From e648b5c0512c9e9257224c57a3d2d786ffd7f9ce Mon Sep 17 00:00:00 2001
From: Marc Alff <marc.alff@oracle.com>
Date: Fri, 4 Nov 2022 16:49:40 +0100
Subject: [PATCH 01/13] WIP

---
 CMakeLists.txt                                | 52 +++++++++++++++++--
 api/include/opentelemetry/nostd/shared_ptr.h  |  2 +-
 api/include/opentelemetry/nostd/string_view.h |  2 +-
 api/include/opentelemetry/nostd/unique_ptr.h  |  2 +-
 4 files changed, 52 insertions(+), 6 deletions(-)

diff --git a/CMakeLists.txt b/CMakeLists.txt
index e7597fc87a..1d49ad6536 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -107,14 +107,60 @@ else()
   )
 endif()
 
-option(WITH_STL "Whether to use Standard Library for C++ latest features" OFF)
+set(WITH_STL "OFF" CACHE STRING "Which version of the Standard Library for C++ to use")
+
 option(WITH_GSL
        "Whether to use Guidelines Support Library for C++ latest features" OFF)
 
 option(WITH_ABSEIL "Whether to use Abseil for C++latest features" OFF)
 
+if(WITH_STL STREQUAL "OFF")
+  if(NOT DEFINED CMAKE_CXX_STANDARD)
+    set(CMAKE_CXX_STANDARD 11)
+  endif()
+  # STL not used.
+elseif(WITH_STL STREQUAL "CXX11")
+  add_definitions(-DOPENTELEMETRY_HAVE_CXX11)
+  if(NOT DEFINED CMAKE_CXX_STANDARD)
+    set(CMAKE_CXX_STANDARD 11)
+  endif()
+elseif(WITH_STL STREQUAL "CXX14")
+  add_definitions(-DOPENTELEMETRY_HAVE_CXX11)
+  add_definitions(-DOPENTELEMETRY_HAVE_CXX14)
+  if(NOT DEFINED CMAKE_CXX_STANDARD)
+    set(CMAKE_CXX_STANDARD 14)
+  endif()
+elseif(WITH_STL STREQUAL "CXX17")
+  add_definitions(-DOPENTELEMETRY_HAVE_CXX11)
+  add_definitions(-DOPENTELEMETRY_HAVE_CXX14)
+  add_definitions(-DOPENTELEMETRY_HAVE_CXX17)
+  if(NOT DEFINED CMAKE_CXX_STANDARD)
+    set(CMAKE_CXX_STANDARD 17)
+  endif()
+elseif(WITH_STL STREQUAL "CXX20")
+  add_definitions(-DOPENTELEMETRY_HAVE_CXX11)
+  add_definitions(-DOPENTELEMETRY_HAVE_CXX14)
+  add_definitions(-DOPENTELEMETRY_HAVE_CXX17)
+  add_definitions(-DOPENTELEMETRY_HAVE_CXX20)
+  if(NOT DEFINED CMAKE_CXX_STANDARD)
+    set(CMAKE_CXX_STANDARD 20)
+  endif()
+elseif(WITH_STL STREQUAL "ON")
+  # "ON" corresponds to "CXX20" at this time.
+  add_definitions(-DOPENTELEMETRY_HAVE_CXX11)
+  add_definitions(-DOPENTELEMETRY_HAVE_CXX14)
+  add_definitions(-DOPENTELEMETRY_HAVE_CXX17)
+  add_definitions(-DOPENTELEMETRY_HAVE_CXX20)
+  if(NOT DEFINED CMAKE_CXX_STANDARD)
+    set(CMAKE_CXX_STANDARD 20)
+  endif()
+else()
+  message(FATAL_ERROR "WITH_STL must be ON, OFF, CXX11, CXX14, CXX17 or CXX20")
+endif()
+
+
 if(NOT DEFINED CMAKE_CXX_STANDARD)
-  if(WITH_STL)
+  if(NOT WITH_STL STREQUAL "OFF")
     # Require at least C++17. C++20 is needed to avoid gsl::span
     if(CMAKE_VERSION VERSION_GREATER 3.11.999)
       # Ask for 20, may get anything below
@@ -128,7 +174,7 @@ if(NOT DEFINED CMAKE_CXX_STANDARD)
   endif()
 endif()
 
-if(WITH_STL)
+if(NOT WITH_STL STREQUAL "OFF")
   # These definitions are needed for test projects that do not link against
   # opentelemetry-api library directly. We ensure that variant implementation
   # (absl::variant or std::variant) in variant unit test code is consistent with
diff --git a/api/include/opentelemetry/nostd/shared_ptr.h b/api/include/opentelemetry/nostd/shared_ptr.h
index e1eac61561..0d37924215 100644
--- a/api/include/opentelemetry/nostd/shared_ptr.h
+++ b/api/include/opentelemetry/nostd/shared_ptr.h
@@ -2,7 +2,7 @@
 // SPDX-License-Identifier: Apache-2.0
 
 #pragma once
-#ifdef HAVE_CPP_STDLIB
+#ifdef OPENTELEMETRY_HAVE_CXX11
 #  include "opentelemetry/std/shared_ptr.h"
 #else
 #  include <cstdlib>
diff --git a/api/include/opentelemetry/nostd/string_view.h b/api/include/opentelemetry/nostd/string_view.h
index ac27c3dc79..1f203fb6a5 100644
--- a/api/include/opentelemetry/nostd/string_view.h
+++ b/api/include/opentelemetry/nostd/string_view.h
@@ -3,7 +3,7 @@
 
 #pragma once
 
-#ifdef HAVE_CPP_STDLIB
+#ifdef OPENTELEMETRY_HAVE_CXX17
 #  include "opentelemetry/std/string_view.h"
 #else
 #  include <algorithm>
diff --git a/api/include/opentelemetry/nostd/unique_ptr.h b/api/include/opentelemetry/nostd/unique_ptr.h
index a97111b9d0..23c12cd9db 100644
--- a/api/include/opentelemetry/nostd/unique_ptr.h
+++ b/api/include/opentelemetry/nostd/unique_ptr.h
@@ -3,7 +3,7 @@
 
 #pragma once
 
-#ifdef HAVE_CPP_STDLIB
+#ifdef OPENTELEMETRY_HAVE_CXX11
 #  include "opentelemetry/std/unique_ptr.h"
 #else
 #  include <cstddef>

From 72ea66e4694256d4e5e412d480a3ad14df7dd406 Mon Sep 17 00:00:00 2001
From: Marc Alff <marc.alff@oracle.com>
Date: Mon, 7 Nov 2022 15:25:41 +0100
Subject: [PATCH 02/13] WIP

---
 CMakeLists.txt                                | 28 +++++++++----------
 api/include/opentelemetry/nostd/shared_ptr.h  |  2 +-
 api/include/opentelemetry/nostd/string_view.h |  2 +-
 api/include/opentelemetry/nostd/unique_ptr.h  |  2 +-
 api/include/opentelemetry/nostd/utility.h     |  2 +-
 5 files changed, 18 insertions(+), 18 deletions(-)

diff --git a/CMakeLists.txt b/CMakeLists.txt
index 1d49ad6536..921680cac0 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -120,37 +120,37 @@ if(WITH_STL STREQUAL "OFF")
   endif()
   # STL not used.
 elseif(WITH_STL STREQUAL "CXX11")
-  add_definitions(-DOPENTELEMETRY_HAVE_CXX11)
+  add_definitions(-DOPENTELEMETRY_HAVE_STL_CXX11)
   if(NOT DEFINED CMAKE_CXX_STANDARD)
     set(CMAKE_CXX_STANDARD 11)
   endif()
 elseif(WITH_STL STREQUAL "CXX14")
-  add_definitions(-DOPENTELEMETRY_HAVE_CXX11)
-  add_definitions(-DOPENTELEMETRY_HAVE_CXX14)
+  add_definitions(-DOPENTELEMETRY_HAVE_STL_CXX11)
+  add_definitions(-DOPENTELEMETRY_HAVE_STL_CXX14)
   if(NOT DEFINED CMAKE_CXX_STANDARD)
     set(CMAKE_CXX_STANDARD 14)
   endif()
 elseif(WITH_STL STREQUAL "CXX17")
-  add_definitions(-DOPENTELEMETRY_HAVE_CXX11)
-  add_definitions(-DOPENTELEMETRY_HAVE_CXX14)
-  add_definitions(-DOPENTELEMETRY_HAVE_CXX17)
+  add_definitions(-DOPENTELEMETRY_HAVE_STL_CXX11)
+  add_definitions(-DOPENTELEMETRY_HAVE_STL_CXX14)
+  add_definitions(-DOPENTELEMETRY_HAVE_STL_CXX17)
   if(NOT DEFINED CMAKE_CXX_STANDARD)
     set(CMAKE_CXX_STANDARD 17)
   endif()
 elseif(WITH_STL STREQUAL "CXX20")
-  add_definitions(-DOPENTELEMETRY_HAVE_CXX11)
-  add_definitions(-DOPENTELEMETRY_HAVE_CXX14)
-  add_definitions(-DOPENTELEMETRY_HAVE_CXX17)
-  add_definitions(-DOPENTELEMETRY_HAVE_CXX20)
+  add_definitions(-DOPENTELEMETRY_HAVE_STL_CXX11)
+  add_definitions(-DOPENTELEMETRY_HAVE_STL_CXX14)
+  add_definitions(-DOPENTELEMETRY_HAVE_STL_CXX17)
+  add_definitions(-DOPENTELEMETRY_HAVE_STL_CXX20)
   if(NOT DEFINED CMAKE_CXX_STANDARD)
     set(CMAKE_CXX_STANDARD 20)
   endif()
 elseif(WITH_STL STREQUAL "ON")
   # "ON" corresponds to "CXX20" at this time.
-  add_definitions(-DOPENTELEMETRY_HAVE_CXX11)
-  add_definitions(-DOPENTELEMETRY_HAVE_CXX14)
-  add_definitions(-DOPENTELEMETRY_HAVE_CXX17)
-  add_definitions(-DOPENTELEMETRY_HAVE_CXX20)
+  add_definitions(-DOPENTELEMETRY_HAVE_STL_CXX11)
+  add_definitions(-DOPENTELEMETRY_HAVE_STL_CXX14)
+  add_definitions(-DOPENTELEMETRY_HAVE_STL_CXX17)
+  add_definitions(-DOPENTELEMETRY_HAVE_STL_CXX20)
   if(NOT DEFINED CMAKE_CXX_STANDARD)
     set(CMAKE_CXX_STANDARD 20)
   endif()
diff --git a/api/include/opentelemetry/nostd/shared_ptr.h b/api/include/opentelemetry/nostd/shared_ptr.h
index 0d37924215..4a7833fba1 100644
--- a/api/include/opentelemetry/nostd/shared_ptr.h
+++ b/api/include/opentelemetry/nostd/shared_ptr.h
@@ -2,7 +2,7 @@
 // SPDX-License-Identifier: Apache-2.0
 
