ENH: Improve handling of old-style compatibility.

  - Remove CMP_0001 (no slash in target name) and restore
    old CMAKE_BACKWARDS_COMPATIBILITY check for it
  - Replace all checks of CMAKE_BACKWARDS_COMPATIBILITY
    with cmLocalGenerator::NeedBackwardsCompatibility calls
  - Create new CMP_0001 to determine whether or not
    CMAKE_BACKWARDS_COMPATIBILITY is used.
    (old = use, new = ignore)
  - Show CMAKE_BACKWARDS_COMPATIBILITY in cache only when
    CMP_0001 is set to OLD or WARN
  - Update documentation of cmake_policy and cmake_minimum_required
    to indicate their relationship and the 2.4 version boundary
  - When no cmake policy version is set in top level makefile
    implicitly call cmake_policy(VERSION 2.4) which restores
    CMAKE_BACKWARDS_COMPATIBILITY and other 2.4 compatibility
  - Fix tests MakeClean and Preprocess to call
    cmake_policy(VERSION 2.6) because they depend on new policies

13 files changed, 128 insertions, 182 deletions

diff --git a/Source/cmAddCustomTargetCommand.cxx b/Source/cmAddCustomTargetCommand.cxx
index 07f00ea..9a3b4b3 100644
--- a/Source/cmAddCustomTargetCommand.cxx
+++ b/Source/cmAddCustomTargetCommand.cxx
@@ -21,18 +21,6 @@ bool cmAddCustomTargetCommand
 ::InitialPass(std::vector<std::string> const& args,
               cmExecutionStatus& status)
 {
-  // This enum must be before an enum is used in a switch statment. 
-  // If not there is an ICE on the itanium version of gcc we are running
-  // on dash8
-  
-  // Keep track of parser state.
-  enum tdoing {
-    doing_command,
-    doing_depends,
-    doing_working_directory,
-    doing_comment,
-    doing_verbatim
-  };
   if(args.size() < 1 )
     {
     this->SetError("called with incorrect number of arguments");
@@ -41,34 +29,20 @@ bool cmAddCustomTargetCommand
 
   // Check the target name.
   if(args[0].find_first_of("/\\") != args[0].npos)
-  {
-    // slashes are not allowed anymore in taret names CMP_0001
-    switch (this->Makefile->GetPolicyStatus(cmPolicies::CMP_0001))
     {
-      case cmPolicies::WARN:
-        this->Makefile->IssueWarning(
-          this->Makefile->GetPolicies()->GetPolicyWarning
-            (cmPolicies::CMP_0001));
-      case cmPolicies::OLD:
-//        if (this->Makefile->IsBWCompatibilityLessThan(2,2))
-//        {
-//          break;
-//        }
-      case cmPolicies::NEW:
-        this->SetError("You included a / or \\ in your target name and "
-          "this is not allowed according to policy CMP_0001. Run "
-          "cmake --help-policy CMP_0001 for more information.");
-        return false;
-      case cmPolicies::REQUIRED_IF_USED:
-      case cmPolicies::REQUIRED_ALWAYS:
-        this->Makefile->IssueError(
-          this->Makefile->GetPolicies()->GetRequiredPolicyError
-            (cmPolicies::CMP_0001).c_str()
-          );
-        return false;
+    if(!this->Makefile->NeedBackwardsCompatibility(2,2))
+      {
+      cmOStringStream e;
+      e << "called with invalid target name \"" << args[0]
+        << "\".  Target names may not contain a slash.  "
+        << "Use ADD_CUSTOM_COMMAND to generate files.  "
+        << "Set CMAKE_BACKWARDS_COMPATIBILITY to 2.2 "
+        << "or lower to skip this check.";
+      this->SetError(e.str().c_str());
+      return false;
+      }
     }
-  }
-    
+
   // Accumulate one command line at a time.
   cmCustomCommandLine currentLine;
 
@@ -83,6 +57,13 @@ bool cmAddCustomTargetCommand
   const char* comment = 0;
 
