Use pre-compiled headers when building Qt with cmake

Some modules define their own manually-maintained lists, and we can rely
on the headers generated by each module to include in the pch as well
e.g. QtCore/QtCore.

There's also e.g. QtWidgetDepends for QtWidgets, but this only
works for modules, not for tools, examples or other applications.
For now we'll use the Qt<Module>/Qt<Module> headers for the
modules we depend on.

Building with PCH can be disabled with -DBUILD_WITH_PCH=NO, and it only
works for versions of CMake newer than 3.15.20190829.

Change-Id: Iae52bd69acfdfd58f4cd20d3cfa3c7f42775f732
Reviewed-by: Qt CMake Build Bot
Reviewed-by: Alexandru Croitor <alexandru.croitor@qt.io>

CMakeLists.txt

@@ -41,6 +41,9 @@ set(QT_BUILD_SHARED_LIBS ${BUILD_SHARED_LIBS})
 ## Should this Qt be built with Werror?
 option(WARNINGS_ARE_ERRORS "Build Qt with warnings as errors" ${FEATURE_developer_build})
 
+## Should Qt be built using PCH?
+option(BUILD_WITH_PCH "Build Qt using precompiled headers?" ON)
+
 ## Decide whether tools will be built.
 qt_check_if_tools_will_be_built()
 

cmake/QtBuild.cmake

@@ -915,6 +915,33 @@ function(qt_register_target_dependencies target public_libs private_libs)
     set_target_properties("${target}" PROPERTIES _qt_target_deps "${target_deps}")
 endfunction()
 
+function(qt_update_precompiled_header target precompiled_header)
+    if (precompiled_header AND BUILD_WITH_PCH)
+        set_property(TARGET "${target}" APPEND PROPERTY "PRECOMPILE_HEADERS" "${precompiled_header}")
+    endif()
+endfunction()
+
+function(qt_update_precompiled_header_with_library target library)
+    if (TARGET "${library}")
+        get_target_property(TARGET_TYPE "${library}" TYPE)
+        if (NOT TARGET_TYPE STREQUAL "INTERFACE_LIBRARY")
+            get_target_property(HEADER "${library}" MODULE_HEADER)
+            qt_update_precompiled_header("${target}" "${HEADER}")
+        endif()
+    endif()
+endfunction()
+
+function(qt_update_ignore_pch_source target sources)
+    if (sources)
+        set_source_files_properties(${sources} PROPERTIES SKIP_PRECOMPILE_HEADERS ON)
+    endif()
+endfunction()
+
+function(qt_ignore_pch_obj_c_sources target sources)
+    list(FILTER sources INCLUDE REGEX "\\.mm$")
+    qt_update_ignore_pch_source("${target}" "${sources}")
+endfunction()
+
 # This function can be used to add sources/libraries/etc. to the specified CMake target
 # if the provided CONDITION evaluates to true.
 function(extend_target target)
@@ -927,8 +954,8 @@ function(extend_target target)
     if (NOT TARGET "${target}")
         message(FATAL_ERROR "Trying to extend non-existing target \"${target}\".")
     endif()
-    qt_parse_all_arguments(arg "extend_target" "HEADER_MODULE" ""
+    qt_parse_all_arguments(arg "extend_target" "HEADER_MODULE" "PRECOMPILED_HEADER"
-        "CONDITION;${__default_public_args};${__default_private_args};COMPILE_FLAGS" ${ARGN})
+        "CONDITION;${__default_public_args};${__default_private_args};COMPILE_FLAGS;NO_PCH_SOURCES" ${ARGN})
     if ("x${arg_CONDITION}" STREQUAL x)
         set(arg_CONDITION ON)
     endif()
@@ -950,6 +977,7 @@ function(extend_target target)
         endforeach()
 
         foreach(lib ${arg_PUBLIC_LIBRARIES} ${arg_LIBRARIES})
+            qt_update_precompiled_header_with_library("${target}" "${lib}")
             string(REGEX REPLACE "_nolink$" "" base_lib "${lib}")
             if(NOT base_lib STREQUAL lib)
                 qt_create_nolink_target("${base_lib}" ${target})
@@ -1034,6 +1062,11 @@ function(extend_target target)
                          ENABLE_AUTOGEN_TOOLS ${arg_ENABLE_AUTOGEN_TOOLS}
                          DISABLE_AUTOGEN_TOOLS ${arg_DISABLE_AUTOGEN_TOOLS})
 
