Make Android detection more robust

Our only way to detect whether the user requests an Android build of Qt
was to peek into the CMake toolchain file if it is specified.  If the
toolchain file contains a certain magic string, we decide that we're
building for Android.

This approach is fragile and bound to break should the Android toolchain
file's magic string ever change.

Now, we assume an Android build if any of our ANDROID_* cache variables
is set. In that case, we do not peek into the toolchain file.

Pick-to: 6.2
Fixes: QTBUG-94955
Change-Id: Ie2f0ac0963f90f09805e311111bb6912d4325ada
Reviewed-by: Alexandru Croitor <alexandru.croitor@qt.io>

1 files changed, 22 insertions, 11 deletions

diff --git a/cmake/QtAutoDetect.cmake b/cmake/QtAutoDetect.cmake
index d79d515ed3..fdd49b95f6 100644
--- a/cmake/QtAutoDetect.cmake
+++ b/cmake/QtAutoDetect.cmake
@@ -73,6 +73,17 @@ function(qt_auto_detect_cmake_generator)
 endfunction()
 
 function(qt_auto_detect_android)
+    # We assume an Android build if any of the ANDROID_* cache variables are set.
+    if(DEFINED ANDROID_SDK_ROOT
+            OR DEFINED ANDROID_NDK_ROOT
+            OR DEFINED ANDROID_ABI
+            OR DEFINED ANDROID_NATIVE_ABI_LEVEL
+            OR DEFINED ANDROID_STL)
+        set(android_detected TRUE)
+    else()
+        set(android_detected FALSE)
+    endif()
+
     # Auto-detect NDK root
     if(NOT DEFINED ANDROID_NDK_ROOT AND DEFINED ANDROID_SDK_ROOT)
         file(GLOB ndk_versions LIST_DIRECTORIES true RELATIVE "${ANDROID_SDK_ROOT}/ndk"
@@ -113,24 +124,24 @@ function(qt_auto_detect_android)
         endif()
     endif()
 
-    if("${CMAKE_TOOLCHAIN_FILE}" STREQUAL ""
-            AND (DEFINED ANDROID_ABI OR DEFINED ANDROID_NATIVE_API_LEVEL))
+    if(NOT DEFINED CMAKE_TOOLCHAIN_FILE AND android_detected)
         message(FATAL_ERROR "An Android build was requested, but no Android toolchain file was "
             "specified nor detected.")
     endif()
 
     if(DEFINED CMAKE_TOOLCHAIN_FILE AND NOT DEFINED QT_AUTODETECT_ANDROID)
-
-        file(READ ${CMAKE_TOOLCHAIN_FILE} toolchain_file_content OFFSET 0 LIMIT 80)
-        string(FIND "${toolchain_file_content}" "The Android Open Source Project" find_result REVERSE)
-        if (NOT ${find_result} EQUAL -1)
-            set(android_detected TRUE)
-        else()
-            set(android_detected FALSE)
+        # Peek into the toolchain file and check if it looks like an Android one.
+        if(NOT android_detected)
+            file(READ ${CMAKE_TOOLCHAIN_FILE} toolchain_file_content OFFSET 0 LIMIT 80)
+            string(FIND "${toolchain_file_content}" "The Android Open Source Project"
+                find_result REVERSE)
+            if(NOT ${find_result} EQUAL -1)
+                set(android_detected TRUE)
+            endif()
         endif()
 
         if(android_detected)
-            message(STATUS "Android toolchain file detected, checking configuration defaults...")
+            message(STATUS "Android build detected, checking configuration defaults...")
             if(NOT DEFINED ANDROID_NATIVE_API_LEVEL)
                 message(STATUS "ANDROID_NATIVE_API_LEVEL was not specified, using API level 23 as default")
                 set(ANDROID_NATIVE_API_LEVEL 23 CACHE STRING "")
@@ -141,7 +152,7 @@ function(qt_auto_detect_android)
         endif()
         set(QT_AUTODETECT_ANDROID ${android_detected} CACHE STRING "")
     elseif (QT_AUTODETECT_ANDROID)
-        message(STATUS "Android toolchain file detected")
+        message(STATUS "Android build detected")
     endif()
 endfunction()