cmake: fix lapack

- added compile check with multiple tries for different configurations
- restored find_package(LAPACK)
- avoided modification of OPENCV_LINKER_LIBS

cmake/OpenCVFindLAPACK.cmake

-macro(_find_file_in_dirs VAR NAME DIRS)
-    find_path(${VAR} ${NAME} ${DIRS} NO_DEFAULT_PATH)
-    set(${VAR} ${${VAR}}/${NAME})
-    unset(${VAR} CACHE)
+macro(_find_header_file_in_dirs VAR NAME)
+  unset(${VAR})
+  unset(${VAR} CACHE)
+  if(" ${ARGN}" STREQUAL " ")
+    check_include_file("${NAME}" HAVE_${VAR})
+    if(HAVE_${VAR})
+      set(${VAR} "${NAME}") # fallback
+    else()
+      set(${VAR} "")
+    endif()
+  else()
+    find_path(${VAR} "${NAME}" ${ARGN} NO_DEFAULT_PATH)
+    if(${VAR})
+      set(${VAR} "${${VAR}}/${NAME}")
+      unset(${VAR} CACHE)
+    else()
+      unset(${VAR} CACHE)
+      set(${VAR} "")
+    endif()
+  endif()
+endmacro()
+
+macro(ocv_lapack_check)
+  string(REGEX REPLACE "[^a-zA-Z0-9_]" "_" _lapack_impl "${LAPACK_IMPL}")
+  message(STATUS "LAPACK(${LAPACK_IMPL}): LAPACK_LIBRARIES: ${LAPACK_LIBRARIES}")
+  _find_header_file_in_dirs(OPENCV_CBLAS_H_PATH_${_lapack_impl} "${LAPACK_CBLAS_H}" "${LAPACK_INCLUDE_DIR}")
+  _find_header_file_in_dirs(OPENCV_LAPACKE_H_PATH_${_lapack_impl} "${LAPACK_LAPACKE_H}" "${LAPACK_INCLUDE_DIR}")
+  if(NOT OPENCV_CBLAS_H_PATH_${_lapack_impl} OR NOT OPENCV_LAPACKE_H_PATH_${_lapack_impl})
+    message(WARNING "LAPACK(${LAPACK_IMPL}): CBLAS/LAPACK headers are not found in '${LAPACK_INCLUDE_DIR}'")
+    unset(LAPACK_LIBRARIES)
+  else()
+    # adding proxy opencv_lapack.h header
+    set(CBLAS_H_PROXY_PATH ${CMAKE_BINARY_DIR}/opencv_lapack.h)
+    set(_lapack_include_str "\#include \"${OPENCV_CBLAS_H_PATH_${_lapack_impl}}\"")
+    if(NOT "${OPENCV_CBLAS_H_PATH_${_lapack_impl}}" STREQUAL "${OPENCV_LAPACKE_H_PATH_${_lapack_impl}}")
+      set(_lapack_include_str "${_lapack_include_str}\n#include \"${OPENCV_LAPACKE_H_PATH_${_lapack_impl}}\"")
+    endif()
+    # update file contents (if required)
+    set(__content_str "")
+    if(EXISTS "${CBLAS_H_PROXY_PATH}")
+      file(READ "${CBLAS_H_PROXY_PATH}" __content_str)
+    endif()
+    if(NOT " ${__content_str}" STREQUAL " ${_lapack_include_str}")
+      file(WRITE "${CBLAS_H_PROXY_PATH}" "${_lapack_include_str}")
+    endif()
+
+    try_compile(__VALID_LAPACK
+        "${OpenCV_BINARY_DIR}"
+        "${OpenCV_SOURCE_DIR}/cmake/checks/lapack_check.cpp"
+        CMAKE_FLAGS "-DINCLUDE_DIRECTORIES:STRING=${LAPACK_INCLUDE_DIR}\;${CMAKE_BINARY_DIR}"
+                    "-DLINK_DIRECTORIES:STRING=${LAPACK_LINK_LIBRARIES}"
+                    "-DLINK_LIBRARIES:STRING=${LAPACK_LIBRARIES}"
+        OUTPUT_VARIABLE TRY_OUT
+    )
+    if(NOT __VALID_LAPACK)
+      #message(FATAL_ERROR "LAPACK: check build log:\n${TRY_OUT}")
+      message(STATUS "LAPACK(${LAPACK_IMPL}): Can't build LAPACK check code. This LAPACK version is not supported.")
+      unset(LAPACK_LIBRARIES)
+    else()
+      message(STATUS "LAPACK(${LAPACK_IMPL}): Support is enabled.")
+      ocv_include_directories(${LAPACK_INCLUDE_DIR})
+      set(HAVE_LAPACK 1)
+    endif()
+  endif()
 endmacro()
 
