Avoid rebuilds when changing sources belonging to bootstraplib

Whenever a source file is touched that belongs to the bootstrap library,
all bootstrap tools are rebuilt.  This includes moc.  The moc binary
however, is a dependency whose invalidation results in a rebuilt of
quite some parts of Qt.

There's no easy way to turn off this dependency.  To mitigate the
rebuilds, the bootstrap lib now can use a copy of the corelib sources.
That means the bootstrap lib is not rebuilt if its sources are changed.
This is basically the situation we had in Qt5.

The sources are not updated on reconfiguration.  There's a new target
'update_bootstrap_sources' that can be built to update the copied source
tree of the bootstrap lib.

This new behavior can be controlled with the variable
QT_USE_BOOTSTRAP_SOURCE_COPY.  It's on by default for developer builds.

Fixes: QTBUG-92269
Change-Id: I50234df66590c39594d208424394c7a600dc5606
Reviewed-by: Alexandru Croitor <alexandru.croitor@qt.io>

1 files changed, 111 insertions, 69 deletions

diff --git a/src/tools/bootstrap/CMakeLists.txt b/src/tools/bootstrap/CMakeLists.txt
index 2f69849538..51a8737860 100644
--- a/src/tools/bootstrap/CMakeLists.txt
+++ b/src/tools/bootstrap/CMakeLists.txt
@@ -8,78 +8,120 @@
 # The bootstrap library has a few manual tweaks compared to other
 # libraries.
 qt_add_library(Bootstrap STATIC)
+
+option(QT_USE_BOOTSTRAP_SOURCE_COPY "Use copies of source files for building the bootstrap lib."
+    ${QT_FEATURE_private_tests})
+
+if(QT_USE_BOOTSTRAP_SOURCE_COPY)
+    # To avoid unnecessary rebuilds whenever a source file of the bootstrap library is touched, we
+    # use a copy of the corelib sources. This copy can be updated manually by building the target
+    # 'update_bootstrap_sources'.
+
+    set(source_root ${CMAKE_CURRENT_BINARY_DIR}/srccopy)
+    if(NOT IS_DIRECTORY "${source_root}")
+        file(COPY "${QtBase_SOURCE_DIR}/src/corelib" DESTINATION "${source_root}")
+    endif()
+
+    file(GLOB_RECURSE source_files
+        LIST_DIRECTORIES FALSE
+        RELATIVE "${QtBase_SOURCE_DIR}/src/corelib"
+        "${QtBase_SOURCE_DIR}/src/corelib/*")
+
+    set(copy_commands)
+    set(allowed_extensions .c .cpp .h .mm)
+    foreach(f IN LISTS source_files)
+        get_filename_component(ext "${f}" LAST_EXT)
+        if(NOT ext IN_LIST allowed_extensions)
+            continue()
+        endif()
+        list(APPEND copy_commands
+            COMMAND "${CMAKE_COMMAND}" -E
+            copy_if_different "${QtBase_SOURCE_DIR}/src/corelib/${f}"
+                              "${source_root}/corelib/${f}")
+    endforeach()
+    set(info_msg "Please run 'cmake --build .' twice, to ensure all relevant files are rebuilt due")
+    string(APPEND info_msg " to the bootstrap source file copy.")
+    add_custom_target(update_bootstrap_sources
+        ${copy_commands}
+        COMMAND ${CMAKE_COMMAND} -E echo "${info_msg}"
+        VERBATIM)
+else()
+    # Directly use the files in the source tree.
+    set(source_root ../..)
+endif()
+
 # special case end
 qt_internal_extend_target(Bootstrap
     SOURCES
-        ../../corelib/global/qendian.cpp
-        ../../corelib/global/qfloat16.cpp
-        ../../corelib/global/qglobal.cpp
-        ../../corelib/global/qlogging.cpp
-        ../../corelib/global/qmalloc.cpp
-        ../../corelib/global/qnumeric.cpp
-        ../../corelib/global/qoperatingsystemversion.cpp