   // Keep track of parser state.
+  enum tdoing {
+    doing_command,
+    doing_depends,
+    doing_working_directory,
+    doing_comment,
+    doing_verbatim
+  };
   tdoing doing = doing_command;
 
   // Look for the ALL option.
diff --git a/Source/cmCMakeMinimumRequired.h b/Source/cmCMakeMinimumRequired.h
index d7a1b7e..25e77f3 100644
--- a/Source/cmCMakeMinimumRequired.h
+++ b/Source/cmCMakeMinimumRequired.h
@@ -70,6 +70,13 @@ public:
       "                         [FATAL_ERROR])\n"
       "If the current version of CMake is lower than that required "
       "it will stop processing the project and report an error.\n"
+      "When a version higher than 2.4 is specified the command implicitly "
+      "invokes\n"
+      "  cmake_policy(VERSION major[.minor[.patch]])\n"
+      "which sets the cmake policy version level to the version specified.\n"
+      "When version 2.4 or lower is given the command implicitly invokes\n"
+      "  cmake_policy(VERSION 2.4)\n"
+      "which enables compatibility features for CMake 2.4 and lower.\n"
       "The FATAL_ERROR option is accepted but ignored.  It is left from "
       "CMake versions 2.4 and lower in which failure to meet the minimum "
       "version was a warning by default.";
diff --git a/Source/cmCMakePolicyCommand.h b/Source/cmCMakePolicyCommand.h
index fcc207e..61f9dd4 100644
--- a/Source/cmCMakePolicyCommand.h
+++ b/Source/cmCMakePolicyCommand.h
@@ -76,7 +76,11 @@ public:
       "to WARN, which is like OLD but also produces a warning.  "
       "This effectively requests behavior preferred as of a given CMake "
       "version and tells newer CMake versions to warn about their new "
-      "policies."
+      "policies.  "
+      "The policy version specified must be at least 2.4 or the command "
+      "will report an error.  "
+      "In order to get compatibility features supporting versions earlier "
+      "than 2.4 see documentation of policy CMP_0001."
       "\n"
       "  cmake_policy(SET <CMP_NNNN> NEW)\n"
       "  cmake_policy(SET <CMP_NNNN> OLD)\n"
diff --git a/Source/cmConfigureFileCommand.cxx b/Source/cmConfigureFileCommand.cxx
index d768886..cac2552 100644
--- a/Source/cmConfigureFileCommand.cxx
+++ b/Source/cmConfigureFileCommand.cxx
@@ -40,29 +40,10 @@ bool cmConfigureFileCommand
   this->CopyOnly = false;
   this->EscapeQuotes = false;
 
-  
   // for CMake 2.0 and earlier CONFIGURE_FILE defaults to the FinalPass,
   // after 2.0 it only does InitialPass
-  this->Immediate = false;
-  const char* versionValue
-    = this->Makefile->GetDefinition("CMAKE_BACKWARDS_COMPATIBILITY");
-  if (versionValue && atof(versionValue) > 2.0)
-  {
-    this->Immediate = true;
-  }
+  this->Immediate = !this->Makefile->NeedBackwardsCompatibility(2,0);
 
-  switch (this->Makefile->GetPolicyStatus(cmPolicies::CMP_0003))
-  {
-    case cmPolicies::WARN:
-    case cmPolicies::OLD:
-      break;
-    case cmPolicies::NEW:
-    case cmPolicies::REQUIRED_IF_USED:
-    case cmPolicies::REQUIRED_ALWAYS:
-      this->Immediate = true;
-  }
-    
-  
   this->AtOnly = false;
   for(unsigned int i=2;i < args.size();++i)
     {
diff --git a/Source/cmFindBase.cxx b/Source/cmFindBase.cxx
index 14987ac..f5f1430 100644
--- a/Source/cmFindBase.cxx
+++ b/Source/cmFindBase.cxx
@@ -109,19 +109,7 @@ bool cmFindBase::ParseArguments(std::vector<std::string> const& argsIn)
   // CMake versions below 2.3 did not search all these extra
   // locations.  Preserve compatibility unless a modern argument is
   // passed.
-  bool compatibility = false;
-  const char* versionValue =
-    this->Makefile->GetDefinition("CMAKE_BACKWARDS_COMPATIBILITY");
-  int major = 0;
-  int minor = 0;
-  if(versionValue && sscanf(versionValue, "%d.%d", &major, &minor) != 2)
-    {
-    versionValue = 0;
-    }
-  if(versionValue && (major < 2 || major == 2 && minor < 3))
-    {
-    compatibility = true;
-    }
+  bool compatibility = this->Makefile->NeedBackwardsCompatibility(2,3);
 
