CMake: Choose better defaults for qt_add_plugin STATIC/SHARED

There was a recent behavior change where the public CMake API
qt_add_plugin API took into account the value of BUILD_SHARED_LIBS
to decide whether the plugin should be a static or shared library.

Instead, use the following new behavior

 - If no explicit option STATIC / SHARED option is passed, default to
   whatever flavor Qt was built as.
   Aka if Qt was configured with -shared, qt_add_plugin defaults
   to creating shared plugins. If it's a -static Qt, create static
   plugins.
 - If an explicit STATIC / SHARED option is set, override the default
   computed value with the given value.

As a result BUILD_SHARED_LIBS does not affect Qt plugins anymore. This
is more in line with Qt expectations.

Add SHARED as a new valid option to pass to qt_add_plugin (it wasn't
before).

Add tests to check for the above behavior.

Amends aa4a1006cbccbc180c600f9b4dc9e882bb5ed5ca

Fixes: QTBUG-92361
Task-number: QTBUG-88763
Change-Id: Iae806024ddd5cf10cfe58ddbcebd2818084b0bd7
Reviewed-by: Joerg Bornemann <joerg.bornemann@qt.io>
(cherry picked from commit d0c2425d791edd75e35cce65ddbcfaab9a7f16ed)
Reviewed-by: Qt Cherry-pick Bot <cherrypick_bot@qt-project.org>

2 files changed, 35 insertions, 4 deletions

diff --git a/src/corelib/Qt6CTestMacros.cmake b/src/corelib/Qt6CTestMacros.cmake
index 9062985ac0..5a96e15ea6 100644
--- a/src/corelib/Qt6CTestMacros.cmake
+++ b/src/corelib/Qt6CTestMacros.cmake
@@ -114,10 +114,19 @@ function(_qt_internal_set_up_test_run_environment testname)
 endfunction()
 
 # Checks if the test project can be built successfully.
+#
+# TESTNAME: a custom test name to use instead of the one derived from the source directory name
+# BUILD_OPTIONS: a list of -D style CMake definitions to pass to ctest's --build-options (which
+#                are ultimately passed to the CMake invocation of the test project)
 macro(_qt_internal_test_expect_pass _dir)
-  cmake_parse_arguments(_ARGS "" "BINARY" "" ${ARGN})
-  string(REPLACE "(" "_" testname "${_dir}")
-  string(REPLACE ")" "_" testname "${testname}")
+  cmake_parse_arguments(_ARGS "" "BINARY;TESTNAME" "BUILD_OPTIONS" ${ARGN})
+
+  if(_ARGS_TESTNAME)
+      set(testname "${_ARGS_TESTNAME}")
+  else()
+      string(REPLACE "(" "_" testname "${_dir}")
+      string(REPLACE ")" "_" testname "${testname}")
+  endif()
 
   set(__expect_pass__prefixes "${CMAKE_PREFIX_PATH}")
   string(REPLACE ";" "\;" __expect_pass__prefixes "${__expect_pass__prefixes}")
@@ -131,6 +140,7 @@ macro(_qt_internal_test_expect_pass _dir)
       --build-makeprogram "${CMAKE_MAKE_PROGRAM}"
       --build-project "${_dir}"
       --build-options "-DCMAKE_PREFIX_PATH=${__expect_pass__prefixes}" ${BUILD_OPTIONS_LIST}
+                      ${_ARGS_BUILD_OPTIONS}
       --test-command ${_ARGS_BINARY})
   add_test(${testname} ${CMAKE_CTEST_COMMAND} ${ctest_command_args})
   if(_ARGS_BINARY)
diff --git a/src/corelib/Qt6CoreMacros.cmake b/src/corelib/Qt6CoreMacros.cmake
index 9e9b0f1e56..3d1a10ff0a 100644
--- a/src/corelib/Qt6CoreMacros.cmake
+++ b/src/corelib/Qt6CoreMacros.cmake
@@ -1423,6 +1423,7 @@ endfunction()
 macro(_qt_internal_get_add_plugin_keywords option_args single_args multi_args)
     set(${option_args}
         STATIC
+        SHARED
     )
     set(${single_args}
         TYPE
@@ -1455,7 +1456,27 @@ function(qt6_add_plugin target)
         unset(arg_CLASSNAME)
     endif()
 
-    if (arg_STATIC OR NOT BUILD_SHARED_LIBS)
+    if(arg_STATIC AND arg_SHARED)
+        message(FATAL_ERROR
+            "Both STATIC and SHARED options were given. Only one of the two should be used."
+        )
+    endif()
+
+    # If no explicit STATIC/SHARED option is set, default to the flavor of the Qt build.
+    if(QT6_IS_SHARED_LIBS_BUILD)
+        set(create_static_plugin FALSE)
+    else()
+        set(create_static_plugin TRUE)
+    endif()
+
+    # Explicit option takes priority over the computed default.
+    if(arg_STATIC)
+        set(create_static_plugin TRUE)
+    elseif(arg_SHARED)
+        set(create_static_plugin FALSE)
+    endif()
+
+    if (create_static_plugin)
         add_library(${target} STATIC)
         target_compile_definitions(${target} PRIVATE QT_STATICPLUGIN)
     else()