 #pragma once
-#ifdef OPENTELEMETRY_HAVE_CXX11
+#ifdef OPENTELEMETRY_HAVE_STL_CXX11
 #  include "opentelemetry/std/shared_ptr.h"
 #else
 #  include <cstdlib>
diff --git a/api/include/opentelemetry/nostd/string_view.h b/api/include/opentelemetry/nostd/string_view.h
index 1f203fb6a5..3923563e33 100644
--- a/api/include/opentelemetry/nostd/string_view.h
+++ b/api/include/opentelemetry/nostd/string_view.h
@@ -3,7 +3,7 @@
 
 #pragma once
 
-#ifdef OPENTELEMETRY_HAVE_CXX17
+#ifdef OPENTELEMETRY_HAVE_STL_CXX17
 #  include "opentelemetry/std/string_view.h"
 #else
 #  include <algorithm>
diff --git a/api/include/opentelemetry/nostd/unique_ptr.h b/api/include/opentelemetry/nostd/unique_ptr.h
index 23c12cd9db..7f930f65cc 100644
--- a/api/include/opentelemetry/nostd/unique_ptr.h
+++ b/api/include/opentelemetry/nostd/unique_ptr.h
@@ -3,7 +3,7 @@
 
 #pragma once
 
-#ifdef OPENTELEMETRY_HAVE_CXX11
+#ifdef OPENTELEMETRY_HAVE_STL_CXX11
 #  include "opentelemetry/std/unique_ptr.h"
 #else
 #  include <cstddef>
diff --git a/api/include/opentelemetry/nostd/utility.h b/api/include/opentelemetry/nostd/utility.h
index bb350594ad..f333f6e283 100644
--- a/api/include/opentelemetry/nostd/utility.h
+++ b/api/include/opentelemetry/nostd/utility.h
@@ -3,7 +3,7 @@
 
 #pragma once
 
-#ifdef HAVE_CPP_STDLIB
+#ifdef OPENTELEMETRY_HAVE_STL_CXX14
 #  include "opentelemetry/std/utility.h"
 #else
 

From 294a766ddeee70d199623a49bc308ecec42d4e2c Mon Sep 17 00:00:00 2001
From: Marc Alff <marc.alff@oracle.com>
Date: Thu, 8 Dec 2022 01:06:46 +0100
Subject: [PATCH 03/13] WIP

---
 CMakeLists.txt                                | 20 ++++++-------------
 api/include/opentelemetry/nostd/shared_ptr.h  |  3 ++-
 api/include/opentelemetry/nostd/string_view.h |  2 +-
 api/include/opentelemetry/nostd/unique_ptr.h  |  2 +-
 api/include/opentelemetry/nostd/utility.h     |  2 +-
 5 files changed, 11 insertions(+), 18 deletions(-)

diff --git a/CMakeLists.txt b/CMakeLists.txt
index 921680cac0..a3a04957ea 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -115,42 +115,34 @@ option(WITH_GSL
 option(WITH_ABSEIL "Whether to use Abseil for C++latest features" OFF)
 
 if(WITH_STL STREQUAL "OFF")
+  add_definitions(-DOPENTELEMETRY_STL_VERSION=0)
   if(NOT DEFINED CMAKE_CXX_STANDARD)
     set(CMAKE_CXX_STANDARD 11)
   endif()
   # STL not used.
 elseif(WITH_STL STREQUAL "CXX11")
-  add_definitions(-DOPENTELEMETRY_HAVE_STL_CXX11)
+  add_definitions(-DOPENTELEMETRY_STL_VERSION=2011)
   if(NOT DEFINED CMAKE_CXX_STANDARD)
     set(CMAKE_CXX_STANDARD 11)
   endif()
 elseif(WITH_STL STREQUAL "CXX14")
-  add_definitions(-DOPENTELEMETRY_HAVE_STL_CXX11)
-  add_definitions(-DOPENTELEMETRY_HAVE_STL_CXX14)
+  add_definitions(-DOPENTELEMETRY_STL_VERSION=2014)
   if(NOT DEFINED CMAKE_CXX_STANDARD)
     set(CMAKE_CXX_STANDARD 14)
   endif()
 elseif(WITH_STL STREQUAL "CXX17")
-  add_definitions(-DOPENTELEMETRY_HAVE_STL_CXX11)
-  add_definitions(-DOPENTELEMETRY_HAVE_STL_CXX14)
-  add_definitions(-DOPENTELEMETRY_HAVE_STL_CXX17)
+  add_definitions(-DOPENTELEMETRY_STL_VERSION=2017)
   if(NOT DEFINED CMAKE_CXX_STANDARD)
     set(CMAKE_CXX_STANDARD 17)
   endif()
 elseif(WITH_STL STREQUAL "CXX20")
-  add_definitions(-DOPENTELEMETRY_HAVE_STL_CXX11)
-  add_definitions(-DOPENTELEMETRY_HAVE_STL_CXX14)
-  add_definitions(-DOPENTELEMETRY_HAVE_STL_CXX17)
-  add_definitions(-DOPENTELEMETRY_HAVE_STL_CXX20)
+  add_definitions(-DOPENTELEMETRY_STL_VERSION=2020)
   if(NOT DEFINED CMAKE_CXX_STANDARD)
     set(CMAKE_CXX_STANDARD 20)
   endif()
 elseif(WITH_STL STREQUAL "ON")
   # "ON" corresponds to "CXX20" at this time.
-  add_definitions(-DOPENTELEMETRY_HAVE_STL_CXX11)
-  add_definitions(-DOPENTELEMETRY_HAVE_STL_CXX14)
-  add_definitions(-DOPENTELEMETRY_HAVE_STL_CXX17)
-  add_definitions(-DOPENTELEMETRY_HAVE_STL_CXX20)
+  add_definitions(-DOPENTELEMETRY_STL_VERSION=2020)
   if(NOT DEFINED CMAKE_CXX_STANDARD)
     set(CMAKE_CXX_STANDARD 20)
   endif()
diff --git a/api/include/opentelemetry/nostd/shared_ptr.h b/api/include/opentelemetry/nostd/shared_ptr.h
index 4a7833fba1..43a405cd4b 100644
--- a/api/include/opentelemetry/nostd/shared_ptr.h
+++ b/api/include/opentelemetry/nostd/shared_ptr.h
@@ -2,7 +2,8 @@
 // SPDX-License-Identifier: Apache-2.0
 
 #pragma once
-#ifdef OPENTELEMETRY_HAVE_STL_CXX11
+
+#if OPENTELEMETRY_STL_VERSION >= 2011
 #  include "opentelemetry/std/shared_ptr.h"
 #else
 #  include <cstdlib>
diff --git a/api/include/opentelemetry/nostd/string_view.h b/api/include/opentelemetry/nostd/string_view.h
index 3923563e33..a42a148522 100644
--- a/api/include/opentelemetry/nostd/string_view.h
+++ b/api/include/opentelemetry/nostd/string_view.h
@@ -3,7 +3,7 @@
 
 #pragma once
 
-#ifdef OPENTELEMETRY_HAVE_STL_CXX17
+#if OPENTELEMETRY_STL_VERSION >= 2017
 #  include "opentelemetry/std/string_view.h"
 #else
 #  include <algorithm>
diff --git a/api/include/opentelemetry/nostd/unique_ptr.h b/api/include/opentelemetry/nostd/unique_ptr.h
index 7f930f65cc..1553f31e95 100644
--- a/api/include/opentelemetry/nostd/unique_ptr.h
+++ b/api/include/opentelemetry/nostd/unique_ptr.h
@@ -3,7 +3,7 @@
 