 if(WITH_LAPACK)
-    ocv_update(LAPACK_IMPL "Unknown")
-    if(NOT LAPACK_LIBRARIES)
-        include(cmake/OpenCVFindMKL.cmake)
-        if(HAVE_MKL)
-            set(LAPACK_INCLUDE_DIR  ${MKL_INCLUDE_DIRS})
-            set(LAPACK_LIBRARIES    ${MKL_LIBRARIES}   )
-            set(LAPACK_CBLAS_H      "mkl_cblas.h"      )
-            set(LAPACK_LAPACKE_H    "mkl_lapack.h"    )
-            set(LAPACK_IMPL         "MKL")
-        endif()
+  ocv_update(LAPACK_IMPL "Unknown")
+  if(NOT OPENCV_LAPACK_FIND_PACKAGE_ONLY)
+    if(NOT LAPACK_LIBRARIES AND NOT OPENCV_LAPACK_DISABLE_MKL)
+      include(cmake/OpenCVFindMKL.cmake)
+      if(HAVE_MKL)
+        set(LAPACK_INCLUDE_DIR  ${MKL_INCLUDE_DIRS})
+        set(LAPACK_LIBRARIES    ${MKL_LIBRARIES})
+        set(LAPACK_CBLAS_H      "mkl_cblas.h")
+        set(LAPACK_LAPACKE_H    "mkl_lapack.h")
+        set(LAPACK_IMPL         "MKL")
+        ocv_lapack_check()
+      endif()
     endif()
     if(NOT LAPACK_LIBRARIES)
-        include(cmake/OpenCVFindOpenBLAS.cmake)
-        if(OpenBLAS_FOUND)
-            set(LAPACK_INCLUDE_DIR  ${OpenBLAS_INCLUDE_DIR} )
-            set(LAPACK_LIBRARIES    ${OpenBLAS_LIB}         )
-            set(LAPACK_CBLAS_H      "cblas.h"      )
-            set(LAPACK_LAPACKE_H    "lapacke.h"    )
-            set(LAPACK_IMPL         "OpenBLAS")
-        endif()
+      include(cmake/OpenCVFindOpenBLAS.cmake)
+      if(OpenBLAS_FOUND)
+        set(LAPACK_INCLUDE_DIR  ${OpenBLAS_INCLUDE_DIR})
+        set(LAPACK_LIBRARIES    ${OpenBLAS_LIB})
+        set(LAPACK_CBLAS_H      "cblas.h")
+        set(LAPACK_LAPACKE_H    "lapacke.h")
+        set(LAPACK_IMPL         "OpenBLAS")
+        ocv_lapack_check()
+      endif()
     endif()
     if(NOT LAPACK_LIBRARIES AND UNIX)
-        include(cmake/OpenCVFindAtlas.cmake)
-        if(ATLAS_FOUND)
-            set(LAPACK_INCLUDE_DIR  ${Atlas_INCLUDE_DIR})
-            set(LAPACK_LIBRARIES    ${Atlas_LIBRARIES}  )
-            set(LAPACK_CBLAS_H      "cblas.h"      )
-            set(LAPACK_LAPACKE_H    "lapacke.h"    )
-            set(LAPACK_IMPL "Atlas")
-        endif()
+      include(cmake/OpenCVFindAtlas.cmake)
+      if(ATLAS_FOUND)
+        set(LAPACK_INCLUDE_DIR  ${Atlas_INCLUDE_DIR})
+        set(LAPACK_LIBRARIES    ${Atlas_LIBRARIES})
+        set(LAPACK_CBLAS_H      "cblas.h")
+        set(LAPACK_LAPACKE_H    "lapacke.h")
+        set(LAPACK_IMPL         "Atlas")
+        ocv_lapack_check()
+      endif()
     endif()
+  endif()
 
