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importing gsl::span if std::span is not available #1167

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merged 7 commits into from
Jan 25, 2022
Merged

importing gsl::span if std::span is not available #1167

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c676c16
importing gsl::span if std::span is not available
esigo Jan 1, 2022
3da1084
Merge branch 'main' into importing-gsl--span-if-std--span-is-not-avai…
esigo Jan 9, 2022
9af60ec
Merge branch 'main' into importing-gsl--span-if-std--span-is-not-avai…
esigo Jan 12, 2022
3071ae7
stop defining have_gsl
esigo Jan 16, 2022
32cd796
Merge branch 'main' into importing-gsl--span-if-std--span-is-not-avai…
esigo Jan 16, 2022
f6a32fc
Merge branch 'main' into importing-gsl--span-if-std--span-is-not-avai…
esigo Jan 20, 2022
7350a45
Merge branch 'main' into importing-gsl--span-if-std--span-is-not-avai…
lalitb Jan 22, 2022
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30 changes: 17 additions & 13 deletions CMakeLists.txt
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Original file line number Diff line number Diff line change
Expand Up @@ -102,7 +102,9 @@ else()
)
endif()

option(WITH_STL "Whether to use Standard Library for C++latest features" OFF)
option(WITH_STL "Whether to use Standard Library for C++ latest features" OFF)
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)

Expand Down Expand Up @@ -137,18 +139,6 @@ if(WITH_STL)
# (absl::variant or std::variant) in variant unit test code is consistent with
# the global project build definitions.
add_definitions(-DHAVE_CPP_STDLIB)
add_definitions(-DHAVE_GSL)

# Guidelines Support Library path. Used if we are not on not get C++20.
#
# TODO: respect WITH_ABSEIL as alternate implementation of std::span
find_package(Microsoft.GSL QUIET)
if(TARGET Microsoft.GSL::GSL)
list(APPEND CORE_RUNTIME_LIBS Microsoft.GSL::GSL)
else()
set(GSL_DIR third_party/ms-gsl)
include_directories(${GSL_DIR}/include)
endif()

# Optimize for speed to reduce the hops
if(CMAKE_CXX_COMPILER_ID STREQUAL "MSVC")
Expand All @@ -165,6 +155,20 @@ if(WITH_STL)
endif()
endif()

if(WITH_GSL)
add_definitions(-DHAVE_GSL)
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@lalitb lalitb Jan 13, 2022 •
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Just to clarify- with this PR, GSL library will only be used if the WITH_GSL flag is enabled?

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yes it is enabled only when the user explicitly asks for it.

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@lalitb lalitb Jan 13, 2022 •
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Ok, I was thinking about this part in cmake:

opentelemetry-cpp/api/CMakeLists.txt

Lines 48 to 51 in 05d43d6

if(WITH_STL)
message("Building with standard library types...")
target_compile_definitions(opentelemetry_api INTERFACE HAVE_CPP_STDLIB
HAVE_GSL)

As it looks we are enabling HAVE_GSL macro with WITH_STL option, which would mean try using gsl::span from submodule if STL doesn't have std::span implementation.

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@esigo esigo Jan 16, 2022 •
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that is covered in

opentelemetry-cpp/api/include/opentelemetry/std/span.h

Lines 29 to 31 in bc1b469

# if !__has_include(<gsl/gsl>)
# undef HAVE_GSL
# endif
as the header is not available when the WITH_GSL is off.
We shouldn't define it though, I cleaned it from the CMake file.

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ok, thanks for the clarification.


# Guidelines Support Library path. Used if we are not on not get C++20.
#
find_package(Microsoft.GSL QUIET)
if(TARGET Microsoft.GSL::GSL)
list(APPEND CORE_RUNTIME_LIBS Microsoft.GSL::GSL)
else()
set(GSL_DIR third_party/ms-gsl)
include_directories(${GSL_DIR}/include)
endif()
endif()

option(WITH_OTLP "Whether to include the OpenTelemetry Protocol in the SDK" OFF)
option(WITH_ZIPKIN "Whether to include the Zipkin exporter in the SDK" OFF)

Expand Down
4 changes: 2 additions & 2 deletions api/include/opentelemetry/std/span.h
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Expand Up @@ -11,7 +11,7 @@
#if defined __has_include
# if __has_include(<version>) // Check for __cpp_{feature}
# include <version>
# if defined(__cpp_lib_span)
# if defined(__cpp_lib_span) && __cplusplus > 201703L
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Why is this check required?

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because __cpp_lib_span is defined for C++17 on g++-10:g++-10 (Ubuntu 10.3.0-1ubuntu1~20.04) 10.3.0.
I use these CMake options for build:
-DCMAKE_CXX_COMPILER=g++-10 -DCMAKE_CXX_STANDARD=17

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Which should be ok right? If the HAVE_CPP_STDLIB option is specified, and the standard library provides the implementation ( stable or experimental) it should get selected. What is the behavior now with these changes on g++-10/C++17 - compilation failure as std::span is not available?

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The behavior for g++-10/C++17 is that nostd::span will be picked if the WITH_GSL option was not used. I think we shouldn't use std::span if the user explicitly asks for C++17.
Shall I enable std::span if C++17 was used and std::span is available?

# define HAVE_SPAN
# endif
# endif
Expand All @@ -21,7 +21,7 @@
# define HAVE_SPAN
# endif
# // Check for other compiler span implementation
# if !defined(_MSVC_LANG) && __has_include(<span>)
# if !defined(_MSVC_LANG) && __has_include(<span>) && __cplusplus > 201703L
// This works as long as compiler standard is set to C++20
# define HAVE_SPAN
# endif
Expand Down
1 change: 1 addition & 0 deletions sdk/include/opentelemetry/sdk/instrumentationlibrary/instrumentation_library.h
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Expand Up @@ -3,6 +3,7 @@

#pragma once

#include <string>
#include "opentelemetry/nostd/string_view.h"
#include "opentelemetry/nostd/unique_ptr.h"
#include "opentelemetry/version.h"
Expand Down