CPack add necessary check to detect/warns/error on ABSOLUTE DESTINATION

The [usually] wrong usage of absolute DESTINATION in INSTALL rules
keeps popping-up on the ML. We shall have some way to:
  1) easily detect it.
  2) forbids this for some CPack generator like NSIS
In fact it should certainly be forbidden for *any* generators
when used on Windows but we may implements that on top of the current
patch.
The patch ask the task to the generated cmake_install.cmake scripts.
Those scripts are a little bit more complicated with that but
iff there are absolute DESTINATION. This cost nothing if relative
DESTINATION are used.
Two new vars are introduced (and documented to handle that):
CPACK_WARN_ON_ABSOLUTE_INSTALL_DESTINATION
and
CPACK_ERROR_ON_ABSOLUTE_INSTALL_DESTINATION

Source/CPack/cmCPackDocumentVariables.cxx

@@ -77,4 +77,20 @@ void cmCPackDocumentVariables::DefineVariables(cmake* cm)
          "which is done right before packaging the files."
          " The script is not called by e.g.: make install.", false,
          "Variables common to all CPack generators");
+
+  cm->DefineProperty
+        ("CPACK_WARN_ON_ABSOLUTE_INSTALL_DESTINATION", cmProperty::VARIABLE,
+         "Ask CPack to warn each time a file with absolute INSTALL"
+         " DESTINATION is encountered.",
+         "", false,
+         "Variables common to all CPack generators");
+
+  cm->DefineProperty
+        ("CPACK_ERROR_ON_ABSOLUTE_INSTALL_DESTINATION", cmProperty::VARIABLE,
+         "Ask CPack to error out as soon as a file with absolute INSTALL"
+         " DESTINATION is encountered",
+         "The fatal error is emitted before the installation of "
+         "the offending file takes place. Some CPack generators, like NSIS,"
+         "enforce this internally.", false,
+         "Variables common to all CPack generators");
 }

Source/CPack/cmCPackGenerator.cxx

@@ -849,8 +849,27 @@ int cmCPackGenerator::InstallProjectViaInstallCMakeProjects(
           filesBefore = glB.GetFiles();
           std::sort(filesBefore.begin(),filesBefore.end());
           }
+
+        // If CPack was asked to warn on ABSOLUTE INSTALL DESTINATION
+        // then forward request to cmake_install.cmake script
+        if (this->GetOption("CPACK_WARN_ON_ABSOLUTE_INSTALL_DESTINATION"))
+          {
+            mf->AddDefinition("CPACK_WARN_ON_ABSOLUTE_INSTALL_DESTINATION",
+                              "1");
+          }
+        // If current CPack generator does support
+        // ABSOLUTE INSTALL DESTINATION or CPack has been asked for
+        // then ask cmake_install.cmake script to error out
+        // as soon as it occurs (before installing file)
+        if (!SupportsAbsoluteDestination() ||
+            this->GetOption("CPACK_ERROR_ON_ABSOLUTE_INSTALL_DESTINATION"))
+          {
+            mf->AddDefinition("CPACK_ERROR_ON_ABSOLUTE_INSTALL_DESTINATION",
+                              "1");
+          }
         // do installation
         int res = mf->ReadListFile(0, installFile.c_str());
+
         // Now rebuild the list of files after installation
         // of the current component (if we are in component install)
         if (componentInstall)
@@ -1460,6 +1479,12 @@ cmCPackGenerator::SupportsSetDestdir() const
   return cmCPackGenerator::SETDESTDIR_SUPPORTED;
 }
 
+//----------------------------------------------------------------------
+bool cmCPackGenerator::SupportsAbsoluteDestination() const
+{
+  return true;
+}
+
 //----------------------------------------------------------------------
 bool cmCPackGenerator::SupportsComponentInstallation() const
 {

Source/CPack/cmCPackGenerator.h

@@ -206,12 +206,21 @@ protected:
 
   /**
    * Does the CPack generator support CPACK_SET_DESTDIR?
-   * The default legacy value is 'true' generator
+   * The default legacy value is 'SETDESTDIR_SUPPORTED' generator
    * have to override it in order change this.
    * @return CPackSetDestdirSupport
    */
   virtual enum CPackSetDestdirSupport SupportsSetDestdir() const;
 
+  /**
+   * Does the CPack generator support absolute path
+   * in INSTALL DESTINATION?
+   * The default legacy value is 'true' generator
+   * have to override it in order change this.
+   * @return true if supported false otherwise
+   */
+  virtual bool SupportsAbsoluteDestination() const;
+
   /**
    * Does the CPack generator support component installation?.
    * Some Generators requires the user to set

Source/CPack/cmCPackNSISGenerator.cxx

@@ -638,6 +638,12 @@ cmCPackNSISGenerator::SupportsSetDestdir() const
   return cmCPackGenerator::SETDESTDIR_SHOULD_NOT_BE_USED;
 }
 
+//----------------------------------------------------------------------
+bool cmCPackNSISGenerator::SupportsAbsoluteDestination() const
+{
+        return false;
+}
+
 //----------------------------------------------------------------------
 bool cmCPackNSISGenerator::SupportsComponentInstallation() const
 {

Source/CPack/cmCPackNSISGenerator.h

@@ -45,6 +45,7 @@ protected:
     std::vector<std::string>& dirs);
 
   enum cmCPackGenerator::CPackSetDestdirSupport SupportsSetDestdir() const;
+  virtual bool SupportsAbsoluteDestination() const;
   virtual bool SupportsComponentInstallation() const;
 
   /// Produce a string that contains the NSIS code to describe a

Source/cmInstallGenerator.cxx

@@ -80,6 +80,15 @@ void cmInstallGenerator
                  }
              }
      os << "\")\n";
+     os << indent << "IF (CPACK_WARN_ON_ABSOLUTE_INSTALL_DESTINATION)\n";
+     os << indent << indent << "message(WARNING \"ABSOLUTE path INSTALL "
+        << "DESTINATION : ${CPACK_ABSOLUTE_DESTINATION_FILES}\")\n";
+     os << indent << "ENDIF (CPACK_WARN_ON_ABSOLUTE_INSTALL_DESTINATION)\n";
+
+     os << indent << "IF (CPACK_ERROR_ON_ABSOLUTE_INSTALL_DESTINATION)\n";
+     os << indent << indent << "message(FATAL_ERROR \"ABSOLUTE path INSTALL "
+        << "DESTINATION forbidden (by CPack): ${CPACK_ABSOLUTE_DESTINATION_FILES}\")\n";
+     os << indent << "ENDIF (CPACK_ERROR_ON_ABSOLUTE_INSTALL_DESTINATION)\n";
      }
   os << "FILE(INSTALL DESTINATION \"" << dest << "\" TYPE " << stype.c_str();
   if(optional)