z3/cmake/compiler_warnings.cmake

################################################################################
# Compiler warning flags
################################################################################
# These are passed to relevant compiler provided they are supported
set(GCC_AND_CLANG_WARNINGS
  "-Wall"
)
set(GCC_ONLY_WARNINGS "")
# Disable C++98 compatibility warnings to prevent excessive warning output
# when building with clang-cl or when -Weverything is enabled.
# These warnings are not useful for Z3 since it requires C++20.
#
# The "-Wno-zero-length-array" is for cases where Z3 is fetched by a CMake build
# to serve as a component in another system.  Z3 has many classes whose last member
# is a zero-length array of some type T, indicating a variable-length array of T.
# If the including system compiles with "-Wzero-length-array", there will be
# many warnings.  Overriding this prevents such warnings in the Z3 portion of the
# build of the including system.
set(CLANG_ONLY_WARNINGS
  "-Wno-c++98-compat"
  "-Wno-c++98-compat-pedantic"
  "-Wno-zero-length-array"
)
set(MSVC_WARNINGS "/W3")

################################################################################
# Serious warnings
################################################################################
# This declares the flags that are passed to the compiler when
# `WARNINGS_AS_ERRORS` is set to `SERIOUS_ONLY`. Only flags that are supported
# by the compiler are used.
#
# In effect this a "whitelist" approach where we explicitly tell the compiler
# which warnings we want to be treated as errors. The alternative would be a
# "blacklist" approach where we ask the compiler to treat all warnings are
# treated as errors but then we explicitly list which warnings which should be
# allowed.
#
# The "whitelist" approach seems simpiler because we can incrementally add
# warnings we "think are serious".

# TODO: Add more warnings that are considered serious enough that we should
# treat them as errors.
set(GCC_AND_CLANG_WARNINGS_AS_ERRORS
  # https://clang.llvm.org/docs/DiagnosticsReference.html#wodr
  "-Werror=odr"
  # https://clang.llvm.org/docs/DiagnosticsReference.html#wreturn-type
  "-Werror=return-type"
)
set(GCC_WARNINGS_AS_ERRORS
  ""
)
set(CLANG_WARNINGS_AS_ERRORS
  # https://clang.llvm.org/docs/DiagnosticsReference.html#wdelete-non-virtual-dtor
  "-Werror=delete-non-virtual-dtor"
  # https://clang.llvm.org/docs/DiagnosticsReference.html#woverloaded-virtual
  "-Werror=overloaded-virtual"
  # warn the user if a class with virtual functions has a
  # non-virtual destructor. This helps catch hard to
  # track down memory errors
  "-Werror=non-virtual-dtor"
  # warn if a null dereference is detected
  "-Werror=null-dereference"
  # warn for potential performance problem casts
  # "-Werror=cast-align"
  # warn if float is implicit promoted to double
  # "-Werror=double-promotion"
  "-Werror=no-unreachable-code-return"
  # warn the user if a variable declaration shadows one from a parent context
  # "-Werror=shadow"
  # warn for c-style casts
  # "-Werror=old-style-cast"
  # warn on sign conversions
  # "-Werror=sign-conversion"
  # warn on type conversions that may lose data
  # "-Werror=conversion"
  # warn on anything being unused
  # "-Werror=unused"
)

################################################################################
# Test warning/error flags
################################################################################
set(WARNING_FLAGS_TO_CHECK "")
set(WARNING_AS_ERROR_FLAGS_TO_CHECK "")
if (CMAKE_CXX_COMPILER_ID MATCHES "GNU")
  list(APPEND WARNING_FLAGS_TO_CHECK ${GCC_AND_CLANG_WARNINGS})
  list(APPEND WARNING_FLAGS_TO_CHECK ${GCC_ONLY_WARNINGS})
  list(APPEND WARNING_AS_ERROR_FLAGS_TO_CHECK ${GCC_AND_CLANG_WARNINGS_AS_ERRORS})
  list(APPEND WARNING_AS_ERROR_FLAGS_TO_CHECK ${GCC_WARNINGS_AS_ERRORS})
elseif (CMAKE_CXX_COMPILER_ID MATCHES "Clang")
  list(APPEND WARNING_FLAGS_TO_CHECK ${GCC_AND_CLANG_WARNINGS})
  list(APPEND WARNING_FLAGS_TO_CHECK ${CLANG_ONLY_WARNINGS})
  list(APPEND WARNING_AS_ERROR_FLAGS_TO_CHECK ${GCC_AND_CLANG_WARNINGS_AS_ERRORS})
  list(APPEND WARNING_AS_ERROR_FLAGS_TO_CHECK ${CLANG_WARNINGS_AS_ERRORS})
elseif (CMAKE_CXX_COMPILER_ID STREQUAL "MSVC")
  list(APPEND WARNING_FLAGS_TO_CHECK ${MSVC_WARNINGS})