 #pragma once
 
-#ifdef OPENTELEMETRY_HAVE_STL_CXX11
+#if OPENTELEMETRY_STL_VERSION >= 2011
 #  include "opentelemetry/std/unique_ptr.h"
 #else
 #  include <cstddef>
diff --git a/api/include/opentelemetry/nostd/utility.h b/api/include/opentelemetry/nostd/utility.h
index f333f6e283..599db26d39 100644
--- a/api/include/opentelemetry/nostd/utility.h
+++ b/api/include/opentelemetry/nostd/utility.h
@@ -3,7 +3,7 @@
 
 #pragma once
 
-#ifdef OPENTELEMETRY_HAVE_STL_CXX14
+#if OPENTELEMETRY_STL_VERSION >= 2014
 #  include "opentelemetry/std/utility.h"
 #else
 

From 22537db7b8c850d0aa8f37d030cd121581cddf7f Mon Sep 17 00:00:00 2001
From: Marc Alff <marc.alff@oracle.com>
Date: Thu, 31 Aug 2023 15:18:14 +0200
Subject: [PATCH 04/13] Fixes #1071

---
 CMakeLists.txt                                | 51 -------------------
 api/CMakeLists.txt                            | 24 +++++++--
 api/include/opentelemetry/nostd/span.h        |  4 +-
 api/include/opentelemetry/nostd/type_traits.h |  4 +-
 api/include/opentelemetry/nostd/variant.h     |  2 +-
 api/test/nostd/span_test.cc                   | 15 ------
 api/test/nostd/string_view_test.cc            |  2 +-
 7 files changed, 26 insertions(+), 76 deletions(-)

diff --git a/CMakeLists.txt b/CMakeLists.txt
index d9a4c5f668..664cc229ea 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -122,42 +122,6 @@ option(WITH_GSL
 
 option(WITH_ABSEIL "Whether to use Abseil for C++latest features" OFF)
 
-if(WITH_STL STREQUAL "OFF")
-  add_definitions(-DOPENTELEMETRY_STL_VERSION=0)
-  if(NOT DEFINED CMAKE_CXX_STANDARD)
-    set(CMAKE_CXX_STANDARD 11)
-  endif()
-  # STL not used.
-elseif(WITH_STL STREQUAL "CXX11")
-  add_definitions(-DOPENTELEMETRY_STL_VERSION=2011)
-  if(NOT DEFINED CMAKE_CXX_STANDARD)
-    set(CMAKE_CXX_STANDARD 11)
-  endif()
-elseif(WITH_STL STREQUAL "CXX14")
-  add_definitions(-DOPENTELEMETRY_STL_VERSION=2014)
-  if(NOT DEFINED CMAKE_CXX_STANDARD)
-    set(CMAKE_CXX_STANDARD 14)
-  endif()
-elseif(WITH_STL STREQUAL "CXX17")
-  add_definitions(-DOPENTELEMETRY_STL_VERSION=2017)
-  if(NOT DEFINED CMAKE_CXX_STANDARD)
-    set(CMAKE_CXX_STANDARD 17)
-  endif()
-elseif(WITH_STL STREQUAL "CXX20")
-  add_definitions(-DOPENTELEMETRY_STL_VERSION=2020)
-  if(NOT DEFINED CMAKE_CXX_STANDARD)
-    set(CMAKE_CXX_STANDARD 20)
-  endif()
-elseif(WITH_STL STREQUAL "ON")
-  # "ON" corresponds to "CXX20" at this time.
-  add_definitions(-DOPENTELEMETRY_STL_VERSION=2020)
-  if(NOT DEFINED CMAKE_CXX_STANDARD)
-    set(CMAKE_CXX_STANDARD 20)
-  endif()
-else()
-  message(FATAL_ERROR "WITH_STL must be ON, OFF, CXX11, CXX14, CXX17 or CXX20")
-endif()
-
 set(OPENTELEMETRY_INSTALL_default ON)
 if(NOT CMAKE_SOURCE_DIR STREQUAL CMAKE_CURRENT_SOURCE_DIR)
   set(OPENTELEMETRY_INSTALL_default OFF)
@@ -167,21 +131,6 @@ option(OPENTELEMETRY_INSTALL "Whether to install opentelemetry targets"
 
 include("${PROJECT_SOURCE_DIR}/cmake/tools.cmake")
 
-if(NOT DEFINED CMAKE_CXX_STANDARD)
-  if(NOT WITH_STL STREQUAL "OFF")
-    # Require at least C++17. C++20 is needed to avoid gsl::span
-    if(CMAKE_VERSION VERSION_GREATER 3.11.999)
-      # Ask for 20, may get anything below
-      set(CMAKE_CXX_STANDARD 20)
-    else()
-      # Ask for 17, may get anything below
-      set(CMAKE_CXX_STANDARD 17)
-    endif()
-  else()
-    set(CMAKE_CXX_STANDARD 11)
-  endif()
-endif()
-
 if(NOT WITH_STL STREQUAL "OFF")
   # These definitions are needed for test projects that do not link against
   # opentelemetry-api library directly. We ensure that variant implementation
diff --git a/api/CMakeLists.txt b/api/CMakeLists.txt
index 41b6997980..de5fd09110 100644
--- a/api/CMakeLists.txt
+++ b/api/CMakeLists.txt
@@ -51,11 +51,27 @@ if(WITH_ABSEIL)
        "absl_bits" "absl_city")
 endif()
 
-if(WITH_STL)
-  message("Building with standard library types...")
-  target_compile_definitions(opentelemetry_api INTERFACE HAVE_CPP_STDLIB)
+if(WITH_STL STREQUAL "OFF")
+  message(STATUS "Building WITH_STL=OFF")
+  target_compile_definitions(opentelemetry_api INTERFACE OPENTELEMETRY_STL_VERSION=0)
+elseif(WITH_STL STREQUAL "CXX11")
+  message(STATUS "Building WITH_STL=CXX1")
+  target_compile_definitions(opentelemetry_api INTERFACE OPENTELEMETRY_STL_VERSION=2011)
+elseif(WITH_STL STREQUAL "CXX14")
+  message(STATUS "Building WITH_STL=CXX14")
+  target_compile_definitions(opentelemetry_api INTERFACE OPENTELEMETRY_STL_VERSION=2014)
+elseif(WITH_STL STREQUAL "CXX17")
+  message(STATUS "Building WITH_STL=CXX17")
+  target_compile_definitions(opentelemetry_api INTERFACE OPENTELEMETRY_STL_VERSION=2017)
+elseif(WITH_STL STREQUAL "CXX20")
+  message(STATUS "Building WITH_STL=CXX20")
+  target_compile_definitions(opentelemetry_api INTERFACE OPENTELEMETRY_STL_VERSION=2020)
+elseif(WITH_STL STREQUAL "ON")
+  message(STATUS "Building WITH_STL=ON")
+  # "ON" corresponds to "CXX20" at this time.
+  target_compile_definitions(opentelemetry_api INTERFACE OPENTELEMETRY_STL_VERSION=2020)
 else()
-  message("Building with nostd types...")
+  message(FATAL_ERROR "WITH_STL must be ON, OFF, CXX11, CXX14, CXX17 or CXX20")
 endif()
 
 if(WITH_GSL)
diff --git a/api/include/opentelemetry/nostd/span.h b/api/include/opentelemetry/nostd/span.h
index 3022a913d9..389e26b178 100644
--- a/api/include/opentelemetry/nostd/span.h
+++ b/api/include/opentelemetry/nostd/span.h
@@ -4,7 +4,7 @@
 #pragma once
 
 // Try to use either `std::span` or `gsl::span`
-#ifdef HAVE_CPP_STDLIB
+#if OPENTELEMETRY_STL_VERSION >= 2020
 #  include <array>
 #  include <cstddef>
 #  include <iterator>
@@ -26,7 +26,7 @@
 #  if OPENTELEMETRY_OPTION_USE_STD_SPAN
 #    include "opentelemetry/std/span.h"
 #  endif
-#endif
+#endif /* OPENTELEMETRY_STL_VERSION >= 2020 */
 
 // Fallback to `nostd::span` if necessary
 #if !defined(HAVE_SPAN)
diff --git a/api/include/opentelemetry/nostd/type_traits.h b/api/include/opentelemetry/nostd/type_traits.h
index 3d212ea3e2..709e2afb89 100644
--- a/api/include/opentelemetry/nostd/type_traits.h
+++ b/api/include/opentelemetry/nostd/type_traits.h
@@ -3,7 +3,7 @@
 
 #pragma once
 
-#ifdef HAVE_CPP_STDLIB
+#if OPENTELEMETRY_STL_VERSION >= 2011
 #  include "opentelemetry/std/type_traits.h"
 #else
 #  include <array>
@@ -154,4 +154,4 @@ struct is_trivially_move_assignable
 #  endif
 }  // namespace nostd
 OPENTELEMETRY_END_NAMESPACE
-#endif
+#endif /* OPENTELEMETRY_STL_VERSION >= 2011 */
diff --git a/api/include/opentelemetry/nostd/variant.h b/api/include/opentelemetry/nostd/variant.h
index b6b2326998..536786bd05 100644
--- a/api/include/opentelemetry/nostd/variant.h
+++ b/api/include/opentelemetry/nostd/variant.h
@@ -5,7 +5,7 @@
 
