cmake: Print compiler and linker flags in summary

CMakeLists.txt

@@ -78,6 +78,8 @@ message("\n")
 message("Configure summary")
 message("=================")
 message("C++ compiler .......................... ${CMAKE_CXX_COMPILER_ID} ${CMAKE_CXX_COMPILER_VERSION}, ${CMAKE_CXX_COMPILER}")
+include(FlagsSummary)
+flags_summary()
 message("\n")
 if(configure_warnings)
     message("  ******\n")

cmake/module/FlagsSummary.cmake

@@ -0,0 +1,70 @@
+# Copyright (c) 2024-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)
+
+function(indent_message header content indent_num)
+  if(indent_num GREATER 0)
+    string(REPEAT " " ${indent_num} indentation)
+    string(REPEAT "." ${indent_num} tail)
+    string(REGEX REPLACE "${tail}$" "" header "${header}")
+  endif()
+  message("${indentation}${header} ${content}")
+endfunction()
+
+# Print tools' flags on best-effort. Include the abstracted
+# CMake flags that we touch ourselves.
+function(print_flags_per_config config indent_num)
+  string(TOUPPER "${config}" config_uppercase)
+
+  include(GetTargetInterface)
+  get_target_interface(definitions "${config}" core_interface COMPILE_DEFINITIONS)
+  indent_message("Preprocessor defined macros ..........." "${definitions}" ${indent_num})
+
+  string(STRIP "${CMAKE_CXX_FLAGS} ${CMAKE_CXX_FLAGS_${config_uppercase}}" combined_cxx_flags)
+  string(STRIP "${combined_cxx_flags} ${CMAKE_CXX${CMAKE_CXX_STANDARD}_STANDARD_COMPILE_OPTION}" combined_cxx_flags)
+  if(CMAKE_POSITION_INDEPENDENT_CODE)
+    string(JOIN " " combined_cxx_flags ${combined_cxx_flags} ${CMAKE_CXX_COMPILE_OPTIONS_PIC})
+  endif()
+  get_target_interface(core_cxx_flags "${config}" core_interface COMPILE_OPTIONS)
+  string(STRIP "${combined_cxx_flags} ${core_cxx_flags}" combined_cxx_flags)
+  indent_message("C++ compiler flags ...................." "${combined_cxx_flags}" ${indent_num})
+
+  string(STRIP "${CMAKE_CXX_FLAGS} ${CMAKE_CXX_FLAGS_${config_uppercase}}" combined_linker_flags)
+  string(STRIP "${combined_linker_flags} ${CMAKE_EXE_LINKER_FLAGS}" combined_linker_flags)
+  get_target_interface(common_link_options "${config}" core_interface LINK_OPTIONS)
+  string(STRIP "${combined_linker_flags} ${common_link_options}" combined_linker_flags)
+  if(CMAKE_CXX_LINK_PIE_SUPPORTED)
+    string(JOIN " " combined_linker_flags ${combined_linker_flags} ${CMAKE_CXX_LINK_OPTIONS_PIE})
+  endif()
+  indent_message("Linker flags .........................." "${combined_linker_flags}" ${indent_num})
+endfunction()
+
+function(flags_summary)
+  get_property(is_multi_config GLOBAL PROPERTY GENERATOR_IS_MULTI_CONFIG)
+  if(is_multi_config)
+    list(JOIN CMAKE_CONFIGURATION_TYPES ", " configs)
+    message("Available build configurations ........ ${configs}")
+    if(CMAKE_GENERATOR MATCHES "Visual Studio")
+      set(default_config "Debug")
+    else()
+      list(GET CMAKE_CONFIGURATION_TYPES 0 default_config)
+    endif()
+    message("Default build configuration ........... ${default_config}")
+    foreach(config IN LISTS CMAKE_CONFIGURATION_TYPES)
+      message("")
+      message("'${config}' build configuration:")
+      print_flags_per_config("${config}" 2)
+    endforeach()
+  else()
+    message("CMAKE_BUILD_TYPE ...................... ${CMAKE_BUILD_TYPE}")
+    print_flags_per_config("${CMAKE_BUILD_TYPE}" 0)
+  endif()
+  message("")
+  message([=[
+NOTE: The summary above may not exactly match the final applied build flags
+      if any additional CMAKE_* or environment variables have been modified.
+      To see the exact flags applied, build with the --verbose option.
+]=])
+endfunction()

cmake/module/GetTargetInterface.cmake

@@ -0,0 +1,53 @@
+# 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)
+
+# Evaluates config-specific generator expressions in a list.
+# Recognizable patterns are:
+#  - $<$<CONFIG:[config]>:[value]>
+#  - $<$<NOT:$<CONFIG:[config]>>:[value]>
+function(evaluate_generator_expressions list config)
+  set(input ${${list}})
+  set(result)
+  foreach(token IN LISTS input)
+    if(token MATCHES "\\$<\\$<CONFIG:([^>]+)>:([^>]+)>")
+      if(CMAKE_MATCH_1 STREQUAL config)
+        list(APPEND result ${CMAKE_MATCH_2})
+      endif()
+    elseif(token MATCHES "\\$<\\$<NOT:\\$<CONFIG:([^>]+)>>:([^>]+)>")
+      if(NOT CMAKE_MATCH_1 STREQUAL config)
+        list(APPEND result ${CMAKE_MATCH_2})
+      endif()
+    else()
+      list(APPEND result ${token})
+    endif()
+  endforeach()
+  set(${list} ${result} PARENT_SCOPE)
+endfunction()
+
+
+# Gets target's interface properties recursively.
+function(get_target_interface var config target property)
+  get_target_property(result ${target} INTERFACE_${property})
+  if(result)
+    evaluate_generator_expressions(result "${config}")
+    list(JOIN result " " result)
+  else()
+    set(result)
+  endif()
+
+  get_target_property(dependencies ${target} INTERFACE_LINK_LIBRARIES)
+  if(dependencies)
+    evaluate_generator_expressions(dependencies "${config}")
+    foreach(dependency IN LISTS dependencies)
+      if(TARGET ${dependency})
+        get_target_interface(dep_result "${config}" ${dependency} ${property})
+        string(STRIP "${result} ${dep_result}" result)
+      endif()
+    endforeach()
+  endif()
+
+  set(${var} "${result}" PARENT_SCOPE)
+endfunction()