Improve the internal handling of unity build

- Removed the NO_UNITY_BUILD argument from commands that disable it by
  default.
- Add a warning in case NO_UNITY_BUILD or NO_UNITY_BUILD_SOURCES is
  being used where it is already disabled, e.g., qt_internal_add_test
- Exclude all sources of a target from unity build if NO_UNITY_BUILD
  is set on the target. This sounds a bit harsh, but I have noticed that
  sometimes the same source file can be included somewhere else, and
  some unexpected collision may occur.
- qt_examples_build_end excludes all its examples from the unity build.
- qt_build_test now sets the CMAKE_UNITY_BUILD to OFF before configuring
  the tests, and restore its value when done.

Task-number: QTBUG-109394
Change-Id: Ia42e7dd5a5bfb151db241deb639325720fd91eec
Reviewed-by: Alexandru Croitor <alexandru.croitor@qt.io>
(cherry picked from commit 360293623094a31586981206e59c92aa6235163d)
Reviewed-by: Qt Cherry-pick Bot <cherrypick_bot@qt-project.org>

cmake/Qt3rdPartyLibraryHelpers.cmake

@@ -50,12 +50,6 @@ function(qt_internal_add_common_qt_library_helper target)
         set(arg_MODULE STATIC)
     endif()
 
-    if(arg_NO_UNITY_BUILD)
-        set(arg_NO_UNITY_BUILD NO_UNITY_BUILD)
-    else()
-        set(arg_NO_UNITY_BUILD "")
-    endif()
-
     _qt_internal_add_library(${target} ${arg_STATIC} ${arg_SHARED} ${arg_MODULE} ${arg_INTERFACE})
 
     if(arg_NO_UNITY_BUILD)
@@ -85,6 +79,7 @@ function(qt_internal_add_cmake_library target)
         "${multi_args}"
     )
     _qt_internal_validate_all_args_are_parsed(arg)
+    _qt_internal_validate_no_unity_build(arg)
 
     qt_remove_args(library_helper_args
         ARGS_TO_REMOVE
@@ -110,12 +105,6 @@ function(qt_internal_add_cmake_library target)
         )
     endif()
 
-    if(arg_NO_UNITY_BUILD)
-        set(arg_NO_UNITY_BUILD NO_UNITY_BUILD)
-    else()
-        set(arg_NO_UNITY_BUILD "")
-    endif()
-
     qt_internal_extend_target("${target}"
         SOURCES ${arg_SOURCES}
         INCLUDE_DIRECTORIES
@@ -137,8 +126,7 @@ function(qt_internal_add_cmake_library target)
         MOC_OPTIONS ${arg_MOC_OPTIONS}
         ENABLE_AUTOGEN_TOOLS ${arg_ENABLE_AUTOGEN_TOOLS}
         DISABLE_AUTOGEN_TOOLS ${arg_DISABLE_AUTOGEN_TOOLS}
-        NO_UNITY_BUILD_SOURCES ${arg_NO_UNITY_BUILD_SOURCES}
+        NO_UNITY_BUILD # Disabled by default
-        ${arg_NO_UNITY_BUILD}
     )
 endfunction()
 
@@ -167,6 +155,7 @@ function(qt_internal_add_3rdparty_library target)
         "${multi_args}"
     )
     _qt_internal_validate_all_args_are_parsed(arg)
+    _qt_internal_validate_no_unity_build(arg)
 
     qt_remove_args(library_helper_args
         ARGS_TO_REMOVE

cmake/QtBuildInternals/QtBuildInternalsConfig.cmake

@@ -669,6 +669,8 @@ function(qt_internal_get_standalone_tests_config_file_name out_var)
 endfunction()
 
 macro(qt_build_tests)
+    set(CMAKE_UNITY_BUILD OFF)
+
     if(QT_BUILD_STANDALONE_TESTS)
         # Find location of TestsConfig.cmake. These contain the modules that need to be
         # find_package'd when testing.
@@ -739,6 +741,8 @@ macro(qt_build_tests)
             add_subdirectory(manual)
         endif()
     endif()
+
+    set(CMAKE_UNITY_BUILD ${QT_UNITY_BUILD})
 endmacro()
 
 function(qt_compute_relative_path_from_cmake_config_dir_to_prefix)
@@ -953,6 +957,7 @@ macro(qt_examples_build_end)
         if(TARGET Qt::Widgets)
             qt_autogen_tools(${target} ENABLE_AUTOGEN_TOOLS "uic")
         endif()
+        set_target_properties(${target} PROPERTIES UNITY_BUILD OFF)
     endforeach()
 