-        ../../corelib/global/qrandom.cpp
-        ../../corelib/io/qabstractfileengine.cpp
-        ../../corelib/io/qbuffer.cpp
-        ../../corelib/io/qdebug.cpp
-        ../../corelib/io/qdir.cpp
-        ../../corelib/io/qdiriterator.cpp
-        ../../corelib/io/qfile.cpp
-        ../../corelib/io/qfiledevice.cpp
-        ../../corelib/io/qfileinfo.cpp
-        ../../corelib/io/qfilesystemengine.cpp
-        ../../corelib/io/qfilesystementry.cpp
-        ../../corelib/io/qfsfileengine.cpp
-        ../../corelib/io/qfsfileengine_iterator.cpp
-        ../../corelib/io/qiodevice.cpp
-        ../../corelib/io/qloggingcategory.cpp
-        ../../corelib/io/qloggingregistry.cpp
-        ../../corelib/io/qresource.cpp
-        ../../corelib/io/qsavefile.cpp
-        ../../corelib/io/qstandardpaths.cpp
-        ../../corelib/kernel/qcoreapplication.cpp
-        ../../corelib/kernel/qcoreglobaldata.cpp
-        ../../corelib/kernel/qiterable.cpp
-        ../../corelib/kernel/qmetacontainer.cpp
-        ../../corelib/kernel/qmetatype.cpp
-        ../../corelib/kernel/qsystemerror.cpp
-        ../../corelib/kernel/qvariant.cpp
-        ../../corelib/plugin/quuid.cpp
-        ../../corelib/serialization/qcborcommon.cpp
-        ../../corelib/serialization/qcborstreamwriter.cpp
-        ../../corelib/serialization/qcborvalue.cpp
-        ../../corelib/serialization/qdatastream.cpp
-        ../../corelib/serialization/qjsonarray.cpp
-        ../../corelib/serialization/qjsoncbor.cpp
-        ../../corelib/serialization/qjsondocument.cpp
-        ../../corelib/serialization/qjsonobject.cpp
-        ../../corelib/serialization/qjsonparser.cpp
-        ../../corelib/serialization/qjsonvalue.cpp
-        ../../corelib/serialization/qjsonwriter.cpp
-        ../../corelib/serialization/qtextstream.cpp
-        ../../corelib/text/qbytearray.cpp
-        ../../corelib/text/qbytearraylist.cpp
-        ../../corelib/text/qbytearraymatcher.cpp
-        ../../corelib/text/qlocale.cpp
-        ../../corelib/text/qlocale_tools.cpp
-        ../../corelib/text/qregularexpression.cpp
-        ../../corelib/text/qstring.cpp
-        ../../corelib/text/qstringbuilder.cpp
-        ../../corelib/text/qstringconverter.cpp
-        ../../corelib/text/qstringlist.cpp
-        ../../corelib/text/qvsnprintf.cpp
-        ../../corelib/time/qcalendar.cpp
-        ../../corelib/time/qdatetime.cpp
-        ../../corelib/time/qgregoriancalendar.cpp
-        ../../corelib/time/qromancalendar.cpp
-        ../../corelib/tools/qarraydata.cpp
-        ../../corelib/tools/qbitarray.cpp
-        ../../corelib/tools/qcommandlineoption.cpp
-        ../../corelib/tools/qcommandlineparser.cpp
-        ../../corelib/tools/qcryptographichash.cpp
-        ../../corelib/tools/qhash.cpp
-        ../../corelib/tools/qringbuffer.cpp
-        ../../corelib/tools/qversionnumber.cpp
+        ${source_root}/corelib/global/qendian.cpp
+        ${source_root}/corelib/global/qfloat16.cpp
+        ${source_root}/corelib/global/qglobal.cpp
+        ${source_root}/corelib/global/qlogging.cpp
+        ${source_root}/corelib/global/qmalloc.cpp
+        ${source_root}/corelib/global/qnumeric.cpp
+        ${source_root}/corelib/global/qoperatingsystemversion.cpp
+        ${source_root}/corelib/global/qrandom.cpp
+        ${source_root}/corelib/io/qabstractfileengine.cpp