 #include "opentelemetry/version.h"
 
-#ifdef HAVE_CPP_STDLIB
+#if OPENTELEMETRY_STL_VERSION >= 2017
 #  include "opentelemetry/std/variant.h"
 #else
 
diff --git a/api/test/nostd/span_test.cc b/api/test/nostd/span_test.cc
index 98e825142d..5c13ee590e 100644
--- a/api/test/nostd/span_test.cc
+++ b/api/test/nostd/span_test.cc
@@ -60,11 +60,6 @@ TEST(SpanTest, PointerCountConstruction)
   span<int, 3> s2{array.data(), array.size()};
   EXPECT_EQ(s2.data(), array.data());
   EXPECT_EQ(s2.size(), array.size());
-
-#ifndef HAVE_CPP_STDLIB
-  /* This test is not supposed to fail with STL. Why is this invalid construct? */
-  EXPECT_DEATH((span<int, 2>{array.data(), array.size()}), ".*");
-#endif
 }
 
 TEST(SpanTest, RangeConstruction)
@@ -78,11 +73,6 @@ TEST(SpanTest, RangeConstruction)
   span<int, 3> s2{std::begin(array), std::end(array)};
   EXPECT_EQ(s2.data(), array);
   EXPECT_EQ(s2.size(), 3);
-
-#ifndef HAVE_CPP_STDLIB
-  /* This test is not supposed to fail with STL. Why is this invalid construct? */
-  EXPECT_DEATH((span<int, 2>{std::begin(array), std::end(array)}), ".*");
-#endif
 }
 
 TEST(SpanTest, ArrayConstruction)
@@ -122,11 +112,6 @@ TEST(SpanTest, ContainerConstruction)
   EXPECT_EQ(s2.data(), v.data());
   EXPECT_EQ(s2.size(), v.size());
 
-#ifndef HAVE_CPP_STDLIB
-  /* This test is not supposed to fail with STL. Why is this invalid construct? */
-  EXPECT_DEATH((span<int, 2>{v.data(), 3}), ".*");
-#endif
-
   EXPECT_FALSE((std::is_constructible<span<int>, std::vector<double>>::value));
   EXPECT_FALSE((std::is_constructible<span<int>, std::list<int>>::value));
 }
diff --git a/api/test/nostd/string_view_test.cc b/api/test/nostd/string_view_test.cc
index fc580debc1..3db28096a7 100644
--- a/api/test/nostd/string_view_test.cc
+++ b/api/test/nostd/string_view_test.cc
@@ -71,7 +71,7 @@ TEST(StringViewTest, SubstrPortion)
 TEST(StringViewTest, SubstrOutOfRange)
 {
   string_view s = "abc123";
-#if __EXCEPTIONS || defined(HAVE_CPP_STDLIB)
+#if __EXCEPTIONS || (OPENTELEMETRY_STL_VERSION >= 2020)
   EXPECT_THROW(s.substr(10), std::out_of_range);
 #else
   EXPECT_DEATH({ s.substr(10); }, "");

From 14bccb5b2ffabe66554b115196f129b92f426a9c Mon Sep 17 00:00:00 2001
From: Marc Alff <marc.alff@oracle.com>
Date: Mon, 11 Sep 2023 17:42:04 +0200
Subject: [PATCH 05/13] build cleanup

---
 CMakeLists.txt               |  4 +++-
 api/CMakeLists.txt           | 18 ++++++++++++------
 ext/test/http/CMakeLists.txt |  2 +-
 3 files changed, 16 insertions(+), 8 deletions(-)

diff --git a/CMakeLists.txt b/CMakeLists.txt
index 719a7b2475..d388f30fac 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -115,7 +115,9 @@ endif()
 
 option(WITH_NO_DEPRECATED_CODE "Do not include deprecated code" OFF)
 
-set(WITH_STL "OFF" CACHE STRING "Which version of the Standard Library for C++ to use")
+set(WITH_STL
+    "OFF"
+    CACHE STRING "Which version of the Standard Library for C++ to use")
 
 option(WITH_GSL
        "Whether to use Guidelines Support Library for C++ latest features" OFF)
diff --git a/api/CMakeLists.txt b/api/CMakeLists.txt
index de5fd09110..9e50bc51f0 100644
--- a/api/CMakeLists.txt
+++ b/api/CMakeLists.txt
@@ -53,23 +53,29 @@ endif()
 
 if(WITH_STL STREQUAL "OFF")
   message(STATUS "Building WITH_STL=OFF")
-  target_compile_definitions(opentelemetry_api INTERFACE OPENTELEMETRY_STL_VERSION=0)
+  target_compile_definitions(opentelemetry_api
+                             INTERFACE OPENTELEMETRY_STL_VERSION=0)
 elseif(WITH_STL STREQUAL "CXX11")
   message(STATUS "Building WITH_STL=CXX1")
-  target_compile_definitions(opentelemetry_api INTERFACE OPENTELEMETRY_STL_VERSION=2011)
+  target_compile_definitions(opentelemetry_api
+                             INTERFACE OPENTELEMETRY_STL_VERSION=2011)
 elseif(WITH_STL STREQUAL "CXX14")
   message(STATUS "Building WITH_STL=CXX14")
-  target_compile_definitions(opentelemetry_api INTERFACE OPENTELEMETRY_STL_VERSION=2014)
+  target_compile_definitions(opentelemetry_api
+                             INTERFACE OPENTELEMETRY_STL_VERSION=2014)
 elseif(WITH_STL STREQUAL "CXX17")
   message(STATUS "Building WITH_STL=CXX17")
-  target_compile_definitions(opentelemetry_api INTERFACE OPENTELEMETRY_STL_VERSION=2017)
+  target_compile_definitions(opentelemetry_api
+                             INTERFACE OPENTELEMETRY_STL_VERSION=2017)
 elseif(WITH_STL STREQUAL "CXX20")
   message(STATUS "Building WITH_STL=CXX20")
-  target_compile_definitions(opentelemetry_api INTERFACE OPENTELEMETRY_STL_VERSION=2020)
+  target_compile_definitions(opentelemetry_api
+                             INTERFACE OPENTELEMETRY_STL_VERSION=2020)
 elseif(WITH_STL STREQUAL "ON")
   message(STATUS "Building WITH_STL=ON")
   # "ON" corresponds to "CXX20" at this time.
-  target_compile_definitions(opentelemetry_api INTERFACE OPENTELEMETRY_STL_VERSION=2020)
+  target_compile_definitions(opentelemetry_api
+                             INTERFACE OPENTELEMETRY_STL_VERSION=2020)
 else()
   message(FATAL_ERROR "WITH_STL must be ON, OFF, CXX11, CXX14, CXX17 or CXX20")
 endif()
diff --git a/ext/test/http/CMakeLists.txt b/ext/test/http/CMakeLists.txt
index 3ce72b3b83..328f78638b 100644
--- a/ext/test/http/CMakeLists.txt
+++ b/ext/test/http/CMakeLists.txt
@@ -25,7 +25,7 @@ endif()
 set(URL_PARSER_FILENAME url_parser_test)
 add_executable(${URL_PARSER_FILENAME} ${URL_PARSER_FILENAME}.cc)
 target_link_libraries(${URL_PARSER_FILENAME} ${GTEST_BOTH_LIBRARIES}
-                      ${CMAKE_THREAD_LIBS_INIT})
+                      ${CMAKE_THREAD_LIBS_INIT} opentelemetry_api)
 gtest_add_tests(
   TARGET ${URL_PARSER_FILENAME}
   TEST_PREFIX ext.http.urlparser.

From 85cb90de3a3c00abef2bc30e397f1600176453e4 Mon Sep 17 00:00:00 2001
From: Marc Alff <marc.alff@oracle.com>
Date: Tue, 12 Sep 2023 10:09:09 +0200
Subject: [PATCH 06/13] cleanup

---
 api/CMakeLists.txt                            |  2 --
 api/include/opentelemetry/nostd/shared_ptr.h  | 13 ++++---
 api/include/opentelemetry/nostd/span.h        | 36 ++++++++++---------
 api/include/opentelemetry/nostd/string_view.h | 13 ++++---
 api/include/opentelemetry/nostd/type_traits.h | 13 ++++---
 api/include/opentelemetry/nostd/unique_ptr.h  | 13 ++++---
 api/include/opentelemetry/nostd/utility.h     | 12 ++++---
 api/include/opentelemetry/nostd/variant.h     | 13 ++++---
 api/include/opentelemetry/std/span.h          | 16 ++++-----
 api/test/nostd/string_view_test.cc            |  2 +-
 10 files changed, 81 insertions(+), 52 deletions(-)

diff --git a/api/CMakeLists.txt b/api/CMakeLists.txt
index 9e50bc51f0..208d9b4c26 100644
--- a/api/CMakeLists.txt
+++ b/api/CMakeLists.txt
@@ -53,8 +53,6 @@ endif()
 
 if(WITH_STL STREQUAL "OFF")
   message(STATUS "Building WITH_STL=OFF")
-  target_compile_definitions(opentelemetry_api
-                             INTERFACE OPENTELEMETRY_STL_VERSION=0)
 elseif(WITH_STL STREQUAL "CXX11")
   message(STATUS "Building WITH_STL=CXX1")
   target_compile_definitions(opentelemetry_api
diff --git a/api/include/opentelemetry/nostd/shared_ptr.h b/api/include/opentelemetry/nostd/shared_ptr.h
index 1227df3c82..0222352030 100644
--- a/api/include/opentelemetry/nostd/shared_ptr.h
+++ b/api/include/opentelemetry/nostd/shared_ptr.h
@@ -3,9 +3,14 @@
 