-    if(NOT LAPACK_LIBRARIES AND APPLE)
-        set(LAPACK_INCLUDE_DIR  "Accelerate")
-        set(LAPACK_LIBRARIES    "-framework Accelerate")
-        set(LAPACK_CBLAS_H      "cblas.h"      )
-        set(LAPACK_LAPACKE_H    "lapacke.h"    )
-        set(LAPACK_IMPL         "Apple")
+  if(NOT LAPACK_LIBRARIES)
+    if(WIN32 AND NOT OPENCV_LAPACK_SHARED_LIBS)
+      set(BLA_STATIC 1)
+    endif()
+    find_package(LAPACK)
+    if(LAPACK_FOUND)
+      if(NOT DEFINED LAPACKE_INCLUDE_DIR)
+        find_path(LAPACKE_INCLUDE_DIR "lapacke.h")
+      endif()
+      if(NOT DEFINED MKL_LAPACKE_INCLUDE_DIR)
+        find_path(MKL_LAPACKE_INCLUDE_DIR "mkl_lapack.h")
+      endif()
+      if(MKL_LAPACKE_INCLUDE_DIR AND NOT OPENCV_LAPACK_DISABLE_MKL)
+        set(LAPACK_INCLUDE_DIR  ${MKL_LAPACKE_INCLUDE_DIR})
+        set(LAPACK_CBLAS_H      "mkl_cblas.h")
+        set(LAPACK_LAPACKE_H    "mkl_lapack.h")
+        set(LAPACK_IMPL         "LAPACK/MKL")
+        ocv_lapack_check()
+      endif()
+      if(LAPACKE_INCLUDE_DIR AND NOT HAVE_LAPACK)
+        set(LAPACK_INCLUDE_DIR  ${LAPACKE_INCLUDE_DIR})
+        set(LAPACK_CBLAS_H      "cblas.h")
+        set(LAPACK_LAPACKE_H    "lapacke.h")
+        set(LAPACK_IMPL         "LAPACK/Generic")
+        ocv_lapack_check()
+      elseif(APPLE)
+        set(LAPACK_CBLAS_H      "Accelerate/Accelerate.h")
+        set(LAPACK_LAPACKE_H    "Accelerate/Accelerate.h")
+        set(LAPACK_IMPL         "LAPACK/Apple")
+        ocv_lapack_check()
+      else()
+        unset(LAPACK_LIBRARIES CACHE)
+      endif()
     endif()
+  endif()
 
-    set(LAPACK_INCLUDE_DIR  ${LAPACK_INCLUDE_DIR}            CACHE PATH      "Path to BLAS include dir" FORCE)
-    set(LAPACK_CBLAS_H      ${LAPACK_CBLAS_H}     CACHE STRING    "Alternative name of cblas.h" FORCE)
-    set(LAPACK_LAPACKE_H    ${LAPACK_LAPACKE_H}   CACHE STRING    "Alternative name of lapacke.h" FORCE)
-    set(LAPACK_LIBRARIES    ${LAPACK_LIBRARIES}            CACHE STRING    "Names of BLAS & LAPACK binaries (.so, .dll, .a, .lib)" FORCE)
-    set(LAPACK_IMPL ${LAPACK_IMPL} CACHE STRING "Lapack implementation id" FORCE)
+  if(NOT LAPACK_LIBRARIES AND APPLE AND NOT OPENCV_LAPACK_FIND_PACKAGE_ONLY)
+    set(LAPACK_INCLUDE_DIR  "")
+    set(LAPACK_LIBRARIES    "-framework Accelerate")
+    set(LAPACK_CBLAS_H      "Accelerate/Accelerate.h")
+    set(LAPACK_LAPACKE_H    "Accelerate/Accelerate.h")
+    set(LAPACK_IMPL         "Apple")
+    ocv_lapack_check()
+  endif()
 