+        qt_update_precompiled_header("${target}" "${arg_PRECOMPILED_HEADER}")
+        qt_update_ignore_pch_source("${target}" "${arg_NO_PCH_SOURCES}")
+        ## Ignore objective-c files for PCH (not supported atm)
+        qt_ignore_pch_obj_c_sources("${target}" "${arg_SOURCES}")
+
     else()
         if(QT_CMAKE_DEBUG_EXTEND_TARGET)
             message("extend_target(${target} CONDITION ${arg_CONDITION} ...): Skipped")
@@ -1218,8 +1251,8 @@ function(add_qt_module target)
     # Process arguments:
     qt_parse_all_arguments(arg "add_qt_module"
         "NO_MODULE_HEADERS;STATIC;DISABLE_TOOLS_EXPORT;EXCEPTIONS;INTERNAL_MODULE;NO_SYNC_QT;NO_PRIVATE_MODULE;HEADER_MODULE"
-        "CONFIG_MODULE_NAME"
+        "CONFIG_MODULE_NAME;PRECOMPILED_HEADER"
-        "${__default_private_args};${__default_public_args};QMAKE_MODULE_CONFIG;EXTRA_CMAKE_FILES;EXTRA_CMAKE_INCLUDES" ${ARGN})
+        "${__default_private_args};${__default_public_args};QMAKE_MODULE_CONFIG;EXTRA_CMAKE_FILES;EXTRA_CMAKE_INCLUDES;NO_PCH_SOURCES" ${ARGN})
 
     if(NOT DEFINED arg_CONFIG_MODULE_NAME)
         set(arg_CONFIG_MODULE_NAME "${module_lower}")
@@ -1275,6 +1308,8 @@ function(add_qt_module target)
         set_property(TARGET "${target}" APPEND PROPERTY PUBLIC_HEADER "${module_headers_public}")
         set_property(TARGET "${target}" APPEND PROPERTY PUBLIC_HEADER "${module_include_dir}/${module}Depends")
         set_property(TARGET "${target}" APPEND PROPERTY PRIVATE_HEADER "${module_headers_private}")
+        set_property(TARGET "${target}" PROPERTY MODULE_HEADER "${module_include_dir}/${module}")
+
         if(module_headers_qpa)
             qt_install(FILES ${module_headers_qpa} DESTINATION ${INSTALL_INCLUDEDIR}/${module}/${PROJECT_VERSION}/${module}/qpa)
         endif()
@@ -1369,6 +1404,8 @@ function(add_qt_module target)
         MOC_OPTIONS ${arg_MOC_OPTIONS}
         ENABLE_AUTOGEN_TOOLS ${arg_ENABLE_AUTOGEN_TOOLS}
         DISABLE_AUTOGEN_TOOLS ${arg_DISABLE_AUTOGEN_TOOLS}
+        PRECOMPILED_HEADER ${arg_PRECOMPILED_HEADER}
+        NO_PCH_SOURCES ${arg_NO_PCH_SOURCES}
     )
 
     if(NOT ${arg_EXCEPTIONS} AND NOT ${arg_HEADER_MODULE})

qmake/CMakeLists.txt

@@ -116,12 +116,13 @@ add_qt_tool(qmake # special case
         library
         $<TARGET_PROPERTY:Qt::CorePrivate,INTERFACE_INCLUDE_DIRECTORIES> # special case
         ${CMAKE_BINARY_DIR}/src/corelib/global # special case: for qconfig.cpp
+    PRECOMPILED_HEADER
+        "qmake_pch.h"
 )
 
 qt_internal_add_target_aliases(Bootstrap) # special case
 
 #### Keys ignored in scope 1:.:.:qmake.pro:<TRUE>:
-# PRECOMPILED_HEADER = "qmake_pch.h"
 # _OPTION = "host_build"
 
 ## Scopes:

src/concurrent/CMakeLists.txt

@@ -29,11 +29,11 @@ add_qt_module(Concurrent
         Qt::CorePrivate
     PUBLIC_LIBRARIES
         Qt::Core
+    PRECOMPILED_HEADER
+        "../corelib/global/qt_pch.h"
 )
 
 #### Keys ignored in scope 1:.:.:concurrent.pro:<TRUE>:
-# CONFIG = "exceptions"
-# PRECOMPILED_HEADER = "../corelib/global/qt_pch.h"
 # _LOADED = "qt_module"
 
 ## Scopes:

src/corelib/CMakeLists.txt

@@ -250,6 +250,11 @@ add_qt_module(Core
     PUBLIC_LIBRARIES  # special case:
         Qt::Platform # special case:
     DISABLE_TOOLS_EXPORT # special case:
+    PRECOMPILED_HEADER
+        global/qt_pch.h
+    NO_PCH_SOURCES
+        text/qstring_compat.cpp
+        tools/qvector_msvc.cpp
     # special case begin
     # Generated in QtBaseGlobalTargets
     EXTRA_CMAKE_FILES ${QT_CORE_RESOURCE_GENERATED_FILE_PATH}

src/gui/CMakeLists.txt

@@ -264,6 +264,10 @@ add_qt_module(Gui
         ZLIB::ZLIB
     PUBLIC_LIBRARIES
         Qt::Core
+    NO_PCH_SOURCES
+        "painting/qdrawhelper.cpp"
+    PRECOMPILED_HEADER
+        "kernel/qt_gui_pch.h"
 )
 