 #pragma once
 
-#if OPENTELEMETRY_STL_VERSION >= 2011
-#  include "opentelemetry/std/shared_ptr.h"
-#else
+#if defined(OPENTELEMETRY_STL_VERSION)
+#  if OPENTELEMETRY_STL_VERSION >= 2011
+#    include "opentelemetry/std/shared_ptr.h"
+#    define OPENTELEMETRY_HAVE_STD_SHARED_PTR
+#  endif
+#endif
+
+#if !defined(OPENTELEMETRY_HAVE_STD_SHARED_PTR)
 #  include <cstdlib>
 #  include <memory>
 #  include <utility>
@@ -202,4 +207,4 @@ inline bool operator!=(std::nullptr_t, const shared_ptr<T> &rhs) noexcept
 }
 }  // namespace nostd
 OPENTELEMETRY_END_NAMESPACE
-#endif
+#endif /* OPENTELEMETRY_HAVE_STD_SHARED_PTR */
diff --git a/api/include/opentelemetry/nostd/span.h b/api/include/opentelemetry/nostd/span.h
index 389e26b178..da0f385cf0 100644
--- a/api/include/opentelemetry/nostd/span.h
+++ b/api/include/opentelemetry/nostd/span.h
@@ -4,32 +4,34 @@
 #pragma once
 
 // Try to use either `std::span` or `gsl::span`
-#if OPENTELEMETRY_STL_VERSION >= 2020
-#  include <array>
-#  include <cstddef>
-#  include <iterator>
-#  include <type_traits>
+#if defined(OPENTELEMETRY_STL_VERSION)
+#  if OPENTELEMETRY_STL_VERSION >= 2020
+#    include <array>
+#    include <cstddef>
+#    include <iterator>
+#    include <type_traits>
 
 /**
  * @brief Clang 14.0.0 with libc++ do not support implicitly construct a span
  * for a range. We just use our fallback version.
  *
  */
-#  if !defined(OPENTELEMETRY_OPTION_USE_STD_SPAN) && defined(_LIBCPP_VERSION)
-#    if _LIBCPP_VERSION <= 14000
-#      define OPENTELEMETRY_OPTION_USE_STD_SPAN 0
+#    if !defined(OPENTELEMETRY_OPTION_USE_STD_SPAN) && defined(_LIBCPP_VERSION)
+#      if _LIBCPP_VERSION <= 14000
+#        define OPENTELEMETRY_OPTION_USE_STD_SPAN 0
+#      endif
+#    endif
+#    ifndef OPENTELEMETRY_OPTION_USE_STD_SPAN
+#      define OPENTELEMETRY_OPTION_USE_STD_SPAN 1
+#    endif
+#    if OPENTELEMETRY_OPTION_USE_STD_SPAN
+#      include "opentelemetry/std/span.h"
 #    endif
-#  endif
-#  ifndef OPENTELEMETRY_OPTION_USE_STD_SPAN
-#    define OPENTELEMETRY_OPTION_USE_STD_SPAN 1
-#  endif
-#  if OPENTELEMETRY_OPTION_USE_STD_SPAN
-#    include "opentelemetry/std/span.h"
-#  endif
-#endif /* OPENTELEMETRY_STL_VERSION >= 2020 */
+#  endif /* OPENTELEMETRY_STL_VERSION >= 2020 */
+#endif   /* OPENTELEMETRY_STL_VERSION */
 
 // Fallback to `nostd::span` if necessary
-#if !defined(HAVE_SPAN)
+#if !defined(OPENTELEMETRY_HAVE_SPAN)
 #  include <array>
 #  include <cassert>
 #  include <cstddef>
diff --git a/api/include/opentelemetry/nostd/string_view.h b/api/include/opentelemetry/nostd/string_view.h
index 3adec00fa1..9f9fb42180 100644
--- a/api/include/opentelemetry/nostd/string_view.h
+++ b/api/include/opentelemetry/nostd/string_view.h
@@ -3,9 +3,14 @@
 
 #pragma once
 
-#if OPENTELEMETRY_STL_VERSION >= 2017
-#  include "opentelemetry/std/string_view.h"
-#else
+#if defined(OPENTELEMETRY_STL_VERSION)
+#  if OPENTELEMETRY_STL_VERSION >= 2017
+#    include "opentelemetry/std/string_view.h"
+#    define OPENTELEMETRY_HAVE_STD_STRING_VIEW
+#  endif
+#endif
+
+#if !defined(OPENTELEMETRY_HAVE_STD_STRING_VIEW)
 #  include <algorithm>
 #  include <cstddef>
 #  include <cstring>
@@ -216,4 +221,4 @@ struct hash<OPENTELEMETRY_NAMESPACE::nostd::string_view>
   }
 };
 }  // namespace std
-#endif
+#endif /* OPENTELEMETRY_HAVE_STD_STRING_VIEW */
diff --git a/api/include/opentelemetry/nostd/type_traits.h b/api/include/opentelemetry/nostd/type_traits.h
index 709e2afb89..46d11c89cb 100644
--- a/api/include/opentelemetry/nostd/type_traits.h
+++ b/api/include/opentelemetry/nostd/type_traits.h
@@ -3,9 +3,14 @@
 
 #pragma once
 
-#if OPENTELEMETRY_STL_VERSION >= 2011
-#  include "opentelemetry/std/type_traits.h"
-#else
+#if defined(OPENTELEMETRY_STL_VERSION)
+#  if OPENTELEMETRY_STL_VERSION >= 2011
+#    include "opentelemetry/std/type_traits.h"
+#    define OPENTELEMETRY_HAVE_STD_TYPE_TRAITS
+#  endif
+#endif
+
+#if !defined(OPENTELEMETRY_HAVE_STD_TYPE_TRAITS)
 #  include <array>
 #  include <type_traits>
 
@@ -154,4 +159,4 @@ struct is_trivially_move_assignable
 #  endif
 }  // namespace nostd
 OPENTELEMETRY_END_NAMESPACE
-#endif /* OPENTELEMETRY_STL_VERSION >= 2011 */
+#endif /* OPENTELEMETRY_HAVE_STD_TYPE_TRAITS */
diff --git a/api/include/opentelemetry/nostd/unique_ptr.h b/api/include/opentelemetry/nostd/unique_ptr.h
index 1553f31e95..f864eb4f04 100644
--- a/api/include/opentelemetry/nostd/unique_ptr.h
+++ b/api/include/opentelemetry/nostd/unique_ptr.h
@@ -3,9 +3,14 @@
 
 #pragma once
 
-#if OPENTELEMETRY_STL_VERSION >= 2011
-#  include "opentelemetry/std/unique_ptr.h"
-#else
+#if defined(OPENTELEMETRY_STL_VERSION)
+#  if OPENTELEMETRY_STL_VERSION >= 2011
+#    include "opentelemetry/std/unique_ptr.h"
+#    define OPENTELEMETRY_HAVE_STD_UNIQUE_PTR
+#  endif
+#endif
+
+#if !defined(OPENTELEMETRY_HAVE_STD_UNIQUE_PTR)
 #  include <cstddef>
 #  include <memory>
 #  include <type_traits>
@@ -172,4 +177,4 @@ bool operator!=(std::nullptr_t, const unique_ptr<T> &rhs) noexcept
 }
 }  // namespace nostd
 OPENTELEMETRY_END_NAMESPACE
-#endif
+#endif /* OPENTELEMETRY_HAVE_STD_UNIQUE_PTR */
diff --git a/api/include/opentelemetry/nostd/utility.h b/api/include/opentelemetry/nostd/utility.h
index 599db26d39..e7ad2d77f0 100644
--- a/api/include/opentelemetry/nostd/utility.h
+++ b/api/include/opentelemetry/nostd/utility.h
@@ -3,10 +3,14 @@
 
 #pragma once
 
-#if OPENTELEMETRY_STL_VERSION >= 2014
-#  include "opentelemetry/std/utility.h"
-#else
+#if defined(OPENTELEMETRY_STL_VERSION)
+#  if OPENTELEMETRY_STL_VERSION >= 2014
+#    include "opentelemetry/std/utility.h"
+#    define OPENTELEMETRY_HAVE_STD_UTILITY
+#  endif
+#endif
 
+#if !defined(OPENTELEMETRY_HAVE_STD_UTILITY)
 #  include <cstddef>
 #  include <initializer_list>
 #  include <type_traits>
@@ -153,4 +157,4 @@ struct in_place_type_t
 };
 }  // namespace nostd
 OPENTELEMETRY_END_NAMESPACE
-#endif
+#endif /* OPENTELEMETRY_HAVE_STD_UTILITY */
diff --git a/api/include/opentelemetry/nostd/variant.h b/api/include/opentelemetry/nostd/variant.h
index 536786bd05..d0b2d96001 100644
--- a/api/include/opentelemetry/nostd/variant.h
+++ b/api/include/opentelemetry/nostd/variant.h
@@ -5,9 +5,14 @@
 
