[CMake] Add option to compile with warnings as errors

https://bugs.webkit.org/show_bug.cgi?id=155047

Reviewed by Michael Catanzaro.

Add `DEVELOPER_MODE_FATAL_WARNINGS` as an option to compile everything
defined through `WEBKIT_TARGET` with warnings as errors. For MSVC
`/WX` is added for everything else `-Werror` is used. An additional
flag, `--[no-]fatal-warnings` was added to the `build-webkit` script.

This value should be set to `ON` by default but is currently turned
`OFF` until the build bots invoke `build-webkit` with
`--no-fatal-warnings`. After that it should be turned to `ON`.

* Source/cmake/WebKitCompilerFlags.cmake:
* Source/cmake/WebKitMacros.cmake:
* Tools/Scripts/webkitperl/FeatureList.pm:

Canonical link: https://commits.webkit.org/254583@main

Source/cmake/WebKitCompilerFlags.cmake

@@ -87,6 +87,20 @@ macro(WEBKIT_ADD_TARGET_CXX_FLAGS _target)
 endmacro()
 
 
+option(DEVELOPER_MODE_FATAL_WARNINGS "Build with warnings as errors if DEVELOPER_MODE is also enabled" OFF)
+if (DEVELOPER_MODE AND DEVELOPER_MODE_FATAL_WARNINGS)
+    if (MSVC)
+        set(FATAL_WARNINGS_FLAG /WX)
+    else ()
+        set(FATAL_WARNINGS_FLAG -Werror)
+    endif ()
+
+    check_cxx_compiler_flag(${FATAL_WARNINGS_FLAG} CXX_COMPILER_SUPPORTS_WERROR)
+    if (CXX_COMPILER_SUPPORTS_WERROR)
+        set(DEVELOPER_MODE_CXX_FLAGS ${FATAL_WARNINGS_FLAG})
+    endif ()
+endif ()
+
 if (COMPILER_IS_GCC_OR_CLANG)
     WEBKIT_APPEND_GLOBAL_COMPILER_FLAGS(-fno-strict-aliasing)
 

Source/cmake/WebKitMacros.cmake

@@ -143,6 +143,10 @@ macro(_WEBKIT_TARGET _target_logical_name _target_cmake_name)
     target_include_directories(${_target_cmake_name} SYSTEM PRIVATE "$<BUILD_INTERFACE:${${_target_logical_name}_SYSTEM_INCLUDE_DIRECTORIES}>")
     target_include_directories(${_target_cmake_name} PRIVATE "$<BUILD_INTERFACE:${${_target_logical_name}_PRIVATE_INCLUDE_DIRECTORIES}>")
 
+    if (DEVELOPER_MODE_CXX_FLAGS)
+        target_compile_options(${_target_cmake_name} PRIVATE ${DEVELOPER_MODE_CXX_FLAGS})
+    endif ()
+
     target_compile_definitions(${_target_cmake_name} PRIVATE "BUILDING_${_target_logical_name}")
     if (${_target_logical_name}_DEFINITIONS)
         target_compile_definitions(${_target_cmake_name} PUBLIC ${${_target_logical_name}_DEFINITIONS})

Tools/Scripts/webkitperl/FeatureList.pm

@@ -87,6 +87,7 @@ my (
     $downloadAttributeSupport,
     $dragSupportSupport,
     $encryptedMediaSupport,
+    $fatalWarnings,
     $filtersLevel2Support,
     $ftlJITSupport,
     $ftpDirSupport,
@@ -191,6 +192,9 @@ my (
 );
 
 my @features = (
+    { option => "fatal-warnings", desc => "Toggle warnings as errors (CMake only)",
+      define => "DEVELOPER_MODE_FATAL_WARNINGS", value => \$fatalWarnings },
+
     { option => "3d-rendering", desc => "Toggle 3D rendering support",
       define => "ENABLE_3D_TRANSFORMS", value => \$threeDTransformsSupport },