From 7acda93e64d34b16466c7e82cfd6582bae22face Mon Sep 17 00:00:00 2001 From: Craig Scott Date: Tue, 16 Mar 2021 12:27:53 +1100 Subject: Prevent static plugin triggering autogen dependency on reconfigure A call to file(WRITE) will unconditionally update the file's timestamp even if the file's contents don't change. The *Plugin.cpp file was being written using configure_file() which avoids that, but the .cpp.in file it was configuring from was being written out using file(WRITE) every time CMake ran. Autogen saw that file as a dependency and then regenerated the mocs_compilation.cpp file, which in turn results in unnecessary rebuilds and relinking when nothing is actually changing. The file(WRITE) - configure_file() dance is no longer needed anyway, since the generated *Plugin.cpp file is very simple with no substitutions required. Therefore, we can simplify that file's generation with a single file(WRITE) that only executes if the file contents will change or the file is missing. Change-Id: I2b7d1ff678b85ea7811969d656555592c9b6865f Reviewed-by: Joerg Bornemann (cherry picked from commit 63a0d263cf233ddf85a60678829298b50e8d1f26) Reviewed-by: Qt Cherry-pick Bot --- cmake/QtPlugins.cmake.in | 22 +++++++++++++++------- 1 file changed, 15 insertions(+), 7 deletions(-) (limited to 'cmake') diff --git a/cmake/QtPlugins.cmake.in b/cmake/QtPlugins.cmake.in index d6d5c829b2..c901f8c47d 100644 --- a/cmake/QtPlugins.cmake.in +++ b/cmake/QtPlugins.cmake.in @@ -119,15 +119,23 @@ if(NOT @BUILD_SHARED_LIBS@) set(_generated_qt_plugin_file_name "${CMAKE_CURRENT_BINARY_DIR}/qt_@QT_MODULE@_${target}.cpp") - set(_generated_qt_plugin_file_name_template "${_generated_qt_plugin_file_name}.in") set(_generated_qt_plugin_file_content "#include \nQ_IMPORT_PLUGIN(${_classname})") - # Generate a source file to import that plug-in. Has to be done with configure_file, - # because file(GENERATE) and target_sources has issues with scopes. - file(WRITE "${_generated_qt_plugin_file_name_template}" - "${_generated_qt_plugin_file_content}") - configure_file("${_generated_qt_plugin_file_name_template}" - "${_generated_qt_plugin_file_name}") + # Generate a source file to import that plug-in. Be careful not to + # update the timestamp of the generated file if we are not going to + # change anything. Otherwise we will trigger CMake's autogen to re-run + # and executables will then need to at least relink. + set(need_write TRUE) + if(EXISTS ${_generated_qt_plugin_file_name}) + file(READ ${_generated_qt_plugin_file_name} old_contents) + if(old_contents STREQUAL "${_generated_qt_plugin_file_content}") + set(need_write FALSE) + endif() + endif() + if(need_write) + file(WRITE "${_generated_qt_plugin_file_name}" + "${_generated_qt_plugin_file_content}") + endif() target_sources(${_module_target} INTERFACE "$<${_plugin_condition}:${_generated_qt_plugin_file_name}>") -- cgit v1.2.3