cmake: Add TryAppendCXXFlags module

cmake/module/TryAppendCXXFlags.cmake

@@ -0,0 +1,138 @@
+# Copyright (c) 2023-present The Bitcoin Core developers
+# Distributed under the MIT software license, see the accompanying
+# file COPYING or https://opensource.org/license/mit/.
+
+include_guard(GLOBAL)
+include(CheckCXXSourceCompiles)
+
+#[=[
+Add language-wide flags, which will be passed to all invocations of the compiler.
+This includes invocations that drive compiling and those that drive linking.
+
+Usage examples:
+
+  try_append_cxx_flags("-Wformat -Wformat-security" VAR warn_cxx_flags)
+
+
+  try_append_cxx_flags("-Wsuggest-override" VAR warn_cxx_flags
+    SOURCE "struct A { virtual void f(); }; struct B : A { void f() final; };"
+  )
+
+
+  try_append_cxx_flags("-fsanitize=${SANITIZERS}" TARGET core_interface
+    RESULT_VAR cxx_supports_sanitizers
+  )
+  if(NOT cxx_supports_sanitizers)
+    message(FATAL_ERROR "Compiler did not accept requested flags.")
+  endif()
+
+
+  try_append_cxx_flags("-Wunused-parameter" TARGET core_interface
+    IF_CHECK_PASSED "-Wno-unused-parameter"
+  )
+
+
+  try_append_cxx_flags("-Werror=return-type" TARGET core_interface
+    IF_CHECK_FAILED "-Wno-error=return-type"
+    SOURCE "#include <cassert>\nint f(){ assert(false); }"
+  )
+
+
+In configuration output, this function prints a string by the following pattern:
+
+  -- Performing Test CXX_SUPPORTS_[flags]
+  -- Performing Test CXX_SUPPORTS_[flags] - Success
+
+]=]
+function(try_append_cxx_flags flags)
+  cmake_parse_arguments(PARSE_ARGV 1
+    TACXXF                            # prefix
+    "SKIP_LINK"                       # options
+    "TARGET;VAR;SOURCE;RESULT_VAR"    # one_value_keywords
+    "IF_CHECK_PASSED;IF_CHECK_FAILED" # multi_value_keywords
+  )
+
+  set(flags_as_string "${flags}")
+  separate_arguments(flags)
+
+  string(MAKE_C_IDENTIFIER "${flags_as_string}" id_string)
+  string(TOUPPER "${id_string}" id_string)
+
+  set(source "int main() { return 0; }")
+  if(DEFINED TACXXF_SOURCE AND NOT TACXXF_SOURCE STREQUAL source)
+    set(source "${TACXXF_SOURCE}")
+    string(SHA256 source_hash "${source}")
+    string(SUBSTRING ${source_hash} 0 4 source_hash_head)
+    string(APPEND id_string _${source_hash_head})
+  endif()
+
+  # This avoids running a linker.
+  set(CMAKE_TRY_COMPILE_TARGET_TYPE STATIC_LIBRARY)
+  set(CMAKE_REQUIRED_FLAGS "${flags_as_string} ${working_compiler_werror_flag}")
+  set(compiler_result CXX_SUPPORTS_${id_string})
+  check_cxx_source_compiles("${source}" ${compiler_result})
+
+  if(${compiler_result})
+    if(DEFINED TACXXF_IF_CHECK_PASSED)
+      if(DEFINED TACXXF_TARGET)
+        target_compile_options(${TACXXF_TARGET} INTERFACE ${TACXXF_IF_CHECK_PASSED})
+      endif()
+      if(DEFINED TACXXF_VAR)
+        string(STRIP "${${TACXXF_VAR}} ${TACXXF_IF_CHECK_PASSED}" ${TACXXF_VAR})
+      endif()
+    else()
+      if(DEFINED TACXXF_TARGET)
+        target_compile_options(${TACXXF_TARGET} INTERFACE ${flags})
+      endif()
+      if(DEFINED TACXXF_VAR)
+        string(STRIP "${${TACXXF_VAR}} ${flags_as_string}" ${TACXXF_VAR})
+      endif()
+    endif()
+  elseif(DEFINED TACXXF_IF_CHECK_FAILED)
+    if(DEFINED TACXXF_TARGET)
+      target_compile_options(${TACXXF_TARGET} INTERFACE ${TACXXF_IF_CHECK_FAILED})
+    endif()
+    if(DEFINED TACXXF_VAR)
+      string(STRIP "${${TACXXF_VAR}} ${TACXXF_IF_CHECK_FAILED}" ${TACXXF_VAR})
+    endif()
+  endif()
+
+  if(DEFINED TACXXF_VAR)
+    set(${TACXXF_VAR} "${${TACXXF_VAR}}" PARENT_SCOPE)
+  endif()
+
+  if(DEFINED TACXXF_RESULT_VAR)
+    set(${TACXXF_RESULT_VAR} "${${compiler_result}}" PARENT_SCOPE)
+  endif()
+
+  if(NOT ${compiler_result} OR TACXXF_SKIP_LINK)
+    return()
+  endif()
+
+  # This forces running a linker.
+  set(CMAKE_TRY_COMPILE_TARGET_TYPE EXECUTABLE)
+  set(CMAKE_REQUIRED_FLAGS "${flags_as_string}")
+  set(CMAKE_REQUIRED_LINK_OPTIONS ${working_linker_werror_flag})
+  set(linker_result LINKER_SUPPORTS_${id_string})
+  check_cxx_source_compiles("${source}" ${linker_result})
+
+  if(${linker_result})
+    if(DEFINED TACXXF_IF_CHECK_PASSED)
+      if(DEFINED TACXXF_TARGET)
+        target_link_options(${TACXXF_TARGET} INTERFACE ${TACXXF_IF_CHECK_PASSED})
+      endif()
+    else()
+      if(DEFINED TACXXF_TARGET)
+        target_link_options(${TACXXF_TARGET} INTERFACE ${flags})
+      endif()
+    endif()
+  else()
+    message(WARNING "'${flags_as_string}' fail(s) to link.")
+  endif()
+endfunction()
+
+if(MSVC)
+  try_append_cxx_flags("/WX /options:strict" VAR working_compiler_werror_flag SKIP_LINK)
+else()
+  try_append_cxx_flags("-Werror" VAR working_compiler_werror_flag SKIP_LINK)
+endif()