From 3d512d17567f365bfd5cc1132830ad814a006dc0 Mon Sep 17 00:00:00 2001
From: Alexandru Croitor <alexandru.croitor@qt.io>
Date: Wed, 23 Jun 2021 12:16:03 +0200
Subject: [PATCH] CMake: Fix 'Cannot find source file' error with older CMakes

Configuring a static qtdeclarative with CMake versions older than
3.18.0 fails at generation phase with

CMake Error at cmake/QtExecutableHelpers.cmake:28 (add_executable):
  Cannot find source file:

   some_path/some_target_plugin_imports_Gui.cpp

Marking the generated file as GENERATED explicitly solves the issue.

Change-Id: Ife0eba61a1aab4f988d9fe7e2217d30eb96774a7
Reviewed-by: Alexey Edelev <alexey.edelev@qt.io>
Reviewed-by: Joerg Bornemann <joerg.bornemann@qt.io>
(cherry picked from commit e2c6f2ba7ed72195d12e9882c174e59a53317097)
---
 cmake/QtExecutableHelpers.cmake | 12 ++++++++++--
 1 file changed, 10 insertions(+), 2 deletions(-)

diff --git a/cmake/QtExecutableHelpers.cmake b/cmake/QtExecutableHelpers.cmake
index db50f4554a9..fba57358032 100644
--- a/cmake/QtExecutableHelpers.cmake
+++ b/cmake/QtExecutableHelpers.cmake
@@ -240,7 +240,9 @@ function(qt_internal_add_executable name)
             set(class_names
                 "${class_names_regular}${class_names_separator}${class_names_current_project}")
 
-            file(GENERATE OUTPUT ${out_file} CONTENT
+            set(out_file_path "${CMAKE_CURRENT_BINARY_DIR}/${out_file}")
+
+            file(GENERATE OUTPUT "${out_file_path}" CONTENT
 "// This file is auto-generated. Do not edit.
 #include <QtPlugin>
 
@@ -248,8 +250,14 @@ Q_IMPORT_PLUGIN($<JOIN:${class_names},)\nQ_IMPORT_PLUGIN(>)
 "
                 CONDITION "$<NOT:$<STREQUAL:${class_names},>>"
             )
+
+            # CMake versions earlier than 3.18.0 can't find the generated file for some reason,
+            # failing at generation phase.
+            # Explicitly marking the file as GENERATED fixes the issue.
+            set_source_files_properties("${out_file_path}" PROPERTIES GENERATED TRUE)
+
             target_sources(${name} PRIVATE
-                "$<$<NOT:$<STREQUAL:${class_names},>>:${out_file}>"
+                "$<$<NOT:$<STREQUAL:${class_names},>>:${out_file_path}>"
             )
             target_link_libraries(${name} PRIVATE
                 "$<TARGET_PROPERTY:${lib},_qt_initial_repo_plugins>"