     install(CODE "

cmake/QtTargetHelpers.cmake

@@ -208,11 +208,16 @@ function(qt_internal_extend_target target)
                          DISABLE_AUTOGEN_TOOLS ${arg_DISABLE_AUTOGEN_TOOLS})
 
         qt_update_precompiled_header("${target}" "${arg_PRECOMPILED_HEADER}")
+        ## Also exclude them from unity build
         qt_update_ignore_pch_source("${target}" "${arg_NO_PCH_SOURCES}")
-        qt_update_ignore_unity_build_sources("${target}" "${arg_NO_UNITY_BUILD_SOURCES}")
         ## Ignore objective-c files for PCH (not supported atm)
         qt_ignore_pch_obj_c_sources("${target}" "${arg_SOURCES}")
 
+        qt_update_ignore_unity_build_sources("${target}" "${arg_NO_UNITY_BUILD_SOURCES}")
+        if(arg_NO_UNITY_BUILD)
+            set_target_properties("${target}" PROPERTIES UNITY_BUILD OFF)
+            qt_update_ignore_unity_build_sources("${target}" "${arg_SOURCES}")
+        endif()
     else()
         if(QT_CMAKE_DEBUG_EXTEND_TARGET)
             message("qt_extend_target(${target} CONDITION ${arg_CONDITION} ...): Skipped")
@@ -230,9 +235,6 @@ function(qt_internal_extend_target target)
             ${sources_property} "${arg_CONDITION_INDEPENDENT_SOURCES}")
     endif()
 
-    if(arg_NO_UNITY_BUILD)
-        set_target_properties(${target} PROPERTIES UNITY_BUILD OFF)
-    endif()
 endfunction()
 
 function(qt_is_imported_target target out_var)

cmake/QtTestHelpers.cmake

@@ -15,6 +15,7 @@ function(qt_internal_add_benchmark target)
         "${__qt_internal_add_executable_multi_args}"
     )
     _qt_internal_validate_all_args_are_parsed(arg)
+    _qt_internal_validate_no_unity_build(arg)
 
     qt_remove_args(exec_args
         ARGS_TO_REMOVE
@@ -239,6 +240,8 @@ function(qt_internal_add_test_to_batch batch_name name)
         arg "${optional_args}" "${single_value_args}" "${multi_value_args}" ${ARGN})
     qt_internal_prepare_test_target_flags(version_arg exceptions_text gui_text ${ARGN})
 
+    _qt_internal_validate_no_unity_build(arg)
+
     _qt_internal_test_batch_target_name(target)
 
     # Lazy-init the test batch
@@ -322,6 +325,7 @@ function(qt_internal_add_test_to_batch batch_name name)
         ENABLE_AUTOGEN_TOOLS ${arg_ENABLE_AUTOGEN_TOOLS}
         DISABLE_AUTOGEN_TOOLS ${arg_DISABLE_AUTOGEN_TOOLS}
         NO_UNITY_BUILD # Tests should not be built using UNITY_BUILD
+        NO_UNITY_BUILD_SOURCES ${arg_SOURCES}
         )
 
     foreach(source ${arg_SOURCES})
@@ -396,6 +400,7 @@ function(qt_internal_add_test name)
         "${multi_value_args}"
     )
     _qt_internal_validate_all_args_are_parsed(arg)
+    _qt_internal_validate_no_unity_build(arg)
 
     if (NOT arg_OUTPUT_DIRECTORY)
         set(arg_OUTPUT_DIRECTORY "${CMAKE_CURRENT_BINARY_DIR}")

cmake/QtUnityBuildHelpers.cmake

@@ -1,6 +1,15 @@
 # Copyright (C) 2023 The Qt Company Ltd.
 # SPDX-License-Identifier: BSD-3-Clause
 
+# Check whether no unity build is requested where it is disabled by default.
+function(_qt_internal_validate_no_unity_build prefix)
+    if(${prefix}_NO_UNITY_BUILD OR ${prefix}_NO_UNITY_BUILD_SOURCES)
+        message(WARNING
+            "Unity build is disabled by default for this target, and its sources. "
+            "You may remove the NO_UNITY_BUILD and/or NO_UNITY_BUILD_SOURCES arguments.")
+    endif()
+endfunction()
+
 function(qt_update_ignore_unity_build_sources target sources)
     if (sources)
         set_source_files_properties(${sources} PROPERTIES SKIP_UNITY_BUILD_INCLUSION ON)