   // copy argsIn into args so it can be modified,
   // in the process extract the DOC "documentation" 
diff --git a/Source/cmListFileCache.cxx b/Source/cmListFileCache.cxx
index 234c8e5..55604a6 100644
--- a/Source/cmListFileCache.cxx
+++ b/Source/cmListFileCache.cxx
@@ -149,6 +149,9 @@ bool cmListFile::ParseFile(const char* filename,
           mf->IssueWarning(
             mf->GetPolicies()->GetPolicyWarning(cmPolicies::CMP_0000)
             );
+
+          // Implicitly set the version for the user.
+          mf->SetPolicyVersion("2.4");
         case cmPolicies::OLD:
           break; 
         default:
diff --git a/Source/cmLocalGenerator.cxx b/Source/cmLocalGenerator.cxx
index f96704f..76b843a 100644
--- a/Source/cmLocalGenerator.cxx
+++ b/Source/cmLocalGenerator.cxx
@@ -1195,15 +1195,7 @@ void cmLocalGenerator::GetIncludeDirectories(std::vector<std::string>& dirs,
 
   // CMake versions below 2.0 would add the source tree to the -I path
   // automatically.  Preserve compatibility.
-  const char* versionValue =
-    this->Makefile->GetDefinition("CMAKE_BACKWARDS_COMPATIBILITY");
-  int major = 0;
-  int minor = 0;
-  if(versionValue && sscanf(versionValue, "%d.%d", &major, &minor) != 2)
-    {
-    versionValue = 0;
-    }
-  if(versionValue && major < 2)
+  if(this->NeedBackwardsCompatibility(1,9))
     {
     includeSourceDir = true;
     }
@@ -2679,6 +2671,28 @@ bool cmLocalGenerator::NeedBackwardsCompatibility(unsigned int major,
                                                   unsigned int minor,
                                                   unsigned int patch)
 {
+  // Check the policy to decide whether to pay attention to this
+  // variable.
+  switch(this->Makefile->GetPolicyStatus(cmPolicies::CMP_0001))
+    {
+    case cmPolicies::WARN:
+      // WARN is just OLD without warning because user code does not
+      // always affect whether this check is done.
+    case cmPolicies::OLD:
+      // Old behavior is to check the variable.
+      break;
+    case cmPolicies::NEW:
+      // New behavior is to ignore the variable.
+      return false;
+    case cmPolicies::REQUIRED_IF_USED:
+    case cmPolicies::REQUIRED_ALWAYS:
+      // This will never be the case because the only way to require
+      // the setting is to require the user to specify version policy
+      // 2.6 or higher.  Once we add that requirement then this whole
+      // method can be removed anyway.
+      return false;
+    }
+
   // Compatibility is needed if CMAKE_BACKWARDS_COMPATIBILITY is set
   // equal to or lower than the given version.
   unsigned int actual_compat = this->GetBackwardsCompatibility();
diff --git a/Source/cmMakefile.cxx b/Source/cmMakefile.cxx
index 1f3bda8..aaea0de 100644
--- a/Source/cmMakefile.cxx
+++ b/Source/cmMakefile.cxx
@@ -1143,13 +1143,8 @@ void cmMakefile::AddLinkLibraryForTarget(const char *target,
       this->GetCMakeInstance()->GetGlobalGenerator()->FindTarget(0,lib);
     if(tgt)
       {
-      bool allowModules = true;
-      const char* versionValue
-        = this->GetDefinition("CMAKE_BACKWARDS_COMPATIBILITY");
-      if (versionValue &&  (atof(versionValue) >= 2.4) )
-        {
-        allowModules = false;
-        }
+      // CMake versions below 2.4 allowed linking to modules.
+      bool allowModules = this->NeedBackwardsCompatibility(2,3);
       // if it is not a static or shared library then you can not link to it
       if(!((tgt->GetType() == cmTarget::STATIC_LIBRARY) ||
            (tgt->GetType() == cmTarget::SHARED_LIBRARY) ||
@@ -2092,15 +2087,7 @@ const char *cmMakefile::ExpandVariablesInString(std::string& source,
           << ":" << line << ":\n"
