Re-order C/C++/Fortran compiler determination logic

Re-organize CMakeDetermine(C|CXX|Fortran)Compiler.cmake to search for
the compiler command-line tool only under generators for which it makes
sense.  For the Visual Studio generators we do not expect to find the
compiler tool from the environment, nor would we use the result anyway.

Furthermore, set CMAKE_${lang}_COMPILER_ID_TEST_FLAGS only when it has a
chance to be used.  Extract _CMAKE_TOOLCHAIN_LOCATION from the compiler
path after running the compiler id step so in the future that step can
help find the path to the compiler.

1 files changed, 59 insertions, 58 deletions

diff --git a/Modules/CMakeDetermineCCompiler.cmake b/Modules/CMakeDetermineCCompiler.cmake
index 171eadd..3ce1a36 100644
--- a/Modules/CMakeDetermineCCompiler.cmake
+++ b/Modules/CMakeDetermineCCompiler.cmake
@@ -39,76 +39,68 @@ if(NOT CMAKE_C_COMPILER_NAMES)
   set(CMAKE_C_COMPILER_NAMES cc)
 endif()
 
-if(NOT CMAKE_C_COMPILER)
-  set(CMAKE_C_COMPILER_INIT NOTFOUND)
-
-  # prefer the environment variable CC
-  if($ENV{CC} MATCHES ".+")
-    get_filename_component(CMAKE_C_COMPILER_INIT $ENV{CC} PROGRAM PROGRAM_ARGS CMAKE_C_FLAGS_ENV_INIT)
-    if(CMAKE_C_FLAGS_ENV_INIT)
-      set(CMAKE_C_COMPILER_ARG1 "${CMAKE_C_FLAGS_ENV_INIT}" CACHE STRING "First argument to C compiler")
+if(${CMAKE_GENERATOR} MATCHES "Visual Studio")
+  set(CMAKE_C_COMPILER_ID_RUN 1)
+  set(CMAKE_C_PLATFORM_ID "Windows")
+  set(CMAKE_C_COMPILER_ID "MSVC")
+  set(CMAKE_C_COMPILER "${CMAKE_GENERATOR_CC}")
+else()
+  if(NOT CMAKE_C_COMPILER)
+    set(CMAKE_C_COMPILER_INIT NOTFOUND)
+
+    # prefer the environment variable CC
+    if($ENV{CC} MATCHES ".+")
+      get_filename_component(CMAKE_C_COMPILER_INIT $ENV{CC} PROGRAM PROGRAM_ARGS CMAKE_C_FLAGS_ENV_INIT)
+      if(CMAKE_C_FLAGS_ENV_INIT)
+        set(CMAKE_C_COMPILER_ARG1 "${CMAKE_C_FLAGS_ENV_INIT}" CACHE STRING "First argument to C compiler")
+      endif()
+      if(NOT EXISTS ${CMAKE_C_COMPILER_INIT})
+        message(FATAL_ERROR "Could not find compiler set in environment variable CC:\n$ENV{CC}.")
+      endif()
     endif()
-    if(NOT EXISTS ${CMAKE_C_COMPILER_INIT})
-      message(FATAL_ERROR "Could not find compiler set in environment variable CC:\n$ENV{CC}.")
+
+    # next try prefer the compiler specified by the generator
+    if(CMAKE_GENERATOR_CC)
+      if(NOT CMAKE_C_COMPILER_INIT)
+        set(CMAKE_C_COMPILER_INIT ${CMAKE_GENERATOR_CC})
+      endif()
     endif()
-  endif()
 
-  # next try prefer the compiler specified by the generator
-  if(CMAKE_GENERATOR_CC)
+    # finally list compilers to try
     if(NOT CMAKE_C_COMPILER_INIT)
-      set(CMAKE_C_COMPILER_INIT ${CMAKE_GENERATOR_CC})
+      set(CMAKE_C_COMPILER_LIST ${_CMAKE_TOOLCHAIN_PREFIX}cc ${_CMAKE_TOOLCHAIN_PREFIX}gcc cl bcc xlc clang)
     endif()
-  endif()
 
-  # finally list compilers to try
-  if(NOT CMAKE_C_COMPILER_INIT)
-    set(CMAKE_C_COMPILER_LIST ${_CMAKE_TOOLCHAIN_PREFIX}cc ${_CMAKE_TOOLCHAIN_PREFIX}gcc cl bcc xlc clang)
-  endif()
+    _cmake_find_compiler(C)
 
-  _cmake_find_compiler(C)
+  else()
 
-else()
+    # we only get here if CMAKE_C_COMPILER was specified using -D or a pre-made CMakeCache.txt
+    # (e.g. via ctest) or set in CMAKE_TOOLCHAIN_FILE
+    # if CMAKE_C_COMPILER is a list of length 2, use the first item as
+    # CMAKE_C_COMPILER and the 2nd one as CMAKE_C_COMPILER_ARG1
 
