CMake: Don't set QT_BUILDING_QT for single standalone tests

Standalone test projects have the following condition in the
beginning of their project:

 if(NOT QT_BUILD_STANDALONE_TESTS AND NOT QT_BUILDING_QT)
     find_package(Qt6BuildInternals COMPONENT STANDALONE_TEST)
 endif()

When configuring the project the first time, QT_BUILDING_QT is not
set, find_package is called, configuration succeeds.
But because standalone projects implicitly include QtSetup.cmake,
that file sets the QT_BUILDING_QT cache var to true, and upon test
reconfiguration, cmake errors out with:
 Unknown CMake command "qt_internal_add_test"
or similar.

This happens because QT_BUILDING_QT is true on the second
reconfiguration and the find_package mentioned above is not executed
anymore, leading to unknown internal command errors.

Set a new QT_INTERNAL_IS_STANDALONE_TEST variable when we detect
a standalone test and check for its value in QtSetup so we don't
set QT_BUILDING_QT to TRUE anymore.

Adjust a few code locations where QT_BUILDING_QT being false might
trigger different behavior for standalone tests.

Task-number: QTBUG-93020
Change-Id: I5413b9f37653225175a1006f7626e023045b5979
Reviewed-by: Qt CI Bot <qt_ci_bot@qt-project.org>
Reviewed-by: Joerg Bornemann <joerg.bornemann@qt.io>
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>
Reviewed-by: Amir Masoud Abdol <amir.abdol@qt.io>

cmake/QtBuildInternals/QtStandaloneTestTemplateProject/Main.cmake

@@ -2,6 +2,7 @@
 # SPDX-License-Identifier: BSD-3-Clause
 
 # Includes QtSetup and friends for private CMake API.
+set(QT_INTERNAL_IS_STANDALONE_TEST TRUE)
 qt_internal_project_setup()
 qt_build_internals_set_up_private_api()
 

cmake/QtSetup.cmake

@@ -3,10 +3,16 @@
 
 ## Set a default build type if none was specified
 
-# Set the QT_IS_BUILDING_QT variable so we can verify whether we are building
+# Set the QT_BUILDING_QT variable so we can verify whether we are building
-# Qt from source
+# Qt from source.
+# Make sure not to set it when building a standalone test, otherwise
+# upon reconfiguration we get an error about qt_internal_add_test
+# not being found due the if(NOT QT_BUILDING_QT) check we have
+# in each standalone test.
+if(NOT QT_INTERNAL_IS_STANDALONE_TEST)
     set(QT_BUILDING_QT TRUE CACHE BOOL
         "When this is present and set to true, it signals that we are building Qt from source.")
+endif()
 
 # Pre-calculate the developer_build feature if it's set by the user via INPUT_developer_build
 if(NOT FEATURE_developer_build AND INPUT_developer_build

src/corelib/Qt6AndroidMacros.cmake

@@ -898,7 +898,7 @@ endfunction()
 # It doesn't overwrite public properties, but instead writes formatted values to internal
 # properties.
 function(_qt_internal_android_format_deployment_paths target)
-    if(QT_BUILD_STANDALONE_TESTS OR QT_BUILDING_QT)
+    if(QT_BUILD_STANDALONE_TESTS OR QT_BUILDING_QT OR QT_INTERNAL_IS_STANDALONE_TEST)
         set(android_deployment_paths_policy NEW)
     else()
         __qt_internal_setup_policy(QTP0002 "6.6.0"
@@ -1008,7 +1008,7 @@ function(_qt_internal_get_android_abi_cmake_dir_path out_path abi)
     else()
         _qt_internal_get_android_abi_prefix_path(prefix_path ${abi})
         if((PROJECT_NAME STREQUAL "QtBase" OR QT_SUPERBUILD) AND QT_BUILDING_QT AND
-            NOT QT_BUILD_STANDALONE_TESTS)
+            NOT QT_BUILD_STANDALONE_TESTS AND NOT QT_INTERNAL_IS_STANDALONE_TEST)
             set(cmake_dir "${QT_CONFIG_BUILD_DIR}")
         else()
             set(cmake_dir "${prefix_path}/${QT6_INSTALL_LIBS}/cmake")