Tests: Simplify RunCMake.try_compile compiler inspection

Detect the compiler id, version, and default standard level
in the test's inspection step rather than passing it all in
from the host CMake build's results.  This avoids repeating
details not known to older versions of CMake, and shortens
the code.

3 files changed, 13 insertions, 48 deletions

diff --git a/Tests/RunCMake/CMakeLists.txt b/Tests/RunCMake/CMakeLists.txt
index 58c1bc8..6bf8f3f 100644
--- a/Tests/RunCMake/CMakeLists.txt
+++ b/Tests/RunCMake/CMakeLists.txt
@@ -502,58 +502,10 @@ if(APPLE)
 endif()
 
 function(add_RunCMake_test_try_compile)
-  if(CMAKE_VERSION VERSION_LESS 3.9.20170907 AND "x${CMAKE_CXX_COMPILER_ID}" STREQUAL "xMSVC")
-    # Older CMake versions do not know about MSVC language standards.
-    # Approximate our logic from MSVC-CXX.cmake.
-    if ((NOT CMAKE_CXX_COMPILER_VERSION VERSION_LESS 19.0.24215.1 AND
-         CMAKE_CXX_COMPILER_VERSION VERSION_LESS 19.10) OR
-         NOT CMAKE_CXX_COMPILER_VERSION VERSION_LESS 19.10.25017)
-      set(CMAKE_CXX_STANDARD_DEFAULT 14)
-    elseif (NOT CMAKE_CXX_COMPILER_VERSION VERSION_LESS 16.0)
-      set(CMAKE_CXX_STANDARD_DEFAULT "")
-    else()
-      unset(CMAKE_CXX_STANDARD_DEFAULT)
-    endif()
-  endif()
-  if(CMAKE_VERSION VERSION_LESS 3.18.20200813 AND "x${CMAKE_C_COMPILER_ID}" STREQUAL "xMSVC")
-    # Older CMake versions do not know about MSVC language standards.
-    # Approximate our logic from MSVC-C.cmake.
-    if(NOT CMAKE_C_COMPILER_VERSION VERSION_LESS 19.27)
-      set(CMAKE_C_STANDARD_DEFAULT 99)
-    else()
-      set(CMAKE_C_STANDARD_DEFAULT "")
-    endif()
-  endif()
-  if(CMAKE_VERSION VERSION_LESS 3.20.20210225 AND "x${CMAKE_C_COMPILER_ID}" STREQUAL "xClang")
-    # Older CMake versions do not know about Clang MSVC compatibility mode
-    # standards. Approximate the logic from Clang-C.cmake.
-    if(CMAKE_C_COMPILER_VERSION VERSION_GREATER_EQUAL 11.0)
-      set(CMAKE_C_STANDARD_DEFAULT 17)
-    elseif(CMAKE_C_COMPILER_VERSION VERSION_GREATER_EQUAL 3.5.2)
-      set(CMAKE_C_STANDARD_DEFAULT 11)
-    endif()
-  endif()
-  if(CMAKE_VERSION VERSION_LESS 3.20.6 AND "x${CMAKE_C_COMPILER_ID}" STREQUAL "xIntelLLVM" AND "x${CMAKE_C_SIMULATE_ID}" STREQUAL "xMSVC")
-    # Older CMake versions accidentally set the default standards to empty when
-    # IntelLLVM targets the MSVC ABI, thus not activating standard selection.
-    # Approximate the logic from IntelLLVM-{C,CXX}.cmake.
-    if(DEFINED CMAKE_C_STANDARD_DEFAULT AND "${CMAKE_C_STANDARD_DEFAULT}" STREQUAL "")
-      set(CMAKE_C_STANDARD_DEFAULT 17)
-    endif()
-    if(DEFINED CMAKE_CXX_STANDARD_DEFAULT AND "${CMAKE_CXX_STANDARD_DEFAULT}" STREQUAL "")
-      set(CMAKE_CXX_STANDARD_DEFAULT 14)
-    endif()
-  endif()
   foreach(
     var
     IN ITEMS
       CMAKE_SYSTEM_NAME
-      CMAKE_C_COMPILER_ID
-      CMAKE_C_COMPILER_VERSION
-      CMAKE_C_STANDARD_DEFAULT
-      CMAKE_CXX_COMPILER_ID
-      CMAKE_CXX_COMPILER_VERSION
-      CMAKE_CXX_STANDARD_DEFAULT
       CMake_TEST_CUDA
       CMake_TEST_ISPC
       CMake_TEST_HIP
diff --git a/Tests/RunCMake/try_compile/Inspect.cmake b/Tests/RunCMake/try_compile/Inspect.cmake
index bfca882..2977d02 100644
--- a/Tests/RunCMake/try_compile/Inspect.cmake
+++ b/Tests/RunCMake/try_compile/Inspect.cmake
@@ -1,3 +1,4 @@
+enable_language(C)
 enable_language(CXX)
 if(CMake_TEST_OBJC)
   enable_language(OBJC)
@@ -6,6 +7,12 @@ endif()
 
 set(info "")
 foreach(var
+    CMAKE_C_COMPILER_ID
+    CMAKE_C_COMPILER_VERSION
+    CMAKE_C_STANDARD_DEFAULT
+    CMAKE_CXX_COMPILER_ID
+    CMAKE_CXX_COMPILER_VERSION
+    CMAKE_CXX_STANDARD_DEFAULT
     CMAKE_CXX_EXTENSIONS_DEFAULT
     CMAKE_OBJC_STANDARD_DEFAULT
     CMAKE_OBJCXX_STANDARD_DEFAULT
diff --git a/Tests/RunCMake/try_compile/RunCMakeTest.cmake b/Tests/RunCMake/try_compile/RunCMakeTest.cmake
index d02a391..ad1cc29 100644
--- a/Tests/RunCMake/try_compile/RunCMakeTest.cmake
+++ b/Tests/RunCMake/try_compile/RunCMakeTest.cmake
@@ -1,6 +1,12 @@
 include(RunCMake)
 
 # Detect information from the toolchain:
+# - CMAKE_C_COMPILER_ID
+# - CMAKE_C_COMPILER_VERSION
+# - CMAKE_C_STANDARD_DEFAULT
+# - CMAKE_CXX_COMPILER_ID
+# - CMAKE_CXX_COMPILER_VERSION
+# - CMAKE_CXX_STANDARD_DEFAULT
 # - CMAKE_CXX_EXTENSIONS_DEFAULT
 # - CMAKE_OBJC_STANDARD_DEFAULT
 # - CMAKE_OBJCXX_STANDARD_DEFAULT