-    if(LAPACK_LIBRARIES) #adding proxy cblas.h header
-        message(STATUS "LAPACK_IMPL: ${LAPACK_IMPL}, LAPACK_LIBRARIES: ${LAPACK_LIBRARIES}")
-        if("${LAPACK_IMPL}" STREQUAL "Apple")
-            set(CBLAS_H_PATH "Accelerate/Accelerate.h")
-            set(LAPACKE_H_PATH "Accelerate/Accelerate.h")
-        else()
-            _find_file_in_dirs(CBLAS_H_PATH "${LAPACK_CBLAS_H}" "${LAPACK_INCLUDE_DIR}")
-            _find_file_in_dirs(LAPACKE_H_PATH "${LAPACK_LAPACKE_H}" "${LAPACK_INCLUDE_DIR}")
-        endif()
-        if(NOT CBLAS_H_PATH OR NOT LAPACKE_H_PATH)
-            message(WARNING "CBLAS/LAPACK headers are not found in '${LAPACK_INCLUDE_DIR}'")
-        endif()
-        ocv_include_directories(${LAPACK_INCLUDE_DIR})
-        list(APPEND OPENCV_LINKER_LIBS ${LAPACK_LIBRARIES})
-        set(HAVE_LAPACK 1)
+  if(NOT HAVE_LAPACK AND LAPACK_LIBRARIES)
+    ocv_lapack_check()
+  endif()
 
-        set(CBLAS_H_PROXY_PATH ${CMAKE_BINARY_DIR}/opencv_lapack.h)
-        set(_include_str "\#include \"${CBLAS_H_PATH}\"")
-        if("${CBLAS_H_PATH}" STREQUAL "${LAPACKE_H_PATH}")
-        else()
-            set(_include_str "${_include_str}\n\#include \"${LAPACKE_H_PATH}\"")
-        endif()
-        file(WRITE ${CBLAS_H_PROXY_PATH} ${_include_str})
-    endif()
+  set(LAPACK_INCLUDE_DIR ${LAPACK_INCLUDE_DIR} CACHE PATH   "Path to BLAS include dir" FORCE)
+  set(LAPACK_CBLAS_H     ${LAPACK_CBLAS_H}     CACHE STRING "Alternative name of cblas.h" FORCE)
+  set(LAPACK_LAPACKE_H   ${LAPACK_LAPACKE_H}   CACHE STRING "Alternative name of lapacke.h" FORCE)
+  set(LAPACK_LIBRARIES   ${LAPACK_LIBRARIES}   CACHE STRING "Names of BLAS & LAPACK binaries (.so, .dll, .a, .lib)" FORCE)
+  set(LAPACK_IMPL        ${LAPACK_IMPL}        CACHE STRING "Lapack implementation id" FORCE)
 endif()

cmake/checks/lapack_check.cpp

+#include "opencv_lapack.h"
+
+static char* check_fn1 = (char*)sgesv_;
+static char* check_fn2 = (char*)sposv_;
+static char* check_fn3 = (char*)spotrf_;
+static char* check_fn4 = (char*)sgesdd_;
+
+int main(int argc, char* argv[])
+{
+    (void)argv;
+    if(argc > 1000)
+        return check_fn1[0] + check_fn2[0] + check_fn3[0] + check_fn4[0];
+    return 0;
+}

modules/core/CMakeLists.txt

 set(the_description "The Core Functionality")
 ocv_add_module(core
                "${OPENCV_HAL_LINKER_LIBS}"
-               PRIVATE_REQUIRED ${ZLIB_LIBRARIES} "${OPENCL_LIBRARIES}" "${VA_LIBRARIES}"
+               PRIVATE_REQUIRED ${ZLIB_LIBRARIES} "${OPENCL_LIBRARIES}" "${VA_LIBRARIES}" "${LAPACK_LIBRARIES}"
                OPTIONAL opencv_cudev
                WRAP java python)