  # CMake's default flags include /W3 already so remove them if
  # they already exist.
  if (CMAKE_CXX_FLAGS MATCHES "/W3")
    string(REPLACE "/W3" "" _cmake_cxx_flags_remove_w3 "${CMAKE_CXX_FLAGS}")
    set(CMAKE_CXX_FLAGS "${_cmake_cxx_flags_remove_w3}" CACHE STRING "" FORCE)
  endif()
else()
  message(AUTHOR_WARNING "Unknown compiler")
endif()

# Loop through flags and use the ones which the compiler supports
foreach (flag ${WARNING_FLAGS_TO_CHECK})
  z3_add_cxx_flag("${flag}")
endforeach()

# TODO: Remove this eventually.
# Detect legacy `WARNINGS_AS_ERRORS` boolean option and covert to new
# to new option type.
get_property(
  WARNINGS_AS_ERRORS_CACHE_VAR_TYPE
  CACHE
  WARNINGS_AS_ERRORS
  PROPERTY
  TYPE
)
if (WARNINGS_AS_ERRORS_CACHE_VAR_TYPE STREQUAL "BOOL")
  message(WARNING "Detected legacy WARNINGS_AS_ERRORS option. Upgrading")
  set(WARNINGS_AS_ERRORS_DEFAULT "${WARNINGS_AS_ERRORS}")
  # Delete old entry
  unset(WARNINGS_AS_ERRORS CACHE)
else()
  set(WARNINGS_AS_ERRORS_DEFAULT "SERIOUS_ONLY")
endif()

set(WARNINGS_AS_ERRORS
  ${WARNINGS_AS_ERRORS_DEFAULT}
  CACHE STRING
  "Treat warnings as errors. ON, OFF, or SERIOUS_ONLY"
)
 # Set GUI options
set_property(
  CACHE
  WARNINGS_AS_ERRORS
  PROPERTY STRINGS
  "ON;OFF;SERIOUS_ONLY"
)

if (WARNINGS_AS_ERRORS STREQUAL "ON")
  message(STATUS "Treating compiler warnings as errors")
  if ((CMAKE_CXX_COMPILER_ID MATCHES "Clang") OR (CMAKE_CXX_COMPILER_ID MATCHES "GNU"))
    list(APPEND Z3_COMPONENT_CXX_FLAGS "-Werror")
  elseif (CMAKE_CXX_COMPILER_ID STREQUAL "MSVC")
    list(APPEND Z3_COMPONENT_CXX_FLAGS "/WX")
  else()
    message(AUTHOR_WARNING "Unknown compiler")
  endif()
elseif (WARNINGS_AS_ERRORS STREQUAL "SERIOUS_ONLY")
  message(STATUS "Treating only serious compiler warnings as errors")
  # Loop through the flags
  foreach (flag ${WARNING_AS_ERROR_FLAGS_TO_CHECK})
    # Add globally because some flags need to be passed at link time.
    z3_add_cxx_flag("${flag}" GLOBAL)
  endforeach()
elseif (WARNINGS_AS_ERRORS STREQUAL "OFF")
  message(STATUS "Not treating compiler warnings as errors")
  if (CMAKE_CXX_COMPILER_ID STREQUAL "MSVC")
    # Warnings as errors is off by default for MSVC so setting this
    # is not necessary but this duplicates the behaviour of the old
    # build system.
    list(APPEND Z3_COMPONENT_CXX_FLAGS "/WX-")
  endif()
else()
  message(FATAL_ERROR
    "WARNINGS_AS_ERRORS set to unsupported value \"${WARNINGS_AS_ERRORS}\""
  )
endif()