+        ${source_root}/corelib/io/qbuffer.cpp
+        ${source_root}/corelib/io/qdebug.cpp
+        ${source_root}/corelib/io/qdir.cpp
+        ${source_root}/corelib/io/qdiriterator.cpp
+        ${source_root}/corelib/io/qfile.cpp
+        ${source_root}/corelib/io/qfiledevice.cpp
+        ${source_root}/corelib/io/qfileinfo.cpp
+        ${source_root}/corelib/io/qfilesystemengine.cpp
+        ${source_root}/corelib/io/qfilesystementry.cpp
+        ${source_root}/corelib/io/qfsfileengine.cpp
+        ${source_root}/corelib/io/qfsfileengine_iterator.cpp
+        ${source_root}/corelib/io/qiodevice.cpp
+        ${source_root}/corelib/io/qloggingcategory.cpp
+        ${source_root}/corelib/io/qloggingregistry.cpp
+        ${source_root}/corelib/io/qresource.cpp
+        ${source_root}/corelib/io/qsavefile.cpp
+        ${source_root}/corelib/io/qstandardpaths.cpp
+        ${source_root}/corelib/kernel/qcoreapplication.cpp
+        ${source_root}/corelib/kernel/qcoreglobaldata.cpp
+        ${source_root}/corelib/kernel/qiterable.cpp
+        ${source_root}/corelib/kernel/qmetacontainer.cpp
+        ${source_root}/corelib/kernel/qmetatype.cpp
+        ${source_root}/corelib/kernel/qsystemerror.cpp
+        ${source_root}/corelib/kernel/qvariant.cpp
+        ${source_root}/corelib/plugin/quuid.cpp
+        ${source_root}/corelib/serialization/qcborcommon.cpp
+        ${source_root}/corelib/serialization/qcborstreamwriter.cpp
+        ${source_root}/corelib/serialization/qcborvalue.cpp
+        ${source_root}/corelib/serialization/qdatastream.cpp
+        ${source_root}/corelib/serialization/qjsonarray.cpp
+        ${source_root}/corelib/serialization/qjsoncbor.cpp
+        ${source_root}/corelib/serialization/qjsondocument.cpp
+        ${source_root}/corelib/serialization/qjsonobject.cpp
+        ${source_root}/corelib/serialization/qjsonparser.cpp
+        ${source_root}/corelib/serialization/qjsonvalue.cpp
+        ${source_root}/corelib/serialization/qjsonwriter.cpp
+        ${source_root}/corelib/serialization/qtextstream.cpp
+        ${source_root}/corelib/text/qbytearray.cpp
+        ${source_root}/corelib/text/qbytearraylist.cpp
+        ${source_root}/corelib/text/qbytearraymatcher.cpp
+        ${source_root}/corelib/text/qlocale.cpp
+        ${source_root}/corelib/text/qlocale_tools.cpp
+        ${source_root}/corelib/text/qregularexpression.cpp
+        ${source_root}/corelib/text/qstring.cpp
+        ${source_root}/corelib/text/qstringbuilder.cpp
+        ${source_root}/corelib/text/qstringconverter.cpp
+        ${source_root}/corelib/text/qstringlist.cpp
+        ${source_root}/corelib/text/qvsnprintf.cpp
+        ${source_root}/corelib/time/qcalendar.cpp
+        ${source_root}/corelib/time/qdatetime.cpp
+        ${source_root}/corelib/time/qgregoriancalendar.cpp
+        ${source_root}/corelib/time/qromancalendar.cpp
+        ${source_root}/corelib/tools/qarraydata.cpp
+        ${source_root}/corelib/tools/qbitarray.cpp
+        ${source_root}/corelib/tools/qcommandlineoption.cpp
+        ${source_root}/corelib/tools/qcommandlineparser.cpp
+        ${source_root}/corelib/tools/qcryptographichash.cpp
+        ${source_root}/corelib/tools/qhash.cpp
+        ${source_root}/corelib/tools/qringbuffer.cpp
+        ${source_root}/corelib/tools/qversionnumber.cpp
     DEFINES
         HAVE_CONFIG_H
         QT_TYPESAFE_FLAGS