           << parser.GetError() << ", when parsing string \""
           << source.c_str() << "\"";
-    const char* versionValue
-      = this->GetDefinition("CMAKE_BACKWARDS_COMPATIBILITY");
-    int major = 0;
-    int minor = 0;
-    if ( versionValue )
-      {
-      sscanf(versionValue, "%d.%d", &major, &minor);
-      }
-    if ( major < 2 || major == 2 && minor < 1 )
+    if(this->NeedBackwardsCompatibility(2,0))
       {
       cmSystemTools::Error(error.str().c_str());
       cmSystemTools::SetFatalErrorOccured();
@@ -3333,9 +3320,7 @@ bool cmMakefile::EnforceUniqueName(std::string const& name, std::string& msg,
         "\n"
         "If you are building an older project it is possible that "
         "it violated this rule but was working accidentally because "
-        "CMake did not previously diagnose this problem.  "
-        "Set CMAKE_BACKWARDS_COMPATIBILITY to 2.4 or lower to disable "
-        "this error.\n";
+        "CMake did not previously diagnose this problem.\n";
       if(isCustom && existing->GetType() == cmTarget::UTILITY)
         {
         e <<
@@ -3422,6 +3407,26 @@ bool cmMakefile::SetPolicy(cmPolicies::PolicyID id,
       IsValidPolicyStatus(id,status))
   {
     this->PolicyStack.back()[id] = status;
+
+    // Special hook for presenting compatibility variable as soon as
+    // the user requests it.
+    if(id == cmPolicies::CMP_0001 &&
+       (status == cmPolicies::WARN || status == cmPolicies::OLD))
+      {
+      if(!(this->GetCacheManager()
+           ->GetCacheValue("CMAKE_BACKWARDS_COMPATIBILITY")))
+        {
+        // Set it to 2.4 because that is the last version where the
+        // variable had meaning.
+        this->AddCacheDefinition
+          ("CMAKE_BACKWARDS_COMPATIBILITY", "2.4",
+           "For backwards compatibility, what version of CMake "
+           "commands and "
+           "syntax should this version of CMake try to support.",
+           cmCacheManager::STRING);
+        }
+      }
+
     return true;
   }
   return false;
diff --git a/Source/cmPolicies.cxx b/Source/cmPolicies.cxx
index 79fecc3..bc123b1 100644
--- a/Source/cmPolicies.cxx
+++ b/Source/cmPolicies.cxx
@@ -84,7 +84,8 @@ public:
 cmPolicies::cmPolicies()
 {
   // define all the policies
-  this->DefinePolicy(CMP_0000, "CMP_0000",
+  this->DefinePolicy(
+    CMP_0000, "CMP_0000",
     "Missing a CMake version specification. You must have a cmake_policy "
     "call.",
     "CMake requires that projects specify what version of CMake they have "
@@ -94,36 +95,32 @@ cmPolicies::cmPolicies()
     "2.6 in that example with the verison of CMake you are writing to. "
     "This policy is being put in place because it aids us in detecting "
     "and maintaining backwards compatibility.",
-    2,6,0, cmPolicies::WARN);
-//  this->PolicyStringMap["CMP_POLICY_SPECIFICATION"] = CMP_0000;
-  
-  this->DefinePolicy(CMP_0001, "CMP_0001",
-    "CMake does not allow target names to include slash characters.",
-    "CMake requires that target names not include any / or \\ characters "
-    "please change the name of any targets to not use such characters."
-    ,
-    2,4,0, cmPolicies::REQUIRED_IF_USED); 
-//  this->PolicyStringMap["CMP_TARGET_NAMES_WITH_SLASHES"] = CMP_0001;
-    
-  this->DefinePolicy(CMP_0002, "CMP_0002",
-    "CMake requires that target names be globaly unique.",
-    "CMake requires that target names not include any / or \\ characters "
-    "please change the name of any targets to not use such characters."
-    ,
-    2,6,0, cmPolicies::WARN);
-//  this->PolicyStringMap["CMP_REQUIRE_UNIQUE_TARGET_NAMES"] = CMP_0002;
+    2,6,0, cmPolicies::WARN
+    );
 
