OpenWatcom: Allow specifying the runtime library

Add a `CMAKE_WATCOM_RUNTIME_LIBRARY` variable to control the
runtime library selection.  Add policy CMP0136 to switch to
in place of the old hard-coded default flags.

Fixes: #23178

4 files changed, 82 insertions, 0 deletions

diff --git a/Tests/WatcomRuntimeLibrary/CMakeLists.txt b/Tests/WatcomRuntimeLibrary/CMakeLists.txt
new file mode 100644
index 0000000000..e8a3edcfcf
--- /dev/null
+++ b/Tests/WatcomRuntimeLibrary/CMakeLists.txt
@@ -0,0 +1,49 @@
+cmake_minimum_required(VERSION 3.23)
+cmake_policy(SET CMP0136 NEW)
+project(WatcomRuntimeLibrary)
+
+function(verify_combinations threads lang src)
+  set(verify_def_MultiThreaded -DVERIFY_MT)
+  set(verify_def_DLL -DVERIFY_DLL)
+  foreach(dll "" DLL)
+    # Construct the name of this runtime library combination.
+    set(rtl "${threads}${dll}")
+
+    # Test that try_compile builds with this RTL.
+    set(CMAKE_WATCOM_RUNTIME_LIBRARY "${rtl}")
+    set(CMAKE_TRY_COMPILE_TARGET_TYPE "STATIC_LIBRARY")
+    try_compile(${rtl}_COMPILES
+      ${CMAKE_CURRENT_BINARY_DIR}/try_compile/${rtl}
+      ${CMAKE_CURRENT_SOURCE_DIR}/${src}
+      COMPILE_DEFINITIONS ${verify_def_${threads}} ${verify_def_${dll}}
+      OUTPUT_VARIABLE ${rtl}_OUTPUT
+      )
+    if(${rtl}_COMPILES)
+      message(STATUS "try_compile with ${rtl} worked")
+    else()
+      string(REPLACE "\n" "\n  " ${rtl}_OUTPUT "  ${${rtl}_OUTPUT}")
+      message(SEND_ERROR "try_compile with ${rtl} failed:\n${${rtl}_OUTPUT}")
+    endif()
+
+    # Test that targets build with this RTL.
+    set(CMAKE_WATCOM_RUNTIME_LIBRARY "$<$<BOOL:$<TARGET_PROPERTY:BOOL_TRUE>>:${rtl}>$<$<BOOL:$<TARGET_PROPERTY:BOOL_FALSE>>:BadContent>")
+    add_library(${rtl}-${lang} ${src})
+    set_property(TARGET ${rtl}-${lang} PROPERTY BOOL_TRUE TRUE)
+    target_compile_definitions(${rtl}-${lang} PRIVATE ${verify_def_${threads}} ${verify_def_${dll}})
+  endforeach()
+endfunction()
+
+function(verify lang src)
+  add_library(default-${lang} ${src})
+  target_compile_definitions(default-${lang} PRIVATE VERIFY_MT VERIFY_DLL)
+
+  verify_combinations(SingleThreaded ${lang} ${src})
+  verify_combinations(MultiThreaded ${lang} ${src})
+
+  # Test known  default behavior when no flag is given.
+  set(CMAKE_WATCOM_RUNTIME_LIBRARY "")
+  add_library(empty-${lang} ${src})
+endfunction()
+
+verify(C verify.c)
+verify(CXX verify.cxx)
diff --git a/Tests/WatcomRuntimeLibrary/verify.c b/Tests/WatcomRuntimeLibrary/verify.c
new file mode 100644
index 0000000000..741bca6b89
--- /dev/null
+++ b/Tests/WatcomRuntimeLibrary/verify.c
@@ -0,0 +1 @@
+#include "verify.h"
diff --git a/Tests/WatcomRuntimeLibrary/verify.cxx b/Tests/WatcomRuntimeLibrary/verify.cxx
new file mode 100644
index 0000000000..741bca6b89
--- /dev/null
+++ b/Tests/WatcomRuntimeLibrary/verify.cxx
@@ -0,0 +1 @@
+#include "verify.h"
diff --git a/Tests/WatcomRuntimeLibrary/verify.h b/Tests/WatcomRuntimeLibrary/verify.h
new file mode 100644
index 0000000000..6c67e6d248
--- /dev/null
+++ b/Tests/WatcomRuntimeLibrary/verify.h
@@ -0,0 +1,31 @@
+#ifdef VERIFY_DLL
+#  ifndef _DLL
+#    error "_DLL not defined by DLL runtime library selection"
+#  endif
+#  ifndef __SW_BR
+#    error "__SW_BR not defined by DLL runtime library selection"
+#  endif
+#else
+#  ifdef _DLL
+#    error "_DLL defined by non-DLL runtime library selection"
+#  endif
+#  ifdef __SW_BR
+#    error "__SW_BR defined by non-DLL runtime library selection"
+#  endif
+#endif
+
+#ifdef VERIFY_MT
+#  ifndef _MT
+#    error "_MT not defined by multi-threaded runtime library selection"
+#  endif
+#  ifndef __SW_BM
+#    error "__SW_BM not defined by multi-threaded runtime library selection"
+#  endif
+#else
+#  ifdef _MT
+#    error "_MT defined by single-threaded runtime library selection"
+#  endif
+#  ifdef __SW_BM
+#    error "__SW_BM defined by single-threaded runtime library selection"
+#  endif
+#endif