Fix the detection of platform definitions directory

Platform definition directory is defined when building qtbase.
Depending on the build type (prefixed/non-prefixed) it should point:
  - To the source directory when building prefixed qtbase.
  - To the installation directory of the prefixed qtbase when building
consumer projects.
  - To the build directory of non-prefixed qtbase when building
non-prefixed qtbase or consumer projects.

TODO: It is desirable to move the logic asssociated with Qt platform
definition to the qt_internal_setup_public_platform_target function.

Fixes: QTBUG-94973
Change-Id: I8530613f9b2029834c66206bbdf02475528a4640
Reviewed-by: Alexandru Croitor <alexandru.croitor@qt.io>
(cherry picked from commit 478f5fcde66a49b710c427447916a0ee0e4d9e0a)

2 files changed, 24 insertions, 16 deletions

diff --git a/cmake/QtBuild.cmake b/cmake/QtBuild.cmake
index 8547ff09d1..8ae9714fa1 100644
--- a/cmake/QtBuild.cmake
+++ b/cmake/QtBuild.cmake
@@ -331,21 +331,30 @@ else()
     set(QT_QMAKE_HOST_MKSPEC "${QT_QMAKE_TARGET_MKSPEC}")
 endif()
 
-# Platform definition dir provided by user on command line.
-# Derive the absolute one relative to the current source dir.
-if(QT_PLATFORM_DEFINITION_DIR)
-    set(QT_DEFAULT_PLATFORM_DEFINITION_DIR "${QT_PLATFORM_DEFINITION_DIR}")
-    get_filename_component(
-        QT_DEFAULT_PLATFORM_DEFINITION_DIR_ABSOLUTE
-        "${QT_PLATFORM_DEFINITION_DIR}"
-        ABSOLUTE)
-elseif(QT_QMAKE_TARGET_MKSPEC)
-    # Used by consumers of prefix builds via INSTALL_INTERFACE (relative path).
-    set(QT_DEFAULT_PLATFORM_DEFINITION_DIR "${INSTALL_MKSPECSDIR}/${QT_QMAKE_TARGET_MKSPEC}")
-    # Used by qtbase itself and consumers of non-prefix builds via BUILD_INTERFACE (absolute path).
-    set(QT_DEFAULT_PLATFORM_DEFINITION_DIR_ABSOLUTE "${QT_MKSPECS_DIR}/${QT_QMAKE_TARGET_MKSPEC}")
+# Used by consumers of prefix builds via INSTALL_INTERFACE (relative path).
+set(QT_DEFAULT_PLATFORM_DEFINITION_DIR "${INSTALL_MKSPECSDIR}/${QT_QMAKE_TARGET_MKSPEC}")
+
+# Used by qtbase in prefix builds via BUILD_INTERFACE
+set(QT_PLATFORM_DEFINITION_BUILD_INTERFACE_BASE_DIR
+    "${CMAKE_CURRENT_LIST_DIR}/../mkspecs/"
+)
+
+# Used by qtbase and consumers in non-prefix builds via BUILD_INTERFACE
+if(NOT QT_WILL_INSTALL)
+    set(QT_PLATFORM_DEFINITION_BUILD_INTERFACE_BASE_DIR
+        "${CMAKE_BINARY_DIR}/${INSTALL_MKSPECSDIR}"
+    )
 endif()
 
+get_filename_component(QT_PLATFORM_DEFINITION_BUILD_INTERFACE_DIR
+    "${QT_PLATFORM_DEFINITION_BUILD_INTERFACE_BASE_DIR}/${QT_QMAKE_TARGET_MKSPEC}"
+    ABSOLUTE
+)
+set(QT_PLATFORM_DEFINITION_BUILD_INTERFACE_DIR
+    "${QT_PLATFORM_DEFINITION_BUILD_INTERFACE_DIR}"
+    CACHE INTERNAL "Path to directory that contains qplatformdefs.h"
+)
+
 if(NOT DEFINED QT_DEFAULT_PLATFORM_DEFINITIONS)
     set(QT_DEFAULT_PLATFORM_DEFINITIONS "")
 endif()
@@ -354,8 +363,7 @@ set(QT_PLATFORM_DEFINITIONS ${QT_DEFAULT_PLATFORM_DEFINITIONS}
     CACHE STRING "Qt platform specific pre-processor defines")
 set(QT_PLATFORM_DEFINITION_DIR "${QT_DEFAULT_PLATFORM_DEFINITION_DIR}"
     CACHE PATH "Path to directory that contains qplatformdefs.h")
-set(QT_PLATFORM_DEFINITION_DIR_ABSOLUTE "${QT_DEFAULT_PLATFORM_DEFINITION_DIR_ABSOLUTE}"
-    CACHE INTERNAL "Path to directory that contains qplatformdefs.h")
+
 set(QT_NAMESPACE "" CACHE STRING "Qt Namespace")
 if(QT_NAMESPACE STREQUAL "")
     set(QT_HAS_NAMESPACE OFF)
diff --git a/cmake/QtPublicTargetsHelpers.cmake b/cmake/QtPublicTargetsHelpers.cmake
index 39ba11b260..82e7354b1a 100644
--- a/cmake/QtPublicTargetsHelpers.cmake
+++ b/cmake/QtPublicTargetsHelpers.cmake
@@ -7,7 +7,7 @@ function(qt_internal_setup_public_platform_target)
     add_library(${INSTALL_CMAKE_NAMESPACE}::Platform ALIAS Platform)
     target_include_directories(Platform
         INTERFACE
-        $<BUILD_INTERFACE:${QT_PLATFORM_DEFINITION_DIR_ABSOLUTE}>
+        $<BUILD_INTERFACE:${QT_PLATFORM_DEFINITION_BUILD_INTERFACE_DIR}>
         $<BUILD_INTERFACE:${PROJECT_BINARY_DIR}/include>
         $<INSTALL_INTERFACE:${QT_PLATFORM_DEFINITION_DIR}>
         $<INSTALL_INTERFACE:${INSTALL_INCLUDEDIR}>