1 files changed, 46 insertions, 10 deletions
diff --git a/Source/cmListFileCache.h b/Source/cmListFileCache.h
index d3cab22..9fa8585 100644
--- a/Source/cmListFileCache.h
+++ b/Source/cmListFileCache.h
@@ -87,17 +87,53 @@ struct cmListFileFunction: public cmCommandContext
   std::vector<cmListFileArgument> Arguments;
 };
 
-class cmListFileBacktrace: private std::vector<cmListFileContext>
+// Represent a backtrace (call stack).  Provide value semantics
+// but use efficient reference-counting underneath to avoid copies.
+class cmListFileBacktrace
 {
-  public:
-    cmListFileBacktrace(cmState::Snapshot snapshot = cmState::Snapshot(),
-                        cmCommandContext const& cc = cmCommandContext());
-    ~cmListFileBacktrace();
-
-    void PrintTitle(std::ostream& out) const;
-    void PrintCallStack(std::ostream& out) const;
-  private:
-    cmState::Snapshot Snapshot;
+public:
+  // Default-constructed backtrace may not be used until after
+  // set via assignment from a backtrace constructed with a
+  // valid snapshot.
+  cmListFileBacktrace();
+
+  // Construct an empty backtrace whose bottom sits in the directory
+  // indicated by the given valid snapshot.
+  cmListFileBacktrace(cmState::Snapshot snapshot);
+
+  // Backtraces may be copied and assigned as values.
+  cmListFileBacktrace(cmListFileBacktrace const& r);
+  cmListFileBacktrace& operator=(cmListFileBacktrace const& r);
+  ~cmListFileBacktrace();
+
+  // Get a backtrace with the given file scope added to the top.
+  // May not be called until after construction with a valid snapshot.
+  cmListFileBacktrace Push(std::string const& file) const;
+
+  // Get a backtrace with the given call context added to the top.
+  // May not be called until after construction with a valid snapshot.
+  cmListFileBacktrace Push(cmListFileContext const& lfc) const;
+
+  // Get a backtrace with the top level removed.
+  // May not be called until after a matching Push.
+  cmListFileBacktrace Pop() const;
+
+  // Get the context at the top of the backtrace.
+  // Returns an empty context if the backtrace is empty.
+  cmListFileContext const& Top() const;
+
+  // Print the top of the backtrace.
+  void PrintTitle(std::ostream& out) const;
+
+  // Print the call stack below the top of the backtrace.
+  void PrintCallStack(std::ostream& out) const;
+private:
+  struct Entry;
+  cmState::Snapshot Bottom;
+  Entry* Cur;
+  cmListFileBacktrace(cmState::Snapshot bottom, Entry* up,
+                      cmListFileContext const& lfc);
+  cmListFileBacktrace(cmState::Snapshot bottom, Entry* cur);
 };
 
 struct cmListFile