 # Resources:

src/network/CMakeLists.txt

@@ -60,6 +60,8 @@ add_qt_module(Network
         ZLIB::ZLIB
     PUBLIC_LIBRARIES
         Qt::Core
+    PRECOMPILED_HEADER
+        "../corelib/global/qt_pch.h"
 )
 
 #### Keys ignored in scope 1:.:.:network.pro:<TRUE>:

src/platformsupport/edid/CMakeLists.txt

@@ -15,10 +15,11 @@ add_qt_module(EdidSupport
         Qt::CorePrivate
     PUBLIC_LIBRARIES
         Qt::Core
+    PRECOMPILED_HEADER
+        "../../corelib/global/qt_pch.h"
 )
 
 #### Keys ignored in scope 1:.:.:edid.pro:<TRUE>:
 # CONFIG = "static" "internal_module"
 # MODULE = "edid_support"
-# PRECOMPILED_HEADER = "../../corelib/global/qt_pch.h"
 # _LOADED = "qt_module"

src/platformsupport/eglconvenience/CMakeLists.txt

@@ -19,12 +19,13 @@ add_qt_module(EglSupport
         Qt::CorePrivate
         Qt::GuiPrivate
         EGL::EGL # special case
+    PRECOMPILED_HEADER
+        "../../corelib/global/qt_pch.h"
 )
 
 #### Keys ignored in scope 1:.:eglconvenience.pro:<NONE>:
 # CONFIG = "static" "internal_module" "egl"
 # MODULE = "egl_support"
-# PRECOMPILED_HEADER = "../../corelib/global/qt_pch.h"
 # _LOADED = "qt_module"
 
 ## Scopes:

src/platformsupport/eventdispatchers/CMakeLists.txt

@@ -17,12 +17,13 @@ add_qt_module(EventDispatcherSupport
     PUBLIC_LIBRARIES
         Qt::Core
         Qt::Gui
+    PRECOMPILED_HEADER
+        "../../corelib/global/qt_pch.h"
 )
 
 #### Keys ignored in scope 1:.:.:eventdispatchers.pro:<TRUE>:
 # CONFIG = "static" "internal_module"
 # MODULE = "eventdispatcher_support"
-# PRECOMPILED_HEADER = "../../corelib/global/qt_pch.h"
 # _LOADED = "qt_module"
 
 ## Scopes:

src/platformsupport/fbconvenience/CMakeLists.txt

@@ -21,10 +21,11 @@ add_qt_module(FbSupport
     PUBLIC_LIBRARIES
         Qt::Core
         Qt::Gui
+    PRECOMPILED_HEADER
+        "../../corelib/global/qt_pch.h"
 )
 
 #### Keys ignored in scope 1:.:.:fbconvenience.pro:<TRUE>:
 # CONFIG = "static" "internal_module"
 # MODULE = "fb_support"
-# PRECOMPILED_HEADER = "../../corelib/global/qt_pch.h"
 # _LOADED = "qt_module"

src/platformsupport/fontdatabases/CMakeLists.txt

@@ -18,12 +18,13 @@ add_qt_module(FontDatabaseSupport
     PUBLIC_LIBRARIES
         Qt::Core
         Qt::Gui
+    PRECOMPILED_HEADER
+        "../../corelib/global/qt_pch.h"
 )
 
 #### Keys ignored in scope 1:.:.:fontdatabases.pro:<TRUE>:
 # CONFIG = "static" "internal_module"
 # MODULE = "fontdatabase_support"
-# PRECOMPILED_HEADER = "../../corelib/global/qt_pch.h"
 # _LOADED = "qt_module"
 
 ## Scopes:

src/platformsupport/input/CMakeLists.txt

@@ -22,12 +22,13 @@ add_qt_module(InputSupport
         Qt::Core
         Qt::DeviceDiscoverySupport
         Qt::Gui
+    PRECOMPILED_HEADER
+        "../../corelib/global/qt_pch.h"
 )
 
 #### Keys ignored in scope 3:.:.:input-support.pro:<TRUE>:
 # CONFIG = "static" "internal_module"
 # MODULE = "input_support"
-# PRECOMPILED_HEADER = "../../corelib/global/qt_pch.h"
 # _LOADED = "qt_module"
 