-  # we only get here if CMAKE_C_COMPILER was specified using -D or a pre-made CMakeCache.txt
-  # (e.g. via ctest) or set in CMAKE_TOOLCHAIN_FILE
-  # if CMAKE_C_COMPILER is a list of length 2, use the first item as
-  # CMAKE_C_COMPILER and the 2nd one as CMAKE_C_COMPILER_ARG1
-
-  list(LENGTH CMAKE_C_COMPILER _CMAKE_C_COMPILER_LIST_LENGTH)
-  if("${_CMAKE_C_COMPILER_LIST_LENGTH}" EQUAL 2)
-    list(GET CMAKE_C_COMPILER 1 CMAKE_C_COMPILER_ARG1)
-    list(GET CMAKE_C_COMPILER 0 CMAKE_C_COMPILER)
-  endif()
+    list(LENGTH CMAKE_C_COMPILER _CMAKE_C_COMPILER_LIST_LENGTH)
+    if("${_CMAKE_C_COMPILER_LIST_LENGTH}" EQUAL 2)
+      list(GET CMAKE_C_COMPILER 1 CMAKE_C_COMPILER_ARG1)
+      list(GET CMAKE_C_COMPILER 0 CMAKE_C_COMPILER)
+    endif()
 
-  # if a compiler was specified by the user but without path,
-  # now try to find it with the full path
-  # if it is found, force it into the cache,
-  # if not, don't overwrite the setting (which was given by the user) with "NOTFOUND"
-  # if the C compiler already had a path, reuse it for searching the CXX compiler
-  get_filename_component(_CMAKE_USER_C_COMPILER_PATH "${CMAKE_C_COMPILER}" PATH)
-  if(NOT _CMAKE_USER_C_COMPILER_PATH)
-    find_program(CMAKE_C_COMPILER_WITH_PATH NAMES ${CMAKE_C_COMPILER})
-    mark_as_advanced(CMAKE_C_COMPILER_WITH_PATH)
-    if(CMAKE_C_COMPILER_WITH_PATH)
-      set(CMAKE_C_COMPILER ${CMAKE_C_COMPILER_WITH_PATH} CACHE STRING "C compiler" FORCE)
+    # if a compiler was specified by the user but without path,
+    # now try to find it with the full path
+    # if it is found, force it into the cache,
+    # if not, don't overwrite the setting (which was given by the user) with "NOTFOUND"
+    # if the C compiler already had a path, reuse it for searching the CXX compiler
+    get_filename_component(_CMAKE_USER_C_COMPILER_PATH "${CMAKE_C_COMPILER}" PATH)
+    if(NOT _CMAKE_USER_C_COMPILER_PATH)
+      find_program(CMAKE_C_COMPILER_WITH_PATH NAMES ${CMAKE_C_COMPILER})
+      mark_as_advanced(CMAKE_C_COMPILER_WITH_PATH)
+      if(CMAKE_C_COMPILER_WITH_PATH)
+        set(CMAKE_C_COMPILER ${CMAKE_C_COMPILER_WITH_PATH} CACHE STRING "C compiler" FORCE)
+      endif()
     endif()
   endif()
-endif()
-mark_as_advanced(CMAKE_C_COMPILER)
-
-if (NOT _CMAKE_TOOLCHAIN_LOCATION)
-  get_filename_component(_CMAKE_TOOLCHAIN_LOCATION "${CMAKE_C_COMPILER}" PATH)
-endif ()
-
-# Build a small source file to identify the compiler.
-if(${CMAKE_GENERATOR} MATCHES "Visual Studio")
-  set(CMAKE_C_COMPILER_ID_RUN 1)
-  set(CMAKE_C_PLATFORM_ID "Windows")
-  set(CMAKE_C_COMPILER_ID "MSVC")
-endif()
-
-if(NOT CMAKE_C_COMPILER_ID_RUN)
-  set(CMAKE_C_COMPILER_ID_RUN 1)
+  mark_as_advanced(CMAKE_C_COMPILER)
 
   # Each entry in this list is a set of extra flags to try
   # adding to the compile line to see if it helps produce
@@ -120,6 +112,11 @@ if(NOT CMAKE_C_COMPILER_ID_RUN)
     # Try enabling ANSI mode on HP.
     "-Aa"
     )
+endif()
+
+# Build a small source file to identify the compiler.
+if(NOT CMAKE_C_COMPILER_ID_RUN)
+  set(CMAKE_C_COMPILER_ID_RUN 1)
 
   # Try to identify the compiler.
   set(CMAKE_C_COMPILER_ID)
@@ -139,6 +136,10 @@ if(NOT CMAKE_C_COMPILER_ID_RUN)
   endif()
 endif()
 
+if (NOT _CMAKE_TOOLCHAIN_LOCATION)
+  get_filename_component(_CMAKE_TOOLCHAIN_LOCATION "${CMAKE_C_COMPILER}" PATH)
+endif ()
+
 # If we have a gcc cross compiler, they have usually some prefix, like
 # e.g. powerpc-linux-gcc, arm-elf-gcc or i586-mingw32msvc-gcc, optionally
 # with a 3-component version number at the end (e.g. arm-eabi-gcc-4.5.2).