 #include "opentelemetry/version.h"
 
-#if OPENTELEMETRY_STL_VERSION >= 2017
-#  include "opentelemetry/std/variant.h"
-#else
+#if defined(OPENTELEMETRY_STL_VERSION)
+#  if OPENTELEMETRY_STL_VERSION >= 2017
+#    include "opentelemetry/std/variant.h"
+#    define OPENTELEMETRY_HAVE_STD_VARIANT
+#  endif
+#endif
+
+#if !defined(OPENTELEMETRY_HAVE_STD_VARIANT)
 
 #  ifndef HAVE_ABSEIL
 // We use a LOCAL snapshot of Abseil that is known to compile with Visual Studio 2015.
@@ -73,4 +78,4 @@ using absl::visit;
 }  // namespace nostd
 OPENTELEMETRY_END_NAMESPACE
 
-#endif
+#endif /* OPENTELEMETRY_HAVE_STD_VARIANT */
diff --git a/api/include/opentelemetry/std/span.h b/api/include/opentelemetry/std/span.h
index 5fdff57fd5..2a3dc12a84 100644
--- a/api/include/opentelemetry/std/span.h
+++ b/api/include/opentelemetry/std/span.h
@@ -12,18 +12,18 @@
 #  if __has_include(<version>)  // Check for __cpp_{feature}
 #    include <version>
 #    if defined(__cpp_lib_span) && __cplusplus > 201703L
-#      define HAVE_SPAN
+#      define OPENTELEMETRY_HAVE_SPAN
 #    endif
 #  endif
-#  if !defined(HAVE_SPAN)
+#  if !defined(OPENTELEMETRY_HAVE_SPAN)
 #    // Check for Visual Studio span
 #    if defined(_MSVC_LANG) && _HAS_CXX20
-#      define HAVE_SPAN
+#      define OPENTELEMETRY_HAVE_SPAN
 #    endif
 #    // Check for other compiler span implementation
 #    if !defined(_MSVC_LANG) && __has_include(<span>) && __cplusplus > 201703L
 // This works as long as compiler standard is set to C++20
-#      define HAVE_SPAN
+#      define OPENTELEMETRY_HAVE_SPAN
 #    endif
 #  endif
 #  if !__has_include(<gsl/gsl>)
@@ -31,7 +31,7 @@
 #  endif
 #endif
 
-#if !defined(HAVE_SPAN)
+#if !defined(OPENTELEMETRY_HAVE_SPAN)
 #  if defined(HAVE_GSL)
 #    include <type_traits>
 // Guidelines Support Library provides an implementation of std::span
@@ -44,12 +44,12 @@ template <class ElementType, std::size_t Extent = gsl::dynamic_extent>
 using span = gsl::span<ElementType, Extent>;
 }  // namespace nostd
 OPENTELEMETRY_END_NAMESPACE
-#    define HAVE_SPAN
+#    define OPENTELEMETRY_HAVE_SPAN
 #  else
 // No `gsl::span`, no `std::span`, fallback to `nostd::span`
 #  endif
 
-#else  // HAVE_SPAN
+#else  // OPENTELEMETRY_HAVE_SPAN
 // Using std::span (https://wg21.link/P0122R7) from Standard Library available in C++20 :
 // - GCC libstdc++ 10+
 // - Clang libc++ 7
@@ -66,4 +66,4 @@ template <class ElementType, std::size_t Extent = nostd::dynamic_extent>
 using span = std::span<ElementType, Extent>;
 }  // namespace nostd
 OPENTELEMETRY_END_NAMESPACE
-#endif  // of HAVE_SPAN
+#endif  // if OPENTELEMETRY_HAVE_SPAN
diff --git a/api/test/nostd/string_view_test.cc b/api/test/nostd/string_view_test.cc
index 3db28096a7..52c72ea4d8 100644
--- a/api/test/nostd/string_view_test.cc
+++ b/api/test/nostd/string_view_test.cc
@@ -71,7 +71,7 @@ TEST(StringViewTest, SubstrPortion)
 TEST(StringViewTest, SubstrOutOfRange)
 {
   string_view s = "abc123";
-#if __EXCEPTIONS || (OPENTELEMETRY_STL_VERSION >= 2020)
+#if __EXCEPTIONS || ((defined(OPENTELEMETRY_STL_VERSION) && (OPENTELEMETRY_STL_VERSION >= 2020)))
   EXPECT_THROW(s.substr(10), std::out_of_range);
 #else
   EXPECT_DEATH({ s.substr(10); }, "");

From 55777ddefdefaa71b98819be92a9800ea9349526 Mon Sep 17 00:00:00 2001
From: Marc Alff <marc.alff@oracle.com>
Date: Tue, 12 Sep 2023 15:17:52 +0200
Subject: [PATCH 07/13] Changelog

---
 CHANGELOG.md       | 17 +++++++++++++++++
 api/CMakeLists.txt | 10 +++++++---
 2 files changed, 24 insertions(+), 3 deletions(-)

diff --git a/CHANGELOG.md b/CHANGELOG.md
index f09553ce70..28117c6241 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -18,6 +18,23 @@ Increment the:
 * [DEPRECATION] Deprecate ZPAGES
   [#2291](https://github.com/open-telemetry/opentelemetry-cpp/pull/2291)
 
+Breaking changes:
+
+* [BUILD] Need fine-grained HAVE_CPP_STDLIB
+  [#2304](https://github.com/open-telemetry/opentelemetry-cpp/pull/2304)
+  * In `CMAKE`, the boolean option `WITH_STL` as changed to an option
+    that accepts the values `OFF`, `ON`, `CXX11`, `CXX14`, `CXX17`,
+    `CXX20` and `CXX23`.
+  * Applications makefiles that did not set WITH_STL need to use
+    `WITH_STL=OFF` instead (this is the default).
+  * Applications makefiles that did set WITH_STL need to use
+    `WITH_STL=ON` instead, or may choose to pick a specific value.
+  * In the `API` header files, the preprocessor symbol `HAVE_CPP_STDLIB`
+    is no longer used.
+  * Applications that did set `HAVE_CPP_STDLIB` before, need to set
+    `OPENTELEMETRY_STL_VERSION=<version>` instead, to build with a
+    specific STL version (2011, 2014, 2017, 2020, 2023).
+
 ## [1.11.0] 2023-08-21
 
 * [BUILD] Fix more cases for symbol name for 32-bit win32 DLL build
diff --git a/api/CMakeLists.txt b/api/CMakeLists.txt
index 208d9b4c26..2b90011caf 100644
--- a/api/CMakeLists.txt
+++ b/api/CMakeLists.txt
@@ -69,13 +69,17 @@ elseif(WITH_STL STREQUAL "CXX20")
   message(STATUS "Building WITH_STL=CXX20")
   target_compile_definitions(opentelemetry_api
                              INTERFACE OPENTELEMETRY_STL_VERSION=2020)
+elseif(WITH_STL STREQUAL "CXX23")
+  message(STATUS "Building WITH_STL=CXX23")
+  target_compile_definitions(opentelemetry_api
+                             INTERFACE OPENTELEMETRY_STL_VERSION=2023)
 elseif(WITH_STL STREQUAL "ON")
   message(STATUS "Building WITH_STL=ON")
-  # "ON" corresponds to "CXX20" at this time.
+  # "ON" corresponds to "CXX23" at this time.
   target_compile_definitions(opentelemetry_api
-                             INTERFACE OPENTELEMETRY_STL_VERSION=2020)
+                             INTERFACE OPENTELEMETRY_STL_VERSION=2023)
 else()
-  message(FATAL_ERROR "WITH_STL must be ON, OFF, CXX11, CXX14, CXX17 or CXX20")
+  message(FATAL_ERROR "WITH_STL must be ON, OFF, CXX11, CXX14, CXX17, CXX20 or CXX23")
 endif()
 
 if(WITH_GSL)

From 6e829dae86e041c5dee48d2c8bf96e4cd895a9dd Mon Sep 17 00:00:00 2001
From: Marc Alff <marc.alff@oracle.com>
Date: Tue, 12 Sep 2023 16:10:23 +0200
Subject: [PATCH 08/13] Added CI

---
 .github/workflows/ci.yml     | 36 ++++++++++++++++++++++++++++++++++++
 ci/do_ci.sh                  | 26 ++++++++++++++++++++++++++
 docs/building-with-stdlib.md | 13 ++++++++++---
 docs/dependencies.md         |  2 +-
 exporters/etw/README.md      |  2 +-
 5 files changed, 74 insertions(+), 5 deletions(-)

diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
index 2d8db91364..01ea48fb86 100644
--- a/.github/workflows/ci.yml
+++ b/.github/workflows/ci.yml
@@ -316,6 +316,42 @@ jobs:
         CXX: /usr/bin/g++-4.8
       run: ./ci/do_ci.sh cmake.legacy.exporter.otprotocol.test
 
