try_compile: Add policy CMP0066 to honor CMAKE_<LANG>_FLAGS_<CONFIG>

In the `try_compile` source file signature we propagate the caller's
value of `CMAKE_<LANG>_FLAGS` into the test project.  Extend this to
propagate `CMAKE_<LANG>_FLAGS_<CONFIG>` too instead of always using the
default value in the test project.  This will be useful, for example, to
allow the MSVC runtime library to be changed (e.g. `-MDd` => `-MTd`).
However, some projects may currently depend on this not being done,
so we need to activate the behavior using a policy.

This change was originally made by commit v3.6.0-rc1~160^2 (try_compile:
Honor CMAKE_<LANG>_FLAGS_<CONFIG> changes, 2016-04-11) but without the
policy and so had to be reverted during the 3.6 release candidate cycle.

Fixes #16174.

1 files changed, 58 insertions, 0 deletions

diff --git a/Tests/RunCMake/try_compile/CMP0066.cmake b/Tests/RunCMake/try_compile/CMP0066.cmake
new file mode 100644
index 0000000..4b95251
--- /dev/null
+++ b/Tests/RunCMake/try_compile/CMP0066.cmake
@@ -0,0 +1,58 @@
+enable_language(C)
+set(CMAKE_C_FLAGS_RELEASE "-DPP_ERROR ${CMAKE_C_FLAGS_DEBUG}")
+set(CMAKE_TRY_COMPILE_CONFIGURATION Release)
+
+#-----------------------------------------------------------------------------
+message("before try_compile with CMP0066 WARN-default")
+try_compile(RESULT ${CMAKE_CURRENT_BINARY_DIR}
+  ${CMAKE_CURRENT_SOURCE_DIR}/src.c
+  OUTPUT_VARIABLE out
+  )
+string(REPLACE "\n" "\n  " out "  ${out}")
+if(NOT RESULT)
+  message(FATAL_ERROR "try_compile with CMP0066 WARN-default failed but should have passed:\n${out}")
+else()
+  message(STATUS "try_compile with CMP0066 WARN-default worked as expected")
+endif()
+message("after try_compile with CMP0066 WARN-default")
+
+#-----------------------------------------------------------------------------
+set(CMAKE_POLICY_WARNING_CMP0066 ON)
+try_compile(RESULT ${CMAKE_CURRENT_BINARY_DIR}
+  ${CMAKE_CURRENT_SOURCE_DIR}/src.c
+  OUTPUT_VARIABLE out
+  )
+string(REPLACE "\n" "\n  " out "  ${out}")
+if(NOT RESULT)
+  message(FATAL_ERROR "try_compile with CMP0066 WARN-enabled failed but should have passed:\n${out}")
+else()
+  message(STATUS "try_compile with CMP0066 WARN-enabled worked as expected")
+endif()
+
+#-----------------------------------------------------------------------------
+cmake_policy(SET CMP0066 OLD)
+try_compile(RESULT ${CMAKE_CURRENT_BINARY_DIR}
+  ${CMAKE_CURRENT_SOURCE_DIR}/src.c
+  OUTPUT_VARIABLE out
+  )
+string(REPLACE "\n" "\n  " out "  ${out}")
+if(NOT RESULT)
+  message(FATAL_ERROR "try_compile with CMP0066 OLD failed but should have passed:\n${out}")
+else()
+  message(STATUS "try_compile with CMP0066 OLD worked as expected")
+endif()
+
+#-----------------------------------------------------------------------------
+cmake_policy(SET CMP0066 NEW)
+try_compile(RESULT ${CMAKE_CURRENT_BINARY_DIR}
+  ${CMAKE_CURRENT_SOURCE_DIR}/src.c
+  OUTPUT_VARIABLE out
+  )
+string(REPLACE "\n" "\n  " out "  ${out}")
+if(RESULT)
+  message(FATAL_ERROR "try_compile with CMP0066 NEW passed but should have failed:\n${out}")
+elseif(NOT "x${out}" MATCHES "PP_ERROR is defined")
+  message(FATAL_ERROR "try_compile with CMP0066 NEW did not fail with PP_ERROR:\n${out}")
+else()
+  message(STATUS "try_compile with CMP0066 NEW worked as expected")
+endif()