add macro to assist in checking if code snippets compile

RELEASE-NOTES.md

@@ -11,6 +11,7 @@ The project release numbers follow [Semantic Versioning](http://semver.org/spec/
 
 ### Added
 - Added `blt_convert_to_system_includes` macro to convert existing interface includes to system interface includes.
+- `blt_check_code_compiles` which compiles a C++ code snippet and returns the result.
 
 ### Changed
 - Added three extra options to `blt_print_target_properties` macro to print properties of

SetupBLT.cmake

@@ -66,6 +66,13 @@ if (NOT BLT_LOADED)
         cmake_policy(SET CMP0057 NEW)
     endif()
 
+    # Make `check_cxx_source_compiles` honor `CMAKE_CXX_STANDARD`
+    # NOTE: This only works on a few CMake versions even though it was
+    #  added in CMake 3.14. (for example, 3.20.2, 3.21.1, and 3.23.1 did not work)
+    if(POLICY CMP0067)
+      cmake_policy(SET CMP0067 NEW)
+    endif()
+
     # Policy to use <PackageName>_ROOT variable in find_<Package> commands
     # Policy added in 3.12+
     if(POLICY CMP0074)

cmake/BLTMacros.cmake

@@ -1425,3 +1425,75 @@ macro(blt_convert_to_system_includes)
     unset(_include_dirs)
 endmacro()
 
+
+##------------------------------------------------------------------------------
+## blt_check_code_compiles(CODE_COMPILES <variable>
+##                         VERBOSE_OUTPUT <ON|OFF (default OFF)>
+##                         SOURCE_STRING <quoted C++ program>)
+##
+## This macro checks if a snippet of C++ code compiles.
+##
+## SOURCE_STRING The source snippet to compile.
+## Must be a valid C++ program with a main() function.
+## Note: This parameter should be passed in as a quoted string variable. Otherwise,
+## cmake will convert the string into a list and lose the semicolons.
+## E.g. blt_check_code_compiles(SOURCE_STRING "${str_var}" ...)
+##
+## CODE_COMPILES A boolean variable the contains the compilation result.
+##
+## VERBOSE_OUTPUT Optional parameter to output debug information (Default: off)
+##------------------------------------------------------------------------------
+macro(blt_check_code_compiles)
+
+    set(options)
+    set(singleValueArgs CODE_COMPILES VERBOSE_OUTPUT )
+    # NOTE: SOURCE_STRING must be a multiValueArg otherwise CMake removes all semi-colons
+    set(multiValueArgs SOURCE_STRING)
+
+    # Parse the arguments to the macro
+    cmake_parse_arguments(arg
+         "${options}" "${singleValueArgs}" "${multiValueArgs}" ${ARGN})
+
+    # Check the arguments
+    if(NOT DEFINED arg_SOURCE_STRING)
+        message(FATAL_ERROR "blt_check_code_compiles() requires SOURCE_STRING to be specified")
+    endif()
+
+    if(NOT DEFINED arg_CODE_COMPILES)
+        message(FATAL_ERROR "blt_check_code_compiles() requires CODE_COMPILES to be specified")
+    endif()
+
+    if(NOT DEFINED arg_VERBOSE_OUTPUT)
+        set(arg_VERBOSE_OUTPUT FALSE)
+    endif()
+
+    if(${arg_VERBOSE_OUTPUT})
+        message(STATUS "[blt_check_code_compiles] Attempting to compile source string: \n${arg_SOURCE_STRING}")
+    endif()
+
+    # Write string as temp file, try to compile it and then remove file
+    string(RANDOM LENGTH 5 _rand)
+    set(_fname ${CMAKE_CURRENT_BINARY_DIR}/_bltCheckCompiles${_rand}.cpp)
+    file(WRITE ${_fname} "${arg_SOURCE_STRING}")
+    try_compile(${arg_CODE_COMPILES}
+                ${CMAKE_CURRENT_BINARY_DIR}/CMakeTmp
+                SOURCES ${_fname}
+                CXX_STANDARD ${CMAKE_CXX_STANDARD}
+                OUTPUT_VARIABLE _res)
+    file(REMOVE ${_fname})
+
+    if(${arg_VERBOSE_OUTPUT})
+        message(STATUS "[blt_check_code_compiles] Compiler output: \n${_res}\n")
+
+        if(${arg_CODE_COMPILES})
+            message(STATUS "[blt_check_code_compiles] The code snippet successfully compiled")
+        else()
+            message(STATUS "[blt_check_code_compiles] The code snippet failed to compile")
+        endif()
+    endif()
+
+    # clear the variables set within the macro
+    unset(_fname)
+    unset(_res)
+
+endmacro(blt_check_code_compiles)

docs/api/utility.rst

@@ -77,6 +77,54 @@ When using the Intel toolchain within Visual Studio, we use the
 ``MSVC_INTEL`` flag, when provided, with a fallback to the ``MSVC`` flag.
 
 
+.. blt_check_code_compiles:
+
+blt_check_code_compiles
+~~~~~~~~~~~~~~~~~~~~~~~
+
+.. code-block:: cmake
+
+     blt_check_code_compiles(CODE_COMPILES  <variable>
+                             VERBOSE_OUTPUT <ON|OFF (default OFF)>
+                             SOURCE_STRING  <quoted C++ program>)
+
+This macro checks if a snippet of C++ code compiles.
+
+CODE_COMPILES
+  The boolean variable that will be filled with the compilation result.
+
+VERBOSE_OUTPUT
+  Optional parameter to output debug information (Default: OFF)
+
+SOURCE_STRING
+  The source snippet to compile.
+
+``SOURCE_STRING`` must be a valid C++ program with a main() function and
+must be passed in as a quoted string variable. Otherwise, CMake will convert
+the string into a list and lose the semicolons.  You can use any CMake method
+of sending a string, but we recommend the
+`bracket argument method <https://cmake.org/cmake/help/latest/manual/cmake-language.7.html#bracket-argument>`_
+shown below so you do not have to escape your quotes:
+
+.. code-block:: cmake
+
+    blt_check_code_compiles(CODE_COMPILES  hello_world_compiled
+                            SOURCE_STRING
+    [=[
+    #include <iostream>
+
+    int main(int, char**)
+    {
+
+        std::cout << "Hello World!" << std::endl;
+
+        return 0;
+    }
+    ]=])
+
+
+
+
 .. _blt_find_libraries:
 
 blt_find_libraries

tests/internal/unit/CMakeLists.txt

@@ -151,3 +151,25 @@ message(
 "Tests passed for `blt_split_source_list_by_language`.\n"
 "*****************************************************")
 
+message(STATUS "Checking for blt_check_code_compiles")
+
+blt_check_code_compiles(CODE_COMPILES  _hello_world_compiled
+                        VERBOSE_OUTPUT ON
+                        SOURCE_STRING
+[=[
+#include <iostream>
+
+int main(int, char**)
+{
+
+    std::cout << "Hello World!" << std::endl;
+
+    return 0;
+}
+]=])
+
+if(_hello_world_compiled)
+  message(STATUS "... passed")
+else()
+  message(FATAL_ERROR "... failed to compile.")
+endif()