Introduce cmState::Snapshot.

Create snapshots for buildsystem directories during configure time.

This class will be extended in follow up commits to snapshot
all values in the cmState.

Source/cmMakefile.cxx

@@ -54,7 +54,10 @@ public:
 
 // default is not to be building executables
 cmMakefile::cmMakefile(cmLocalGenerator* localGenerator)
-  : Internal(new Internals)
+  : Internal(new Internals),
+    LocalGenerator(localGenerator),
+    StateSnapshot(localGenerator->GetGlobalGenerator()
+                                ->GetCMakeInstance()->GetState())
 {
   const cmDefinitions& defs = cmDefinitions();
   const std::set<std::string> globalKeys = defs.LocalKeys();
@@ -63,6 +66,19 @@ cmMakefile::cmMakefile(cmLocalGenerator* localGenerator)
   this->Internal->VarUsageStack.push(globalKeys);
   this->Internal->IsSourceFileTryCompile = false;
 
+  if (this->LocalGenerator->GetParent())
+    {
+    cmMakefile* parentMf = this->LocalGenerator->GetParent()->GetMakefile();
+    this->StateSnapshot =
+        this->GetState()->CreateSnapshot(parentMf->StateSnapshot);
+    }
+  else
+    {
+    this->StateSnapshot =
+        this->GetState()->CreateSnapshot(this->StateSnapshot);
+    }
+
+
   // Initialize these first since AddDefaultDefinitions calls AddDefinition
   this->WarnUnused = false;
   this->CheckSystemVars = false;

Source/cmMakefile.h

@@ -922,7 +922,7 @@ private:
   cmMakefile& operator=(const cmMakefile& mf);
   void Initialize();
 
-
+  cmState::Snapshot StateSnapshot;
 
   bool ReadListFileInternal(const char* filenametoread,
                             bool noPolicyScope,

Source/cmState.cxx

@@ -22,6 +22,7 @@ cmState::cmState(cmake* cm)
   : CMakeInstance(cm),
     IsInTryCompile(false)
 {
+  this->CreateSnapshot(Snapshot());
   this->Initialize();
 }
 
@@ -466,3 +467,17 @@ const char* cmState::GetBinaryDirectory() const
 {
   return this->BinaryDirectory.c_str();
 }
+
+cmState::Snapshot cmState::CreateSnapshot(Snapshot originSnapshot)
+{
+  PositionType pos = this->ParentPositions.size();
+  this->ParentPositions.push_back(originSnapshot.Position);
+  return cmState::Snapshot(this, pos);
+}
+
+cmState::Snapshot::Snapshot(cmState* state, PositionType position)
+  : State(state),
+  Position(position)
+{
+
+}

Source/cmState.h

@@ -21,10 +21,24 @@ class cmCommand;
 
 class cmState
 {
+  typedef std::vector<std::string>::size_type PositionType;
+  friend class Snapshot;
 public:
   cmState(cmake* cm);
   ~cmState();
 
+  class Snapshot {
+  public:
+    Snapshot(cmState* state = 0, PositionType position = 0);
+
+  private:
+    friend class cmState;
+    cmState* State;
+    cmState::PositionType Position;
+  };
+
+  Snapshot CreateSnapshot(Snapshot originSnapshot);
+
   enum CacheEntryType{ BOOL=0, PATH, FILEPATH, STRING, INTERNAL,STATIC,
                        UNINITIALIZED };
   static CacheEntryType StringToCacheEntryType(const char*);
@@ -106,6 +120,7 @@ private:
   std::map<std::string, cmCommand*> Commands;
   cmPropertyMap GlobalProperties;
   cmake* CMakeInstance;
+  std::vector<PositionType> ParentPositions;
   std::string SourceDirectory;
   std::string BinaryDirectory;
   bool IsInTryCompile;