2 files changed, 65 insertions, 2 deletions

diff --git a/apt-pkg/contrib/error.cc b/apt-pkg/contrib/error.cc
index 837d9e615..8cee21c9c 100644
--- a/apt-pkg/contrib/error.cc
+++ b/apt-pkg/contrib/error.cc
@@ -181,7 +181,13 @@ bool GlobalError::PopMessage(std::string &Text) {
 }
 									/*}}}*/
 // GlobalError::DumpErrors - Dump all of the errors/warns to cerr	/*{{{*/
-void GlobalError::DumpErrors(std::ostream &out, MsgType const &trashhold) {
+void GlobalError::DumpErrors(std::ostream &out, MsgType const &trashhold,
+			     bool const &mergeStack) {
+	if (mergeStack == true)
+		for (std::list<MsgStack>::const_reverse_iterator s = Stacks.rbegin();
+		     s != Stacks.rend(); ++s)
+			Messages.insert(Messages.begin(), s->Messages.begin(), s->Messages.end());
+
 	for (std::list<Item>::const_iterator m = Messages.begin();
 	     m != Messages.end(); m++)
 		if (m->Type >= trashhold)
@@ -211,3 +217,27 @@ bool GlobalError::empty(MsgType const &trashhold) const {
 	return true;
 }
 									/*}}}*/
+// GlobalError::PushToStack						/*{{{*/
+void GlobalError::PushToStack() {
+	MsgStack pack(Messages, PendingFlag);
+	Stacks.push_back(pack);
+	Discard();
+}
+									/*}}}*/
+// GlobalError::RevertToStack						/*{{{*/
+void GlobalError::RevertToStack() {
+	Discard();
+	MsgStack pack = Stacks.back();
+	Messages = pack.Messages;
+	PendingFlag = pack.PendingFlag;
+	Stacks.pop_back();
+}
+									/*}}}*/
+// GlobalError::MergeWithStack						/*{{{*/
+void GlobalError::MergeWithStack() {
+	MsgStack pack = Stacks.back();
+	Messages.insert(Messages.begin(), pack.Messages.begin(), pack.Messages.end());
+	PendingFlag = PendingFlag || pack.PendingFlag;
+	Stacks.pop_back();
+}
+									/*}}}*/
diff --git a/apt-pkg/contrib/error.h b/apt-pkg/contrib/error.h
index fc7b38f1b..73735162d 100644
--- a/apt-pkg/contrib/error.h
+++ b/apt-pkg/contrib/error.h
@@ -206,7 +206,8 @@ public:									/*{{{*/
 	 *  \param[out] out output stream to write the messages in
 	 *  \param WithoutNotice output notices or not
 	 */
-	void DumpErrors(std::ostream &out, MsgType const &trashhold = WARNING);
+	void DumpErrors(std::ostream &out, MsgType const &trashhold = WARNING,
+			bool const &mergeStack = true);
 
 	/** \brief dumps the list of messages to std::cerr
 	 *
@@ -219,6 +220,28 @@ public:									/*{{{*/
 		DumpErrors(std::cerr, trashhold);
 	}
 
+	/** \brief put the current Messages into the stack
+	 *
+	 *  All "old" messages will be pushed into a stack to
+	 *  them later back, but for now the Message query will be
+	 *  empty and performs as no messages were present before.
+	 *
+	 * The stack can be as deep as you want - all stack operations
+	 * will only operate on the last element in the stack.
+	 */
+	void PushToStack();
+
+	/** \brief throw away all current messages */
+	void RevertToStack();
+
+	/** \brief merge current and stack together */
+	void MergeWithStack();
+
+	/** \brief return the deep of the stack */
+	size_t StackCount() const {
+		return Stacks.size();
+	}
+
 	GlobalError();
 									/*}}}*/
 private:								/*{{{*/
@@ -244,6 +267,16 @@ private:								/*{{{*/
 	std::list<Item> Messages;
 	bool PendingFlag;
 
+	struct MsgStack {
+		std::list<Item> const Messages;
+		bool const PendingFlag;
+
+		MsgStack(std::list<Item> const &Messages, bool const &Pending) :
+			 Messages(Messages), PendingFlag(Pending) {};
+	};
+
+	std::list<MsgStack> Stacks;
+
 	bool InsertErrno(MsgType type, const char* Function,
 			 const char* Description, va_list const &args);
 	bool Insert(MsgType type, const char* Description,