From 57b94b58df474ebc268993291a669dbad21a1300 Mon Sep 17 00:00:00 2001
From: Alexandru Croitor <alexandru.croitor@qt.io>
Date: Thu, 13 Aug 2020 17:16:24 +0200
Subject: [PATCH] CMake: Allow opting out of global target promotion

The endless saga of fighting with qt_find_package and global target
promotion. In certain scenarios we want to opt out of target promotion
to global scope.

One such case is in qttools with WrapLibClang and Threads::Threads.
Threads::Threads will be found in the top-level scope via
Qt6Dependencies.
WrapLibClang is declared in src/ directory scope, and
then we try to promote it ands its dependencies to the global scope,
via qt_find_package() ->
qt_find_package_promote_targets_to_global_scope().

This fails because we can't promote Threads::Threads due to it being
added in a different subdirectory scope.

Introduce 2 new functions.
qt_internal_should_not_promote_package_target_to_global and
qt_internal_disable_find_package_global_promotion.

The first one is used to disable promotion of targets to global scope
in qt_find_package.

To mark a target not to be promoted, the second function is used.
It will be used by qttools for the WrapLibClang case.

Task-number: QTBUG-85877
Change-Id: If6caf10a94999402026517a623ae29e3ab1eeb7f
Reviewed-by: Joerg Bornemann <joerg.bornemann@qt.io>
---
 cmake/QtBuild.cmake | 21 +++++++++++++++++++--
 1 file changed, 19 insertions(+), 2 deletions(-)

diff --git a/cmake/QtBuild.cmake b/cmake/QtBuild.cmake
index 0ab5dc2ff4..4921391ebf 100644
--- a/cmake/QtBuild.cmake
+++ b/cmake/QtBuild.cmake
@@ -3318,7 +3318,12 @@ function(qt_internal_walk_libs target out_var dict_name operation)
 
                     get_property(is_imported TARGET ${lib_target_unaliased} PROPERTY IMPORTED)
                     get_property(is_global TARGET ${lib_target_unaliased} PROPERTY IMPORTED_GLOBAL)
-                    if(NOT is_global AND is_imported)
+
+                    # Allow opting out of promotion. This is useful in certain corner cases
+                    # like with WrapLibClang and Threads in qttools.
+                    qt_internal_should_not_promote_package_target_to_global(
+                        "${lib_target_unaliased}" should_not_promote)
+                    if(NOT is_global AND is_imported AND NOT should_not_promote)
                         set_property(TARGET ${lib_target_unaliased} PROPERTY IMPORTED_GLOBAL TRUE)
                     endif()
                 endif()
@@ -5649,7 +5654,9 @@ macro(qt_find_package)
 
                 get_property(is_global TARGET ${qt_find_package_target_name} PROPERTY
                                                                              IMPORTED_GLOBAL)
-                if(NOT is_global)
+                qt_internal_should_not_promote_package_target_to_global(
+                    "${qt_find_package_target_name}" should_not_promote)
+                if(NOT is_global AND NOT should_not_promote)
                     set_property(TARGET ${qt_find_package_target_name} PROPERTY
                                                                        IMPORTED_GLOBAL TRUE)
                     qt_find_package_promote_targets_to_global_scope(
@@ -6149,6 +6156,16 @@ function(qt_internal_strip_target_directory_scope_token target out_var)
     set("${out_var}" "${target}" PARENT_SCOPE)
 endfunction()
 
+# Sets out_var to to TRUE if the target was marked to not be promoted to global scope.
+function(qt_internal_should_not_promote_package_target_to_global target out_var)
+    get_property(should_not_promote TARGET "${target}" PROPERTY _qt_no_promote_global)
+    set("${out_var}" "${should_not_promote}" PARENT_SCOPE)
+endfunction()
+
+function(qt_internal_disable_find_package_global_promotion target)
+    set_target_properties("${target}" PROPERTIES _qt_no_promote_global TRUE)
+endfunction()
+
 include(QtApp)
 
 # Compatibility macros that should be removed once all their usages are removed.