Update method of detecting and linking quadmath

[mborland]

Fixes: #191

The next step in the never ending battle to get this correct. @pdimov Do you see any potential issues with this? I replaced check_cxx_source_compiles with check_cxx_source_runs due to Reuben's previous issue (#176) where the header existed, but the compiled library did not.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 94.01%. Comparing base (007ac06) to head (f2d2aca).

Additional details and impacted files

@@           Coverage Diff            @@
##           develop     #193   +/-   ##
========================================
  Coverage    94.01%   94.01%           
========================================
  Files           66       66           
  Lines         8439     8439           
========================================
  Hits          7934     7934           
  Misses         505      505           

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[pdimov]

This looks OK to me, by visual inspection alone.

[mborland]

Looking at the old CI runs the posix-cmake-test suite all yielded -- Boost.Charconv: quadmath support OFF. Now the macOS runs show -- Boost.Charconv: quadmath support OFF as they should, and Ubuntu runs show -- Boost.Charconv: quadmath support ON.

[erikbs]

@mborland This change breaks cross-compilation (CMake Error: try_run() invoked in cross-compiling mode ). I grep-ed the Boost source archive after check_cxx_source_ and this seems to be the only place where _runs is used instead of _compiles. Following the pattern elsewhere I did this:

@@ -9,0 +10,2 @@ project(boost_charconv VERSION "${BOOST_SUPERPROJECT_VERSION}" LANGUAGES CXX)
+include(CheckCXXSourceCompiles)
+
@@ -22,14 +23,0 @@ target_include_directories(boost_charconv PUBLIC include)
-include(CheckCXXSourceRuns)
-set(BOOST_CHARCONV_QUADMATH_TEST_SOURCE
-"
-#include <quadmath.h>
-int main()
-{
-    __float128 f = -2.0Q;
-    f = fabsq(f);
-    __float128 big = HUGE_VALQ;
-
-    return f == big;
-}
-")
-
@@ -37 +25 @@ set(CMAKE_REQUIRED_LIBRARIES "quadmath")
-check_cxx_source_runs("${BOOST_CHARCONV_QUADMATH_TEST_SOURCE}" BOOST_CHARCONV_QUADMATH_FOUND)
+check_cxx_source_compiles("#include <${CMAKE_CURRENT_SOURCE_DIR}/config/has_float128.cpp>" BOOST_CHARCONV_QUADMATH_FOUND)

which seems to fix the problem for me (revert to cxx_check_source_compiles, but keep CMAKE_REQUIRED_LIBRARIES and set the source to including has_float128.cpp, because the original check had an incorrect source file containing nothing but that file path). From what I understand, _compiles is insufficient on Alpine because the header is present while the library is not? But wouldn't set(CMAKE_REQUIRED_LIBRARIES "quadmath") catch that case? I don't have an Alpine installation to test on, but I tested a minimal CMake example that has a check_cxx_source_compiles, then set CMAKE_REQUIRED_LIBRARIES to "does_not_exist" and it failed as expected.

[mborland]

@erikbs your patch has been merged in #284. It was confirmed fine on the referenced Alpine Linux environment.

[erikbs]

Great! Thanks!