-  this->DefinePolicy(CMP_0003, "CMP_0003",
-    "CMake configures file immediately after 2.0.",
-    "In CMake 2.0 and earlier the configure_file command would not "
-    "configure the file until after processing all CMakeLists files. "
-    "In CMake 2.2 and later the default behavior is that it will "
-    "configure the file right when the command is invoked."
-    ,
-    2,6,0, cmPolicies::NEW);
-//  this->PolicyStringMap["CMP_CONFIGURE_FILE_IMMEDIATE"] = CMP_0003;
+  this->DefinePolicy(
+    CMP_0001, "CMP_0001",
+    "CMAKE_BACKWARDS_COMPATIBILITY should no longer be used.",
+    "The OLD behavior is to check CMAKE_BACKWARDS_COMPATIBILITY and present "
+    "it to the user.  "
+    "The NEW behavior is to ignore CMAKE_BACKWARDS_COMPATIBILITY "
+    "completely.\n"
+    "In CMake 2.4 and below the variable CMAKE_BACKWARDS_COMPATIBILITY was "
+    "used to request compatibility with earlier versions of CMake.  "
+    "In CMake 2.6 and above all compatibility issues are handled by policies "
+    "and the cmake_policy command.  "
+    "However, CMake must still check CMAKE_BACKWARDS_COMPATIBILITY for "
+    "projects written for CMake 2.4 and below.",
+    2,6,0, cmPolicies::WARN
+    );
 
-  }
+  this->DefinePolicy(
+    CMP_0002, "CMP_0002",
+    "CMake requires that target names be globaly unique.",
+    "....",
+    2,6,0, cmPolicies::WARN
+    );
+}
 
 cmPolicies::~cmPolicies()
 {
@@ -187,27 +184,18 @@ bool cmPolicies::ApplyPolicyVersion(cmMakefile *mf,
   // it is an error if the policy version is less than 2.4
   if (majorVer < 2 || majorVer == 2 && minorVer < 4)
   {
-    mf->IssueError("An attempt was made to set the policy version of "
-      "CMake to something earlier than 2.4, this is an error!");
+    mf->IssueError(
+      "An attempt was made to set the policy version of CMake to something "
+      "earlier than \"2.4\".  "
+      "In CMake 2.4 and below backwards compatibility was handled with the "
+      "CMAKE_BACKWARDS_COMPATIBILITY variable.  "
+      "In order to get compatibility features supporting versions earlier "
+      "than 2.4 set policy CMP_0001 to OLD to tell CMake to check the "
+      "CMAKE_BACKWARDS_COMPATIBILITY variable.  "
+      "One way to so this is to set the policy version to 2.4 exactly."
+      );
   }
-  
-  // if the version is 2.4 then make sure the backwards compatibility variable is visible
-  if (majorVer == 2 && minorVer == 4)
-  {
-    // set the default BACKWARDS compatibility to be visible
-    mf->GetCacheManager()->GetCacheIterator(
-      "CMAKE_BACKWARDS_COMPATIBILITY").SetType
-        (cmCacheManager::STRING);
-    // const char *cbcValue = 
-      // mf->GetCacheManager()->
-        // GetCacheValue("CMAKE_BACKWARDS_COMPATIBILITY");
-    // mf->AddCacheDefinition
-      // ("CMAKE_BACKWARDS_COMPATIBILITY",cbcValue, 
-       // "For backwards compatibility, what version of CMake commands and "
-       // "syntax should this version of CMake allow.",
-       // cmCacheManager::STRING);
-  }
-  
+
   // now loop over all the policies and set them as appropriate
   std::map<cmPolicies::PolicyID,cmPolicy *>::iterator i 
     = this->Policies.begin();
diff --git a/Source/cmPolicies.h b/Source/cmPolicies.h
index 68745da..7e976d6 100644
--- a/Source/cmPolicies.h
+++ b/Source/cmPolicies.h
@@ -38,12 +38,12 @@ public:
   enum PolicyStatus { OLD, WARN, NEW, REQUIRED_IF_USED, REQUIRED_ALWAYS };
   static const char* PolicyStatusNames[];
 
