ENH: Handle missing unsetenv and add check for environ

Source/CMakeLists.txt

@@ -23,6 +23,23 @@ INCLUDE_DIRECTORIES(
 
 # let cmake know it is supposed to use it
 ADD_DEFINITIONS(-DCMAKE_BUILD_WITH_CMAKE)
+INCLUDE(CheckSymbolExists)
+CHECK_SYMBOL_EXISTS(unsetenv "stdlib.h" HAVE_UNSETENV)
+INCLUDE("${CMAKE_ROOT}/Modules/CheckCXXSourceCompiles.cmake")
+CHECK_CXX_SOURCE_COMPILES(
+  "int main(int argc, char* argv[]) { return sizeof(environ); }"
+  HAVE_ENVIRON_WITHOUT_SIGNATURE)
+IF(NOT HAVE_ENVIRON_WITHOUT_SIGNATURE)
+  CHECK_CXX_SOURCE_COMPILES(
+    "
+    #ifdef _WIN32
+    extern __declspec( dllimport ) char** environ;
+    #else
+    extern char** environ;
+    #endif
+    int main(int argc, char* argv[]) { return sizeof(environ); }"
+    HAVE_ENVIRON_WITH_SIGNATURE)
+ENDIF(NOT HAVE_ENVIRON_WITHOUT_SIGNATURE)
 
 OPTION(CMAKE_REGENERATE_YACCLEX
   "Regenerate YACC and LEXX files" OFF)

Source/cmSystemTools.cxx

@@ -56,7 +56,14 @@
 # pragma set woff 1375 /* base class destructor not virtual */
 #endif
 
-extern char** environ; // For GetEnvironmentVariables
+#if !defined(HAVE_ENVIRON_WITHOUT_SIGNATURE)
+// For GetEnvironmentVariables
+# if defined(_WIN32)
+extern __declspec( dllimport ) char** environ;
+# else
+extern char** environ;
+# endif
+#endif
 
 bool cmSystemTools::s_RunCommandHideConsole = false;
 bool cmSystemTools::s_DisableRunCommandOutput = false;
@@ -1280,9 +1287,17 @@ bool cmSystemTools::PutEnv(const char* value)
   return ret == 0;
 }
 
+#ifdef CMAKE_BUILD_WITH_CMAKE
 bool cmSystemTools::UnsetEnv(const char* value)
 {
-  return false;
+#if !defined(HAVE_UNSETENV)
+  std::string var = value;
+  var += "=";
+  return cmSystemTools::PutEnv(var.c_str());
+#else
+  unsetenv(value);
+  return true;
+#endif
 }
 
 std::vector<std::string> cmSystemTools::GetEnvironmentVariables()
@@ -1295,6 +1310,7 @@ std::vector<std::string> cmSystemTools::GetEnvironmentVariables()
     }
   return env;
 }
+#endif
 
 void cmSystemTools::EnableVSConsoleOutput()
 {

Source/cmSystemTools.h

@@ -295,11 +295,13 @@ public:
       of the form var=value */
   static bool PutEnv(const char* value);
 
+#ifdef CMAKE_BUILD_WITH_CMAKE
   /** Remove an environment variable */
   static bool UnsetEnv(const char* value);
 
   /** Get the list of all environment variables */
   static std::vector<std::string> GetEnvironmentVariables();
+#endif
 
   /** Setup the environment to enable VS 8 IDE output.  */
   static void EnableVSConsoleOutput();

Source/cmake.cxx

@@ -831,6 +831,7 @@ int cmake::ExecuteCMakeCommand(std::vector<std::string>& args)
       return 0;
       }
 
+#if defined(CMAKE_BUILD_WITH_CMAKE)
     // Command to create a symbolic link.  Fails on platforms not
     // supporting them.
     else if (args[1] == "environment" )
@@ -843,6 +844,7 @@ int cmake::ExecuteCMakeCommand(std::vector<std::string>& args)
         }
       return 0;
       }
+#endif
 
     // Remove file
     else if (args[1] == "remove" && args.size() > 2)