 7.2, 7.3 - issue #590

     {

-        span<int> s1 = make_span(arr);

+        gsl::span<int> s1 = make_span(arr);

 

-        static span<int> s2;

+        static gsl::span<int> s2;

         s2 = s1;

 

 #if defined(__GNUC__) && __GNUC__ == 6 && (__GNUC_MINOR__ == 4 || __GNUC_MINOR__ == 5) &&          \

@@ -194,7 +194,7 @@ TEST(span_ext_test, make_span_from_container_constructor)
 TEST(span_test, interop_with_gsl_at)

 {

     int arr[5] = {1, 2, 3, 4, 5};

-    span<int> s{arr};

+    gsl::span<int> s{arr};

     EXPECT_TRUE(at(s, 0) == 1);

     EXPECT_TRUE(at(s, 1) == 2);

 }

@@ -202,7 +202,7 @@ TEST(span_test, interop_with_gsl_at)
 TEST(span_ext_test, iterator_free_functions)

 {

     int a[] = {1, 2, 3, 4};

-    span<int> s{a};

+    gsl::span<int> s{a};

 

     EXPECT_TRUE((std::is_same<decltype(s.begin()), decltype(begin(s))>::value));

     EXPECT_TRUE((std::is_same<decltype(s.end()), decltype(end(s))>::value));

@@ -232,7 +232,7 @@ TEST(span_ext_test, iterator_free_functions)
 TEST(span_ext_test, ssize_free_function)

 {

     int a[] = {1, 2, 3, 4};

-    span<int> s{a};

+    gsl::span<int> s{a};

 

     EXPECT_FALSE((std::is_same<decltype(s.size()), decltype(ssize(s))>::value));

     EXPECT_TRUE(s.size() == static_cast<std::size_t>(ssize(s)));

@@ -242,8 +242,8 @@ TEST(span_ext_test, ssize_free_function)
 TEST(span_ext_test, comparison_operators)

 {

     {

-        span<int> s1;

-        span<int> s2;

+        gsl::span<int> s1;

+        gsl::span<int> s2;

         EXPECT_TRUE(s1 == s2);

         EXPECT_FALSE(s1 != s2);

         EXPECT_FALSE(s1 < s2);

@@ -260,8 +260,8 @@ TEST(span_ext_test, comparison_operators)
 

     {

         int arr[] = {2, 1};

-        span<int> s1 = arr;

-        span<int> s2 = arr;

+        gsl::span<int> s1 = arr;

+        gsl::span<int> s2 = arr;

 

         EXPECT_TRUE(s1 == s2);

         EXPECT_FALSE(s1 != s2);

@@ -280,8 +280,8 @@ TEST(span_ext_test, comparison_operators)
     {

         int arr[] = {2, 1}; // bigger

 

-        span<int> s1;

-        span<int> s2 = arr;

+        gsl::span<int> s1;

+        gsl::span<int> s2 = arr;

 

         EXPECT_TRUE(s1 != s2);

         EXPECT_TRUE(s2 != s1);

@@ -300,8 +300,8 @@ TEST(span_ext_test, comparison_operators)
     {

         int arr1[] = {1, 2};

         int arr2[] = {1, 2};

-        span<int> s1 = arr1;

-        span<int> s2 = arr2;

+        gsl::span<int> s1 = arr1;

+        gsl::span<int> s2 = arr2;

 

         EXPECT_TRUE(s1 == s2);

         EXPECT_FALSE(s1 != s2);

@@ -320,8 +320,8 @@ TEST(span_ext_test, comparison_operators)
     {

         int arr[] = {1, 2, 3};

 

-        span<int> s1 = {&arr[0], 2}; // shorter

-        span<int> s2 = arr;          // longer

+        gsl::span<int> s1 = {&arr[0], 2}; // shorter

+        gsl::span<int> s2 = arr;          // longer

 

         EXPECT_TRUE(s1 != s2);

         EXPECT_TRUE(s2 != s1);

@@ -341,8 +341,8 @@ TEST(span_ext_test, comparison_operators)
         int arr1[] = {1, 2}; // smaller

         int arr2[] = {2, 1}; // bigger

 

-        span<int> s1 = arr1;

-        span<int> s2 = arr2;

+        gsl::span<int> s1 = arr1;

+        gsl::span<int> s2 = arr2;

 

         EXPECT_TRUE(s1 != s2);

         EXPECT_TRUE(s2 != s1);

diff --git a/tests/span_tests.cpp b/tests/span_tests.cpp
index 1e0222e..33ccf56 100644
--- a/tests/span_tests.cpp
+++ b/tests/span_tests.cpp
@@ -43,7 +43,6 @@
 
 #include "deathTestCommon.h"
 
-using namespace std;
 using namespace gsl;
 
 namespace
@@ -1085,7 +1084,7 @@ TEST(span_test, as_bytes)
 
     int b[5] = {1, 2, 3, 4, 5};
     {
-        span<int> sp(begin(b), static_cast<size_t>(-2));
+        span<int> sp(std::begin(b), static_cast<size_t>(-2));
         EXPECT_DEATH((void) sp.size_bytes(), expected);
     }
 }
diff --git a/tests/string_span_tests.cpp b/tests/string_span_tests.cpp
index ed42b38..45a67d9 100644
--- a/tests/string_span_tests.cpp
+++ b/tests/string_span_tests.cpp
@@ -30,7 +30,6 @@
 
 #include "deathTestCommon.h"
 
-using namespace std;
 using namespace gsl;
 
 // Generic string functions