+  cmake_test_cxx14_gcc:
+    name: CMake C++14 test(GCC)
+    runs-on: ubuntu-20.04
+    steps:
+    - uses: actions/checkout@v4
+      with:
+        submodules: 'recursive'
+    - name: setup
+      env:
+        CMAKE_VERSION: 3.20.6
+      run: |
+        sudo -E ./ci/setup_ci_environment.sh
+        sudo -E ./ci/setup_cmake.sh
+    - name: run tests (enable stl)
+      env:
+        CXX_STANDARD: '14'
+      run: ./ci/do_ci.sh cmake.c++14.stl.test
+
+  cmake_test_cxx17_gcc:
+    name: CMake C++17 test(GCC)
+    runs-on: ubuntu-20.04
+    steps:
+    - uses: actions/checkout@v4
+      with:
+        submodules: 'recursive'
+    - name: setup
+      env:
+        CMAKE_VERSION: 3.20.6
+      run: |
+        sudo -E ./ci/setup_ci_environment.sh
+        sudo -E ./ci/setup_cmake.sh
+    - name: run tests (enable stl)
+      env:
+        CXX_STANDARD: '17'
+      run: ./ci/do_ci.sh cmake.c++17.stl.test
+
   cmake_test_cxx20_gcc:
     name: CMake C++20 test(GCC)
     runs-on: ubuntu-20.04
diff --git a/ci/do_ci.sh b/ci/do_ci.sh
index 6452faa451..04063eb6ba 100755
--- a/ci/do_ci.sh
+++ b/ci/do_ci.sh
@@ -221,6 +221,32 @@ elif [[ "$1" == "cmake.c++20.test" ]]; then
   eval "$MAKE_COMMAND"
   make test
   exit 0
+elif [[ "$1" == "cmake.c++14.stl.test" ]]; then
+  cd "${BUILD_DIR}"
+  rm -rf *
+  cmake ${CMAKE_OPTIONS[@]}  \
+        -DWITH_METRICS_EXEMPLAR_PREVIEW=ON \
+        -DCMAKE_CXX_FLAGS="-Werror $CXXFLAGS" \
+        -DWITH_ASYNC_EXPORT_PREVIEW=ON \
+        -DWITH_STL=CXX14 \
+        ${IWYU} \
+        "${SRC_DIR}"
+  eval "$MAKE_COMMAND"
+  make test
+  exit 0
+elif [[ "$1" == "cmake.c++17.stl.test" ]]; then
+  cd "${BUILD_DIR}"
+  rm -rf *
+  cmake ${CMAKE_OPTIONS[@]}  \
+        -DWITH_METRICS_EXEMPLAR_PREVIEW=ON \
+        -DCMAKE_CXX_FLAGS="-Werror $CXXFLAGS" \
+        -DWITH_ASYNC_EXPORT_PREVIEW=ON \
+        -DWITH_STL=CXX17 \
+        ${IWYU} \
+        "${SRC_DIR}"
+  eval "$MAKE_COMMAND"
+  make test
+  exit 0
 elif [[ "$1" == "cmake.c++20.stl.test" ]]; then
   cd "${BUILD_DIR}"
   rm -rf *
diff --git a/docs/building-with-stdlib.md b/docs/building-with-stdlib.md
index a90a14a6ed..b52b58ff90 100644
--- a/docs/building-with-stdlib.md
+++ b/docs/building-with-stdlib.md
@@ -138,14 +138,21 @@ Visual Studio provides 1st class debug experience for the standard library.
 Supported build flavors:
 
 * `nostd` - OpenTelemetry backport of classes for C++11. Not using standard lib.
-* `stdlib`   - Standard Library. Full native experience with C++20 compiler.
-  C++17 works but with additional dependencies, e.g. either MS-GSL or Abseil for
+* `stdlib` - Standard Library. Native experience with
+  C++11/C++14/C++17/C++20/C++23 compiler.
+  Depending on the stdlib level in effect,
+  C++ features are used from the standard library,
+  completed with `nostd` replacement implementations.
+  C++17 and below works but with additional dependencies, e.g. either MS-GSL or Abseil for
   `std::span` implementation (`gsl::span` or `absl::Span`).
 * `absl`  - TODO: this should allow using Abseil C++ library only (no MS-GSL).
 
 Currently only `nostd` and `stdlib` configurations are implemented in CMake
 build. `absl` is reserved for future use. Build systems other than CMake need to
-`#define HAVE_CPP_STDLIB` to enable the Standard Library classes.
+`#define OPENTELEMETRY_STL_VERSION=<version>` to enable the Standard Library classes.
+
+Valid values for `OPENTELEMETRY_STL_VERSION` are `2011`, `2014`, `2017`, `2020` and
+`2023`.
 
 ### Build matrix
 
diff --git a/docs/dependencies.md b/docs/dependencies.md
index 62fbefc297..c8a2271ef5 100644
--- a/docs/dependencies.md
+++ b/docs/dependencies.md
@@ -24,7 +24,7 @@ Both these dependencies are listed here:
   [SDK](/sdk):
   - Uses Standard C++ library for latest features (std::string_view,
     std::variant, std::span, std::shared_ptr, std::unique_ptr) with  C++14/17/20
-    compiler if `WITH_STL` cmake option is enabled or `HAVE_CPP_STDLIB` macro is
+    compiler if cmake option `WITH_STL` is enabled or macro `OPENTELEMETRY_STL_VERSION` is
     defined. License: `GNU General Public License`
     - For C++11/14/17 compilers, fallback to gsl::span if [GSL C++
       library](https://github.com/microsoft/GSL) is installed. License: `MIT
diff --git a/exporters/etw/README.md b/exporters/etw/README.md
index 29dc3de430..3339223fa6 100644
--- a/exporters/etw/README.md
+++ b/exporters/etw/README.md
@@ -121,7 +121,7 @@ compiled:
 
 | Name        | Description                                                      |
 |---------------------|------------------------------------------------------------------------------------------------------------------------|
-| HAVE_CPP_STDLIB   | Use STL classes for API surface. This option requires at least C++17. C++20 is recommended. Some customers may benefit from STL library provided with the compiler instead of using custom OpenTelemetry `nostd::` implementation due to security and performance considerations. |
+| OPENTELEMETRY_STL_VERSION | Use STL classes for API surface. C++20 is recommended. Some customers may benefit from STL library provided with the compiler instead of using custom OpenTelemetry `nostd::` implementation due to security and performance considerations. |
 | HAVE_GSL      | Use [Microsoft GSL](https://github.com/microsoft/GSL) for `gsl::span` implementation. Library must be in include path. Microsoft GSL claims to be the most feature-complete implementation of `std::span`. It may be used instead of `nostd::span` implementation in projects that statically link OpenTelemetry SDK. |
 | HAVE_TLD      | Use ETW/TraceLogging Dynamic protocol. This is the default implementation compatible with existing C# "listeners" / "decoders" of ETW events. This option requires an additional optional Microsoft MIT-licensed `TraceLoggingDynamic.h` header. |
 

From dd3d4f1742caed0193bb8b6bebf701b984e8c6a8 Mon Sep 17 00:00:00 2001
From: Marc Alff <marc.alff@oracle.com>
Date: Tue, 12 Sep 2023 16:37:30 +0200
Subject: [PATCH 09/13] cleanup

---
 exporters/otlp/test/otlp_grpc_exporter_test.cc            | 4 ++--
 exporters/otlp/test/otlp_http_exporter_test.cc            | 4 ++--
 exporters/otlp/test/otlp_http_log_record_exporter_test.cc | 4 ++--
 exporters/zipkin/test/zipkin_exporter_test.cc             | 4 ++--
 4 files changed, 8 insertions(+), 8 deletions(-)

diff --git a/exporters/otlp/test/otlp_grpc_exporter_test.cc b/exporters/otlp/test/otlp_grpc_exporter_test.cc
index 3298e5390d..3be2bcc653 100644
--- a/exporters/otlp/test/otlp_grpc_exporter_test.cc
+++ b/exporters/otlp/test/otlp_grpc_exporter_test.cc
@@ -1,7 +1,7 @@
 // Copyright The OpenTelemetry Authors
 // SPDX-License-Identifier: Apache-2.0
 
-#ifndef HAVE_CPP_STDLIB
+#ifndef OPENTELEMETRY_STL_VERSION
 // Unfortunately as of 04/27/2021 the fix is NOT in the vcpkg snapshot of Google Test.
 // Remove above `#ifdef` once the GMock fix for C++20 is in the mainline.
 //
@@ -284,4 +284,4 @@ TEST_F(OtlpGrpcExporterTestPeer, ConfigUnknownInsecureFromEnv)
 }  // namespace otlp
 }  // namespace exporter
 OPENTELEMETRY_END_NAMESPACE
-#endif
+#endif /* OPENTELEMETRY_STL_VERSION */
diff --git a/exporters/otlp/test/otlp_http_exporter_test.cc b/exporters/otlp/test/otlp_http_exporter_test.cc
index 2ac698b0de..42258d2b45 100644
--- a/exporters/otlp/test/otlp_http_exporter_test.cc
+++ b/exporters/otlp/test/otlp_http_exporter_test.cc
@@ -1,7 +1,7 @@
 // Copyright The OpenTelemetry Authors
 // SPDX-License-Identifier: Apache-2.0
 