-  enum PolicyID {CMP_0000, CMP_POLICY_SPECIFICATION = CMP_0000,
-                 CMP_0001, CMP_TARGET_NAMES_WITH_SLASHES = CMP_0001,
-                 CMP_0002, CMP_REQUIRE_UNIQUE_TARGET_NAMES = CMP_0002,
-                 CMP_0003, CMP_CONFIGURE_FILE_IMMEDIATE = CMP_0003
-                 };
-
+  enum PolicyID
+  {
+    CMP_0000, // Policy version specification
+    CMP_0001, // Ignore old compatibility variable
+    CMP_0002
+  };
 
   ///! convert a string policy ID into a number
   bool GetPolicyID(const char *id, /* out */ cmPolicies::PolicyID &pid);
diff --git a/Source/cmake.cxx b/Source/cmake.cxx
index e9d92b3..356772a 100644
--- a/Source/cmake.cxx
+++ b/Source/cmake.cxx
@@ -1899,19 +1899,6 @@ int cmake::ActualConfigure()
        cmCacheManager::INTERNAL);
     }
 
-  // set the default BACKWARDS compatibility to the current version
-  if(!this->CacheManager->GetCacheValue("CMAKE_BACKWARDS_COMPATIBILITY"))
-    {
-    char ver[256];
-    sprintf(ver,"%i.%i",cmVersion::GetMajorVersion(),
-            cmVersion::GetMinorVersion());
-    this->CacheManager->AddCacheEntry
-      ("CMAKE_BACKWARDS_COMPATIBILITY",ver, 
-       "For backwards compatibility, what version of CMake commands and "
-       "syntax should this version of CMake allow.",
-       cmCacheManager::INTERNAL);
-    }
-
   // no generator specified on the command line
   if(!this->GlobalGenerator)
     {
@@ -2392,20 +2379,6 @@ int cmake::LoadCache()
     {
     return -3;
     }
-
-  // set the default BACKWARDS compatibility to the current version
-  if(!this->CacheManager->GetCacheValue("CMAKE_BACKWARDS_COMPATIBILITY"))
-    {
-    char ver[256];
-    sprintf(ver,"%i.%i",cmVersion::GetMajorVersion(),
-            cmVersion::GetMinorVersion());
-    this->CacheManager->AddCacheEntry
-      ("CMAKE_BACKWARDS_COMPATIBILITY",ver, 
-       "For backwards compatibility, what version of CMake commands and "
-       "syntax should this version of CMake allow.",
-       cmCacheManager::INTERNAL);
-    }
-
   return 0;
 }
 
diff --git a/Tests/MakeClean/ToClean/CMakeLists.txt b/Tests/MakeClean/ToClean/CMakeLists.txt
index bc51876..47542e8 100644
--- a/Tests/MakeClean/ToClean/CMakeLists.txt
+++ b/Tests/MakeClean/ToClean/CMakeLists.txt
@@ -1,3 +1,4 @@
+cmake_policy(VERSION 2.6)
 PROJECT(ToClean)
 
 # Build a simple project.
diff --git a/Tests/Preprocess/CMakeLists.txt b/Tests/Preprocess/CMakeLists.txt
index fdda65f..b1f95f4 100644
--- a/Tests/Preprocess/CMakeLists.txt
+++ b/Tests/Preprocess/CMakeLists.txt
@@ -1,3 +1,4 @@
+cmake_policy(VERSION 2.6)
 project(Preprocess)
 
 # This test is meant both as a test and as a reference for supported