 ## Scopes:

src/platformsupport/input/xkbcommon/CMakeLists.txt

@@ -19,12 +19,13 @@ add_qt_module(XkbCommonSupport
         Qt::Core
         Qt::Gui
         XKB::XKB
+    PRECOMPILED_HEADER
+        "../../../corelib/global/qt_pch.h"
 )
 
 #### Keys ignored in scope 1:.:.:xkbcommon.pro:<TRUE>:
 # CONFIG = "static" "internal_module"
 # MODULE = "xkbcommon_support"
-# PRECOMPILED_HEADER = "../../../corelib/global/qt_pch.h"
 # _LOADED = "qt_module"
 
 ## Scopes:

src/platformsupport/linuxaccessibility/CMakeLists.txt

@@ -39,10 +39,11 @@ add_qt_module(LinuxAccessibilitySupport
         Qt::Core
         Qt::DBus
         Qt::Gui
+    PRECOMPILED_HEADER
+        "../../corelib/global/qt_pch.h"
 )
 
 #### Keys ignored in scope 1:.:.:linuxaccessibility.pro:<TRUE>:
 # CONFIG = "static" "internal_module"
 # MODULE = "linuxaccessibility_support"
-# PRECOMPILED_HEADER = "../../corelib/global/qt_pch.h"
 # _LOADED = "qt_module"

src/platformsupport/services/CMakeLists.txt

@@ -17,12 +17,13 @@ add_qt_module(ServiceSupport
     PUBLIC_LIBRARIES
         Qt::Core
         Qt::Gui
+    PRECOMPILED_HEADER
+        "../../corelib/global/qt_pch.h"
 )
 
 #### Keys ignored in scope 1:.:.:services.pro:<TRUE>:
 # CONFIG = "static" "internal_module"
 # MODULE = "service_support"
-# PRECOMPILED_HEADER = "../../corelib/global/qt_pch.h"
 # _LOADED = "qt_module"
 
 ## Scopes:

src/platformsupport/vkconvenience/CMakeLists.txt

@@ -20,10 +20,11 @@ add_qt_module(VulkanSupport
     PUBLIC_LIBRARIES
         Qt::Core
         Qt::Gui
+    PRECOMPILED_HEADER
+        "../../corelib/global/qt_pch.h"
 )
 
 #### Keys ignored in scope 1:.:.:vkconvenience.pro:<TRUE>:
 # CONFIG = "static" "internal_module"
 # MODULE = "vulkan_support"
-# PRECOMPILED_HEADER = "../../corelib/global/qt_pch.h"
 # _LOADED = "qt_module"

src/sql/CMakeLists.txt

@@ -27,11 +27,12 @@ add_qt_module(Sql
         Qt::CorePrivate
     PUBLIC_LIBRARIES
         Qt::Core
+    PRECOMPILED_HEADER
+        "../corelib/global/qt_pch.h"
 )
 
 #### Keys ignored in scope 1:.:.:sql.pro:<TRUE>:
 # MODULE_PLUGIN_TYPES = "sqldrivers"
-# PRECOMPILED_HEADER = "../corelib/global/qt_pch.h"
 # SQL_P = "sql"
 # _LOADED = "qt_module"
 

src/widgets/CMakeLists.txt

@@ -63,6 +63,8 @@ add_qt_module(Widgets
     PUBLIC_LIBRARIES
         Qt::Core
         Qt::Gui
+    PRECOMPILED_HEADER
+        "kernel/qt_widgets_pch.h"
 )
 
 add_dependencies(Widgets ${QT_CMAKE_EXPORT_NAMESPACE}::uic)  # special case

src/xml/CMakeLists.txt

@@ -19,7 +19,6 @@ add_qt_module(Xml
 )
 
 #### Keys ignored in scope 1:.:.:xml.pro:<TRUE>:
-# PRECOMPILED_HEADER = <EMPTY>
 # _LOADED = "qt_module"
 
 ## Scopes:

util/cmake/pro2cmake.py

@@ -1534,6 +1534,18 @@ def write_sources_section(cm_fh: typing.IO[str], scope: Scope, *,
         for mo in moc_options:
             cm_fh.write('{}        "{}"\n'.format(ind, mo))
 
+    precompiled_header = scope.get('PRECOMPILED_HEADER')
+    if precompiled_header:
+        cm_fh.write('{}    PRECOMPILED_HEADER\n'.format(ind))
+        for header in precompiled_header:
+            cm_fh.write('{}        "{}"\n'.format(ind, header))
+
+    no_pch_sources = scope.get('NO_PCH_SOURCES')
+    if no_pch_sources:
+        cm_fh.write('{}    NO_PCH_SOURCES\n'.format(ind))
+        for source in no_pch_sources:
+            cm_fh.write('{}        "{}"\n'.format(ind, source))
+
 
 def is_simple_condition(condition: str) -> bool:
     return ' ' not in condition \