-#ifndef HAVE_CPP_STDLIB
+#ifndef OPENTELEMETRY_STL_VERSION
 
 #  include <chrono>
 #  include <thread>
@@ -612,4 +612,4 @@ TEST_F(OtlpHttpExporterTestPeer, ConfigFromTracesEnv)
 }  // namespace otlp
 }  // namespace exporter
 OPENTELEMETRY_END_NAMESPACE
-#endif
+#endif /* OPENTELEMETRY_STL_VERSION */
diff --git a/exporters/otlp/test/otlp_http_log_record_exporter_test.cc b/exporters/otlp/test/otlp_http_log_record_exporter_test.cc
index 4dc3b5829d..df89ca17fa 100644
--- a/exporters/otlp/test/otlp_http_log_record_exporter_test.cc
+++ b/exporters/otlp/test/otlp_http_log_record_exporter_test.cc
@@ -1,7 +1,7 @@
 // Copyright The OpenTelemetry Authors
 // SPDX-License-Identifier: Apache-2.0
 
-#ifndef HAVE_CPP_STDLIB
+#ifndef OPENTELEMETRY_STL_VERSION
 
 #  include <chrono>
 #  include <thread>
@@ -740,4 +740,4 @@ TEST_F(OtlpHttpLogRecordExporterTestPeer, DefaultEndpoint)
 }  // namespace otlp
 }  // namespace exporter
 OPENTELEMETRY_END_NAMESPACE
-#endif
+#endif /* OPENTELEMETRY_STL_VERSION */
diff --git a/exporters/zipkin/test/zipkin_exporter_test.cc b/exporters/zipkin/test/zipkin_exporter_test.cc
index fab19efb65..870ff427e9 100644
--- a/exporters/zipkin/test/zipkin_exporter_test.cc
+++ b/exporters/zipkin/test/zipkin_exporter_test.cc
@@ -1,7 +1,7 @@
 // Copyright The OpenTelemetry Authors
 // SPDX-License-Identifier: Apache-2.0
 
-#ifndef HAVE_CPP_STDLIB
+#ifndef OPENTELEMETRY_STL_VERSION
 
 #  include "opentelemetry/exporters/zipkin/zipkin_exporter.h"
 #  include "opentelemetry/ext/http/client/curl/http_client_curl.h"
@@ -246,4 +246,4 @@ TEST_F(ZipkinExporterTestPeer, ConfigFromEnv)
 }  // namespace zipkin
 }  // namespace exporter
 OPENTELEMETRY_END_NAMESPACE
-#endif  // HAVE_CPP_STDLIB
+#endif /* OPENTELEMETRY_STL_VERSION */

From af8fd0f1a9e6a9a7344f89e9260747f06b63c314 Mon Sep 17 00:00:00 2001
From: Marc Alff <marc.alff@oracle.com>
Date: Tue, 12 Sep 2023 16:47:24 +0200
Subject: [PATCH 10/13] format

---
 api/CMakeLists.txt           | 3 ++-
 docs/building-with-stdlib.md | 7 ++++---
 docs/dependencies.md         | 5 +++--
 3 files changed, 9 insertions(+), 6 deletions(-)

diff --git a/api/CMakeLists.txt b/api/CMakeLists.txt
index 2b90011caf..88f98591ca 100644
--- a/api/CMakeLists.txt
+++ b/api/CMakeLists.txt
@@ -79,7 +79,8 @@ elseif(WITH_STL STREQUAL "ON")
   target_compile_definitions(opentelemetry_api
                              INTERFACE OPENTELEMETRY_STL_VERSION=2023)
 else()
-  message(FATAL_ERROR "WITH_STL must be ON, OFF, CXX11, CXX14, CXX17, CXX20 or CXX23")
+  message(
+    FATAL_ERROR "WITH_STL must be ON, OFF, CXX11, CXX14, CXX17, CXX20 or CXX23")
 endif()
 
 if(WITH_GSL)
diff --git a/docs/building-with-stdlib.md b/docs/building-with-stdlib.md
index b52b58ff90..d9c73073da 100644
--- a/docs/building-with-stdlib.md
+++ b/docs/building-with-stdlib.md
@@ -138,12 +138,13 @@ Visual Studio provides 1st class debug experience for the standard library.
 Supported build flavors:
 
 * `nostd` - OpenTelemetry backport of classes for C++11. Not using standard lib.
-* `stdlib` - Standard Library. Native experience with
-  C++11/C++14/C++17/C++20/C++23 compiler.
+* `stdlib` - Standard Library.
+  Native experience with C++11/C++14/C++17/C++20/C++23 compiler.
   Depending on the stdlib level in effect,
   C++ features are used from the standard library,
   completed with `nostd` replacement implementations.
-  C++17 and below works but with additional dependencies, e.g. either MS-GSL or Abseil for
+  C++17 and below works but with additional dependencies,
+  e.g. either MS-GSL or Abseil for
   `std::span` implementation (`gsl::span` or `absl::Span`).
 * `absl`  - TODO: this should allow using Abseil C++ library only (no MS-GSL).
 
diff --git a/docs/dependencies.md b/docs/dependencies.md
index c8a2271ef5..d0dc09c54f 100644
--- a/docs/dependencies.md
+++ b/docs/dependencies.md
@@ -24,8 +24,9 @@ Both these dependencies are listed here:
   [SDK](/sdk):
   - Uses Standard C++ library for latest features (std::string_view,
     std::variant, std::span, std::shared_ptr, std::unique_ptr) with  C++14/17/20
-    compiler if cmake option `WITH_STL` is enabled or macro `OPENTELEMETRY_STL_VERSION` is
-    defined. License: `GNU General Public License`
+    compiler if cmake option `WITH_STL` is enabled
+    or macro `OPENTELEMETRY_STL_VERSION` is defined.
+    License: `GNU General Public License`
     - For C++11/14/17 compilers, fallback to gsl::span if [GSL C++
       library](https://github.com/microsoft/GSL) is installed. License: `MIT
       License`

From 7d03b8a6bb2adfa47645abc71d9a216a9b233525 Mon Sep 17 00:00:00 2001
From: Marc Alff <marc.alff@oracle.com>
Date: Tue, 12 Sep 2023 20:37:33 +0200
Subject: [PATCH 11/13] Improve changelog.

---
 CHANGELOG.md | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/CHANGELOG.md b/CHANGELOG.md
index 28117c6241..5ff963b08e 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -34,6 +34,12 @@ Breaking changes:
   * Applications that did set `HAVE_CPP_STDLIB` before, need to set
     `OPENTELEMETRY_STL_VERSION=<version>` instead, to build with a
     specific STL version (2011, 2014, 2017, 2020, 2023).
+  * The opentrelemetry-cpp makefile no longer sets
+    CMAKE_CXX_STANDARD by itself.
+    Instead, the CMAKE_CXX_STANDARD and/or compiler options -stdc++ used
+    by the caller are honored.
+  * Applications that set neither CMAKE_CXX_STANDARD nor -stdc++
+    options may need to provide a C++ standard in their makefiles.
 
 ## [1.11.0] 2023-08-21
 

From 664a1ba2ae75f6f654e44e091f2241123e4f5c57 Mon Sep 17 00:00:00 2001
From: Marc Alff <marc.alff@free.fr>
Date: Thu, 28 Sep 2023 08:59:28 +0200
Subject: [PATCH 12/13] Update api/CMakeLists.txt

Co-authored-by: Lalit Kumar Bhasin <lalit_fin@yahoo.com>
---
 api/CMakeLists.txt | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/api/CMakeLists.txt b/api/CMakeLists.txt
index 5d3b3e18f2..dd1eda3c78 100644
--- a/api/CMakeLists.txt
+++ b/api/CMakeLists.txt
@@ -54,7 +54,7 @@ endif()
 if(WITH_STL STREQUAL "OFF")
   message(STATUS "Building WITH_STL=OFF")
 elseif(WITH_STL STREQUAL "CXX11")
-  message(STATUS "Building WITH_STL=CXX1")
+  message(STATUS "Building WITH_STL=CXX11")
   target_compile_definitions(opentelemetry_api
                              INTERFACE OPENTELEMETRY_STL_VERSION=2011)
 elseif(WITH_STL STREQUAL "CXX14")

From 037bc3141cc69820f0775a60d547f75e37065466 Mon Sep 17 00:00:00 2001
From: Marc Alff <marc.alff@free.fr>
Date: Thu, 28 Sep 2023 08:59:40 +0200
Subject: [PATCH 13/13] Update CHANGELOG.md

Co-authored-by: Lalit Kumar Bhasin <lalit_fin@yahoo.com>
---
 CHANGELOG.md | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/CHANGELOG.md b/CHANGELOG.md
index 762b71904d..b349ba8ec7 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -40,7 +40,7 @@ Breaking changes:
   * Applications that did set `HAVE_CPP_STDLIB` before, need to set
     `OPENTELEMETRY_STL_VERSION=<version>` instead, to build with a
     specific STL version (2011, 2014, 2017, 2020, 2023).
-  * The opentrelemetry-cpp makefile no longer sets
+  * The opentelemetry-cpp makefile no longer sets
     CMAKE_CXX_STANDARD by itself.
     Instead, the CMAKE_CXX_STANDARD and/or compiler options -stdc++ used
     by the caller are honored.