hopefully this workaround of cmake bug #9220 works for MSVC too

blas/CMakeLists.txt

@@ -1,25 +1,19 @@
 
 project(EigenBlas CXX)
 
-if( NOT DEFINED EIGEN_Fortran_COMPILER_WORKS OR EIGEN_Fortran_COMPILER_WORKS)
+include("../cmake/language_support.cmake")
 
+workaround_9220(Fortran EIGEN_Fortran_COMPILER_WORKS)
+
+if(EIGEN_Fortran_COMPILER_WORKS)
   enable_language(Fortran OPTIONAL)
-
-  if(CMAKE_Fortran_COMPILER_WORKS)
-    set(EIGEN_Fortran_COMPILER_WORKS TRUE CACHE INTERNAL "workaround cmake's enable_language issue")
-  else()
-    set(EIGEN_Fortran_COMPILER_WORKS FALSE CACHE INTERNAL "workaround cmake's enable_language issue")
-  endif()
-  
 endif()
 
 add_custom_target(blas)
 
 set(EigenBlas_SRCS single.cpp double.cpp complex_single.cpp complex_double.cpp xerbla.cpp)
 
-if(CMAKE_Fortran_COMPILER_WORKS)
+if(EIGEN_Fortran_COMPILER_WORKS)
-
-message(WARNING " No fortran compiler has been detected, the blas build will be incomplete.")
 
 set(EigenBlas_SRCS ${EigenBlas_SRCS}
     complexdots.f
@@ -29,8 +23,11 @@ set(EigenBlas_SRCS ${EigenBlas_SRCS}
     zhbmv.f  zhpr.f   ztpmv.f chpmv.f  ctbmv.f  ctpsv.f    dsbmv.f  dspr.f   dtpmv.f   sspr2.f
     stbsv.f  zhpmv.f  ztbmv.f  ztpsv.f
 )
+else()
 
-endif(CMAKE_Fortran_COMPILER_WORKS)
+message(WARNING " No fortran compiler has been detected, the blas build will be incomplete.")
+
+endif()
 
 add_library(eigen_blas_static ${EigenBlas_SRCS})
 add_library(eigen_blas SHARED ${EigenBlas_SRCS})
@@ -47,7 +44,7 @@ install(TARGETS eigen_blas eigen_blas_static
         LIBRARY DESTINATION lib
         ARCHIVE DESTINATION lib)
 
-if(CMAKE_Fortran_COMPILER_WORKS)
+if(EIGEN_Fortran_COMPILER_WORKS)
 
 if(EIGEN_LEAVE_TEST_IN_ALL_TARGET)
   add_subdirectory(testing) # can't do EXCLUDE_FROM_ALL here, breaks CTest

cmake/language_support.cmake

@@ -0,0 +1,65 @@
+# cmake/modules/language_support.cmake
+#
+# Temporary additional general language support is contained within this
+# file.  
+
+# This additional function definition is needed to provide a workaround for
+# CMake bug 9220.
+
+# On debian testing (cmake 2.6.2), I get return code zero when calling 
+# cmake the first time, but cmake crashes when running a second time
+# as follows:
+#
+#  -- The Fortran compiler identification is unknown
+#  CMake Error at /usr/share/cmake-2.6/Modules/CMakeFortranInformation.cmake:7 (GET_FILENAME_COMPONENT):
+#    get_filename_component called with incorrect number of arguments
+#  Call Stack (most recent call first):
+#    CMakeLists.txt:3 (enable_language)
+#
+# My workaround is to invoke cmake twice.  If both return codes are zero, 
+# it is safe to invoke ENABLE_LANGUAGE(Fortran OPTIONAL)
+
+function(workaround_9220 language language_works)
+  #message("DEBUG: language = ${language}")
+  set(text
+    "project(test NONE)
+cmake_minimum_required(VERSION 2.6.0)
+enable_language(${language} OPTIONAL)
+"
+    )
+  file(REMOVE_RECURSE ${CMAKE_BINARY_DIR}/language_tests/${language})
+  file(MAKE_DIRECTORY ${CMAKE_BINARY_DIR}/language_tests/${language})
+  file(WRITE ${CMAKE_BINARY_DIR}/language_tests/${language}/CMakeLists.txt
+    ${text})
+  execute_process(
+    COMMAND ${CMAKE_COMMAND} .
+    WORKING_DIRECTORY ${CMAKE_BINARY_DIR}/language_tests/${language}
+    RESULT_VARIABLE return_code
+    OUTPUT_QUIET
+    ERROR_QUIET
+    )
+
+  if(return_code EQUAL 0)
+    # Second run
+    execute_process (
+      COMMAND ${CMAKE_COMMAND} .
+      WORKING_DIRECTORY ${CMAKE_BINARY_DIR}/language_tests/${language}
+      RESULT_VARIABLE return_code
+      OUTPUT_QUIET
+      ERROR_QUIET
+      )
+    if(return_code EQUAL 0)
+      set(${language_works} ON PARENT_SCOPE)
+    else(return_code EQUAL 0)
+      set(${language_works} OFF PARENT_SCOPE)
+    endif(return_code EQUAL 0)
+  else(return_code EQUAL 0)
+    set(${language_works} OFF PARENT_SCOPE)
+  endif(return_code EQUAL 0)
+endfunction(workaround_9220)
+
+# Temporary tests of the above function.
+#workaround_9220(CXX CXX_language_works)
+#message("CXX_language_works = ${CXX_language_works}")
+#workaround_9220(CXXp CXXp_language_works)
+#message("CXXp_language_works = ${CXXp_language_works}")

lapack/CMakeLists.txt

@@ -1,19 +1,14 @@
 
 project(EigenLapack CXX)
 
-if( NOT DEFINED EIGEN_Fortran_COMPILER_WORKS OR EIGEN_Fortran_COMPILER_WORKS)
+include("../cmake/language_support.cmake")
 
+workaround_9220(Fortran EIGEN_Fortran_COMPILER_WORKS)
+
+if(EIGEN_Fortran_COMPILER_WORKS)
   enable_language(Fortran OPTIONAL)
-
-  if(CMAKE_Fortran_COMPILER_WORKS)
-    set(EIGEN_Fortran_COMPILER_WORKS TRUE CACHE INTERNAL "workaround cmake's enable_language issue")
-  else()
-    set(EIGEN_Fortran_COMPILER_WORKS FALSE CACHE INTERNAL "workaround cmake's enable_language issue")
 endif()
 
-endif()
-
-
 add_custom_target(lapack)
 include_directories(../blas)
 
@@ -21,7 +16,7 @@ set(EigenLapack_SRCS
 single.cpp double.cpp complex_single.cpp complex_double.cpp ../blas/xerbla.cpp
 )
 
-if(CMAKE_Fortran_COMPILER_WORKS)
+if(EIGEN_Fortran_COMPILER_WORKS)
 
 get_filename_component(eigen_full_path_to_reference_to_reference_lapack "./reference/" ABSOLUTE)
 if(EXISTS ${eigen_full_path_to_reference_to_reference_lapack})
@@ -358,7 +353,7 @@ reference/ctbcon.f               reference/dormhr.f               reference/sla_
 )
 endif()
 
-endif(CMAKE_Fortran_COMPILER_WORKS)
+endif(EIGEN_Fortran_COMPILER_WORKS)
 
 add_library(eigen_lapack_static ${EigenLapack_SRCS})
 add_library(eigen_lapack SHARED ${EigenLapack_SRCS})