CMake: Let configure guess the compiler from mkspec argument

The arguments -platform, -xplatform and -device determine the mkspec
that's used for the qmake companion files.

If the user specifies a mkspec that indicates usage of clang or icc,
set the respective CMake variables to use one of those compilers.

Fixes: QTBUG-87836
Change-Id: I2b10d819b0eb92a97d7f79672547b1e2d821cf33
Reviewed-by: Alexandru Croitor <alexandru.croitor@qt.io>

cmake/QtProcessConfigureArgs.cmake

@@ -47,6 +47,7 @@ list(TRANSFORM configure_args STRIP)
 list(TRANSFORM configure_args REPLACE "\\\\" "\\\\\\\\")
 unset(generator)
 set(auto_detect_generator TRUE)
+set(auto_detect_compiler TRUE)
 unset(device_options)
 set_property(GLOBAL PROPERTY UNHANDLED_ARGS "")
 while(configure_args)
@@ -57,6 +58,8 @@ while(configure_args)
         list(POP_FRONT configure_args generator)
     elseif(arg STREQUAL "-cmake-use-default-generator")
         set(auto_detect_generator FALSE)
+    elseif(arg STREQUAL "-no-guess-compiler")
+        set(auto_detect_compiler FALSE)
     elseif(arg STREQUAL "-skip")
         list(POP_FRONT configure_args qtrepo)
         push("-DBUILD_${qtrepo}=OFF")
@@ -552,6 +555,22 @@ macro(translate_list_input name cmake_var)
     endif()
 endmacro()
 
+function(guess_compiler_from_mkspec)
+    if(NOT auto_detect_compiler)
+        return()
+    endif()
+    string(REGEX MATCH "(^|;)-DQT_QMAKE_TARGET_MKSPEC=\([^;]+\)" m ${cmake_args})
+    set(mkspec ${CMAKE_MATCH_2})
+    if(mkspec MATCHES "-clang(-|$)")
+        push("-DCMAKE_C_COMPILER=clang")
+        push("-DCMAKE_CXX_COMPILER=clang++")
+    elseif(mkspec MATCHES "-icc(-|$)")
+        push("-DCMAKE_C_COMPILER=icc")
+        push("-DCMAKE_CXX_COMPILER=icpc")
+    endif()
+    set(cmake_args "${cmake_args}" PARENT_SCOPE)
+endfunction()
+
 drop_input(commercial)
 drop_input(confirm-license)
 translate_boolean_input(precompile_header BUILD_WITH_PCH)
@@ -576,6 +595,7 @@ if(NOT "${INPUT_device}" STREQUAL "")
 endif()
 translate_string_input(platform QT_QMAKE_TARGET_MKSPEC)
 translate_string_input(xplatform QT_QMAKE_TARGET_MKSPEC)
+guess_compiler_from_mkspec()
 translate_string_input(qpa_default_platform QT_QPA_DEFAULT_PLATFORM)
 translate_list_input(sanitize ECM_ENABLE_SANITIZERS)
 

config_help.txt

@@ -90,6 +90,8 @@ Build options:
                          CMake instead of auto-detecting one.
   -cmake-use-default-generator ... Turn off auto-detection of the CMake build
                          system generator.
+  -no-guess-compiler ... Do not guess the compiler from the target mkspec.
+                         Only applies to the CMake build.
   -release ............. Build Qt with debugging turned off [yes]
   -debug ............... Build Qt with debugging turned on [no]
   -debug-and-release ... Build two versions of Qt, with and without